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Journal homepage: www.fia.usv.ro/fiajournal
Journal of Faculty of Food Engineering,
Ştefan cel Mare University of Suceava, Romania
Volume XVIII, Issue 3- 2019, pag.176 - 190
NUTRITIONAL QUALITY, AMINO ACID PROFILES, PROTEIN DIGESTIBILITY
CORRECTED AMINO ACID SCORES AND ANTIOXIDANT PROPERTIES OF
FRIED TOFU AND SEITAN
Dina ANWAR1 , *Ghadir EL-CHAGHABY 1
1 Regional center for Food and Feed, Agricultural Research Center, Giza, Egypt
ghadiraly@yahoo.com
*Corresponding author
Received 23th July 2019, accepted 27th September 2019
Abstract: As the world population is increasing, tofu and seitan may play an important role in human
nutrition as inexpensive protein-rich food sources. In order to increase the consumption of tofu and
seitan, modified processes are needed to meet the needs of different consumers. In this study, the aim
of the work is to set up fried tofu and seitan that couple high nutritional value and good sensory
features and to evaluate their nutritional profile and protein quality as well as the consumer’s
acceptance. The average values of tested organoleptic parameters of tofu and seitan resulted in a
positive influence after frying process. Cooking loss due to frying was lower in case of fried seitan
over fried tofu. The protein content of both fried tofu and seitan samples was higher than 20%, fat and
energy of the control were increased after frying process. Minerals and antioxidant capacity were
higher in the modified products as compared to the traditional ones. Most of essential amino acid
values were enhanced after frying seitans especially with wheat flour coated seitan, however, raw tofu
was proven to be a rich source of essential amino acids over fried ones and different seitan samples.
Tofus were found to be higher in essential amino acid index (EAAI) and biological value (BV) over
seitan samples. Tofu samples with higher amino acids content had higher values of digestibility and
PDCAAs. Overall, the new formulations of tofu and seitan could be used to enhance their nutritional
quality and taste.
Keywords: Nutritional profile, protein quality, sensory evaluation, mineral content
1. Introduction
Proteins are the main constituents of
agricultural raw materials with two main
functions: bio- and techno-function. Bio-
functionality of proteins is related to their
nutritional and physiological properties,
while techno-functionality is related to
their physico-chemical ones [1]. One of the
earliest indications of the importance of the
increment of food protein resources was to
overcome the world malnutrition. It is
expected that the world demand for
proteins of animal origin would be doubled
by 2050 [2]. The replacement of animal
proteins by novel plant proteins has been
driven by sustainability assurance in the
protein food sources and considered the
simplest way to solve the shortage in
animal protein sources. Protein rich plant-
based foods are legumes, grains, nuts and
dairy replacers. The current ready-made
meat and dairy replacers are based on
wheat, soy and lupine, more than other
plant based protein sources from the fact
that they have an amino acid composition
of quite high quality [3]. A growing
awareness in the population about healthy
and sustainable foods has lead to a rising
interest in plant protein based meat
alternatives in many European countries
and worldwide [4].
Soybean foods are rich in protein and
have been shown to offer specific health
benefits. Tofu (soy bean curd) is one of the
most important food products made from
soy bean protein [5]. It is an important
food for eastern Asians due to its good
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
177
nutrition and digestibility [6]. Western
countries have recently increased interest
in eating tofu due to its benefits to human
health and the United States has increased
tofu consumption [7]. It has been
increasingly used in numerous Asian
dishes, replacing dairy products due to
comparatively low cost and high protein
bioavailability [8].
Tofu is usually considered as salt –
or acid – coagulated water based gel, with
soy lipids and proteins trapped in its gel
networks [5]. It is a cheap, nutritious and
versatile meat or cheese substitute with
bland taste and porous texture and hence
called “Tofu is meat without bone”. The
main health benefits of tofu will show up
in significantly lower total cholesterol,
triglycerides and low-density lipoprotein
(bad cholesterol) if one eats tofu regularly
instead of meat [9]. On the other hand,
cereals (e.g wheat, oats, etc) can be
considered the other side of plant protein
sources. Wheat gluten is becoming a very
large player in the industry, with new
production facilities for gluten and textural
wheat products expanding all over the
world [10]. Gluten can be readily prepared
by gently washing dough under a stream of
running water. This removes the bulk of
the soluble and particulate matter to leave
a protein aceous mass that retains its
cohesiveness on stretching [11]. Soy
protein and wheat gluten have been the
dominant raw materials for meat
surrogates for a long time. These proteins
have unique techno-functional taste and
nutritional properties depending on their
origin and how they are processed [4].
Historically, wheat protein has been used
for thousands of years as a meat substitute
called seitan in China, Japan, Korea, and
Russia [10]. Gluten can be flavored in a
variety of ways; when simmered in a
traditional broth of soy sauce, ginger,
garlic, it is called seitan. Seitan contains
small amount of sodium and extremely low
fat protein. In addition, gluten (setian) has
a very similar texture to meat, making it
ideal for vegetarian dishes meant to mimic
meat-based ones. Seitan is a great option
for vegans who cannot eat soy. Recently,
western countries have increased the
interest in eating tofu and seitan which are
considered as high protein source
especially for vegetarians. Despite their
high functional properties, they are not
typically consumed in the basic Arab
countries diet because of their unpleasant
flavor. The acceptability level of foods
depends mostly on cultural habits,
therefore, when a food is created or
modified, it is extremely important to
evaluate it with consumers or potential
consumers. Thus, the objective of this
study is to prepare tofu and seitan by two
different methods and to evaluate the
products in terms of sensory
characteristics, nutritional quality, amino
acid scores and antioxidant capacity.
2. Matherials and methods
2.1. Raw material
Dried soy beans (Glycine max), Giza
111 cultivar were obtained from the Field
Crops Research Institute, Agricultural
Research Center. Wheat flour was
purchased from the local market. The
chemicals were obtained from El-
Gomhoria Company for chemicals (El-
Mataria, Egypt).
2.2. Preparation of tofu
Tofu was prepared by the following
method [12]: one kilogram of soy bean
seeds were washed, soaked in 4L of water
for 16 hrs at room temperature, drained
and rinsed with water. Soaked seeds were
then processed by hand dehulling and the
cotyledons were ground in low speed
blender with addition of water (8 L) for 2
minutes followed by high speed for 5
minutes. The resultant bean puree was
heated to 80-85 ͦ C with constant stirring.
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
178
The slurry was filtered through cheese
cloth to separate soy milk from residue
(okara) and the liquid was heated to
boiling. The soy milk was allowed to cool
to 70 ͦ C and while stirring, a saturated
solution of calcium sulphate (2% of dry
soy bean weight) was added to soy milk
until it began to coagulate. The suspension
was allowed to form a curd without further
stirring. After one hour, the curd was
transferred into cheese cloth lined on
plastic strainer. The curd was pressed to
separate the whey. At the end of pressing,
the curd had attained the required firmness
and consistency of tofu. The cloth was
removed and the tofu was stored
refrigerated until used.
2.3. Fried tofu preparation
Fried tofu was prepared by mixing
optimum quantities of onion paste (12%),
corn starch (4.2%), bicarbonate (0.7%),
salt (1.5%), spices (0.6%) and chili sauce
together with fresh tofu (74%). The tofu
mix was then formed into discs of 14g.
The produced tofu patties were coated with
wheat flour (7.0%) and fried using
sunflower oil at 170 ͦC for 20 sec. the fried
tofus were cooled till examination.
2.4. Seitan preparation
To produce seitan, wheat flour was
mixed with tap water as needed to make
dough. The dough was washed repeatedly
under running water to remove starch and
some bran until a gluten- protein was
observed. Seitan was stored in a
refrigerator until used.
2.5. Fried seitan preparation
Seitan (wheat gluten) was soaked in
mixed ingredients of onion juice, yoghurt,
lemon juice, soy sauce, salt and spices and
allowed to rest for one hour. Seitan was
crosswise cut into four pieces then
simmered in water for 15 min.
Cooked seitan was cut into small
pieces then coated with wheat flour (1) or
chickpea flour (2). Coated seitans were
fried using sunflower oil at 170 ͦ C for 20
sec and the fried seitan was cooled till
examination.
2.6. Investigations
For sensory evaluation: samples from
each of tofu and seitan patties were fried in
a preheated pan for 5 min (2.5 min. on
each side) before coded and evaluated for
test, color, odor, texture, bite and overall
acceptability using 10-point descriptive
scales, where a score of 1 denotes for
extremely poor and a score of 10 denotes
for excellent (as described before by [13].
The weight of tofu and seitan patties were
measured before and after frying to
determine cooking loss and calculated
according to the equation below:
Cooking loss% = Cooked weight – raw
weight x 100 (1)
Raw weight
2.7. Chemical determinations
2.7.1. Proximate analysis
Moisture, protein, fat (ether
extractable), fiber and ash contents were
determined according to methods
described in [14]. While, total
carbohydrates were estimated by
difference according to [15].
2.7.2. Minerals content
Potassium, magnesium, phosphorous
and iron were analyzed by atomic
absorption spectrophotometry 3300 Perken
Elmer, while, calcium was analyzed by
ICP optima 2000 DV Perken Elmer
according to the method described in the
[14].
2.7.3. Soluble, in soluble and total
dietary fiber
Soluble dietary fiber (SDF), in
soluble dietary fiber (IDF) and total dietary
fiber (TDF) were determined according to
the methods in [16].
2.7.4. Antioxidant assay
Total antioxidant capacity of the
samples was determined using the
phosphomolebdenum method [17] using
ascorbic acid as standard. The results were
expressed as milligram ascorbic acid
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
179
equivalent per 100 milliliters (mg
AAE/100 ml).
2.7.5. Amino acids content
Amino acids determination was
performed according to [14]. The system
used for the analysis was Eppemdorf LC
3000 EZ chrom.
a- Essential amino acid index (EAAI)
The EAAI was calculated using Eq. (1)
[18].
EAAI =
(2)
Where n is the number of the essential
amino acids; a, b,….h are the
concentrations of the essential amino acids
(lysine, isoleucine, valine, theronine,
leucine, phenylalanine, histidine and
methionine) in test sample, and av, bv,
…..hv are the concentrations of the
essential amino acids in standard protein
(%) (Casein)
b- Nutritional index (NI)
The NI was calculated using Eq. (2).
NI (%) = EAAI x protein (%)
(3)
100
c- Biological value (BV)
The BV was calculated using Eq. (3) [18-
19]: BV = 1.09 x EAAI – 11.7
(4)
d- Predicted protein efficiency ratio
(P-PER)
The P-PER was calculated using the
regression equation, Eq. (4) [20-21]:
P-PER = - 0.468 + 0.454 (LEU) – 0.105
(TYR) (5)
2.7.6. Determination of amino acid
scores
Determination of the amino acid
scores was first based on casein. In this
method, essential amino acids were scored.
Secondly, amino acid score was
calculating using the following formula by
[22]:
Uncorrected amino acid score% = mg of
essential amino acids 1g of test protein
x100 (6)
mg of
amino acid 1g of reference protein
2.7.7. In-vitro protein digestibility
determinations
The in vitro protein digestibility
(IVPD) was measured using a
multienzyme system (pepsin,
chloramphenicol and pancreatin) according
to the method of [23]. Crude protein (CP)
was determined by the macro Kjeldahi
technique (%N x 6.25) [14]. Protein
digestability was calculated with the
formula:
% protein digestibilty = (CP sample – CP
undigested) / (CP sample) x 100 (7)
2.7.8. Protein digestibility corrected
amino acid score (PDCAAs)
The indicator of protein quality was
calculated based on the total amino acid
contents of the sample, considering for its
calculation t he limiting AA (g/16gN) of
the sample in relation to the same AA of a
reference protein and multiplied by the
samples % digestibility according to [24].
The PDCAAs was calculated according to
the following equation:
PDCAAs (protein digestibility corrected
amino acid score) =
Lowest uncorrected
amino acid score x protein digestibility (%)
(8)
3. Results and discussion
3.1. Sensory quality of fried tofu and
seitan
The sensory evaluation was done on a
ten-point scale by a ten panelists and the
results are shown in Table (1). Fried tofu
was scored higher than 8.0 for the
parameters considered (taste, odor, color,
texture, bite and overall acceptability). In
addition, 95% of consumers expressed the
will of buying it. Fried tofu’s taste had a
level of acceptance near ‘extremely like’,
therefore, incorporation of the ingredients
in fried patties formulation increased the
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
180
pleasant taste of tofu. Tofu has a mild
flavor and a porous texture and, due to its
neutral sensory characteristics, the tofu
texture has an important role in the quality
of the product, as well as in the consumer’s
acceptance [25].
Table 1
Sensory evaluation of fried tofu and seitan
Products
Parameters
Tofu
Seitans
Fried tofu
Fried seitan (1)
Fried seitan (2)
Taste
9.55
8.70
8.80
Color
9.45
8.60
8.45
Odor
8.70
8.15
9.00
Texture
8.25
7.80
7.80
Bite
9.05
6.80
7.15
Over all acceptability
9.00
8.01
8.24
Cooking loss%
26.76%
2.15%
1.56%
(1) Fried seitan coated with wheat flour (2) Fried seitan coated with chickpea flour
The frying process increased the pleasant
taste of the products; it also maintained the
high average of texture. Tofu had high
cooking loss (26.76%) which is probably
due to its lower ability to hold the moisture
during the frying process. Table (1) also
shows the mean scores of the consumer’s
acceptance for fried seitan coated with
wheat or chickpea flour. Both of them
were scored higher than 8.0 for taste, color,
odor and overall acceptability. Although,
the tested seitans were characterized by
similar ingredient contents, the use of
chickpea flour instead of wheat flour
involved an increase of the taste, odor and
overall acceptability, probably due to a
greater acceptance of chickpea by
consumers. Taste and aroma are mostly the
important attributes that influence the
sensory properties of products. Cooking
seitan (deep fat frying/70 ͦ C) resulted in
low cooking loss percentage.
3.2. Proximate composition
The proximate composition of tofus
and seitans are presented in Table (2). The
results showed that moisture percentage
was higher in raw tofu compared to fried
tofu. While, changes in moisture content of
different seitan samples were not
noticeable. The protein content of raw tofu
was 11.29% of fresh matter which was
lower than that of fried tofu (21.21%),
probably due to the high moisture content
of raw tofu.
Table 2
Proximate composition (g/100g) and the energy value of tofus and seitans
Products
Macronutrients
Tofus
Seitans
Raw tofu
Fried tofu
Raw seitan
Fried seitan (1)
Fried seitan (2)
Moisture
74.92
44.61
49.30
48.30
51.59
Protein
11.29
21.21
34.27
21.71
24.52
Fiber
0.36
0.37
0.16
0.02
0.36
Carbohydrate
4.15
14.20
15.24
22.17
16.82
Lipid
7.84
15.08
0.78
6.40
5.09
Ash
1.44
4.53
0.25
1.40
1.62
Energy (Kcal/100g)
132.3
277.36
205.06
233.12
211.17
(1) Fried seitan coated with wheat flour (2) Fried seitan coated with chickpea flour
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
181
Tofu manufacture is in many respects
similar to cheese-making, the essential
difference being that a lactic acid-
producing bacterial starter culture is not
employed in its preparation [26]. Solids of
tofu are composed chiefly of protein of
high quality- the Net protein utilization
(NPU) of tofu is reported to be 65%
making it equivalent to chicken meat in
terms of assimilability and digestibility.
Soybean protein showed
hypochloesterolemic and soy isoflavones
have antiatherogenic effect [27]. It was
also reported that the soy protein decreased
effectively serum concentration of total
cholesterol and triglycerides as compared
to animal proteins [28]. On the other hand,
seitan contained 34.27% of protein while it
reached 21.71% and 24.52% of fresh
matter for fried seitan coated with wheat or
chickpea flour, respectively. It was clear
that use of chickpea flour caused an
increase in protein content of fried seitan
over wheat flour. The fiber content of tofus
and seitans was comprised between 0.02%
and 0.37% of fresh matter. Frying tofu
result an increase in carbohydrates (10%),
lipid (7.24%) and ash (3.1%). Deep-fat
frying of tofu with subsequent fat
absorption increase the energy value (from
132.3 to 277.36 kcal/100g for tofus before
and after frying, respectively). Similar
trends were observed for seitan samples,
the fried seitan either coated with wheat of
chickpea flour contained high
carbohydrates, lipids and ash in compare
with raw seitan. The highest energy value
was recorded for fried seitan with wheat
flour (233.12 kca/100g) over other seitans.
The high energy value in cooked burger
patties was attributed to the reduction in
moisture content during cooking [29]. The
predicted dietary protein intake of 100g of
raw and fried tofu and seitan for males and
females was shown in Fig (1). Raw tofu
can supply about 21.2 and 24.5% of the
protein requirement for males and females,
respectively and this percentage would
increase with fried tofu.
Fig. (1): % Dietary protein intake of raw and fried tofu and seitan
On the other hand, raw seitan can supply
about 61.2 and 74.5% of recommended
daily protein for males and females,
respectively while these percentages were
decrease with fried seitans but it still
provide more than 38% of the protein
requirement for both males and females.
3.4. Mineral content
Mineral content of raw and fried tofu
is shown in the Table (3). The results
showed that K and Mg were the most
abundant minerals in raw tofu; however,
Ca and P recorded higher mean values
over other minerals in fried tofu. The ratio
of Ca/P of raw and fried tofu was 0.707
and 1.383, respectively. According to
many authors a good food has a Ca/P ratio
higher than one, while a poor food has a
ratio lower than 0.5[30]. The ratio of Ca/P
in the food is related to teeth and bone
formation and therefore children and youth
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
182
need higher intakes of calcium and
phosphorus. Since the ratio of Ca/P in
tofus either raw or fried is above 0.5, tofu
can be considered a good food. As regards
the seitan samples, the lowest mean value
of Fe, K and P was recorded by raw seitan.
Fried seitan coated with wheat flour
contained big amounts of K and P which
recorded the highest value among other
seitan samples. On the other hand, fried
seitan with chickpea flour yielded the
highest Mg level followed by raw seitan
and fried seitan with wheat flour. Calcium
was not detected in raw seitan but it was
recorded as 204.0 and 177.3 mg/kg for
fried seitan with wheat and chickpea flour,
respectively. These results may be related
to the yoghurt addition in the seitan’s
broth. A slight increase was also shown in
Ca/P ratio of fried seitan with chickpea
flour over wheat flour.
Finally, the different ingredients added to
tofu and seitan recipes before the frying
process enhanced their mineral content and
thus, fried tofu and seitan can provide high
amount of minerals which are associated
with good human health.
Table 3
Mineral composition (mg/kg) of tofus and seitans
Products
Minerals
Tofus
Seitans
Raw tofu
Fried tofu
Raw seitan
Fried seitan (1)
Fried seitan (2)
Fe
24.00
13.24
22.46
76.88
71.02
K
239.6
411.1
225.8
2688
506.4
Mg
3010
137.3
184.4
69.23
309.0
Ca
12.19
4597
Nd
204.0
177.3
P
17.23
3323
3.51
1603
918.3
Ca/P
0.707
1.383
-
0.127
0.193
(1) Fried seitan coated with wheat flour (2) Fried seitan coated with chickpea flour
3.5. Dietary fiber content
The results of soluble, insoluble and total dietary fiber shown in Table (4) indicate that
total dietary fiber (TDF) levels in the tofu and seitan ranged from 2.12 to 5.95%. On the other
hand, the content of soluble diatery fiber (SDF) and insoluble dietary fiber (IDF) in raw tofu
was lower than that in fried tofu which may be due to the lost soluble carbohydrates in the
whey during tofu making. These results were in agreement with previous results [31] .In the
case of seitans, fried seitan with chickpea flour had highest content of IDF followed by raw
seitan and seitan with wheat flour.
Table (4):
Dietary fiber (%) of tofus and seitans
Products
Fiber
Tofus
Seitans
Raw tofu
Fried tofu
Raw seitan
Fried seitan (1)
Fried seitan (2)
IDF
1.88
2.82
1.57
1.09
4.45
SDF
1.61
1.66
1.77
1.03
1.50
TDF
3.49
4.48
3.34
2.12
5.95
(1) Fried seitan coated with wheat flour (2) Fried seitan coated with chickpea flour
Dietary fibre is regarded as one of the most
important ingredients in human diet [32]. The characteristics of fibre such as particle
size, bulk volume, surface area and
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
183
adsorption as well as organic molecules are
more effective in human digestive system
[32-33]. It was observed that the addition
of dietary fibre in foods can improve the
overall qualities such as cooking
prosperities and textural characteristics as
well as taste [34].
3.6. Antioxidant Capacity
The antioxidant capacity of raw and
fried tofu and seitan is shown in the Fig
(2). Fried tofu showed high antioxidant
level (861.6 mgAAE/100g), up to 1.8 fold
of antioxidant capacity of raw tofu (487.9
mgAAE/100g). In this context, it was
reported that isoflavones, aglycones and
proteins present in tofu have antioxidant
properties protecting from lipid oxidation
[35]. Fried seitan coated with wheat flour
contained higher levels, up to 2.4 fold of
antioxidant than raw seitan. Although it is
believed that that deep-fat frying changes
the quality of fried foods and nutritional
quality of foods [36], but in the present
study, the use of onion paste in fried tofu
recipe and lemon juice for seitan may be
the reason for improvement of their
antioxidant capacity which can reduce the
harmful effects of frying process.
Fig. (2): Antioxidant activity of raw and fried tofu and seitan
3.7. Amino acids profile and protein
quality of tofus and seitans
Amino acid composition is critical
to evaluate the quality of a dietary protein
source through quality also relates to other
food properties (e.g presence of metabolic
interfering substances digestibility and
chemical integrity) with potential to
manipulate the proportion of utilizable
amino acids. Particularly, the essential
amino acids content in protein source
primarily influences the quality of that
protein [37]. Table (5) shows the amino
acids composition of the amino acids
composition of tofu and seitan before and
after frying in g/16gN. The sum of
essential amino acids (TEAA) ranged from
25.77g in fried seitan with chickpea flour
to 37.72g in raw tofu. Raw tofu was higher
than 36% considered for an ideal protein
[38] but it is lower than that in casein
standard of 39.18%. Leucine and lysine
content were higher in tofus and these
values were higher than the recommended
dietary requirements of FAO for adult
foods while, the methionine content was
the lowest amino acid in tofus. Seitan
samples contained low amounts of lysine.
However, fried seitan coated with chickpea
flour caused an increase in lysine content,
up to 1.18 fold than wheat flour and 1.23
fold than raw seitan.Nevertheless, seitans
contained appreciable amount of leucine
and phenylalanine, but it is still lower than
that in tofu samples. Fried seitan coated
with wheat flour contained 1.76g/100g of
methionine which recorded the highest
amount in seitan samples followed by raw
seitan (1.66g/100g) and fried seitan with
chickpea flour (1.65g/100g). These relative
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
184
deficiencies in lysine in seitan samples and
that of methionine in fried tofu can be
largely attributed to their disparate
composition of major storage proteins.
Raw and fried tofus were found to be rich
in valine and phenylalanine. The histidine
content in the studied samples followed a
similar pattern, being the highest in tofus
(Table 5). Histidine has multiple roles
including that in protein interactions,
histamine synthesis, and repair and tissue
growth [39].
Table 5
Amino acid profile of tofus and seitans
Treatments
T1
T2
T3
T4
T5(1)
RDA%*
Amino acids
Essential amino acids (g/100g cp.)
Theronine
3.86
3.78
2.44
2.54
2.51
1.50
Valine
5.06
4.90
3.44
4.00
3.30
2.60
Isoleucine
4.68
4.62
3.30
3.69
3.30
2.00
Leucine
7.91
7.38
6.51
7.02
6.52
3.90
Phenylalanine
5.17
5.03
4.66
4.64
4.28
2.50
Histidine
2.71
2.50
2.03
2.14
1.89
1.00
Lysine
6.40
5.22
1.89
1.97
2.32
3.00
Methionine
1.93
1.40
1.66
1.76
1.65
1.50
Conditionally essential amino acids (g/100g cp.)
Tyrosine
3.71
4.09
3.20
3.11
2.84
-
Arginine
6.97
6.55
3.33
3.40
3.57
-
Cysteine
2.13
1.98
2.29
2.59
2.72
-
Proline
4.84
5.37
11.71
11.85
11.86
-
Glycine
4.48
4.15
3.45
3.95
3.44
-
Non-essential amino acids (g/100g cp.)
Aspartic acid
10.77
10.41
3.08
3.66
4.38
-
Serine
4.88
4.64
4.20
4.45
4.01
-
Glutamic acid
18.20
18.45
39.30
33.80
28.94
-
Alanine
4.73
4.30
2.77
3.50
2.78
-
TEAA
37.72
34.83
25.93
27.76
25.77
TCEA
22.13
22.14
23.98
24.90
24.43
TNEAA
60.71
59.94
73.33
70.31
64.54
(1)T1= tofu, T2 = fried tofu, T3 = seitan, T4 = fried seitan with wheat flour and T5 = fried seitan with chickpea
flour (2) TEAA=total essential amino acids, TCEA=conditionally amino acids, TNEAA=total non essential
amino acids, TSAA=total sulphur amino acids, TArAA=total aromatic amino acids, TAAA=total acidic amino
acids, TBAA= total basic amino acids. *RDA%=recommended dietary allowanced FAO/WHO, 2007 [38].
Recent evidences have indicated the
dietary essentiality of traditionally
considered non essential (dispensable)
amino acids as there is lack of substantive
research on the assumption that
nutritionally non-essential amino acids are
adequately synthesized in human beings to
meet the basal requirements [40]. These
amino acids, termed functional amino
acids include aspartic acid, serine,
glutamic acid, alanine, arginine, proline
and glycine and also play important roles
among others in intestinal integrity [41],
immune responses [42], cell growth and
differentiation [43] and antioxidant defense
[44]. As shown in the Table (5), glutamic
acid was the predominant amino acid
amongst the other amino acids ranging
from 39.3g/100g in raw seitan to
18.20g/100g in raw tofu. Aspartic acid
content was the highest in tofu samples
while proline was found to be the highest
in seitan samples. Both asparatate and
serine play as precursors of other amino
acids. Over all, the amino acids content of
proteins in different samples can vary due
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
185
to the kind of seed’s protein and the
procedures carried out to get the final
products. Variation was found in the
content of some of the amino acids
including lysine, aspartic acid and glutamic
acid. The nutritional quality of tofus and
seitans is presented in the Table (6). Tofu
samples contained higher ratio of essential
amino acids than total amino acids
(TEAA/TAA %) as compared with seitans.
However, the values of tofus and seitans
were above 26% for ideal protein food for
children and 11% for adult [45]. The sum
of the acidic amino acids was higher in
seitan samples than that in tofus.
Conversely, tofu samples were found to
have higher total basic amino acids than
seitans. An observation on Asp/Glu
showed that the level of Asp appeared to
affect the glutamic value and vice versa as
shown in the Table (6).
Table 6
Protein quality of tofu and seitan
Treatments
T1
T2
T3
T4
T5(1)
Parameters Nutritional quality(2)
Total amino acids (TAA)
98.43
94.77
99.26
98.07
90.31
TEAA/TAA %
38.32
36.75
26.12
28.30
28.53
TNEAA/TAA%
61.67
63.24
73.87
71.69
71.46
TEAA/TNEAA
0.62
0.58
0.35
0.39
0.40
TSAA ( Meth. + Cys )
4.06
3.38
3.95
4.35
4.37
Cys / TSAA %
52.46
58.57
57.97
59.54
62.24
TArAA ( Pheny + Tyr)
8.88
9.12
7.86
7.75
7.12
Leu / Ileu ratio
1.69
1.60
1.97
1.90
1.98
Leu-Ileu (difference)
3.23
2.76
3.21
3.33
3.22
Leu / Ileu %
25.66
23.00
32.72
31.09
32.79
TAAA ( Asp + Glu)
28.97
28.86
42.38
37.46
33.32
Asp/ Glu
0.59
0.56
0.08
0.10
0.15
Arg/lys
1.09
1.25
1.76
1.73
1.54
TBAA ( Arg + Lys)
13.37
11.77
5.22
5.37
5.89
TEAA+Arg+His/TAA %
48.15
46.30
31.52
33.95
34.58
P-PER
2.734
2.453
2.152
2.393
1.705
EAAI %
95.90
87.12
64.67
69.07
64.92
BV %
92.83
83.26
58.79
63.58
59.06
Nutritional index %
43.15
33.26
43.72
29.00
32.88
(1)T1= tofu, T2 = fried tofu, T3 = seitan, T4 = fried seitan with wheat flour and T5 = fried seitan with chickpea
flour (2) TEAA=total essential amino acids, TCEA=conditionally amino acids, TAA=total amino acids,
TNEAA=total non essential amino acids, TSAA=total sulphur amino acids, TArAA=total aromatic amino acids,
TAAA=total acidic amino acids, TBAA= total basic amino acids, P-PER= Predicted Protein Efficiency Ratio,
EAAI =essential amino acid index, BV= biological value.
Thus, the lowest Asp/Glu was recorded in
raw seitan (0.08) while, it was of 0.59 in
raw tofu and 0.56 in fried tofu. The Arg/lys
ratios obtained in this work ranged from
1.09 to 1.76. It was previously reported
that high ratio of Arg/Lys in the diet can
produce beneficial hypocholesterolemic
effects, improving the cardiovascular
health, in addition to helps in hypertension
regulation [46-47]. The values of predicted
protein efficiency ratio (P-PER) of seitan
samples were between 1.705 in fried seitan
coated with chickpea flour to 2.393 in fried
seitan with wheat flour whilst, it reached
2.453 for fried tofu and 2.734 for raw tofu
(Table 6). The P-PER in all seitan samples
were lower than 2.88 in that was recorded
in whole hen’s egg [48] and 2.5 that found
in reference casein [49].
Nevertheless, the P-PER in raw tofu was
higher than the value for reference casein
and lower than whole hen’s egg. The
EAAI of tofu samples (raw and fried) were
95.90 and 87.12%, respectively, therefore,
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
186
tofus are considered a good nutritional
quality since the EAAI is ranged 80 – 90%
as previously reported [19]. However,
seitan samples were lower in the present
study as compared with the values
previously reported [19] showing that
protein based food is in adequate when it’s
EAAI below 70%. The predicted BV
exhibited the highest percentage in raw
tofu followed by fried tofu and then fried
seitan coated with wheat flour, while, raw
seitan was the lowest. Scientifically, it is
well known that a protein-based food
nutritional is of good quality when its
biological values (BV) are as high as 70
and up to 100% [19].The increase in BV of
the tofu samples either raw or fried is an
indication of improved digestibility
potential and effective utilization. Table
(6) also showed the Nutritional index (NI)
of tofu and seitan samples. The results
showed that the raw tofu and seitan had
higher NI followed by fried tofu and fried
seitan with chickpea flour while, fried
seitan with wheat flour was the lowest one.
3.7.1. Amino acid scores
Amino acid content in foods can be
used to calculate the amino acid score,
which provides a way to predict how
efficiently protein will meet a person’s
amino acid needs [38]. Table (7) shows
the amino acid scores for tofu and seitan
samples analyzed in this study based on
the essential amino acid content and the
pattern for casein standard. As expected,
lysine was the first limiting amino acid in
cereal products. Seitans expressed the
wheat protein (gluten) and therefore, lysine
amino acid was the lowest score among
other amino acids.
Table 7
Essential amino acid score % of tofu and seitan relative to casein standard
T1= tofu, T2 = fried tofu, T3 = seitan, T4 = fried seitan with wheat flour and T5 = fried seitan with chickpea flour
However, the highest score of seitan
samples was recorded for phenylalanine.
The results of the amino acid scores in tofu
samples indicated that methionine was the
limiting amino acid. It was also reported
that legumes have low values of sulfur-
containing amino acids such as methionine
[50]. Generally, raw tofu had the highest
score in all essential amino acid as
compared with fried tofu and different
seitan samples.
3.8. In-Vitro protein digestibility and
protein digestibility corrected
amino acid scores (PDCAAs)
The in vitro protein digestibilities of
tofu and seitan samples are presented in
Table (8). The lowest values were
observed for fried seitan with chickpea
flour and fried seitan with wheat flour.
Fried seitan with wheat flour had a
relatively high amino acid score as
compared to other seitans.
Treatments
T1
T2
T3
T4
T5
Casein
standard
Essential amino acids
Theronine
102.1
100.0
64.55
67.19
66.40
3.78
Valine
86.94
84.19
59.11
68.72
56.70
5.82
Isoleucine
103.0
101.7
72.69
81.27
72.69
4.54
Leucine
95.53
89.13
78.62
84.78
78.74
8.28
Phenylalanine
113.6
110.5
102.4
101.9
94.07
4.55
Histidine
106.2
98.03
79.61
83.92
74.12
2.55
Lysine
90.26
73.62
26.66
27.78
32.72
7.09
Methionine
75.09
54.47
64.59
68.48
64.20
2.57
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
187
However, protein quality is not on the
amino acid profile, but also on the protein
digestibility. On the other hand, fried
seitan with chickpea flour had low
digestibility but had higher protein content
than wheat flour and these differences in
protein digestibility indicated that the
preparation method may have an effect on
the availability of amino acids. The main
determinant of food protein quality is the
content and availability of essential amino
acids. These nutrients have been shown to
play an important role in the growth,
reproduction and maintenance of the
human body [38].
Table 8
% Protein digestibility and % PDCAAs of tofu and seitan samples
Foods
% Protein digestibility
% PDCAAs
Tofu
93.00
70
Fried tofu
89.64
49
Seitan
84.88
23
Fried seitan (1)
77.37
22
Fried seitan (2)
63.62
21
(1) Fried seitan coated with wheat flour (2) Fried seitan coated with chickpea flour
Bongnar [51] reported that frying without
any additional ingredients, as it is normally
the case, does not change the digestibility
of protein. When reducing substances are
added to the food that is fried, for instance,
carbohydrates (flour), protein digestibility
is lowered slightly, albeit significantly. On
the other hand, the previous data showed
that kind of flour can also affect the protein
digestibility and use of wheat flour as a
coating substance of seitan before frying is
better than the use of chickpea flour to
enhance the protein digestibility. As
regards tofu samples, raw tofu sample was
the highest in % digestibility (93%) as
compared to other samples. These results
are in accordance with previously reported
results [52] showing that the digestibility
for tempeh was 91.41 and this value was
higher than that found in meat (90.79) or
pure beef burger (90.04), even though
temph is a form of soya and it was
processed via fermentation without
thermal processing. This study provided
information on the amino acid content and
protein digestibility of fried tofu and seitan
and this is new information that was not
available for consumers.
The protein digestibility- corrected amino
acid score (PDCAAs) method has been
considered to be a simple and scientifically
sound approach for routine assessment of
dietary protein quality of humans [21].
Higher PDCAAs for raw were recorded for
tofu samples as compared with seitan
samples (Table8). The difference between
the PDCAAs of raw and fried seitan was
small but the PDCAAs of raw tofu were
higher than that of fried tofu. It was earlier
reported that a high protein quality of diets
when PDCAAs values above 70 – 80%.
The vegetable source foods with the lowest
PDCAAS like wheat, maize and cassava, it
is only when 50% of the protein is
exchanged with an animal food source (i.e
milk) that the increases are up to a level of
80% or above[53]. The addition of 25%
milk powder brings PDCAAS values to a
reasonable level, above 70 %, while the
level, when adding meat, is only of 60 %
or slightly above, for wheat and maize.
The data on the composition of fried tofu
and seitan are important to determine the
nutritional value of these diets and can be
useful for improving their protein quality
to make a significant impact on growth.
Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava
Volume XVIII, Issue 3 – 2019
Dina ANWAR, Ghadir EL-CHAGHABY, Nutritional quality, amino acid profiles, protein digestibility corrected amino
acid scores and antioxidant properties of fried tofu and seitan, Food and Environment Safety, Volume XVIII, Issue 3 – 2019,
pag. 176 - 190
188
4. Conclusions
Plant-based food preparations produced
from pulses or grains have always been a
major source of protein in human diet.
Tofu and seitan have a very protein
contents and can be considered as meat
alternatives. This recent trend is being
accompanied and promoted by a growing
number of new food products from various
raw materials. Frying method had a good
effect on the pleasant and acceptability of
tofu and seitan. Fried tofu and seitan
contained a moderate amount of protein,
which was above of 20% and high content
of carbohydrates, lipids and energy in
compare with traditional ones. However,
the new recipes followed by frying process
of tofu and seitan caused an increment in
desired minerals and antioxidant activity.
Fried tofu proved to be a good source of
essential amino acids with respect to
protein quality. A correspondence was
found between essential amino acids of
fried products and % digestibility and
PDCAAs, since tofu samples with higher
amino acids content had higher values of
digestibility and PDCAAs.
5. Acknowledgments
The authors are thanksfull to the Regional
Center for Food and Feed at the
Agricultural Research Center, Giza, Egypt.
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