ArticlePDF Available

Food functionalities and bioactivities of protein isolates recovered from skipjack tuna roe by isoelectric solubilization and precipitation

Wiley
Food Science & Nutrition
Authors:

Abstract and Figures

Four roe protein isolates (RPIs) from skipjack tuna were prepared using isoelectric solubilization (pH 11 and 12) and precipitation (pH 4.5 and 5.5) (ISP) at different pH points to evaluate their physicochemical and functional properties and in vitro bioactivities. Moisture (<6.3%) and protein (71%–77%) content were maintained. Sulfur, sodium, phosphorus, and potassium were the major elements, and glutamic acid and leucine were the prevalent amino acids (12.2–12.8 and 9.6–9.8 g/100 g protein, respectively) in RPIs. RPI-1 showed the highest buffering capacity at pH 7–12. RPIs and casein showed similar water-holding capacities. At pH 12, RPI-1(pH 11/4.5) showed the highest solubility, followed by RPI-3(pH 12/4.5), RPI-2(pH 11/5.5), and RPI-4(pH 12/5.5) (p < .05). Oil-in-water emulsifying activity indices of RPI-1 and RPI-3 significantly differed. At pH 2 and 7–12, pH-shift treatment improved the food functionality of RPIs, which was superior to positive controls (casein and hemoglobin). RPI-1 showed ABTS+ radical scavenging (102.7 μg/ml) and angiotensin-converting enzyme inhibitory activities (44.0%).
This content is subject to copyright. Terms and conditions apply.
1874  
|
Food Sci Nutr. 2020;8:1874–1887.www.foodscience-nutrition.com
1 | INTRODUCTION
Skipjack tuna (Katsuwonus pelamis) is consumed worldwide because
of its abundance, nutritional value, and sensorial attributes (firm tex-
ture and flavorful flesh). This tuna is widely used as a raw material
for sashimi and sushi in Korea and Japan (Lee, Park, et al., 2016). In
2015, 51,201 metric tons of skipjack tuna were canned, account-
ing for 57% of all canned products in Korea (KOSIS, 2016). The an-
nual discard rate of fish processing byproducts has increased with
increasing fish production. The fish processing industry generates
large quantities of byproducts such as heads, skin, frames, roe, vis-
cera, and scales (Narsing Rao, Prabhakara Rao, Satyanarayana, &
Balaswamy, 2012), most of which are not used as sources of high
value-added products for human or animal consumption and are dis-
posed of as waste. However, these byproducts are excellent sources
of proteins (Lee, Lee, et al., 2016). Upcycling or reuse of byproducts
has gained wide attention in the seafood processing industr y owing
to its economic effectiveness (Lee, Lee, et al., 2016). In recent years,
Received: 16 December 2018 
|
Revised: 16 January 2020 
|
Accepted: 29 January 2020
DOI: 10.10 02/f sn3.1470
ORIGINAL RESEARCH
Food functionalities and bioactivities of protein isolates
recovered from skipjack tuna roe by isoelectric solubilization
and precipitation
Jang Woo Cha1| In Seong Yoon1| Gyoon-Woo Lee2| Sang In Kang1|
Sun Young Park1| Jin-Soo Kim1,3| Min Soo Heu2,3
This is an op en access article under t he terms of the Creat ive Commons Attributio n License, which permits use, dist ribution and reproduc tion in any medium,
provide d the orig inal work is proper ly cited .
© 2020 The Authors . Food Scie nce & Nutri tion published by Wiley Perio dicals, Inc.
Cha and Yoon e qually contri buted to this work .
1Depar tment of Seafood and Aquaculture
Science/Instit ute of Mari ne Indus try,
Gyeongsang National University,
Tongyeong, Korea
2Department of Food and Nutrition/
Instit ute of Marine Indus try, Gyeon gsang
Nationa l University, Jinju , Korea
3Research Center for Industrial
Develop ment of Seafood, Gye ongsang
National University, Tongyeong, Korea
Correspondence
Min Soo He u, Department of Food and
Nutrit ion/Ins titute of Marine Industr y,
Gyeongs ang National University, 501
Jinjuda ero, Jinju, Gyeong sangna m-do 52828,
Korea.
Email: minsheu@gnu.ac.kr
Funding information
Ministry of Oceans and Fisheries, Korea
Abstract
Four roe protein isolates (RPIs) from skipjack tuna were prepared using isoelectric
solubilization (pH 11 and 12) and precipitation (pH 4.5 and 5.5) (ISP) at different pH
points to evaluate their physicochemical and functional properties and in vitro bio-
activities. Moisture (<6.3%) and protein (71%–77%) content were maintained. Sulfur,
sodium, phosphorus, and potassium were the major elements, and glutamic acid and
leucine were the prevalent amino acids (12.2–12.8 and 9.6–9.8 g/100 g protein, re-
spectively) in RPIs. RPI-1 showed the highest buffering capacity at pH 7–12. RPIs and
casein showed similar water-holding capacities. At pH 12, RPI-1(pH 11/4.5) showed
the highest solubility, followed by RPI-3(pH 12/4.5), RPI-2(pH 11/5.5), and RPI-4(pH
12/5.5) (p < .05). Oil-in-water emulsifying activity indices of RPI-1 and RPI-3 signifi-
cantly differed. At pH 2 and 7–12, pH-shift treatment improved the food functional-
ity of RPIs, which was superior to positive controls (casein and hemoglobin). RPI-1
showed ABTS+ radical scavenging (102.7 μg/ml) and angiotensin-converting enzyme
inhibitory activities (44.0%).
KEYWORDS
food functionality, physicochemical characterization, roe protein isolates, skipjack tuna
  
|
 1875
CHA et Al .
numerous studies have examined the use of protein-rich seafood
byproducts as nutraceuticals or protein and lipid supplements (Kim,
Yoon, Shim, & Lim, 2016).
Among fish byproducts, roes are nutritionally rich in essential
fatty acids, minerals, and amino acids (Heu et al., 2006; Park et al.,
2016). The production of caviar and roe products from other fish
species has been examined previously (Bledsoe, G., Bledsoe, C., &
Rasco, 2003).
Roe, a byproduct of fish processing (3.0%–30.0% depending on
species), contains 11% albumin, 75% ovoglobulin, and 13% collagen
(Sikorski, 1994) and is generally used as animal feed or in pet food
preparation. The underutilized skipjack tuna roe (STR) requires pro-
cessing methods for conversion to more marketable and acceptable
forms, such as protein concentrates, isolates, and extracts. Previous
studies characterized the ingredients, chemical composition (Heu
et al., 2006; Lee, Lee, et al., 2016), fractions, and characteristics of
the protease inhibitors (Kim et al., 2013), concentrates (Park et al.,
2016; Yoon, Lee, et al., 2018), and protein isolates (Lee, Park, et al.,
2016) in fish roes.
Isoelectric solubilization and precipitation (ISP) promotes the
selective pH-induced water solubility of muscle proteins, segre-
gates lipids, and removes materials unfit for human consumption,
such as bones, scales, and skin (Hultin & Kelleher, 1999). ISP is used
for protein recovery from inaccessible sources such as fish (Chen &
Jaczynski, 20 07), chicken (Tahergorabi, Beamer, Matak, & Jaczynski,
2011), and beef (Mireles, Gomez, & James, 2002) processing byprod-
ucts; additionally, the fat content in the recovered protein isolate
is significantly reduced. A major technology was developed for fea-
sible extraction of functional protein isolates from low-value raw
materials (dark muscle fish and fatty fish) and seafood processing
byproducts (fish cutoffs and fish frame) (Nolsoe & Undeland, 2009).
Proteins recovered from the ISP process exhibit desirable functional
proper ties and may have better gelling properties than proteins ob-
tained by conventional surimi processing (Kristinsson, Theodore,
Demir, & Ingadottir, 2005). Proteins are the basic functional compo-
nents of processed foods and determine the textural and nutritional
proper ties and contribute to the quality and sensorial at tributes of
foods (Mohamed, Xia, Issoufou, & Qixing, 20 09; Park et al., 2016).
No studies have examined the protein isolate preparation of skipjack
tuna roe or its food functional characteristics and bioactivity. The
purpose of this study was to investigate the physicochemical and
functional characteristics of protein isolates recovered from skipjack
tuna roe using the ISP process, as well as their antioxidative and an-
tihypertensive bioactivities.
2 | MATERIALS AND METHODS
2.1 | Chemicals
2,2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) ammo-
nium salt (ABTS), casein, hemoglobin, hippuryl-his-leu acetate salt
(HHL), lung acetone powder from rabbit, mushroom tyrosinase,
potassium persulfate, and sodium L-tartrate were purchased from
Sigma-Aldrich. 3,4-Dihydroxy-L-phenylalanine (L-DOPA) was pur-
chased from Acros Organics. Hydrochloric acid (1 M) and sodium
hydroxide (1 M) were purchased from Yakuri Pure Chemicals Co.,
Ltd.. Folin–Ciocalteu reagent and acetic acid were purchased from
Junsei Chemical Co., Ltd. Sodium dodecyl sulfate (SDS) and glycine
were purchased from Bio Basic, Inc. Soybean oil was purchased from
Ottogi Co., Ltd. All other reagents were of analytical grade.
2.2 | Sample
Skipjack tuna roe was obtained from Dong won F & B Co., Ltd.
(Changwon, Korea), stored at −70°C in sealed polyethylene bags,
and transferred to the laboratory. Frozen roe was partially thawed
for 24 hr at 4°C and then cut into small pieces to 2.0 cm thickness
and minced with a food grinder. Minced roe was frozen at −20°C
until use.
2.3 | Preparation of roe protein isolates (RPIs)
Roe protein isolates were prepared as described by Lee, Lee, et al.
(2016). The frozen minced roe was homogenized with deionized dis-
tilled water (DDW) at a 1:6 (w/v) ratio using a homogenizer. The ho-
mogenate was adjusted to pH 11 and 12 with 2N Na OH. Solubilization
was allowed to occur at 4°C for 1 hr, followed by centrifugation at
12,00 0 × g and 4° C for 30 mi n. After cent rifugat io n, two alka li-so lu ble
(pH 11 and 12) supernatant fractions were collected.
To prepare the RPIs from the alkali-soluble frac tions by acid
precipitation, the pH of the fractions was readjusted to pH 4.5 and
5.5 (similar to the isoelectric point of fish proteins) by adding 2N
HCl. The suspensions were centrifuged at 12,000 × g and 4°C for
30 min. Precipitates obtained after ISP were washed with DDW and
centrifuged at 12,0 00 × g and 4°C for 30 min to remove the NaCl.
After centrifugation, the washed RPIs were lyophilized and labeled
as RPI-1 (pH 11/4.5), RPI-2 (pH 11/5.5), RPI-3 (pH 12/4.5), and RPI-4
(pH 12/5.5). These RPIs were stored at −20°C until further use.
2.4 | Physicochemical properties
2.4.1 | Proximate composition
The proximate composition was determined by the AOAC method
(AOAC, 2005). Moisture content (950.46) was determined by placing
a 0.5-g sample in an aluminum pan and drying in a forced air con-
vection oven at 105°C until a constant mass was reached. The ash
content (920.153) was determined by charring approximately 0.2 g
sample in a ceramic crucible over a hot plate and then heating in a
muffle furnace at 550°C until a constant mass was achieved. The
total crude protein content (928.08) was determined by the semi-
micro Kjeldahl method. Total lipid content (960.39) was determined
1876 
|
   CHA et Al.
by the Soxhlet extraction method. Sample (5 g) was extracted with
dimethyl ether for 30 min at a drip rate of 10 ml/min. The total
lipid content was determined by gravimetry and expressed as a
percentage.
2.4.2 | Protein concentration
The protein concentration of the samples was determined as de-
scribed by Lowry, Rosebrough, Farr, and Randall (1951) using bovine
serum albumin as a standard.
2.4.3 | Total amino acid content
The samples were hydrolyzed by 6 N HCl at 110°C for 24 hr on a
heating block and filtered using a vacuum filtration device. Amino
acids were quantified with an amino acid analyzer (Biochrom 30,
Biochrom Ltd.) using sodium citrate buffers (pH 2.2) in step gradients.
The results are reported in milligrams of amino acid per 100 g protein.
2.4.4 | Mineral analysis
The mineral content of the samples was determined by inductively
coupled plasma optical emission spectrophotometry (Optima
4300 DV, PerkinElmer). The samples were dissolved in 10 ml of
70% (v/v) nitric acid and heated on a hot plate until digestion was
complete. The volume of the samples (in duplicates) was made up
to 100 ml with 2% nitric acid in a volumetric flask. The mineral
concentration was calculated and expressed as milligrams per
100 g sample.
2.4.5 | Color value
The sam ples were equili brate d to 20 ± 2°C for 2 hr prior to Hu nte r
color measurement. Color values were determined using a color
meter (ZE-2000 Nippon Denshoku Inc.). The colorimeter was
calibrated using a standard plate (L* [lightness] = 96.82, a* [red-
ness] = −0.35, b* [yellowness] = 0.59) supplied by the manufac-
turer. The values of the Commission Internationale d’Eclairage of
France (CIE) color system using tri-stimulus color values (L*, a*, and
b*) were determined. Whiteness was calculated using the follow-
ing equation:
2.5 | SDS–polyacrylamide gel electrophoresis
(SDS-PAGE)
The molecular weight distribution of proteins was investigated
by SDS-PAGE, which was performed according to the method of
Laemmli (1970). Briefly, 20 mg sample was solubilized in 5 ml of 5%
SDS. The protein solution was then mixed at a 4:1 (v/v) ratio with
SDS-PAGE sample treatment buffer (pH 6.8) and boiled at 100°C
for 3 min. Samples (20 µg protein) were loaded into a 10% Mini-
PROTEAN® TGX™ precast gel and electrophoresed at a constant
current of 10 mA using a Mini-PROTE AN® tetra cell (Bio-Rad).
2.6 | Protein functionalities
2.6.1 | Buffer capacity
Buffer capacit y was measured as described by Park et al. (2016).
The sample (300 mg) was dispersed in 30 ml distilled water, and
measured volumes of 0.5 M NaOH and HCl were added in small in-
crements. The corresponding changes in pH in alkaline and acidic
ranges were recorded. The amounts of base and acid added were
plotted against the pH, and the buffer capacity in each range was
expressed as the mean value of NaOH or HCl (in millimolar) required
per gram sample to induce a unit change in pH.
2.6.2 | Water-holding capacity (WHC)
The WHC of samples was measured as described by Park et al.
(2016). The sample (300 mg) was mixed with 30 ml DDW in a 50-ml
centrifuge tube. The mixture was thoroughly vortexed for 10 min at
20 ± 2°C and centrifuged at 12,000 × g for 20 min at 4°C. WHC was
determined from the difference in masses and expressed as grams of
water absorbed per gram protein.
where C is protein concentration (%).
2.6.3 | Protein solubility
The protein solubility of samples was determined according the
method of Park et al. (2016). First, 300 mg sample was dispersed in
30 ml DDW and the pH was adjusted to 2–12 with 2N HCl and 2N
NaOH. The mixture was stabilized at room temperature for 30 min
prior to centrifugation at 12,0 00 g for 20 min. Protein content in
the supernatant and total protein content in the sample were deter-
mined by Lowry's method after solubilizing the sample in 2N NaOH.
Protein solubility was calculated as follows:
Each measurement was replicated at least five times, and the re-
sults were expressed as the means ± SD.
Whiteness
=100
(100L*)2+a*2 +b
*2
WHC (g
g protein) =
Mass of pellet (g)
Mass of sample (g)
Mass of sample (g)×C
Solubility (%)
=
Protein content in supernatant
Total protein content in sample
×
100
  
|
 1877
CHA et Al .
2.6.4 | Foaming capacity (FC) and foam stability (FS)
Foaming capacity (FC) and foam stability (FS) of the sample solu-
tion (1%, w/v) were determined as described by Park et al. (2016)
with slight modifications. Ten milliliters of 1% (w/v) sample solution
was transferred to a 25-ml volumetric cylinder. The solution was ho-
mogenized (Polytron® PT 1200E, Kinematica AG) at 12,500 rpm for
1 min at 20 ± 2°C. The sample was allowed to stand for 0, 15, 30, and
60 min, and FC and FS were calculated using the following equations:
where VT is the total volume after whipping, V0 is the initial volume,
and Ft and Vt are the total foam and total volume, respectively, after
standing at room temperature for different durations (t = 15, 30, and
60 min).
2.6.5 | Emulsifying properties
The emulsif ying activity index (E AI) and emulsion stability index (ESI)
were determined as described by Park et al. (2016). Soybean oil (Ottogi
Co., Ltd.) and 1% (w/v) sample at a 1:3 (v/v) ratio were homogenized at
a rate of 12,500 rpm for 1 min. An aliquot of the emulsion (50 μl) was
pipetted from the bottom of the volumetric cylinder 0 and 10 min after
homogenization and mixed with 5 ml of 0.1% SDS solution. The absorb-
ance of the mixture was measured at 500 nm (UV-2900, Hitachi).
The absorbances measured immediately (A0min) and at 10 min
(A10min) after emulsification were used to calculate EAI and ESI as
follows:
where A is the absorbance at 500 nm, DF is the dilution factor (100), l is
the path length of the cuvette (1 cm), φ is the oil volume fraction (0.25),
and C is the protein concentration in the aqueous phase (g/ml).
where ΔA = A0 min–A10min and Δt = 10 min. A0min and A10min are the
absorbance values measured at 0 and 10 min after emulsification,
respectively.
2.7 | Antioxidative and antihypertensive activity
2.7.1| ABTS+ radical scavenging activity
ABTS+ radical scavenging activit y was determined using the ABTS
assay with slight modification based on the method of Binsan et al.
(20 08). Fresh ABT S+ solutions in ethanol were prepared for each assay.
Samples (1 ml) were mixed with 3 ml ABTS+ solution and incubated at
room temperatu re for 30 min in th e dark . Ab so rbance was mea su re d at
734 nm with a spectrophotometer. The IC50 value was defined as the
concentration required to scavenge 50% of ABTS+ radical.
Absorb an ce was mea su re d im me di at el y (A 734), and ABTS+ radical
scavenging activity was calculated as follows:
where control734 is the absorbance of the same reaction system with-
out the sample.
2.7. 2 | Tyrosinase inhibitory activity
The tyrosinase inhibitory activity was determined as described by Iida
et al. (1995) with some modifications. Briefly, 900 μl (50 U/ml reaction
mixture) mushroom tyrosinase was preincubated with the sample in
50 mM phosphate buffer (pH 6.8) for 30 min at room temperature.
Next, 300 μl 10 mM L-DOPA was added to the reaction mix ture, and
enzyme activity was monitored at room temperature by measuring the
change in abs or ba nce at 475 nm (UV-2900, Hi tachi) for 30 mi n at 1-min
intervals, which corresponded to the formation of dopachrome.
Samples without inhibitor were used as controls. The percentage
inhibition of enzyme activity by the active compounds was calcu-
lated as follows:
where control475 is the absorbance of a reac tion system without the
sample.
2.7. 3 | Angiotensin-converting enzyme (ACE)
inhibitory activity
Angiotensin-converting enzyme inhibitory activity was estimated
as described by Cushman and Cheung (1971) with slight modifica-
tions. ACE was extracted from 5 g lung acetone powder from rab-
bit with 100 ml 0.05 M sodium borate buffer (pH 8.3) containing
300 mM NaCl. A mixture of 100 μl sample, 50 μl ACE extract s and
50 μl 0.05 M sodium borate buffer (pH 8.3), was preincubated at
room temperature for 30 min before incubation with 50 μl substrate
(5 mM HHL in 0.05 M sodium borate buffer, pH 8.3) for 60 min at
37°C in a water bath. The reaction was terminated by adding 250 μl
1N HCl. The resulting hippuric acid was extracted with 1.5 ml ethyl
acetate. After centrifugation (1,890 × g, 10 min, 4°C), 1.0 ml of the
upper layer was transferred into a test tube and evaporated at 100°C
for 1 hr in a heating block. The hippuric acid was dissolved in 1.0 ml
distilled water, and absorbance was measured at 228 nm with a UV
Foaming capacity (%)
=
VT
V0
×
100
Foam stability (%)
=
(FtVt)
(FT
VT) ×
100
EAI (m
2g) =
2×2.303×A×DF
l×𝜑×C
×
100
ESI ( min )
=
A0×Δt
ΔA
ABTS
+radical scavenging activity (%) =
(Control
734
Sample
734
)
Control734
×
100
=
475
475)
Control
×
1878 
|
   CHA et Al.
spectrophotometer. Absorbance was measured immediately (A2 28)
and used to calculate the ACE inhibitory activity as follows:
where the sample blank is the absorbance of the inactivated sample
before adding HHL and control blank is the absorbance of the inacti-
vated control before adding HHL.
2.8 | Statistical analysis
All analyses were performed in triplicate. Data were averaged, and
the SD was calculated. Data were analyzed by analysis of variance
using SPSS 12.0 K software (SPSS, Inc.) for Windows. Mean com-
parisons were performed using the multiple range Duncan's test
(p < .05).
3 | RESULTS AND DISCUSSION
3.1 | Physicochemical properties
3.1.1| Proximate composition
Roe protein isolates were recovered from STR by ISP. The proxi-
mate composition, mineral content, and Hunter's color values of
the RPIs and positive controls (casein and hemoglobin) are shown in
Table 1. Freeze-dried STR (FDSTR) contained 6.2 ± 0.9% moisture,
71.1 ± 0.7% protein, 15. 2 ± 1.3% lipid, and 7.2 ± 0.1% ash. FDSTR
yield and protein yield were 26.7 and 19.0 g/100 g of STR , respec-
tively. The yields of RPIs produced from STR by ISP differed slightly
by 10.3%–13.0%. The recovery of RPIs from STR by ISP was 54.2%–
68.4%. This low protein recovery may be attributed to the presence
of alkaline insoluble proteins that did not dissolve during alkaline
solubilization (Lee, Lee, et al., 2016; Yoon, Kang, et al., 2018). The
RPI-2 showed the highest protein content (76.8 ± 0.3%), followed
by RPI-4 (75.4 ± 0.4%), RPI-1 (71.4 ± 0.8%), and RPI-3 (70.8 ± 0.7%).
However, these values were lower than those of the positive con-
trols (85.5 ± 0.0% for casein, 94.4 ± 0.4% for hemoglobin). The
protein content of RPIs was higher than those reported for fish pro-
tein powders from arrowtooth flounder and herring (Sathivel et al.,
2004). The protein content in fish eggs (Sathivel, Yin, Bechtel, &
King, 2009) and surimi (Huda, Abdullah, & Babji, 2001) was similar
to those in the RPIs. Lipid (13.8 ± 2.5–15.6 ± 1.0%) and ash content
(1.8 ± 0.6–3.6 ± 0.1%) in the RPIs were lower than those in FDSTR
(p < .05). This reduction in lipid and mineral content occurred be-
cause of mineral and fat migration into the processed water during
ISP (Lee et al., 2017; Lee, Lee, et al., 2016). The protein content of
RPI-2 and RPI-4 precipitated at pH 5.5 after alkaline solubilization
was significantly higher than that of RPI-1 and RPI-3 precipitated at
pH 4.5 (p < .05). In contrast, the total yield (10.3–10.9 g/100 g) and
protein yield (7.8–7.9 g/100 g) of RPI-1 and RPI-2 were significantly
lower than those of RPI-3 and RPI-4 (p < .05). Thus, alkali solubiliza-
tion at pH 12 was better than that at pH 11, while acid precipitation
did not affect protein yield (p < .05).
3.1.2 | Minerals
The mineral content of FDSTR, RPIs, and positive controls is
shown in Table 1. The major minerals in FDSTR were potassium
(1,097.4 ± 9.0 mg/100 g), sulfur (974.3 ± 57.7 mg/100 g), sodium
(615.2 ± 1.4 mg/100 g), and phosphorus (247.9 ± 1.5 mg/100 g). The
predominant minerals in casein were sulfur (1,984.1 ± 3.2 mg/100 g),
calcium (987.2 ± 17.3 mg/100 g), and sodium (706.3 ± 10.9 mg/100 g),
and their levels were higher than those in FDSTR. Sulfur
(442.0 ± 46.2 mg/100 g), iron (250.1 ± 1.8 mg/100 g), and sodium
(212.6 ± 1.8 mg/100 g) were the major minerals in hemoglobin, and
their levels were lower than those in FDSTR, except for iron. The sul-
fur and potassium content in RPIs were 482.5 ± 89.5–782.1 ± 47.2
and 18.4 ± 3.1–70.3 ± 0.6 mg/100 g, respectively, which were
significantly lower than those in FDSTR. The sodium (70.1 ± 0.6–
166.9 ± 1.1 mg/100 g) and phosphorus (482.5–782.1 mg/100 g)
levels in the RPIs were also significantly lower than those in
FDSTR (p < .05), while magnesium and calcium levels showed simi-
lar trends. However, the sodium content in the RPIs was lower
than those in crab (266.8 mg/100 g) (Gokoglu & Yerlikaya, 2003),
hoki (620.0 mg/100 g) (Gokoglu, Yerlikaya, & Cengiz, 2004), and
fish-based dishes (222.8 mg/100 g) (Martinez-Valverde, Periago,
Santaella, & Ros, 20 00). Phosphorus content in the RPIs was higher
than that in rainbow trout (337.8 mg/100 g) (Gokoglu et al., 20 04)
and European perch (215–230.0 mg /100 g) (Orban et al., 2007).
Overall, the total mineral content in RPI-1 (pH 11/4.5) and RPI-3 (pH
12/4.5) was significantly lower than those in RPI-2 (pH 11/5.5) and
RPI-4 (pH 12/5.5) (p < .05). Acid precipitation at pH 4.5 during ISP
was found to be effective for removing minerals (potassium, sodium,
sulfur, and phosphorus) except for iron. Therefore, most minerals
in FDSTR migrated into the processed water during ISP (Lee et al.,
2017; Lee, Lee, et al., 2016).
3.1.3 | Color values
The color properties of FDSTR and the RPIs are shown in
Table 1. The L* value of FDSTR (59.2) was higher than those of the
RPIs (51.9 ± 0.4–55.0 ± 0.2), and the overall brightness of the RPIs
obtained after ISP was decreased (p < .05). RPI-1 and RPI-3 showed
lower a* values (4.1 ± 0.0 and 4.3 ± 0.1, respectively) than the other
RPIs. Additionally, the b* value and color difference (ΔE) showed
similar trends, confirming that acid precipitation at pH 4.5 during ISP
caused color fading. The whiteness of RPI-1 (52.0 ± 0.1) and RPI-3
(49.6 ± 0.4) was significantly higher than those of the other RPIs
(p < .05), but lower than that of FDSTR (53.6 ± 0.3) (p < .05). The RPIs
obtained after ISP were also fainter than the dark brown FDSTR. The
ACE inhibitory activity (%)
=
[
1
Sample
228
Control Blank
228
Control228 Control Blank228 ]
×
100
  
|
 1879
CHA et Al .
TABLE 1 Proximate composition and mineral content of roe protein isolates (RPIs) recovered from skipjack tuna roe (STR) by isoelectric solubilization and precipitation process
FDSTR RPI −1 RP I−2 RPI−3 RPI−4 Casein Hb
Yield  (g) 26.7 10.9 10.3 13.0 12.2
Protein yield  (g) 19.0 7.8 7.9 9. 2 9.2
Moisture (%) 6.2 ± 0.9a5.7 ± 0. 3a4.5 ± 0.1bc 6.3 ± 0.1a4.9 ± 0.3b4.0 ± 0.2c2.0 ± 0.0d
Protein (%) 71.1 ± 0.7e71.4 ± 0.8e76.8 ± 0.3c70.8 ± 0.7e75.4 ± 0.4d85.5 ± 0.0b94.4 ± 0.4a
Lipid (%) 15.2 ± 1.3a15.6 ± 1.0a14.0 ± 2.7a14.7 ± 2.0a13.8 ± 2.5aND ND
Ash (%) 7.2 ± 0.1a3.6 ± 0.1b1.8 ± 0.6c3.3 ± 0.4b2.0 ± 0.1cND ND
Minerals (mg/100 g) K 1,097.4 ± 9.0a18.4 ± 3.1e70.3 ± 0.6c25.8 ± 2.9e45.2 ± 2.1d912.0 ± 12.3b71.4 ± 3.0c
Na 615.2 ± 1.4ab 70.1 ± 0.6b113.9 ± 3.2b147.0 ± 2.1b166.9 ± 1.1b706.3 ± 10.9a212.6 ± 1.8b
Mg 66.9 ± 0.1a1.7 ± 0.1e7.1 ± 0.1c2.3 ± 0.1d7.6 ± 0.2bND ND
Zn 39.3 ± 0.3c8.3 ± 0.0d46.5 ± 0.5b7.6 ± 0.1d51.4 ± 0.9aND ND
Ca 36.3 ± 0.2b4.8 ± 0.1d15.6 ± 0.3cd 7.8 ± 0.2d15.5 ± 0.2cd 987.2 ± 17.3a21.2 ± 0. 2c
Fe 9.2 ± 0.2de 10.8 ± 0.2d16.4 ± 0.3b12 .1 ± 0.2c16.4 ± 0.2b4.8 ± 0.0 f250.1 ± 1.8a
P247.9 ± 1.5a111.9 ± 0.6e115.5 ± 1.0 d120.3 ± 1.0c131.5 ± 1.4b34.7 ± 0.4f29.1 ± 0.3g
S974.3 ± 57.7b482.5 ± 89.5ef 683.7 ± 83.6cd 573.7 ± 72.1de 782.1 ± 47.2c1984.1 ± 3.2a442.0 ± 46.2f
Color values L* 59.2 ± 0.3a55.0 ± 0.2b52.2 ± 0.5c52.6 ± 0.5c51.9 ± 0.4c
a* 6.8 ± 0.1a4.1 ± 0.0 e5.3 ± 0.1b4.3 ± 0.1d5.1 ± 0.1c
b* 21.2 ± 0.0a16.2 ± 0.2d17.2 ± 0.2b16. 8 ± 0.2c17.3 ± 0.1b
ΔE 43.5 ± 0.3d44.7 ± 0.3c48.0 ± 0.4a47.3 ± 0.4b48.3 ± 0.3a
Whiteness 53.6 ± 0. 3a52.0 ± 0.1b48.9 ± 0.4d49.6 ± 0.4c48.6 ± 0.3d
Note: Value s are mean ± SD of triplicate determinations. Means with different letters within the s ame row are signific antly different at p < .05 by Duncan's multiple range test.
FDSTR, freeze-dried skipjack tuna roe; Hb, hemoglobin. ND: not determined; RPI-1 and RPI-2, roe protein isolate adjusted to pH 4.5 and 5.5, respectively, after alkaline solubilization at pH 11; RPI-3 and
RPI-4, roe protein isolate adjusted to pH 4.5 and 5.5, respectively, after alkaline solubilization at pH 12.
Yield is weight (g) of each sample obtained from 100 g of raw STR .
Protein yield (g) = yield × protein (%).
1880 
|
   CHA et Al.
differences in color values may have resulted from the fractionation
effect of the pigment induced by ISP. The relatively low L* and high
a* values indic ate that the product was brown. The color and white-
ness of the fish protein isolates may be partially affected by the pres-
ence of connective tissues, which increase brightness, whereas lipid
retention can affect yellowness. Additionally, the yellow-brownish
color of the product may be attributed to the deposition of heme
proteins, which may affect redness, or to the denaturation and oxi-
dation of hemoglobin (K ristinsson & Rasco, 2000).
3.1.4 | Total amino acids
The total amino acid composition (g/100 g protein, %) of FDSTR ,
RPIs, and positive controls is shown in Table 2. The protein content
of all samples ranged from 75.8% to 96.3% based on the dry weight.
The RPIs contained high levels of glutamic acid, aspartic acid, leu-
cine, and lysine, which accounted for 12.2%–12.8%, 8.8%–9.0%,
9.6%–9.8%, and 8.4%–8.8% of the total amino acids, respectively.
Intarasirisawat, Benjakul, and Visessanguan (2011) reported that the
major nonessential amino acids (NEAA) in defatted tuna roes were
glutamic acid and aspartic acid, while leucine and lysine were the
predominant essential amino acids (EAA), which agrees with our re-
sults. The lysine content in the RPIs was higher than that in Channa
striatus (6.94%) and Lates calcarifer (6.86%) (Narsing Rao et al., 2012).
The EAAs in the RPIs ranged from 52.9% to 53.8%, which was higher
than that in FDSTR (50.1%). The EA A/NEAA ratio in the RPIs ranged
from 1.12 to 1.17, which was higher than that in casein (0.92) and
slightly lower than that in hemoglobin (1.33). The protein nutritional
value of the RPIs was improved by 12%–17% compared with that
of FDSTR because of the decrease in NEAA content during ISP.
The amino acid compositions of FDSTR and the RPIs were similar
to those of mullet, cod, pollock, chinook salmon roe, and yellow fin
tuna roe isolates (Bledsoe et al., 2003; Lee, Park, et al., 2016). The
hydrophobic amino acid content in the RPIs and positive controls
was 45.0%–45.9% and 44.6%–49.5%, respectively. The significantly
lower content of proline and glycine in the RPIs compared with in
FDSTR may be because of the precipitation of collagenous mate-
rial (alkaline insolubles) during alkali solubilization (Lee, Lee, et al.,
2016; Yoon, Kim, & Heu, 2018). However, the hydrophobic amino
acid content , apart from glycine and proline, in the RPIs was signifi-
cantly higher than that in FDSTR ( p < .05). Overall, the EAA content
in FDSTR and the RPIs were higher than those in casein (47.9%) but
lower than those in hemoglobin (57.1%). Therefore, the concen-
trates and isolates from fish roe differed in composition based on
the habitat environment, although fish roe proteins showed excel-
lent nutritional at tributes (Lee, Lee, et al., 2016; Park et al., 2016).
Water-holding or fat-binding capacities are functional features that
are closely related to texture by interactions between water, oil, or
other food components. These functional properties are affected by
the degree of exposure of hydrophilic (Asp, Glu, Lys, and Arg) and
hydrophobic (Tyr, Ile, Val and Phe etc.) amino acid residues within
the protein (Jellouli et al., 2011).
3.2 | SDS–PAGE
The SDS-PAGE profiles of the STR and RPIs are shown in Figure 1.
The major protein fractions of STR were observed at 100–75, 50–37,
25, 15, and 15–10 kDa. A dense protein band at 103 kDa was de-
tected in the soluble and insoluble fractions of Alaska walleye pol-
lock roe (Bechtel, Chantarachoti, Oliveira, & Sathivel, 20 07), and
four dense protein bands of 40–100-kDa were observed in spray-
dried catfish protein powder (Sathivel et al., 2009). In the RPI protein
bands, the 42-kDa protein band of STR was absent and the 75–100-
kDa bands were weaker than those of STR. The disappearance of
the 42-kDa protein band indicates that this protein was not read-
ily soluble during alkaline solubilization. The protein bands of acid-
precipitated RPIs af ter alkaline solubilization were 75–100, 25, and
10 –15 kDa.
Al-Holy and Rasco (2006) predicted that three protein bands in
salmon caviar, with molecular weights of 96, 20, and 10 kDa, were vi-
tellin-like protein, lysozyme, and phosvitin, respectively. Additionally,
a protein with a molecular weight of 27 kDa in Sturgeon's caviar may
be an ovomucoid, which is generally a glycoprotein with a MW of
27–29 kDa (Al-Holy & Rasco, 2006). Intarasirisawat et al. (2011) re-
ported that protein bands of 32.5, 29, and 32.5 kDa were detected
in skipjack, tongol, and bonito roes, respectively, which were ovomu-
coid or phosvitin.
3.3 | Food functionalities
3.3.1 | Buffer capacity
Buffer capacit y is defined as the volume (ml) or amount (mmol) of
HCl or NaOH required to induce a unit change in pH. The buffer
capacities of the RPIs and positive controls are shown in Figure 2a.
Over a pH range of 2–6, RPI-4 required 23.2 mM HCl (average) to
cause unit pH change, which is higher than that required by the other
RPIs (19.9–22.8 mM HCl). In contrast, in the pH range of 6–12, RPI-1
required a higher alkali concentration (63.9 mM NaOH) to cause a
unit pH change compared with the other RPIs (39.9–51.8 mM NaOH).
In comparison, casein and hemoglobin required 18.1 and 26.3 mM
HCl (pH range 2–6) and 33.8 and 21.8 mM NaOH (pH range 6–12),
respectively, to cause a unit pH change. These values were signifi-
cantly lower than those required for the RPIs (p < .05). Therefore, the
buffer capacities of the RPIs and casein were higher under alkaline
conditions than under acidic conditions, showing a similar trend as
roe concentrates of yellowfin tuna (Park et al., 2016). Chalamaiah,
Balaswamy, Narsing Rao, Prabhakara Rao, and Jyothirmayi (2013)
reported that dehydrated egg protein concentrate required an aver-
age of 0.65 mmol HCl and 1.22 mmol NaOH/g to induce a unit pH
change under both acidic and alkaline conditions, which was higher
than that for defatted egg protein concentrate. The lower buffer ca-
pacity of the dehydrated egg protein concentrate may be related to
the presence of fatty components, which require more acid or alkali
to induce a unit pH change.
  
|
 1881
CHA et Al .
Thus, RPIs recovered from STR were superior to those from
other species and may resist changes in external pH. These RPIs with
excellent buffering capacity can be used to develop protein-fortified
food components under different processing environments.
3.3.2 | WHC
Water-holding capacity depends on protein–water interactions that
affect protein function. Mohamed, Xia, Issoufou, and Qixing (2012)
reported that interactions between proteins and water or oil are
important in food systems, as they affect the flavor and texture of
food. WHC s (g per g protein) with or without pH-shift treatment (pH
2.0–12.0) of the RPIs and positive controls are shown in Figure 2b. In
the control samples, the WHCs of RPI-1 and RPI-3 (5.1 and 5.4 g/g
protein, respectively) were higher than those of RPI-2, RPI-4, and ca-
sein (3.3–3.8 g/g protein). After alkaline solubilization, the WHCs of
RPI-1 and RPI-3 (recovered at pH 4.5) were significantly higher than
those of RPI-2 and RPI-4 (recovered at pH 5.5). This may be because
of the fractionation effect between the recovered RPIs during ISP.
The WHC of solubilized hemoglobin (0.9 g/g protein) after pH-shift
treatment was significantly lower than those of the RPIs and casein
(p < .05).
The WHCs of the RPIs were 20.7 ± 0.0–36.7 ± 0.9 g/g protein
at pH 2 and 19.8 ± 8.8–40.6 ± 0.0 g/g protein at pH 10–12. Among
the RPIs, RPI-2 showed a relatively high WHC. In contrast, at pH
4–8, the WHC of the RPIs (3–6 g/g protein) was similar to that of the
control. Thus, pH-shift treatment significantly improved the WHC of
RPIs at pH values other than pH 4–8, at which WHC was minimized
because of increased electrostatic repulsion. Mohamed et al. (2012)
Amino acid FDSTR
RPIs
Casein HbRP I−1 R PI−2 RPI−3 RPI−4
Protein content
(%)
75.8 75.7 80.4 75.6 79. 3 8 9.1 96.3
Thr 5.1a4.8bc 4.9b4.8bc 4.9b3 .9d4.7c
Val6.2d6.3cd 6.1e6.4c6.4c7. 3 b10.2a
Met2.8b3.1a3 .1a3.1 a3.2a1.3c0.0d
ILe5.1d6.3ab 6.2b6.4a6.4a5.7c0.8e
Leu8.3e9.8 b9.7bc 9. 6c9.8 b9.1d13.3a
Phe4.1d4.8bc 4.7c4.8bc 4.9b5.0b7. 6 a
His 3.5b2.9c3.0c2.9c3.0c2.9c6.4a
Lys 8.4d8.7b8.6c8.4d8.8b8.3d10. 3a
Arg 6.6a6.6a6.6a6.4b6.5ab 4.4c3.8d
EAAs (%) 50.1 53.3 52.9 52.9 53.8 47.9 57. 1
Asp 9.0b8.8c8.8c9. 0 b9.0b8.2d11.2a
Ser 6.0a5.9a5.7b5.6b5.4c4.0e4.4d
Glu 13.2b12.2e12.4d12.8c12.5d22 .1a9. 3f
Pro5.8b4.6c4.2d4.6c4.1de 10.0a4.0e
Gly4.7a3.6b3.6b3.7b3.7b2.4c4.6a
Ala6.8c7.4 b7. 4 b7. 2 bc 7. 2bc 3.8d9.0 a
Cys 1.1a0.9b1.2a0.9b0.8b0.5c0.1d
Tyr 3.4b3.3b3.8a3.4b3.4b1.2c0.3d
NEAAs (%) 49.9 4 6.7 47. 1 47. 1 46.2 52.1 42 .9
Tot al (%) 100.0 100.0 100.0 100.0 100.0 100.0 100.0
EAAs/NEAAs 1.00 1.14 1.12 1.12 1 .17 0.92 1.33
HAAs (%) 43.8 45.9 45.0 45.8 45.7 44.6 4 9.5
Note: Value s with dif ferent letters within the same row are significantly different at p < .05 by
Duncan's multiple range test. Data are means of duplicate determination.
Abbreviations: E AAs, essential amino acids; HA As, hydrophobic amino acids. FDSTR , freeze-dried
skipjack tuna roe; Hb, haemoglobin; NE AAs, nonessential amino acids; RPI-1 and RPI-2, roe protein
isolates adjusted to pH 4.5 and 5.5, respectively, after alkaline solubilization at pH 11; RPI-3 and
RPI-4, roe protein isolates adjusted to pH 4.5 and 5.5, respectively, after alkaline solubilization at
pH 12.
Based on dry basis .
Hydrophobic amino acid.
TABLE 2 Amino acid composition
(g/100 g protein) of protein isolates
recovered from skipjack tuna roe (RPIs)
using isoelectric solubilization and
precipitation process
1882 
|
   CHA et Al.
reported that WHCs of protein isolates from tilapia were 2.63–
2.51 g/g protein, which are lower than those of the RPIs found in this
study. Azadian, Nasab, and Abedi (2012) reported that the WHC of
minced fish reached a minimum near the isoelectric point (pH 4–6).
Chalamaiah et al. (2013) reported that the lack of polar amino groups
on the surface of protein molecules reduced the WHC because
these polar groups are responsible for protein–water interactions.
The WHC of RPIs from STR was superior to that of yellow fin tuna
roe (Park et al., 2016), Labeo rohita fish egg (Balaswamy, Jyothirmayi,
& Rao, 2007), and mrigal egg protein concentrates (Chalamaiah et al.,
2013). Particularly, our results showed that structural changes in
proteins were actively induced at extreme pH (pH 2 and pH 10–12),
which increased the WHC by more than 5–8-fold compared with the
controls. This is because acidic and alkaline pH shif ts cause protein
conformational changes in the RPIs, allowing hydrophilic amino acids
to easily access the surrounding water and increase the WHC.
3.3.3 | Protein solubility
Solubility is an important functional propert y of proteins, as it af-
fects rheological, hydrodynamic, and sur face activity character-
istics. Protein solubility is also important in many protein-based
formulations (Park et al., 2016). The solubilities (%) of the RPIs with
and without pH-shift treatment are shown in Figure 2c. The solu-
bilities of the control RPIs (1.7 ± 0.0–6.7 ± 0.3%) were significantly
lower (p < .05) than that of hemoglobin (71.3 ± 16.8%). However,
the solubility of casein was the lowest (0.4%), and the protein was
nearly insoluble in a 1% dispersion. The solubility of pH-shifted RPIs
FIGURE 1 SDS-PAGE patterns of protein isolates isolated
from skipjack tuna roe (RPIs) using isoelectric solubilization and
precipitation. M, protein maker; STR, skipjack tuna roe; RPI-1, RPI-
2, RPI-3, and RPI-4, roe protein isolates adjusted to pH 4.5 and 5.5
after alkaline solubilization at pH 11 and 12
FIGURE 2 Buffer capacity (a), water-holding capacity (b), and
solubility (c) of protein isolates recovered from skipjack tuna roe
(RPIs) using isoelectric solubilization and precipitation without
(control) and with pH-shift treatment. Values are expressed as the
mean ± SD of triplicate determinations. Means with different letters
within the sample and pH are significantly different at p < .05 by
Duncan's multiple range test. Hb, hemoglobin
  
|
 1883
CHA et Al .
increased significantly at pH 2 (17.8 ± 0.3–33.1 ± 12.4%) compared
with the controls. At pH 12, their solubilities ranged from 69.1 ± 25.8
to 92.9 ± 18.7%, indicating a higher rate of solubilit y increase at al-
kaline pH. After alkaline solubilization, the solubilities of RPI-1 and
RPI-3 after acid precipitation at pH 4.5 were significantly higher
than those of RPI-2 and RPI-4 recovered at pH 5.5. However, the
solubility of hemoglobin (82.3 ± 4.0–99.9 ± 17.9%) was not affected
by pH-shift treatment (pH 2–12). Casein at pH 2 (42.7 ± 4.9%) and
pH 7–12 (83.8 ± 7.2–90.3 ± 9.0%) showed significantly higher sol-
ubility than the controls. The RPIs and casein showed the lowest
solubilities near the isoelectric point of pH 4–6 because of acid- and
alkali-limited protein solubilization. These results indicate that ex-
treme pH changes (such as pH 2 and 12) affected protein solubil-
ity by exposing more charged and polar groups to the surrounding
water (Kristinsson & Rasco, 2000). The pH-dependent solubility of
proteins is important in food functional properties and food system
applications, particularly when the pH is below 4 or over 7, and is af-
fected by protein–protein and protein–solvent interactions and the
surface hydrophilic–hydrophobic balance (Gbogouri, Linder, Fanni, &
Parmentier, 2004). The high solubility of fish proteins is important
in food applications because it affects other functional properties
such as foam and emulsification characteristics (Kristinsson & Rasco,
2000).
3.3.4 | FC and FS
Dispersions (1%, w/v) of the RPIs and positive controls were pre-
pared in DDW to measure FC and FS. Before centrifugation, the FCs
of 1%-dispersed RPI-1 and RPI-3 (125.3 ± 2.2–128.6 ± 3.4%) were
lower than that of hemoglobin (138.9 ± 18.3%), although the dif-
ference was not significant (p > .05), while RPI-2, RPI-4, and casein
showed no FC. The FSs of RPI-1, RPI-3, and hemoglobin were rela-
tively st able at 81.1 ± 8.0–88.0 ± 4.0±% for 60 min (Table 3). The FC
and FS of the supernatant from dispersed samples af ter centrifuga-
tion with and without pH-shift treatment are shown in Table 3.
The FCs of RPI-1, RPI-3, and casein increased by 147.0 ± 4.6%,
135.8 ± 4.8%, and 109.4 ± 11.1%, respectively, compared with
the dispersed samples; however, RPI-2 and RPI-4 showed no
foaming. The FC of hemoglobin decreased (138.9 ± 18.3% to
120.9 ± 11.9%) after centrifugation. During pH-shift treatment
(pH 2–12), the FCs of RPI-1 and RPI-3 was significantly increased
at pH 2 (191.3 ± 5.8% and 159.3 ± 6.3% , respectively) and pH
10–12 (139.9 ± 0.9–208.7 ± 7.6%) compared with the controls
(147.0 ± 4.6% and 135.8 ± 4.8%, respectively) (p < .05); however,
FCs at pH 4–8 (128.8 ± 5.6–154.0 ± 2.8%) showed no significant
difference (p > .05). The FCs of RPI-2 and RPI-4 were significantly
increased at pH 2 (185.1 ± 10.8% and 168.7 ± 4.2%, respectively)
and pH 7–12 (118.6 ± 0.4–186.7 ± 13.0%) compared with the
controls, whereas no FC (100.0%) was observed at pH 4–6. The
maximum FC of the RPIs (183.4 ± 25.0–208.7 ± 7.6%) and casein
(184.8 ± 65.0%) were observed at pH 12 and 8, respectively. At
pH 2–12, hemoglobin showed 115.1 ± 8.8–140.0 ± 22.5% FC;
however, pH-shift treatment did not induce a significant differ-
ence (p > .05). Regardless of pH-shift treatment, the FCs of RPI-1
and RPI-3 were superior to those of RPI-2, RPI-4, casein, and he-
moglobin. Proteins must rapidly migrate to the air–water inter-
face, unfold, and rearrange at the interface to show good foam
performance. Mutilangi, Panyam, and Kilara (1996) suggested that
the foaming ability of proteins could be improved by increasing
flexibility, which exposes a larger number of hydrophobic residues
and reduces surface tension. The FS of hemoglobin (81.4 ± 3.4%)
was maintained for up to 60 min in control 2 (without pH-shift),
but the RPIs and casein showed no FS ( Table 3). The FSs of RPIs
(59.1 ± 4.3–77.2 ± 8.0%) were more stable at pH 7–12 than at pH
2–6 un til 60 min af ter wh ipp ing . Add iti o nal ly, RPI -1 and RP I-3 we re
more stable than RPI-2 and RPI-4, and the foam characteristics of
RPI-1 were superior to those of RPI-3. All samples showed a low
foaming capacity at pH 4–6 because of their low WHC and solu-
bility (Figure 2) near the isoelectric point, and FS depends on the
degree of protein–water and protein–protein interactions within
the matrix (Mutilangi et al., 1996).
3.3.5 | EAI and ESI
The oil-in-water EAI and ESI were determined to evaluate the ability
of the samples to emulsify in foods such as soups, sauces, confec-
tionery breads, and dairy product s. The EAI (m2/g protein) and ESI
(min) of the RPIs and positive controls are shown in Table 3. The
EAI of the dispersed RPIs (control 1) was 1.8 ± 0.1–3.9 ± 0.5 m2/g
protein, and RPI-3 showed the highest EAI (3.9 ± 0.5 m2/g protein).
However, the EAI of the RPIs was significantly lower than that of
hemoglobin (18.4 ± 2.1 m2/g protein) (p < .05). After centrifugation
(control 2), the EAI of the supernatant of the dispersed samples was
generally increased, except for that of RPI-4 (2.3 ± 0.5 m2/g protein).
The EAIs of RPI-1 (14.7 ± 1.1), RPI-3 (15.9 ± 2.1), and casein (7.0 ± 0.9)
were notably higher than those of the dispersions before centrifuga-
tion (control 1).
Th e ES I of he mo g l ob i n (c o n t r o l 1) wi t h an EAI of 18 . 4 ± 2.1 m2/g
protein was 20.0 ± 6.4 min, while those of the RPIs and casein
were undetectable. Af ter centrifugation (control 2), there was no
significant difference in the ESIs (30.7 ± 7.0–34.5 ± 4.6 min) of
RPI-1, RPI-3, and casein (p > .05), although their ESIs were signifi-
cantly higher than that of hemoglobin (20.1 ± 3.7 min) (p < .05).
The increase in EAI and ESI after centrifugation may be related
to the presence of insoluble par ticles in the dispersion that in-
terfere with emulsion layer formation. EAI assessment of RPIs
and positive controls after pH-shift (pH 2–12) treatment showed
that RPI-2, RPI-4, casein, and hemoglobin had the lowest EAIs
(2.3 ± 0.5–12.9 ± 1.7 m2/g protein) at pH 4 and RPI-1 and RPI-3
had the lowest EAIs (13.3 ± 0.8 and 9.2 ± 0.4 m2/g protein, re-
spectively) at pH 6 (Table 3). These results suggest that the FC
and emulsifying activity are closely related to protein solubility
in food, which was minimal in the RPIs and positive controls at
pH 4–6. At pH 2 and 7–12, the EAIs of all samples, except for
1884 
|
   CHA et Al.
hemoglobin, were higher than that of control 2. At all pH ranges
except for pH 2, the EAIs of RPI-1 and RPI-3 were higher than
those of RPI-2 and RPI-4. The EAI of the RPIs showed no sig-
nificant differences (p > .05) at pH 2 and 7–12; however, the
emulsifying activity significantly increased with pH (p < .05). The
emulsion stability did not increase in proportion to the increase
in emulsif ying activity with pH. The large deviation in emulsion
stability after pH-shif t treatment may have occurred bec ause
of the nonuniformit y of emulsified particles. Mutilangi et al.
(1996) reported that a higher content of high-MW peptides or
TABLE 3 Foaming capacit y (FC, %), foam stability (FS, %, 60 min), emulsifying activity index (EAI, m2/g of protein), and emulsion stability
(ESI, min) with pH-shift of protein isolates recovered from skipjack tuna roe (RPIs)
Sample
RPI-1 (pH
11/4.5) RPI-2 (pH 11/5.5) RPI-3 (pH 12/4.5) RPI-4 (pH 12/5.5) Casein Hb
FC (%) Control 1 128.6 ± 3.4A100.0 ± 0.0B125.3 ± 2.2 A100.0 ± 0.0B100.0 ± 0.0B138.9 ± 18.3A
Control 2 147.0 ± 4.6Ac 100.0 ± 0.0Cd 135.8 ± 4.8Ac 100.0 ± 0.0Cd 109.4 ± 11.1BCb 120.9 ± 11.9Ba
pH 2 191.3 ± 5.8Ab 185.1 ± 10.8ABa 159.5 ± 6.3CDb 168.7 ± 4.2BCa 140.3 ± 23.6Dab 115.1 ± 8.8Ea
pH 4 148.0 ± 9.9Ac 100.0 ± 0.0Dd 137.8 ± 3.8ABc 100.0 ± 0.0Dd 109.1 ± 10.8CDb 125. 2 ± 18.7BCa
pH 6 144.0 ± 6.8Ac 100.0 ± 0.0Cd 139.8 ± 2.9Ac 100.0 ± 0.0Cd 107.0 ± 8.4BCb 126.1 ± 26.5ABa
pH 7 128.8 ± 5.6ABd 118.6 ± 0.4Bc 145.8 ± 8.4ABc 114.2 ± 5.6Bcd 158.6 ± 37.0Aab 132.0 ± 17.1ABa
pH 8 154.0 ± 2. 8ABc 131.8 ± 0.6ABbc 145.3 ± 3.9ABc 120.5 ± 5.8Bb 184.8 ± 65.0Aa 139.8 ± 21.7ABa
pH 10 197.6 ± 9.5Aab 128.2 ± 0.8Bbc 139.9 ± 0.9Bc 125.4 ± 2.2Bb 135.6 ± 12.8Bab 140.0 ± 22.5Ba
pH 12 208.7 ± 7.6Aa 186.7 ± 13.0Aa 20 0.3 ± 14.8Aa 183.4 ± 25.0Aa 130.5 ± 9.7Bab 129.7 ± 7.8Ba
FS (%,
60 min)
Control 1 88.0 ± 4.0A- 86.1 ± 7.3A- - 81.1 ± 8.0A
Control 2 - - - - - 81.4 ± 3.4a
pH 2 - 28.4 ± 1.8Bc -56.4 ± 4.9Ab 41.3 ± 9.8ABb 52.4 ± 12.2Ac
pH 4 - - - - 73.6 ± 3.1Ba 52.9 ± 7.5Ac
pH 6 43.3 ± 6.8Bb -- -76.9 ± 0.7Aa 76.0 ± 11.5Aab
pH 7 68.9 ± 8.0Aa - 71.8 ± 3.0Aa - 74.4 ± 4.5Aa 74.5 ± 6.6Aabc
pH 8 77.2 ± 8.0Aa - 73.7 ± 0.2Aa 65.4 ± 7.3Aab 43.1 ± 18.9Bb 63.0 ± 5.9Aabc
pH 10 73.6 ± 6.3ABa 78.4 ± 6.2Aa 75.0 ± 2.6Aa 70.4 ± 4.5ABa 62.4 ± 1.7ABa 56.1 ± 20.7Bbc
pH 12 69.2 ± 2.3Aa 59.1 ± 4.3Ab 60.5 ± 7.9Ab 61.7 ± 3.5Aab 69.1 ± 9.1Aa 57.1 ± 16.6Abc
EAI (m2/g
protein)
Control 1 3.1 ± 0.1BC 1.8 ± 0.1CD 3.9 ± 0.5B3.4 ± 0.2BC 0.4 ± 0.3D18.4 ± 2.1A
Control 2 14.7 ± 1.1Be 3.9 ± 0.9De 15.9 ± 2.1Be 2.3 ± 0.5Dd 7.0 ± 0.9Ce 19.1 ± 1.9Aab
pH 2 15.5 ± 1.2Be 20.3 ± 1.4Ac 14.2 ± 0.9Be 19.2 ± 3.9Ac 11.9 ± 1.1Bcd 20.1 ± 1 2.3Aab
pH 4 14.8 ± 0.9ABe 5.5 ± 0.1Ce 15.6 ± 2.9Ae 5.6 ± 0.3Cd 2.3 ± 0.5Df 12.9 ± 1.7Bc
pH 6 13.3 ± 0.8Ce 9.8 ± 2.5Dd 9.2 ± 0.4Df 23.8 ± 1.2Ac 9.1 ± 1.7Dde 18.1 ± 1.3Bab
pH 7 21.0 ± 0.2 ABd 18.8 ± 1.8Bc 20.5 ± 0.4Bd 23.7 ± 1.7Ac 13.8 ± 2.6Cc 18.4 ± 1.8Bab
pH 8 27.3 ± 0.9Ac 22.2 ± 1.0Bc 26.5 ± 1.7Ac 26.2 ± 1.3Ac 12. 8 ± 1.3Dc 18. 3 ± 0.5Cab
pH 10 33.6 ± 2.4Ab 36. 5 ± 0.7Ab 33.4 ± 2.7Ab 34.2 ± 5.4Ab 23.7 ± 2.7Bb 16.1 ± 4.4Cbc
pH 12 54.2 ± 4.8Aa 54.0 ± 4.1Aa 55.0 ± 0.6Aa 53.8 ± 9.2Aa 36.8 ± 2.2Ba 20.8 ± 1.5Ca
ESI (min) Control 1 - - - - 20.0 ± 6.4C
Control 2 30.7 ± 7.0Abc - 34.5 ± 4.6Ab - 31.8 ± 3.6Ab 20.1 ± 3.7B ab
pH 2 15.3 ± 1.5ABc 16.9 ± 1.7ABb 17.0 ± 1.1ABc 20.2 ± 7.9ABc 13.2 ± 2.3Bc 21.2 ± 2.0Aa
pH 4 16.7 ± 1.7Cc 56.2 ± 15.1Ab 17.2 ± 1.7Cc 29.1 ± 4.0BCc 37.6 ± 13.9Bb 18.5 ± 2.1Cab
pH 6 31.2 ± 3.7Bbc 61.0 ± 18.1Ab 55.3 ± 0.0Ab 53.1 ± 17.4Ab 23.5 ± 4.3Bbc 18.6 ± 1.2B ab
pH 7 56.2 ± 4.5Bab 58.2 ± 8.1ABb 37.3 ± 4.3Cab 67.6 ± 8.8Aab 14.8 ± 1.7Dc 18.4 ± 2.7Dab
pH 8 25.2 ± 2.9Bbc 70.5 ± 11.9Ab 23.6 ± 1.8Bab 63.4 ± 1.3Aab 16.0 ± 2.3Bc 18.3 ± 1.8Bab
pH 10 27.5 ± 6.3CDbc 38.2 ± 5.5Bb 29.8 ± 3.3BCb 53.5 ± 7.3Ab 26.1 ± 6.9CDbc 18.0 ± 1.2Dab
pH 12 83.4 ± 49.2ABa 127.2 ± 74.8Aa 114.3 ± 48.3Aa 83.8 ± 26.4ABa 62.7 ± 13.9ABa 16.6 ± 1.8Bb
Note: Controls 1 and 2 refer to the s amples before and after centrifugation of the 1% dispersions, respectively. Values represent the mean ± SD of
n = 3. Means with different capital letters within same row and small letters within the same column are significantly different at p < .05 by Duncan's
multiple range test.
-, not detected
  
|
 1885
CHA et Al .
hydrophobic peptides contributes to the stabilit y of emulsions.
Additionally, low-MW peptides exhibit good emulsification prop-
erties, although they are not amphipathic. The emulsifying prop-
erties of proteins are largely af fected by solubility, molecular size,
surface hydrophobicity, net charge, steric hindrance, and molecu-
lar flexibility (Gbogouri et al., 200 4).
3.4 | Antioxidative and antihypertensive activity
Table 4 shows the ABTS+ radical scavenging activity (IC50, μg /ml ),
tyrosinase inhibitory activity (%), and ACE inhibitory activity (%)
of RPI-1. The ABTS+ radical scavenging assay can be performed
on both lipophilic and hydrophilic compounds and has been
widely used as an antioxidant activity assay. The ABTS+ radical
scavenging activity (IC50) of RPI-1 (1.5 ± 0.1 mg protein/ml) was
102.7 ± 1.0 μg/ml, which was better than those of alcalase and
Protamex hydrolysates from shrimp processing byproducts (160
and 170 µg/ml, respectively) (Kim et al., 2016). UV irradiation can
generate reactive oxygen species that influence skin pigmenta-
tion. Tyrosinase inhibitors have recently gained attention in the
medical and cosmetic industries because of their association with
hyper-pigmentation (Choi, Kim, & Lee, 2011). The tyrosinase in-
hibitory activity of RPI-1 was 13.5 ± 1.7%, and some whitening
effects were predicted. Choi et al. (2011) reported a tyrosinase
inhibitory activity of 31% for tuna cooking drip, but this value
increased with the dose of gamma irradiation. Choi et al. (2017)
reported that anchovy muscles not subjected to subcritical water
hydrolysis inhibited t yrosinase activity by 14.65%. In these ex-
perimental results and reports, tyrosinase inhibitory activity was
also observed in proteinous materials containing proteins or amino
acids, but its inhibitory activity was low. The inhibition of ACE, a
key enzyme that regulates blood pressure, has been recognized
as an effective therapy for treating hypertension. The ACE inhib-
itory activity of RPI-1 was 44.0 ± 4.9%. The current search for
natural ACE-inhibiting peptides has extended into seafood protein
sources, particularly seafood byproduct s. The hydrolysates of the
byproducts of skin (Ngo, Ryu, & Kim, 2014) and yellow sole frame
(Jung et al., 2006) showed 35%–86% ACE inhibitory activities,
which are consistent with our results. These results suggest that
RPIs from STR possess antioxidative and antihypertensive activi-
ties, which can be improved by enzymatic hydrolysis.
4 | CONCLUSION
The aims of this study were to investigate the physicochemical and
functional properties of protein isolates recovered from skipjack
tuna roe (STR) by ISP. The roe protein isolates (RPIs) were similar
or superior to the positive controls (casein and hemoglobin) and
other fish protein isolates in terms of buffering capacity, foaming
ability, and emulsifying ability. The RPIs were rich in proteins con-
taining essential amino acids and exhibited suitable functional char-
acteristics for supplementing surimi-based products and traditional
foods. They also showed in vitro antioxidant and antihypertensive
activities. This study suggests that high value-added produc ts can
be developed from fish roes, which are currently underutilized in the
seafood processing industry.
ACKNOWLEDGMENTS
This research was a par t of the projected titled “Development and
commercialization of traditional seafood products based on the
Korean coastal marine resources (2016),” funded by the Ministry of
Oceans and Fisheries, Korea.
CONFLICT OF INTEREST
The authors claim no conflict s of interest.
ETHICAL APPROVAL
This study did not involve human or animal testing.
ORCID
Min Soo Heu https://orcid.org/0000-0001-7609-0303
REFERENCES
Al-Holy, M. A ., & Rasco, B. A. (20 06). Characterisation of salmon
(Oncorhynchus keta) and sturgeon (Acipenser transmontanus) caviar
proteins. Journal of Food Biochemistry, 30, 422–428.
AOAC. (2005). Official methods of ana lysis. 18th ed. Methods 925.45,
923.03, 976.05, 991.36. Gaithersburg: AOAC International
Publishing.
Azadian, M., Nasab, M. M., & Abedi, E. (2012). Comparison of func-
tional proper ties and SDS-PAGE patterns between fish pro-
tein isolate and surimi produced from silver carp. European Food
Research and Technology, 235, 83–90. https ://doi.org/10.1007/
s0 0217-012-1721-z
Balasw amy, K., Jyot hirmayi, T., & Rao, D. G. (2 007). Chemic al composition
and some functional prop erties of fish eg g (roes) protein concentrate
Sample Protein  (mg/ml)
ABTS+, IC50 (μg/
ml)
Tyrosinase
inhibitory
activity (%)
ACE inhibitory
activity (%)
RP I −11.5 ± 0.1 102.7 ± 1.0 13.5 ± 1.7 44.0 ± 4.9
Note: Values represent the mean ± SD of n = 3.
Abbreviations: IC50, the half maximal inhibitory concentration.
Based on the Lowry's (1951) methods.
Supernatant of 1% dispersion after centrifugation.
TABLE 4 ABTS+ radical scavenging
activity, tyrosinase inhibitory activit y, and
angiotensin-converting enzyme (ACE)
inhibitory activity of roe protein isolate-1
(R P I -1)
1886 
|
   CHA et Al.
of rohu (Labeo rohita). Journ al of Food Science and Technology, 44,
293–296.
Bechtel, P. J., Chantarachoti, J., Oliveira, A. C. M., & Sathivel, S. (2007).
Charac terization of protein fractions from immature Alaska walleye
pollock (Theragra chalcogramma) roe. Journal of Food Science, 72,
S33 8–S343. https ://doi.or g/10 .1111/j.1750-3 841 .2007.00396. x
Binsan, W., Benjakul, S., Visessanguan, W., Royt rakul, S., Tanaka, M., &
Kishimura, H. (20 08). Antioxidative activity of Mungoong, an extract
paste, from the cephalothorax of white shrimp (Litopenaeus vanna-
mei). Food Chemistry, 10 6, 185–193. https ://doi.org/10.1016/j.foodc
hem.2007.05.065
Bledsoe, G. E., Bledsoe, C. D., & Rasco, B. (2003). Caviars and fish roe
products. Critical Reviews in Foo d Science and Nutrition, 43, 233–271.
https ://doi.org/10.1080/10408 69039 0826545
Chalamaiah, M., Balaswamy, K., Narsing Rao, G., Prabhakara Rao, P. G.,
& Jyothirmayi, T. (2013). Chemical composition and functional prop-
erties of mrigal (Cirrhinus mrigala) egg protein concentrates and their
application in pasta. Jo urnal of Food Technology, 50, 514–520. https ://
do i. org /10.10 07/s1 319 7-011- 0 35 7-5
Chen, Y. C., & Jaczynski, J. (20 07). Protein recover y from rainbow trout
(Oncorhynchus mykiss) processing by-products via isoelectric sol-
ubilization/precipitation and its gelation properties as affected by
functional additives. Journal of Agricultura l and Food Chemistr y, 55,
9079–9088.
Choi, J. S., Jang, D. B., Moon, H. E., Roh, M. K., Kim, Y. D., Cho, K. K.,
& Choi, I. S . (2017). Physiological properties of Engraulis japoni-
cus muscle protein hydrolysates prepared by subcritical water hy-
drolysis. Journal of Environmental Biology, 38, 283 –28 9. ht tps ://doi .
org/10. 22438/ jeb/38/2/MRN-973
Choi, J. I., Kim, J. H., & Lee, J. W. (2011). Physiological properties of tuna
cooking drip hydrolysate prepared with gamma irradiation. Process
Biochemistry, 46, 1875–1878. https ://doi.org/10.1016/j.procb
io.2011.06.005
Cushman, D. W., & Cheung, H. S. (1971). Spectrophotometric assay
and properties of the angiotensin-converting enzyme of rab-
bit lung. Biochemical Pharmacology, 20, 16 37–1648. ht tps ://doi.
org /10.1016/0 006-2952(71)9 0292-9
Gbogouri, G. A., Linder, M., Fanni, J., & Parmentier, M. (20 04). Influence
of hydrolysis degree on the func tional proper ties of salmon byprod-
uct hydrolysates. Journal of Food Scien ce, 69, 615–622.
Gokoglu, N., & Yerlikaya , P. (2003). Determination of proximate com-
position and mineral contents of blue crab (Callinectes sapidus) and
swim crab (Portunus pelagicus) caught off the Gulf of Antalya. Food
Chemistry, 80, 495–498.
Gokoglu, N., Yerlikaya , P., & Cengiz, E. (20 04). Effect of cooking methods
on the proximate composition and mineral content s of rainbow trout
(Oncorhynchus mykiss). Food Chemistry, 84, 19–22.
Heu, M. S., Kim, H. S., Jung, S. C., Park, C. H., Park , H. J., Yeum, D. M.,
… Kim, J.-S. (20 06). Food component charac teristics of skipjack
(Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) roes.
Journal of the Korean Fisheries Society, 39, 1–8.
Huda, N., Abdullah, A., & Babji, A. S. (2001). Functional properties of
surimi powder from three Malaysian marine fish. International
Journal of Food Science and Technolog y, 36, 401–406. ht tps ://doi.
org /10.10 46/j.13 65-2621.2001.00 473. x
Hultin, H. O., & Kelleher, S. D. (1999). Process for iso lating a protein comp o-
sition from a muscle source and protein composition. Advanced Protein
Technologies Inc, assignee. US Pat. No. 6,005,073.
Iida, K., Hase, K., Shimomura, K., Sudo, S., Katota, S., & Namba, T. (1995).
Potent inhibitors of t yrosinase activity and melanin biosynthesis
from Rheum officinale. Planta Medica, 61, 425–428.
Intarasirisawat, R., Benjakul, S., & Visessanguan, W. (2011). Chemical com-
positions of the roes from skipjack, tongol and bonito. Food Chemistry,
124, 1328–1334. https ://doi.org/10.1016/j.foodc hem.2010.07.076
Jellouli, K., Balti, R ., Bougatef, A., Hmidet, N., Barkia, A., & Nasri, M .
(2011). Chemic al composition and charac teristics of skin gela-
tin from grey triggerfish (Balistes capriscus). LW T- Foo d Sc i enc e
and Technology, 44, 1965–1970. https ://doi.org/10.1016/j.
lwt.2011.05.005
Jung, W., Mendis, E., Je, J., Park, P., Son, B. W., Kim, H . C., … Kim, S.-
K. (2006). Angiotensin I-converting enzyme inhibitory peptide from
yellowf in sole (Limanda aspera) frame protein and its antihyper ten-
sive effect in spontaneously hypertensive rats. Food Chemistry, 94,
26–32. https ://doi.org/10.1016/j.foodc hem.2004.09.048
Kim, H. J., Kim, K. H., Song, S. M., Kim, I. Y., Park, S. H., Gu, E. J., … Heu,
M. S. (2013). Fractionation and characterization of protease inhib-
itors from fish eggs based on protein solubilit y. Korean Journal of
Fisheries and Aquatic Sciences, 46, 119–128. https ://doi.org/10.5657/
KFAS. 2013.0 119
Kim, S. B., Yoon, N. Y., Shim, K. B., & Lim, C. W. (2016). Antioxidant and
angiotensin I-converting enzyme inhibitory activities of nor thern
shrimp (Pandalus borealis) by-products hydrolysate by enzymatic
hydrolysis. Fisheries and Aquatic Sciences, 19(29), 1–6. https ://doi.
org/10.1186/s41240-016-0028-6
KOSIS. Korean statistical information service, Regional statistics. 2016.
http://kosis.kr/st ati st ic s Lis t/stat i sti cs List _ 01List. jsp?v wcd=MT_
ZTITL E&parmT abId=M_01_01#SubCo nt/. Accessed 15 July 2017.
Kristinsson, H. G., &Rasco, B. A . (2000). Biochemical and functional
proper ties of Atlantic salmon (Salmo salar) muscle hydrolyzed with
various alkaline proteases. Journal of Agricultural an d Food Chemistry,
48, 657–666.
Kristinsson, H. G., Theodore, A. E., Demir, N., & Ingadottir, B. (2005).
A comparative study between acid-and alkali-aided processing and
surimi processing for the recovery of proteins from channel cat-
fish muscle. Journal of Food Science, 70, C298–C306. https ://doi.
org /10.1111/j.1365 -2621.2005.tb071 77.x
Laemmli, U. K. (1970). Cleavage of structural proteins during the assem-
bly of the head of bacteriophage T4. Nature, 227, 680–685. https ://
doi.org /10.1038/227680a 0
Lee, G. W., Yoon, I. S., Kang, S. I., Lee, S. G., Kim, J. I., Kim, J. S., & Heu, M.
S. (2017). Func tionality and biologic al activity of isolate processed
water generated during protein isolate preparation of fish roes using
an isoelectric solubilization and precipitation process. Korean Journal
of Fisheries and Aquatic Sciences, 50, 694–706.
Lee, H. J., Lee, G. W., Yoon, I. S., Park , S. H., Park, S. Y., Kim, J. S., & Heu,
M. S. (2016). Preparation and char acterization of p rotein isolate from
yellowf in tuna Thunnus albacares roe by isoelectric solubilization/
precipitation process. Fisheries and Aquatic Sciences, 19, 1–10. https
://doi.org/10.1186/s41240-016-0014-z
Lee, H. J., Park, S. H., Yoon, I. S., Lee, G. W., Kim, Y. J., Kim, J. S., & Heu,
M. S. (2016). Chemical composition of protein concentrate prepared
from yellowfin tuna Thunnus albacares roe by cook-dried process.
Fisheries and Aquatic Sciences, 19, 1–8. https ://doi.org/10.1186/
s41240-016-0012-1
Lowry, O. H., Rosebrough, N. J., Farr, A. L., & Randall, R. J. (1951). Protein
measurement with the Folin phenol reagent. Journal of Biological
Chemistry, 193, 265–275.
Martinez-Valverde, I., Periago, M. J., Sant aella, M., & Ros, G. (200 0). The
content and nutritional significance of minerals on fish flesh in the
presence and absence of bone. Food Chemistry, 71, 503–509. ht tp s ://
doi.org /10.1016/S03 08-8146(00 )0 0197-7
Mireles DeWitt, C. A., Gomez, G., & James, J. M. (2002). Protein ex-
traction from beef hear t using acid solubilization. Journal of Food
Science, 67, 3335–3341. https ://doi.org/10.1111/j.1365-2621.2002.
t b 0 9 5 8 8 . x
Mohamed, B. K. F., Xia, W., Issoufou, A., & Qixing, J. (2012). Influence
of pH shift on functional properties of protein isolated of tilapia
(Oreochromis niloticus) muscles and of soy protein isolate. Food and
  
|
 1887
CHA et Al .
Bioprocess Technology, 5, 2192–2200. https ://doi.org/10.1007/
s11947-010-0496-0
Mohamed, T. K ., Zhu, K., Issoufou, A., & Fatmata, T. (2009). Functionalit y,
in vitro digestibility and physicochemical proper ties of t wo varieties
of defatted foxtail millet protein concentrates. International Journal
of Molecular Sciences, 10, 5224–5238. https ://doi.o rg/10.3390/i jms1
01252 24
Mutilangi, W. A. M., Panyam, D., & Kilara, A. (1996). Functional prop-
erties of hydrolys ates from proteolysis of heat-denatured whey
protein isolate. Journal of Food Science, 61, 27 0–274. ht tp s ://do i.
org /10.1111/j.1365 -2621.1996.tb141 74.x
Narsing Rao, G., Prabhakara Rao, P., Satyanarayana, A., & Balaswamy,
K. (2012). Functional properties and in vitro antioxidant activ-
ity of roe protein hydrolysates of Channa striatus and Labeo rohita.
Food Chemistry, 135, 1479–1484. ht tps ://doi.org/10.1016/j.foodc
hem.2012.05.098
Ngo, D. H., Ryu, B., & Kim, S. K. (2014). Active peptides from skate
(Okamejei kenojei) skin gelatin diminish angiotensin-I converting
enzyme activity and intracellular free radical-mediated oxidation.
Food Chemistry, 14 3, 246–255. https ://doi.org/10.1016/j.foodc
hem.2013.07.067
Nolsoe, H., & Undeland, I. (2009). The acid and alkaline solubilization
process for the isolation of muscle proteins. Food and Bioprocess
Technology, 2, 1–27.
Orban, E., Nevigato, T., Masci, M., Di Lena, G ., Casini, I., Caproni,
R., … Rampacci, M. (2007). Nutritional quality and safety of
European perch (Perca fluviatilis) from three lakes of central Italy.
Food Chemistry, 10, 482–490. https ://doi.org/10.1016/j.foodc
hem.2005.09.069
Park, S. H., Lee, H . J., Yoon, I. S., Lee, G. W., Kim, J. S., & Heu, M. S.
(2016). Protein functionality of concentrates prepared from yel-
lowfin tuna (Thunnus albacares) roe by cook-dried process. Food
Science and Biotechnology, 25, 1569–1575. https ://doi.org/10.1007/
s10068-016-0242-0
Sathivel, S., Bechtel, P. J., Babbit t, J. K., Prinyawiwatkul, W., Negulescu,
I. I., & Reppond, K . D. (200 4). Properties of protein powders from
arrowtooth flounder (Atheresthes stomias) and herring (Clupea
harengus) byproduc ts. Journal of A gricultu ral and Food Chemistr y, 52,
5040–5046.
Sathivel, S., Yin, H., Bechtel, P. J., & King, J. M. (2009). Physical and nu-
tritional properties of catfish roe spray dried protein powder and its
application in an emulsion system. Journal of Food Engineering, 95,
76–81. https ://doi.org/10.1016/j.jfood eng.2009.04.011
Sikorski, Z. E. (1994). The contents of proteins and other nitroge-
nous compounds in marine animals. In Z. E. Sikorski, B. S. Pan, &
F. Shahidi (Eds.), Seafood Proteins (pp. 6–12). New York: Chapman
and Hall.
Tahergorabi, R., Beamer, S. K., Matak, K . E., & Jac zynski, J. (2011). Effect of
isoelectric solubilisation/precipitation and titanium dioxide on whiten-
ing and tex ture of proteins recovered from dark chicken-meat process-
ing by-products. LWT-Food Science and Technology, 44, 896–903.
Yoon, I. S., Kang, S. I., Park, S . Y., Cha, J. W., Kim, D. Y., Kim, J. S., & Heu,
M. S. (2018). Physicochemical properties of alkaline-insoluble frac-
tions recovered from bastard halibut Paralichthys olivaceus and skip-
jack tuna Katsuwonus pelamis roes by alkaline solubilization. Korea n
Journal of Fisherie s and Aquatic Sciences, 51, 230–237.
Yoon, I. S., Kim, J. S., & Heu, M. S. (2018). Food functionality of collag-
enous protein fractions recovered from fish roe by alkaline solubili-
zation. Korean Journal of Fisheries and Aquatic Sciences, 51, 351–3 61 .
Yoon, I. S., Lee, G. W., Kang, S. I., Park, S. Y., Lee, J. S., Kim, J. S., & Heu,
M. S. (2018). Chemical composition and functional properties of roe
concentrates from skipjack tuna (Katsuwonus pelamis) by cook-dried
process. Food Science & Nutrition, 6, 1276–1286.
How to cite this article: Cha JW, Yoon IS, Lee G-W, et al.
Food functionalities and bioactivities of protein isolates
recovered from skipjack tuna roe by isoelectric solubilization
and precipitation. Food Sci Nutr. 2020;8:1874–1887.
https ://doi.org/10.1002/fsn3.1470
... ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ 2 화, 비타민 및 무기질소재와 같은 기능성 식품소재 (Galla et al., 2012b;Kim et al., 2016) 또는 단백질 및 지질추출소재 (Heu et al., 2006;Mahmoud et al., 2008)로서의 이용에 관한 연구 (Guerard et al., 2010;Kadam and Prabhasankar, 2010)를 통해 식품 또는 식품소재로 개발될 경우 그 가치는 5배 이상 증가할 것이라고 예상하였다 (Liu et al., 2015). 최근 수산가공 부산물의 식량자원화 또는 소재화를 위해, 고 영양원이면서 저 활용 식품자원인 어류 알의 식품기능성과 생 리활성에 대한 관심 또한 높아지고 있으나 (Intarasirisawat et al., 2014;Park et al., 2016;Cha et al., 2020;Yoon et al., 2020Yoon et al., , 2023Kang et al., 2023), 명태, 대구, 숭어, 가다랑어 등 일부의 어류 알만이 염장 발효식품인 알젓의 형태로 소비되고 있을 뿐, 대부분의 어류 알은 식품소재로 이용되지 못하고 있다. 이러한 일면에서 어류 알로부터 영양 강화를 위한 단백질 소 재로 이용하고자 하는 노력 (Yoon et al., 2019Cha et al., 2020;Kwon et al., 2022;Kang et al., 2023) (Galla et al., 2012b;Mohamed et al., 2012;Park et al., 2016), 특히 단백질 용해도(protein solubility)는 거품, 유화 및 겔 형성과 같은 식품단백질 기능성에 영향을 미치는 중요인자 이기도 하다 (Kristinsson and Rasco, 2000;Mohan et al., 2007;Azadian et al., 2012). ...
... 최근 수산가공 부산물의 식량자원화 또는 소재화를 위해, 고 영양원이면서 저 활용 식품자원인 어류 알의 식품기능성과 생 리활성에 대한 관심 또한 높아지고 있으나 (Intarasirisawat et al., 2014;Park et al., 2016;Cha et al., 2020;Yoon et al., 2020Yoon et al., , 2023Kang et al., 2023), 명태, 대구, 숭어, 가다랑어 등 일부의 어류 알만이 염장 발효식품인 알젓의 형태로 소비되고 있을 뿐, 대부분의 어류 알은 식품소재로 이용되지 못하고 있다. 이러한 일면에서 어류 알로부터 영양 강화를 위한 단백질 소 재로 이용하고자 하는 노력 (Yoon et al., 2019Cha et al., 2020;Kwon et al., 2022;Kang et al., 2023) (Galla et al., 2012b;Mohamed et al., 2012;Park et al., 2016), 특히 단백질 용해도(protein solubility)는 거품, 유화 및 겔 형성과 같은 식품단백질 기능성에 영향을 미치는 중요인자 이기도 하다 (Kristinsson and Rasco, 2000;Mohan et al., 2007;Azadian et al., 2012). 한편, 거품성(foaming capacity, FC) 및 거품안정성(foam stability, FS)은 식품의 신선감(refreshment), 부드러운 촉감(softening) 그리고 방향성분의 분산과 같은 독특 한 특성을 부여하며 (Mutilangi et al., 1996;Damodaran, 1997;Klompong et al., 2007), 그리고 유화능(emulsifying activity index, EAI)과 유화 안정성(emulsion stability index, ESI)은 water-oil 계면에서 단백질이 oil을 흡착하여 유화층의 형성 및 이를 유지시키는 능력을 말한다 (Karaca et al., 2011). ...
... 또한 식품소재의 생리활성(bioactivity)에는 DPPH (2,2-diphenyl-1-picrylhydrazyl) 라디칼 (Klompong et al., 2007) 및 ABTS + (2,2'-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt) 라디칼 소거활성 (You et al., 2010) 그리고 SOD (superoxide dismutase) 유사활성과 환원력(reducing power) 등의 항산화활성과 ACE (angiotensin-I converting enzyme) 저해활성을 (Mohan et al., 2007;Lee et al., 2016;Yoon et al., 2019). 앞서의 연구에서는 넙치 알을 대상으로 하 여, 가열건조 농축물의 식품성분 (Kwon et al., 2022)과 식품기 능성 , 그리고 ISP 공정을 통해 회수한 분리 단백질의 식품성분 특성 Alvarez et al., 2018;Yoon et al., 2019;Cha et al., 2020). ...
Article
Full-text available
We investigated the functional properties and in vitro bioactivity of protein isolates (RPIs) recovered from olive floun�der Paralichthys olivaceus roes by isoelectric solubilization/precipitation process, according to pH-shift treatments. The buffer capacity of RPIs was shown to be stronger in alkaline pH than in acidic pH. Water holding capacity of RPIs was in range of 4.5–5.2 g/g protein with no significant differences (P>0.05). The foaming capacity and emulsifying activ�ity index of RPIs did not show any significant differences between RPI-1 (pH 11/4.5) and 3 (pH 12/4.5), however they were superior to RPI-2 (pH 11/5.5) and 4 (pH 12/5.5). The 2,2′-azino-bis-3-ethylbenzo-thiazoline-6-sulfonic acid radical scavenging activity of RPI-3 (2.5 mg protein/mL) was 102.4 μg/mL, and the angiotensin I converting enzyme inhibitory activity was 30.8%. Among the RPIs, RPI-3 was relatively superior in protein functional properties such as buffer capacity, foaming capacity, emulsification, and anti-oxidative activity. Therefore, we suggest that RPI prepared from olive flounder roes could serve as a potential food resource.
... The protein solubility of the selected TLPPs was examined using the method described by Cha et al. (2020) with slight modifications. In brief, a 10-mg portion of TLPPs was dissolved in 10 mL of DW and the pH of the suspension was adjusted in the range of 2 to 13 using 0.1 mol/L HCl or 0.1 mol/L NaOH. ...
... The foaming capacity (FC) and foaming stability (FS) of the TLPPs were performed using the method of Cha et al. (2020). In brief, the foam was generated by whipping the TLPP solution (10 mg/mL) at 10,000 rpm for 3 min using a homogenizer before being transferred to a 50 mL accredited cylinder. ...
... The relative protein solubility (%) of TLPPs, EW, and SP in the pH range of 2 to 12 is depicted in Figure 2. The minimum solubilities of the TLPPs were observed at pHs 3-8 (0.13-34.96%) which could be attributed to the proximity between the pH of the solution and the isoelectric point of the protein. This consequently enhanced protein precipitation (Cha et al., 2020). These findings agreed well with those from a study of proteins derived from salmon, cod, and herring byproducts which demonstrated the lowest protein solubilities at pHs 4-8 for the same reason (Abdollahi and Undeland, 2018). ...
Article
Tuna livers (TL), which are often discarded as waste, are a valuable source of protein for human consumption. However, the preparation method used affects the nutritional and functional characteristics of protein powders. This work aimed to investigate the effects of different preparation methods on the physical, chemical, and functional properties of tuna liver protein powders (TLPPs) following heat (H) treatment, heat and ultrasound-assisted (HU) extraction, alkaline pH shift (APS) process, and supercritical carbon dioxide fluid (SC-CO2 ) extraction. H at 85°C (H85), HU at 80 kHz and 100 W (HU-80-100), APS at pH 11.5 (APS 11.5), and SC-CO2 at 350 bars (SC-CO2 -350) resulted in the remarkably highest total protein content among the different preparation conditions. All TLPPs, except for APS 11.5, showed lighter color characteristics. The most abundant amino acids in all TLPPs were glutamic acid, aspartic acid and alanine. The protein solubility and foaming capacity were efficiently improved by SC-CO2-350. Nevertheless, the emulsion properties and oil holding capacity were greatly enhanced by H85 and HU-80-100, and a significant foaming stability and water holding capacity were found in APS 11.5. Therefore, the TLPPs obtained following different preparation methods are unique and could be potentially utilized as a source of protein ingredients in several food systems.
... OFR, Olive flounder roe; RPI-1 and RPI-2, Roe protein isolate adjusted to pH 4.5 and 5.5, respectively, after alkaline solubilization at pH 11; RPI-3 and RPI-4, Roe protein isolate adjusted to pH 4.5 and 5.5, respectively, after alkaline solubilization at pH 12. Data are given as mean values±SD (n = 3 (Sathivel et al., 2004), herring (Sathivel et al., 2004), salmon Alaska pollock , (Sathivel et al., 2009) surimi (Huda et al., 2001) . (Li et al., 2004;Mahmoodani et al., 2014;Lee et al., 2016b;Yoon et al., 2018b;Cha et al., 2020). RPIs Table 3 . ...
... RPIs (154.0-304.2 mg/100 g) (148.0 mg/100 g) ISP 2 , / 2 N NaOH HCl NaCl (Lee et al., 2016b;Cha et al., 2020). ...
... sea bream (Orban et al., 2000) Baltic herring (Tahvonen et al., 2000) 2 . Lee et al. (2016b) , , , (Lee et al., 2016b;Cha et al., 2020). ISP OFR Table 3. Mineral contents of roe protein isolates recovered from olive flounder Paralichthys olivaceus by isoelectric solubilization and precipitation process Minerals (mg/100 g) OFR 1 RPI-1 (pH 11/4.5) ...
Article
Four roe protein isolates (RPIs) from olive flounder Paralichthys olivaceus roes (OFR) were recovered by isoelectric solubilization (pH 11 and 12) and precipitation (pH 4.5 and 5.5) and investigated for their food characteristics. RPIs contained 4.5–9.6% moisture, 64.1-69.5% protein, 16.1-19.8% lipid, and 1.0-3.9% ash. The protein yields of RPIs ranged from 50.1 to 56.8%, which was significantly different depending on the recovery conditions. A difference was observed in the SDS-PAGE protein band (25–100 kDa) between the alkaline solubilization at pH 11 (RPI-1 and 2) and pH 12 (RPI-3 and 4). The major amino acids of RPIs were Leu, Lys, Asp, Glu and Ala and major mineral components were sulfur, sodium, phosphorus, and magnesium, which were significantly different from OFR (P<0.05). Additionally, the lead and cadmium content was below the chemical hazard standard of the Korean food standards code. The Hunter color and whiteness of RPIs also showed significant differences according to the treatment conditions of the ISP process (P<0.05). This suggests that protein isolates recovered from olive flounder roes have high potential as nutritional supplements.
... , 180 mesh SDC . Tyrosinase 저해활성 tyrosinase Cha et al. (2020) . , 300 L 900 L mushroom tyrosinase (50 Unit/mL) 1.5 mL 50 mM phosphate buffer (pH 6.8) 30 min , 300 L of 10 mM 3,4-dihydroxy-L-phenylalanine (L-DOPA) ...
... Angiotensin I-converting enzyme (ACE) Cha et al. (2020) . ...
Article
Full-text available
In the present study, protein hydrolysates were prepared from olive flounder Paralichthys olivaceus roe concentrate using different commercial proteases, and their functional properties and bioactivities were examined. Protamex (PR; 21.6%) showed the highest degree of hydrolysis, followed by alcalase (AL; 21.1%) and aroase AP-10 (AA; 20.2%). With regard to foaming activity, trypsin, chymotrypsin (CH), and bromelain (BR) had values ranging 181–188%, followed by neutrase (152%) and AA (141%). CH (36%) and BR (70%) maintained foam stability for up to 15 min. The oil-in-water emulsifying activity index of CH (10.6 m2/g) was the highest among all the hydrolysates. Notably, the 2,2′-azino-bis-3-ethylbenzo-thiazoline-6-sulfonic acid (ABTS+) radical scavenging activities (IC50) were significantly higher in pantidase NP-2 (68.1 μg/mL) and flavourzyme (FL, 69.8 μg/mL) than in other hydrolysates. The tyrosinase inhibitory activities of FL, PR, and AA were inhibited by 12.5–19.8%. Aangiotensin I converting enzyme inhibitory activity of the control was 80.9%, and that of the hydrolysates of CH, AA, PR, and AL, which exhibited higher inhibitory activity, ranged 87.6–90.7%. CH, BR, and AA AP-10 hydrolysates exhibited superior bioactivity and functional properties. Therefore, these hydrolysates can be used as food ingredients in novel types of functional food-enhancing seafood and food processing industries.
... Conversely, in V-MWD and CAD processing with low temperature, the changes in these four components are not significant in some treatments. Besides the effect of heat intensity on β-sheets and α-helix, there is almost a general impact of germination, increase in β-sheets and decrease in α-helix, corresponding to partial denaturation and unfolding of proteins which could lead to enhanced protein solubility and emulsifying properties (Cha et al., 2020;Setia et al., 2019). ...
... Solubility is an important and useful functional property in food preparation, which has an impact on some other factors such as surface activity, emulsification, foaming, and gelation (Cha et al., 2020;Ghavidel & Prakash, 2006). The protein solubility of raw and treated lentil flours using MW-IRD, V-MWD, roasting, and CAD at different drying conditions are presented in Table 1. ...
... Consequently, this alteration in charge affects the membrane's interaction with the desired compounds, either facilitating attraction or causing repulsion [39]. At low pH values (pH = 6), the highest resistances occur (Fig. 3b-d), mainly because the proteins have their isoelectric point in acidic pHs, usually around 3 to 6 [40]. At this point, the protein load approaches zero, which increases precipitation and aggregation, increasing resistance to elution through membranes [41]; additionally, the repulsion by the membrane is reduced, which promotes fouling and plugging of the pores [42]. ...
Article
Full-text available
Problem Earthworm is a valuable source of biologically and pharmacologically active compounds, with applications in the treatment of various types of diseases; however, the main application they have been given is in the production of organic fertilizer. One of the alternatives for obtaining bioactive compounds is by means of enzymatic hydrolysis. Aim This study proposes the optimization of the fractionation of the antioxidant enzymatic hydrolysate from Californian red worm (Eisenia fetida) protein. Methodology For this purpose, the worms were separated and hydrolyzed using the enzyme Alcalase 2.4L for 4000s. The obtained hydrolysate was fractionated by means of a crossflow tangential ultrafiltration system, with a 3 kDa molecular weight cut-off ceramic membrane. A response surface design of the composite central factorial type was implemented to evaluate the effect of pH, transmembrane pressure, and flow factors on the response variables transmission, volume reduction factor (VRF) and permeate flow resistance. The transmissions focused on the antioxidant peptides, measured by three conventional methods such as TEAC, FRAP, ORAC, also known as TTEAC, TFRAP and TORAC, respectively. The evaluated resistances were the total resistance (Rtotal), fouling resistance (Rfouling), and gel resistance (Rgel). Result The results showed that the three factors evaluated affect all the response variables either in their linear or quadratic terms or by some interaction. For each response variable, a mathematical model was obtained, with statistical significance and a non-significant lack of adjustment. The models obtained were used for a multi-objective optimization process in which transfers were maximized, and resistances were minimized. The efficiency of the optimum ultrafiltration process was 25 %. Conclusion The neutral-alkaline pH is ideal for the ultrafiltration process of bioactive peptides, as it is where the highest transmissions of peptides with antioxidative capacity are found. Under optimal conditions, the 3 kDa membrane permeate was found to exhibit higher antioxidant capacity than the retentate and feed. Based on this, the fraction of less than 3 kDa emerges as a potential multifunctional ingredient, thanks to its antioxidant properties.
... Then, the gel was stained with Bio-Rad Coomassie Blue R-250 followed by destaining several times. The bands obtained from the samples were compared with reference to the migration of the wide range molecular weight standard [32]. ...
Article
Full-text available
Fish head byproducts derived from surimi processing contribute about 15% of the total body weight, which are beneficial to health because they contain essential nutrients. In this study, olive flounder (OF) was the target species in order to maximize the byproduct utilization. In RAW 264.7 macrophages, the seven hydrolysates from OF head byproducts were examined for their inhibitory potential against inflammation and the oxidative stress induced by lipopolysaccharides (LPS). The pepsin hydrolysate (OFH–PH) demonstrated strong anti-inflammatory activity via the down-regulation of NO production, with an IC50 value of 299.82 ± 4.18 µg/mL. We evaluated the inhibitory potential of pro-inflammatory cytokines and PGE2 to confirm these findings. Additionally, iNOS and COX-2 protein expressions were confirmed using western blotting. Furthermore, the results from the in vivo zebrafish model demonstrated that OFH–PH decreased the LPS-elevated heart rate, NO production, cell death, and intracellular ROS level, while increasing the survival percentage. Hence, the obtained results of this study serve as a platform for future research and provide insight into the mediation of inflammatory disorders. These results suggest that OFH–PH has the potential to be utilized as a nutraceutical and functional food ingredient.
... The powder exhibited highest solubility at pH 3 (Fig. 2), with no significant differences in solubility between pH 4 and 9. Poor solubility found at pH 2 was related to the aggregation of proteins under strong electrostatic interaction. This result concurred with a previous report that soybean protein had good solubility over a wide range of pH from 3 to 9 [52] and revealed the advantage of powder over animal protein that easily precipitated at pH between 4 and 8 [28]. Values are mean ± standard error (n = 3). ...
Article
Full-text available
This study investigated the potential of collagenous protein fractions (CPFs) as functional foods. The specific CPFs studied were recovered from the roe of bastard halibut (BH), Paralichthys olivaceus; skipjack tuna (ST), Katsuwonus pelamis; and yellowfin tuna (YT), Thunnus albacares through the alkaline solubilization process at pH 11 and 12. The buffer capacity, water-holding capacity and solubility of CPFs with pH-shift treatment were significantly better at alkaline pH (10-12) than at acidic pH (2.0). At pH-shift treatment (pH 2 and 12), the foaming capacities of CPFs from ST and YT were improved compared to those of controls, but they were unstable compared to BH CPFs. The emulsi-fying activity index (EAI, m 2 /g protein) of CPFs (controls) was 16.0-21.1 for BH, 20.1-23.9 for ST and 9.3-13.7 for YT (P<0.05). CPFs adjusted to pH 12 showed improved EAI and YT CPFs showed significantly greater emulsifying ability than those from BH and ST. CPFs recovered from fish roe are not only protein sources but also have a wide range of food functionalities, confirming the high availability of fish sausage and surimi-based products as protein or reinforcing materials for functional foods and alternative raw materials.
Article
Full-text available
This study investigated the food and nutritional characteristics of alkaline-insoluble fractions (AIFs) recovered from bastard halibut Paralichthys olivaceus (BH) and skipjack tuna Katsuwonus pelamis (ST) roes using the alkaline solubilization. The moisture content of AIFs ranged from 4.8% to 12.8%, and ST provided significantly better yields (9.5 for STAIF-11 and 7.1 g/100 g roe for STAIF-12) than did BH (P<0.05). The protein content of AIFs ranged from 71.7% to 79.2%, with the highest level yielded by STAIF-11 (6.8 g/100 g roe). The crude fat content of AIFs was 10.9-14.3% and the mineral content was 0.7-3.4%. The major mineral components of AIFs were sulfur, sodium, potassium, and phosphorus. Color values showed that BHAIFs were significantly brighter than STAIFs. Total contents of essential amino acids were significantly higher in STAIFs (47.5-49.5%) than in BHAIFs. The major essential amino acids found in AIFs from both sources were Val, Leu, Lys, and Arg. Therefore, AIFs were significantly superior to whole BH roe in terms of physicochemical and nutritional status, and we identified species-specific differences between BH and ST. Protein is a major component of AIFs recovered from fish roes, which suggests that they have potential for use as a protein source.
Article
Full-text available
The objective of this study was to investigate physicochemical properties of protein concentrate from skipjack tuna roe by a cook‐dried (boiled or steamed‐dried) process, and to evaluate their food functional properties. The yields of boil‐dried concentrate (BDC) and steam‐dried concentrate (SDC) prepared from skipjack tuna roe were 22.4 for BDC and 24.4% for SDC. Their protein yields were 16.8 and 18.4%, respectively. In terms of major minerals of the BDC and SDC, sulfur (853.2 and 816.6 mg/100 g) exhibited the highest levels followed by potassium, sodium and phosphorus. The prominent amino acids of roe protein concentrates (RPCs) were Glu, Asp, Leu and Val. The BDC and SDC showed a higher buffer capacity than egg white (EW) at the pH‐shift range. The pH‐shift treatment significantly improved the water holding capacities of RPCs, except pH 6. But they had a low solubility across the pH‐shift range. The foaming capacities (104%–119%) of BDC and SDC were significantly lower than those of EW (p < .05), and their foam stabilities were not observed. Emulsifying activity index (m²/g protein) of RPCs and EW was 2.3 for BDC, 11.1 for SDC and 18.0 for EW. RPCs in the food and seafood processing industries will be available as egg white alternative protein sources and will be available as ingredients of surimi‐based products in particular.
Article
Full-text available
This study evaluated the protein recovery, functional properties and biological activity of isolate processed water (IPW) generated in the preparation of protein isolates from fish roes (BH, bastard halibut Paralichthys olivaceus; ST, skipjack tuna Katsuwonus pelamis; YT, yellowfin tuna Thunnus albacares) by an isoelectric solubilization and precipitation process. The IPWs contained 2.7-5.4 mg/mL of protein, and the protein losses were 8-21% (P<0.05). The form capacity of IPW-3 for BH and ST, and IPW-4 for YT was 155, 194, and 164%, respectively. The emulsifying activity index (27-43 m2/g) of the YT-IPWs was the strongest, followed by ST (7-29 m2/g) and BH (10-19 m2/g). The 2,2-diphenyl-1-picrylhydrazyl scavenging activities of IPW-1 and -3 were higher than those of IPW-2 and -4. The 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid scavenging activity (IC50, mg/mL) of IPW-2 and -4 was 0.03 mg/mL for BH, 0.04-0.08 mg/mL for ST, and 0.04-0.07 mg/mL for YT. BH IPW-3 had the strongest reducing power (0.41 mg/mL) and superoxide dismutase-like activity (1.68 mg/mL). The angiotensin-I converting enzyme inhibitory activity of IPW-3 was the highest for ST (1.52 mg/mL), followed by BH and YT. The common predominant amino acids in the IPWs were the essential amino acids Val, Leu, Lys, and Arg and the non-essential amino acids Ser, Glu, and Ala.
Article
Full-text available
Three kinds of roe protein concentrates (RPCs: boil-dried concentrate, BDC; steam-dried concentrate, SDC; freeze-dried concentrate, FDC) were prepared from yellowfin tuna to produce value added products for food applications. The buffer capacities of the RPCs were higher under alkaline than under acidic conditions. The water holding capacities of the RPCs were in range 4.5–4.7 g/g protein at pH 6.0. The protein solubility of the FDC (14.2%) was higher than those of the BDC (5.4%) and SDC (5.5%) at pH 6.0. The foaming capacity of the FDC (156.8%) was higher than those of the BDC (109.7%) and SDC (109.4%); the FDC foam was stable for 60 min. The oil-in-water emulsifying activity index of the FDC (12.2m2/g protein) exceeded those of the BDC and SDC (2.2m2/g protein). Protein concentrates from yellowfin tuna roe may be useful as a potential protein source and as a high-value food ingredient.
Article
Full-text available
In the present study, we investigated to the antioxidant and angiotensin I-converting enzyme (ACE) inhibitory activities of the northern shrimp (Pandalus borealis) by-products (PBB) hydrolysates prepared by enzymatic hydrolysis. The antioxidant and ACE inhibitory activities of five enzymatic hydrolysates (alcalase, protamex, flavourzyme, papain, and trypsin) of PBB were evaluated by the 2, 2′-azino-bis [3-ethylbenzothiazoline-6-sulfonic acid] (ABTS+) radical scavenging and superoxide dismutase (SOD)-like activities, reducing power and Li’s method for ACE inhibitory activity. Of these PBB hydrolysates, the protamex hydrolysate exhibited the most potent ACE inhibitory activity with IC50 value of 0.08 ± 0.00 mg/mL. The PBB protamex hydrolysate was fractionated by two ultrafiltration membranes with 3 and 10 kDa (below 3 kDa, between 3 and 10 kDa, and above 10 kDa). These three fractions were evaluated for the total amino acids composition, antioxidant, and ACE inhibitory activities. Among these fractions, the < 3 kDa and 3–10 kDa fractions showed more potent ABTS+ radical scavenging activity than that of > 10 kDa fraction, while the > 10 kDa fraction exhibited the significant reducing power than others. In addition, 3–10 kDa and > 10 kDa fractions showed the significant ACE inhibitory activity. These results suggested that the high molecular weight enzymatic hydrolysate derived from PBB could be used for control oxidative stress and prevent hypertension.
Article
Full-text available
Isoelectric solubilization/precipitation (ISP) processing allows selective, pH-induced water solubility of proteinswith concurrent separation of lipids and removal of materials not intended for human consumption such asbone, scales, skin, etc. Recovered proteins retain functional properties and nutritional value. Four roe proteinisolates (RPIs) from yellowfin tuna roe were prepared under different solubilization and precipitation condition(pH 11/4.5, pH 11/5.5, pH 12/4.5 and pH 12/5.5). RPIs contained 2.3–5.0 % moisture, 79.1–87.8 % protein, 5.6–7.4%lipidand3.0–3.8 % ash. Protein content of RPI-1 and RPI-2 precipitated at pH 4.5 and 5.5 after alkalinesolubilization at pH 11, was higher than those of RPI-3 and RPI-4 after alkaline solubilization at pH 12 (P< 0.05).Lipid content (5.6–7.4 %) of RPIs was lower than that of freeze-dried concentrate (10.6 %). And leucine and lysineof RPIs were the most abundant amino acids (8.8–9.4 and 8.5–8.9 g/100 g protein, respectively). S, Na, P, K asminerals were the major elements in RPIs. SDS-PAGE of RPIs showed bands at 100, 45, 25 and 15 K. Moisture andprotein contents of process water as a 2’nd byproduct were 98.9–99.0 and 1.3–1.8 %, respectively. Therefore,yellowfin tuna roe isolate could be a promising source of valuable nutrients for human food and animal feeds.
Article
Full-text available
Roe is the term used to describe fish eggs (oocytes) gathered in skeins and is one of the most valuable food products from fishery sources. Thus, means of processing are required to convert the underutilized yellowfin tuna roes (YTR) into more marketable and acceptable forms as protein concentrate. Roe protein concentrates (RPCs) were prepared by cooking condition (boil-dried concentrate, BDC and steam-dried concentrate, SDC, respectively) and un-cooking condition (freeze-dried concentrate, FDC) from yellowfin tuna roe. The yield of RPCs was in the range from 22.2 to 25.3 g/100 g of roe. RPCs contained protein (72.3–77.3 %), moisture (4.3–5.6 %), lipid (10.6–11.3 %) and ash (4.3–5.7 %) as the major constituents. The prominent amino acids of RPCs were aspartic acid, 8.7–9.2, glutamic acid, 13.1–13.2, and leucine, 8.5–8.6 g/100 g of protein. Major differences were not observed in each of the amino acid. K, S, Na, and P as minerals were the major elements in RPCs. No difference noted in sodium dodecyl sulfate polyacrylamide gel electrophoresis protein band (15–100 K) possibly representing partial hydrolysis of myosin. Therefore, RPCs from YTR could be use potential protein ingredient for human food and animal feeds.
Article
Aim: To evaluate the beneficial biological activities of Engraulis japonicus muscle protein, the antioxidant and tyrosinase inhibitory activities of E. japonicus muscle protein hydrolysates prepared by subcritical water hydrolysis were investigated. Methodology: To evaluate the bioactivity of E japonicus subcritical hydrolysates, the applied temperature (pressure) was 140°C (2.6 bar); the reaction times were 0,5,10,15 and 20 min. Results: After 10 min of subcritical hydrolysis of particles obtained using 80-200 mesh, 46.39% of the E.japonicus muscle protein was hydrolyzed at 140°C. According to the response surface methodology results, particles generated with 80-200 mesh £ japonicus powder exhibited an increased yield of hydrolysates. The highest DPPH-radical-scavenging activity (34.91%) occurred in 60-80-mesh sized protein hydrolysates treated at 140°C for 15 min, and the highest tyrosinase inhibitory activity (99.24%) was identified in 80-200-mesh sized protein hydrolysates treated at 140°C for 5 min. Changes in the molecular weight distribution of E. japonicus muscle proteins after subcritical water hydrolysis were assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Interpretation: Subcritical water hydrolysis is a suitable technique for generating E. japonicus muscle protein hydrolysates with useful biological activities, within a short (5-15 min) time frame.