The Effects of Dairy Processes and Storage on Insulin-Like Growth Factor-I (IGF-I) Content in Milk and in Model IGF-I–Fortified Dairy Products

Abstract

The effects of several dairy processes on insulin-like growth factor-I (IGF-I) concentrations in milk and the storage stability of IGF-I-fortified dairy products were examined. The IGF-I content in raw milk determined by radioimmunoassay was significantly changed by the strength of heat treatments. In commercial manufacture of whole milk dry powder, IGF-I concentration was not significantly changed. A significant reduction in IGF-I content was found as the result of fermentation with a commercial starter culture. The IGF-I content in fortified milk and dried milk powder exhibited no significant changes over the tested storage periods (12 d for milk, 4 wk for dried milk powder), but the IGF-I content in the yogurt decreased significantly during storage. The use of IGF-I was varied by lactic strains and was apparent in the viable cells. When IGF-I was encapsulated using the surface-reforming process, the remaining IGF-I content after fermentation was significantly higher compared with that of the untreated control. Therefore, enteric coating of IGF-I before fermentation might be an effective method for the prevention of IGF-I degradation during fermentation.

Full text

J. Dairy Sci. 89:402–409
©American Dairy Science Association, 2006.
The Effects of Dairy Processes and Storage on Insulin-Like
Growth Factor-I (IGF-I) Content in Milk and in Model
IGF-I–Fortified Dairy Products
S. H. Kang,* J. U. Kim,† J. Y. Imm,‡ S. Oh,§ and S. H. Kim†
1
*Institute of Dairy Food Research, Seoul Dairy Cooperative, Ansan 425-838, Korea
†Division of Food Science, Korea University, Seoul 136-701, Korea
‡Department of Food & Nutrition, Kookmin University, Seoul 136-702, Korea
§Department of Animal Sci., Chonnam National University, Gwangju 500-757, Korea
ABSTRACT
The effects of several dairy processes on insulin-like
growth factor-I (IGF-I) concentrations in milk and the
storage stability of IGF-I–fortified dairy products were
examined. The IGF-I content in raw milk determined
by radioimmunoassay was significantly changed by
the strength of heat treatments. In commercial manu-
facture of whole milk dry powder, IGF-I concentration
was not significantly changed. A significant reduction
in IGF-I content was found as the result of fermenta-
tion with a commercial starter culture. The IGF-I con-
tent in fortified milk and dried milk powder exhibited
no significant changes over the tested storage periods
(12 d for milk, 4 wk for dried milk powder), but the IGF-
I content in the yogurt decreased significantly during
storage. The use of IGF-I was varied by lactic strains
and was apparent in the viable cells. When IGF-I was
encapsulated using the surface-reforming process, the
remaining IGF-I content after fermentation was sig-
nificantly higher compared with that of the untreated
control. Therefore, enteric coating of IGF-I before fer-
mentation might be an effective method for the preven-
tion of IGF-I degradation during fermentation.
Key words: insulin-like growth factor I, dairy process,
lactic acid bacteria, encapsulation
INTRODUCTION
Insulin-like growth factors (IGF-I and IGF-II) com-
prise the principal growth factors in milk, and can be
found in all mammalian species. Insulin-like growth
factor I is a mitogenic polypeptide, the molecular struc-
ture of which is quite similar to that of insulin. This
compound stimulates growth, differentiation, and me-
tabolism in a variety of cell types, acting via IGF-I
receptors (Zapf et al., 1984; Rechler and Brown, 1988).
Received August 31, 2005.
Accepted September 29, 2005.
1
Corresponding author: saehkim@korea.ac.kr
402
Insulin-like growth factor I is a 7.5-kDa single chain
peptide, which belongs to a family of growth factors
that are identical in human, porcine, ovine, and bovine
species (Tavakkol et al., 1988). Houle et al. (1997) re-
ported on the effects of orally administered IGF-I with
regard to the development of intestinal disaccharidase
enzymes and villus height in pigs. Insulin-like growth
factor I has also been reported to stimulate cellular
growth and DNA synthesis in cultured bovine (Sha-
may et al., 1988) and ovine mammary tissues (Winder
et al., 1989). In addition, IGF-I is a mammary
apoptosis inhibitor (Neuenschwander et al., 1996; Ros-
fjord and Dickson, 1999). Burrin et al. (1994) reported
that skeletal muscle and jejunal protein synthesis
rates were higher in colostrum-fed piglets, and IGF-I
in colostrum may be partially responsible for these
effects. Insulin-like growth factor I content in bovine
and porcine milk has been reported to be in the range
of 22 to 26 ng/mL (Collier et al., 1991), and 1.27 to
8.10 ng/mL (Donovan et al., 1994), respectively. The
concentration of IGF-I in bovine colostrum showed
wide variation. Vega et al. (1991) reported that it was
highest at 2 wk prepartum (2,949 ±1,158 ng/mL) and
lowest in bovine milk at 49 d postpartum (5.0 ±2.0 ng/
mL). The IGF-I concentration was shown to increase in
the final period of pregnancy (Donovan et al., 1994),
and served an important function in the development
of the postnatal gastrointestinal tract (Philipps et al.,
1997). In this regard, supplementation with milk-
borne IGF-I may prove to be therapeutic with regard
to growth retardation in preterm infants.
Limited studies have been conducted regarding
changes in IGF-I content during dairy processes.
Juskevich and Guyer (1990) reported that the IGF-I
contents in raw and pasteurized milk were 5.6 ±0.56
and 8.2 ±0.35 ng/mL, respectively, and that concentra-
tions were reduced by 0.5 ng/mL or more when the
same milk samples were subjected to the infant for-
mula process. However, no other follow-up studies
have been reported.

EFFECTS OF DAIRY PROCESSES ON IGF-I CONTENT IN DAIRY PRODUCTS 403
The objectives of this study were to determine the
effects of a variety of dairy processes, including homog-
enization, sterilization, spray drying, and fermenta-
tion on IGF-I contents in milk, and to monitor changes
in IGF-I contents during the storage of model IGF-I-
fortified dairy products.
MATERIALS AND METHODS
Milk and Colostrum
Raw bulk milk and colostrum were obtained at dairy
farms in the northern Kyung-ki province of South Ko-
rea. Colostrum samples were collected from Holstein
cows within 24 h postpartum, and were immediately
frozen and stored at −40°C. After thawing, samples
were skimmed by centrifugation at 9,000 ×gfor 20
min at 4°C. The skimmed samples were diluted twice
with distilled water and casein was removed from the
samples by adjusting to pH 4.6 using 2 NHCl. Whey
was obtained by centrifugation at 1,500 ×gfor 15 min.
The colostrum whey was then freeze-dried, and used
as a source of crude IGF-I.
Effects of Homogenization and Heating on IGF-I
Concentrations in Milk
Raw bulk milk was homogenized at 70°C with a
homogenizer (APV-1000, APV, Silkeborg, Denmark)
at a pressure of 150,000 kPa. The homogenized milk
sample was divided into 3 portions. Two portions were
heated at 75 and 85°C for 15 min, respectively, using
a tubular-type heat exchanger (Kirchfeld, Germany),
and the remaining portion was autoclaved at 121°C
for 20 min.
Changes in IGF-I Concentration During Whole
Dried Milk Powder Process
Whole dried milk was prepared using commercial
spray dryer (APV) at the Yang-ju plant of Seoul Dairy
Co. (Seoul, Korea). Raw milk was clarified, preheated
at 55°C, homogenized at a pressure of 100,000 to
120,000 kPa using an homogenizer (Type 1030 MC 18-
5TPS, APV), and then UHT-pasteurized (130°C for 2
s). The pasteurized milk was concentrated in a 4-effect
falling film vacuum evaporator (vvaporator type-2
TVR F IV, APV) at a maximum feed rate of 15,000 L/
h. The temperatures of the first, second, third, and
fourth effects were 73, 71, 60, and 55°C, respectively.
The concentrated milk containing 40 to 45% of total
milk solids was subjected to spray drying. During
spray drying, the inlet chamber temperature was
maintained at 140 to 150°C, and the outlet air temper-
ature was maintained at about 85°C. Samples were
Journal of Dairy Science Vol. 89 No. 2, 2006
collected from raw milk, after the concentration step,
and from the final whole milk powder. The IGF-I con-
centrations in all of the samples were then analyzed.
Changes in IGF-I Concentrations
During Fermentation
Skim milk powder (Seoul Dairy Co.) was reconstitu-
ted in distilled water to give 10% total solids before
pasteurization. The pasteurized reconstituted milk
was inoculated with 1.5% commercial yogurt starter
culture (Lactococcus delbrueckii ssp. bulgaricus and
Streptococcus salivarius ssp. thermophilus, Culture
Systems, Inc., Mishawaka, IN). During the fermenta-
tion process, aliquots of the samples were collected
every 3 h until the pH of samples was close to 4.0. All
of the collected samples were immediately frozen at
−40°C, until the analysis of IGF-I concentration was
conducted.
Use of Recombinant IGF-I by Single Lactic Strains
Because IGF-I concentration was decreased signifi-
cantly during the fermentation process, IGF-I avail-
ability by single lactic strains was assessed. The lactic
strains used in this study were obtained from the Food
Microbiology Laboratory at Korea University (Seoul,
Korea). Lactococcus delbrueckii ssp. bulgaricus, and
Lactococcus acidophilus 4356 were grown at 37°Cinde
Man, Rogosa, and Sharpe (MRS) broth (Difco, Detroit,
MI) for 18 h, and S. salivarius ssp. thermophilus ABT-
4 was incubated at 42°C in M17 broth with 0.5% lactose
for 24 h. Before their use in experiments, the lactic
strains were subcultured at least 3 times. Recombi-
nant human IGF-I (500 ng/mL, Gropep Pty. Ltd., Ade-
laide, Australia) was added to the MRS broth, M17
broth, and cell-free spent broth at lag phase, log phase
(12 h after fermentation), and death phase (18 h after
fermentation), respectively. All of the collected sam-
ples were immediately frozen at −40°C, until the anal-
ysis of IGF-I concentration was conducted.
Changes in IGF-I Concentration in Model
IGF-I–Fortified Dairy Products During Storage
Model IGF-I–fortified milk and whole milk powder
were prepared by the addition of crude IGF-I (freeze-
dried colostral whey) to local city milk (10%, wt/vol)
or whole milk powder (10%, wt/wt), respectively. For
the preparation of yogurt, crude IGF-I (10%, wt/vol)
was added to yogurt premix (14% total solids) before
fermentation. Commercial starter culture (1.5%, Cul-
ture Systems, Inc.) was inoculated, and fermentation
continued in a 42°C incubator until the pH reached 4.0.

KANG ET AL.404
Table 1. Changes in IGF-I content of milk by homogenization and by heat treatments
1
Process
Heat treatment
Raw milk Homogenized 75°C, 15 min 85°C, 15 min Autoclaved
IGF-I (ng/mL) 36.5 ±8.4
a
33.4 ±7.7
a
20.1 ±5.0
b
20.0 ±4.5
b
ND
a,b
Different superscripts indicate significant differences at P<0.05.
1
All values are expressed as mean ±(n = 52); ND = not detected.
After fortification, the model products were vigorously
stirred to ensure complete mixing, and then sealed
tightly in cap tubes. The IGF-I–fortified milk and the
whole milk powder were stored at 4°C for 12 d, and
at 25°C for 4 wk, respectively. The yogurt samples
were then stored at 4°C for 18 d. Throughout the stor-
age period, changes in IGF-I concentrations were mon-
itored. All treatment and analytical measurements
were repeated 3 times, using different samples.
IGF-I Analysis
The IGF-I concentrations in the samples were ana-
lyzed using the method of Donovan et al. (1991). Insu-
lin-like growth factor-binding proteins were removed
by acid-ethanol treatment (HCl:ethanol = 12.5:87.5),
and then neutralized. After removal of IGF-binding
proteins, the sample was mixed with 0.1 mL of radio-
immunoassay (RIA) buffer (30 mMsodium phosphate,
0.02% protamine sulfate, 10 mMEDTA, 0.05% Tween-
20, 0.02% sodium azide, pH 7.5), containing rabbit
antihuman IGF-I polyclonal antiserum (GroPep Pty.,
Ltd.) and [
125
I] IGF-I, and incubated for 16 h at 4°C.
After the incubation, 0.1 mL of goat antirabbit IgG
antibody (GroPep Pty., Ltd.) was added, and the mix-
ture was incubated for 1 h, followed by an additional
1 h of incubation with 0.1 mL of normal rabbit serum
at 4°C. After the addition of 1 mL of RIA buffer, the
tubes were centrifuged for 10 min at 3,000 ×gat 4°C.
The supernatant was aspirated, and the pellets were
counted with a gamma counter (COBRA, Packard In-
strument Co., Meriden, CT) for 1 min. All determina-
tions were performed in triplicate.
Encapsulation of Crude IGF-I
The effects of encapsulation on IGF-I degradation
during the fermentation process were also determined.
The surface of freeze-dried colostral whey (crude IGF-
I) was reformed with the enteric coating ingredient,
Eudragit L100-55 (Ro
¨hm GmbH, Darmstadt, Ger-
many), in a hybridization system (model NSH-0, Nara
Machinery Co., Ltd., Tokyo, Japan). In a preliminary
experiment to optimize the encapsulation process, we
Journal of Dairy Science Vol. 89 No. 2, 2006
had determined an optimal formulation ratio of 9:1
(wt/wt, crude IGF-I: Eudragit L100-55), a running
time of 3 min, and a rotor speed of 17,500 ×g. The
temperature of the hybridization chamber was main-
tained below 30°C by the circulation of cooled water
within a jacket. During the surface-reforming process,
fine wall materials adhered to the surfaces of bacterio-
cin particles in the dry state by friction and collision
as described by Ishizaka et al. (1989).
Microstructure of Encapsulated Crude IGF-I
The microstructure of the encapsulated crude IGF-
I was visualized with a scanning electron microscope
(Hitachi S-2380, Ltd., Tokyo, Japan). The samples
were coated for 60 s with gold-palladium in an E-1010
ion sputter coater (Hitachi Ltd.), and the topography
of the particles was observed at 15 kV.
Statistical Analyses
All data were analyzed using the GLM procedure of
SAS (SAS Institute, 1985). Significant differences (P
<0.05) between treatment means were assessed using
the LSD (least significant difference) method.
RESULTS
Changes in IGF-I Concentrations
During Dairy Processes
Changes in IGF-I concentration during the homoge-
nization and heating are shown in Table 1. The IGF-
I concentration in raw milk whey was found to be 36.5
±8.4 ng/mL, which was only slightly altered (33.4 ±
7.7 ng/mL) by homogenization. When the milk was
heated at either 75°C or 85°C for 15 min, the IGF-I
concentration was significantly decreased by 45.0 and
45.2%, respectively, compared with that of unheated
raw milk (P<0.05). When milk was autoclaved (121°C
for 15 min), no IGF-I was detected in the sample. This
indicates that the native IGF-I concentration in the
samples was affected by heating strength. The spray-
drying step, in combination with pasteurization, re-

EFFECTS OF DAIRY PROCESSES ON IGF-I CONTENT IN DAIRY PRODUCTS 405
Table 2 Changes in IGF-I concentration during the production of
whole milk powder
1
Process
2
Raw milk Concentrated Spray-dried
IGF-I (ng/mL) 47.2 ±6.9
a
69.5 ±8.2
b
42.5 ±7.3
a
a,b
Different superscripts indicate significant differences at P<0.05.
1
All values are expressed as mean ±SE (n = 19).
2
Raw milk was concentrated yielding 40 to 45% of total milk solids.
Whole milk powder was reconstituted to the same solid content as
in raw milk.
sulted in no substantial changes in IGF-I concentra-
tion (Table 2). Only a minor reduction of IGF-I content
could be observed when whole milk powder was recon-
stituted to the same solid content as in city milk.
Interestingly, IGF-I concentrations decreased dra-
matically, from 30.3 ±7.5 to 5.0 ±2.2 ng/mL, after the
completion of fermentation (Table 3).
Changes in IGF-I Concentrations During the
Storage of IGF-I-Fortified Dairy Products
The freeze-dried colostral whey and raw milk whey
contained about 2,473 and 32.8 ±14.5 ng/mL of IGF-
I, respectively. The IGF-I concentration in raw milk
whey after fortification (10%, wt/vol) was approxi-
mately 274.4 ±23.9 ng/mL. The IGF-I concentration
in the samples exhibited no significant changes for up
to 12 d of storage at 4°C (Figure 1). The IGF-I–fortified
whole milk powder contained 125.5 ±6.6 ng/mL of
IGF-I after fortification, and there were no significant
differences in IGF-I concentration occurring after 4
wk of storage at 25°C (Figure 2).
For IGF-I–fortified yogurt, however, IGF-I concen-
trations decreased significantly; only about 20% of the
initial IGF-I remained after the completion of fermen-
tation. No further decreases in IGF-I concentrations
were detected after 18 d of storage at 4°C (Figure 3).
Use of IGF-I by a Single Lactic Acid Bacteria Strain
To determine the reason for the decrease in IGF-I
concentrations during fermentation, recombinant hu-
man IGF-I was added to both MRS and M17 broths.
Table 3. Changes in IGF-I concentration during fermentation of milk
1
pH
6.32 5.02 4.45 4.20 4.06
IGF-I (ng/mL) 30.3 ±7.5
a
31.8 ±5.9
a
31.3 ±5.3
a
26.0 ±4.0
a
5.0 ±2.2
b
a,b
Different superscripts indicate significant differences at P<0.05.
1
All values are expressed as mean ±SE (n = 28).
Journal of Dairy Science Vol. 89 No. 2, 2006
Figure 1. Changes of IGF-I concentration in IGF-I–fortified milk
during storage at 4°C. Each bar represents the mean ±, SE (n = 13).
The raw milk was fortified with crude IGF-I at the level of 10%
(wt/vol).
Each lactic acid strain was then separately inoculated,
at either log phase or death phase. As shown in Figure
4, a marked decrease in the IGF-I concentration was
observed in both log phase and death phase. Among
the tested strains, L. delbrueckii ssp. bulgaricus and
L. acidophilus 4356 used IGF-I more readily than did
S. salivarius ssp. thermophilus ABT-4. The recovery
rates of IGF-I associated with L. delbrueckii ssp. bulg-
aricus and L. acidophilus 4356 were in the range of 22
to 33%, whereas that of S. salivarius ssp. thermophilus
ABT-4 ranged from 65 to 67%.
Significant reductions in IGF-I concentrations were
not observed in the cell-free supernatant, regardless
of the inoculated strain. This demonstrates that IGF-
I use occurred principally as an activity of lactic acid
bacteria, and that the extent to which it occurred var-
ied depending on the characteristics of the lactic
strain used.
Stability of Encapsulated IGF-I
During Fermentation
To prevent IGF-I loss during fermentation, crude
IGF-I was encapsulated by a surface-reforming pro-

KANG ET AL.406
Figure 2. Changes of IGF-I concentration in IGF-I–fortified whole
milk powder during storage at 20°C. Each bar represents the mean
±SE (n = 15). The raw milk was fortified with crude IGF-I at the
level of 10% (wt/wt).
cess (hybridization) using enteric coating materials
(Eudragit L100-55). Figure 5 shows the size and shape
of the encapsulated IGF-I. The encapsulation process
resulted in smooth-surfaced spherical beads, each
about 20 ␮m in diameter. The microencapsulated IGF-
I was then used to fortify the yogurt premix and
changes in IGF-I concentrations during fermentation
were monitored.
As shown in Figure 6, fermentation resulted in a
90% decrease in IGF-I concentration in the control,
but only about a 20% decrease in the IGF-I concentra-
tion of the yogurt fortified with the encapsulated IGF-
I. Although a gradual decrease in IGF-I concentration
was observed during storage, about 58% of the initial
Figure 3. Changes of IGF-I concentration in IGF-I–fortified yogurt
during storage at 4°C. Each bar represents the least squares mean
±SE (n = 18).
Journal of Dairy Science Vol. 89 No. 2, 2006
Figure 4. The changes of IGF-I concentration during lactic fermen-
tation using single strain lactic acid bacteria. Recombinant human
IGF-I (500 ng/mL) was added at each stage of fermentation. Each
bar represents the least squares mean ±SE (n = 60). LB = L. del-
brueckii ssp. bulgaricus;LA=L. acidophilus 4356; ST = S. salivarius
ssp. thermophilus.
IGF-I concentration remained in the yogurt fortified
with the encapsulated IGF-I after 18 d of storage.
DISCUSSION
Milk and colostrum contain valuable biologically ac-
tive substances, in addition to their essential nutri-
ents. Milk proteins are one of the richest sources of
functional substances present in milk and colostrum.
Milk peptide and growth factors constitute 2 major
groups of biologically active dairy proteins. Several
studies have pointed to the prospective biological ac-
tivities of milk peptides (Clare and Swaisgood, 2000;
Gobbetti et al., 2002), whereas the application and
efficacy of milk-derived growth factors, including IGF-
I and transforming growth factor β, remain controver-
sial. However, Howarth et al. (1996) reported that the
oral administration of growth factor extracted from
cheese whey might serve to ameliorate intestinal dam-
age in methotrexate-treated rats. Although the biolog-
ical activities exhibited by milk-derived growth factors
may not be wholly analogous to their human counter-
parts, some efficacy should be expected, as a great
deal of structural homology is shared between cow and
human growth factors.
To date, reports regarding the effects of dairy pro-
cessing on the concentrations of IGF-I have been quite
limited. Previously, Donovan et al. (1991) and Collier

EFFECTS OF DAIRY PROCESSES ON IGF-I CONTENT IN DAIRY PRODUCTS 407
Figure 5. Morphology of crude IGF-I before and after encapsula-
tion. A) Before encapsulation (crude IGF-I); B) after encapsulation
with Eudragit L100-55.
et al. (1991) investigated the effect of heating on IGF-
I concentration. According to these studies, IGF-I con-
centration in both human and cow’s milk were not
changed under normal pasteurization conditions, such
as exposure to a temperature of 56°C for 30 min or to
79°C for 45 s. However, the above reports did not ad-
dress the effects of other heating conditions on IGF-I
concentration. More recently, Elfstrand et al. (2002)
attempted to determine the effects of various pro-
cesses, including filtration, pasteurization, and freeze-
drying, on immunoglobulins, growth factors, and
growth hormone content in bovine colostrums. They
reported that heating (60°C for 45 min) and freeze-
drying of colostral whey resulted in a 75% reduction in
immunoglobulin content, but the content of the growth
factors remained unaffected. Our results demon-
Journal of Dairy Science Vol. 89 No. 2, 2006
Figure 6. The changes of IGF-I concentration in yogurt containing
encapsulated IGF-I. Each bar represents the least squares mean ±
SE (n = 40).
strated significantly decreasing patterns of IGF-I con-
centrations when raw milk was heated at 75 and 85°C
for 15 min (Table 1). In the present study, IGF-I con-
centrations were unaffected by homogenization.
Collier et al. (1991) reported that the use of higher
temperatures (121°C for 5 min) during the preparation
of infant formula resulted in the denaturation of IGF-
I to the extent that IGF-I was no longer recognized by
the antibodies used during the RIA procedure. How-
ever, IGF-I concentrations showed little changes un-
der commercial whole dried milk processing (Table 2).
The most significant reduction of IGF-I concentra-
tion was observed during fermentation. Our IGF-I re-
covery test confirmed that IGF-I was primarily used
by lactic acid bacteria; substantial IGF-I loss did not
occur in the cell-free spent broth. This result suggested
that the observed reduction in IGF-I content during
fermentation might be attributable to the activities of
lactic acid bacteria, many of which are able to use IGF-
I or IGF-binding protein complex as their sole nutrient
source. The extent to which IGF-I was used varied
depending on the bacterial strain used; IGF-I was used
preferentially by L. delbrueckii ssp. bulgaricus and
L. acidophilus 4356 compared with S. salivarius ssp.
thermophilus. It is presumed that the observed reduc-
tions in IGF-I concentrations were not due to acid pro-
duction by lactic acid bacteria, but instead to use of
IGF-I as a nitrogen source by lactic acid bacteria.
The stability of IGF-I during storage was evaluated
using model crude IGF-I–fortified dairy products. We
detected no significant changes in the IGF-I concentra-
tions of market milk or whole milk powder under typi-
cal storage conditions. However, the same pattern of
IGF-I loss was found in the IGF-I–fortified yogurt, and

KANG ET AL.408
only 20% of the initial IGF-I concentration remained
immediately after the completion of fermentation.
To prevent IGF-I loss during fermentation, a new
food matrix was generated using microencapsulation.
The enteric coating material Eudragit L100 was se-
lected and used to protect the IGF-I from the acidic
environment during fermentation. This enteric coat-
ing effectively reduced IGF-I degradation during fer-
mentation; about half of the fortified IGF-I remained
after storage, compared with what was observed in
the uncoated treatment. This result implies that lactic
acid bacteria are unable to use encapsulated IGF-I for
their growth. The gradual decrease in IGF-I concentra-
tion observed during storage might be attributable to
use of insufficiently coated IGF-I.
It is generally believed that lactic acid bacteria ex-
hibit very limited proteolytic activity (Axelsson, 1998).
Beshkova et al. (1998) demonstrated that S. ther-
mophilus 13a possesses poor proteolytic properties,
and that the proteolytic activity exerted during lactic
acid fermentation is important in that it requires an
exogenous nitrogen source, and affects the use of pep-
tides and proteins from the growth medium. Our recov-
ery test indicated that IGF-I use in the 3 selected
strains was much greater during the logarithmic
phase. The utilization of IGF-I by S. salivarius ssp.
thermophilus ABT-4 was found to be much lower than
that of the above 2 strains (66.9 and 64.8% recovery
rates of L. delbrueckii ssp. bulgaricus and L. acido-
philus 4356, respectively).
CONCLUSIONS
Insulin-like growth factor I appears to have some
potential as a nutraceutical in the food industry, or as
a pharmaceutical agent, akin to insulin for diabetes.
Two dairy processes critically affected IGF-I concen-
tration in milk and dairy products. Both homogeniza-
tion and commercial whole dried milk process scarcely
affected IGF-I concentration but it was significantly
decreased either by heat treatment (75 and 85°C for 15
min) and fermentation. The decreased IGF-I content
determined in the fermented products might be related
to lactic acid bacteria, which are capable of utilizing
either IGF-I or IGF-binding protein complex as their
nutrition source. The microencapsulation of colostrum
whey with enteric coating materials before fermenta-
tion yielded good results with regard to the mainte-
nance of IGF-I content during shelf life.
ACKNOWLEDGMENT
This work was supported by a grant (20050401-034-
698-151-00-00) from BioGreen 21 Program, Rural De-
velopment Administration, Republic of Korea.
Journal of Dairy Science Vol. 89 No. 2, 2006
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