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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


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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.
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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†
*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
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
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.
Corresponding author:
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.
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.
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
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.
Table 1. Changes in IGF-I content of milk by homogenization and by heat treatments
Heat treatment
Raw milk Homogenized 75°C, 15 min 85°C, 15 min Autoclaved
IGF-I (ng/mL) 36.5 ±8.4
33.4 ±7.7
20.1 ±5.0
20.0 ±4.5
Different superscripts indicate significant differences at P<0.05.
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 [
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.
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-
Table 2 Changes in IGF-I concentration during the production of
whole milk powder
Raw milk Concentrated Spray-dried
IGF-I (ng/mL) 47.2 ±6.9
69.5 ±8.2
42.5 ±7.3
Different superscripts indicate significant differences at P<0.05.
All values are expressed as mean ±SE (n = 19).
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
6.32 5.02 4.45 4.20 4.06
IGF-I (ng/mL) 30.3 ±7.5
31.8 ±5.9
31.3 ±5.3
26.0 ±4.0
5.0 ±2.2
Different superscripts indicate significant differences at P<0.05.
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%
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-
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.
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
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
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).
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.
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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... Despite milk consumption being associated with acne incidence, no correlation was found between yogurt consumption and acne incidence [7]. Yoghurt has lower levels of IGF-1 due to probiotic bacteria during fermentation [37]. Furthermore, fermented milk enriched with lactoferrin has been shown to reduce skin surface lipid triglycerides, resulting in reduced sebum production, preventing acne [38]. ...
Acne vulgaris is a common skin condition that is mostly seen in young adults. It has always been an enigma for physicians and patients if diet or environmental factors are responsible for developing acne. This article presents the relationship between air pollution, cigarette smoking, dietary factors and acne through the pathogenesis of acne.
... This re ects that endocrine factors are involved in acne because milk is an insulinotropic nutrient and has a high glycemic index which increases serum insulin and IGF-1 levels. Other mechanisms for the dairy-induced impact of acne include IGF-1 which is a forceful mitogen that promotes proliferation of sebaceous glands and sebaceous lipogenesis, generates overproduction of androgens and oncogenic phosphoinositide − 3-kinase which helps exaggerate acne 28 .It also downregulates Fox -O1 which increases oxidative stress and hence promotes acne 29 Our study found that yogurt consumption was lower in acne vulgaris patients and is consistent with the ndings by several studies 30 . When added to milk during the fermentation process, probiotic bacteria (speci cally Lactobacilli) utilize IGF-1 and lower IGF-1 levels in fermented milk.This might explain the association of milk with acne vulgaris occurrence in contrast to fermented dairy products such as yogurt. ...
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Background Acne vulgaris affects millions of adults. Despite extensive research, its etiology pertaining to food remains elusive. Objective To assess the correlation between dietary intake and acne through a case-control survey of 300 respondents aged 15–25 years living in Pakistan. Method 150 acne patients and 150 age- and ethnicity-matched controls were subjected to a questionnaire. Using SPSS-22, cases and controls were separated and univariate analysis was done using chi-square test. p value < 0.05 was considered statistically significant. Adjusted odds ratio was used to assess the strength of association with 95% confidence interval. Results Most of the respondents were females (91.3%). Most(48.7%) acne patients were aged 20–25 years .Acne severity was mild in 50%, moderate in 34%, severe in 14% and very severe in 2%.Frequent low-fat foods (p < 0.001)(OR = 3.22),fat intake(p = 0.03)(OR = 1.629),sweet snacks i.e. biscuits and candies etc. (p = 0.013) (OR = 1.9254), soft drinks(p = 0.045)(OR = 1.9091),butter(p < 0.001) (OR = 1.8185),dairy products(p = 0.043)(OR = 0.624),salty foods(p = 0.011)(OR = 1.961),chocolate (p = 0.028)(OR = 1.669), were associated with increased acne risk. No association was found in terms of fried foods, desserts, fruit juices, raw fruit intake, fast foods, vegetables, cheese, soy product, salt intake and corn. Increased butter and chocolate consumption were linked to more severe forms of acne (p = 0.049 and p = 0.005 respectively). Most respondents (n = 218) thought they had healthy eating habits showing that they were not educated on dietary aspect of acne treatment. Conclusions Participants without acne had healthier eating habits. Dietary awareness is critical for convincing adolescents to reduce acne. Further studies must be conducted to develop a causative relationship between different dietary components and acne.
... Whereas fermented dairy products can provide probiotics to supplement and balance the gut microbial community, thereby reducing cancer risk [109]. In addition, IGF-I amount that may increase BC risk is significantly reduced in processed heat-treated or fermented dairy products [87,110]. Combined with the above mechanisms, it may help explain that consumption of fermented dairy products can reduce BC incidence in postmenopausal population. ...
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Background The effect of dairy products intake on breast cancer (BC) is highly controversial. This study aims to investigate the relationship between dairy intake and BC incidence. Methods A search was carried out in PubMed, EBSCO, Web of Science, and Cochrane Library databases before January 2021. The primary objective was the risk of BC and intake of dairy products were exposure variables. Results The meta-analysis comprised 36 articles with 1,019,232 participants. Total dairy products have a protective effect on female population (hazard ratio (HR) =0.95, 95% confidence interval (CI) =0.91–0.99, p = 0.019), especially for estrogen receptor-positive (ER+) (HR = 0.79, p = 0.002) and progesterone receptor-positive (PR+) BC (HR = 0.75, p = 0.027). For ER+/PR+ BC, there is a trend of protection, but it has not reached statistical significance (HR = 0.92, p = 0.075). Fermented dairy products can reduce BC risk in postmenopausal population (HR = 0.96, 95%CI = 0.93–0.99, p = 0.021), but have no protective effect on premenopausal population (HR = 0.98, 95%CI = 0.94–1.03, p = 0.52). Non-fermented dairy products have no significant effect on BC occurrence ( p > 0.05). High-fat dairy products are harmful to women, without statistical difference (HR = 1.06, 95%CI = 1.00–1.13, p = 0.066). On the contrary, low-fat dairy products can protect the premenopausal population (HR = 0.94, 95%CI = 0.89–1.00, p = 0.048). Conclusion The intake of dairy products can overall reduce BC risk in the female population, but different dairy products have varying effects on different BC subtypes and menopausal status.
... It also presents data that reinforce the most recent Dietary Guidelines for Americans, which recommends choosing nutrient-dense options within the dairy group, such as unsweetened, low fat milk, yogurt, and cheese [8]. It is also worth noting that sweetened dairy products are commonly processed to the point where they are categorized as ultra-processed foods, which may reduce their nutritional value/density (alterations or biochemical changes in milk constituents, macronutrients and bioactive factors) [7,50], and may be related to obesity [51]. Moreover, the addition of sugar, and also cocoa, which is very common in Israeli dairy puddings, flavored milk, and ice cream, may adversely affect the availability of calcium from such products. ...
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PurposeMilk consumption is associated with increased height primarily in early childhood. However, in adolescents, data are scarce with inconsistent results. Since height is a proxy for overall health and well-being, this study evaluated the association of dairy intake with height in adolescents.Methods Students in 7th–12th grades, participating in the 2015–2016 Israeli Health and Nutrition Youth Survey, a school-based cross-sectional study, completed self-administered questionnaires, including a semi-quantitative food frequency questionnaire (n = 3529, 48% males, 15.2 ± 1.6 years). Anthropometric measurements were also performed. Dairy servings were calculated as the calcium equivalent of 1 cup of milk, and consumption was divided into four categories from very low (< 1 serving/day) to high (3 + servings/day). BMI- and Height-for-age z scores (HAZs) were calculated according to WHO growth standard; relatively short stature (RSS) was defined as HAZ < − 0.7 SD (< 25th percentile). Multivariable linear and logistic regression analyses were performed to evaluate the association of dairy intake with HAZ and prevalence of RSS, respectively.ResultsMedian consumption of dairy products was 2 servings/day, 1.4 from unsweetened products (milk, cheese and yogurt). Controlling for age, sex, BMI-z-score and socioeconomic status, each increment of unsweetened dairy intake was associated with on average 0.04 higher HAZ (equivalent to 0.3–0.4 cm, p < 0.05), and with reduced risk for RSS: OR 0.90, 95%CI: 0.84, 0.97, p < 0.01. No such associations were found with sweetened dairy products.Conclusion Consumption of unsweetened dairy products (3–4 servings/day) appears to contribute to achieving growth potential in adolescents. Intervention studies are necessary to determine the causal relationship between dairy intake and linear growth.
... It has been speculated that the anti-inflammatory effects of probiotics and their ability to inhibit the production of harmful enzymes prevent the development of colon cancer [20]. Further, it has been suggested that yogurt reduces the concentration of insulin-like growth factor I in dairy products, which promotes cancer development [21]. These experimental observations support our finding that higher yogurt intake is associated with lower cancer-related mortality. ...
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Background Dairy products are known as health-promoting foods. This study prospectively examined the association between milk and yogurt intake and mortality in a community-based population. Methods The study population comprised of 14,264 subjects aged 40–74 years who participated in an annual health checkup. The frequency of yogurt and milk intake was categorized as none (< 1/month), low (< 1/week), moderate (1–6/week), and high (> 1/day) intake. The association between yogurt and milk intake and total, cardiovascular, and cancer-related mortalities was determined using the Cox proportional hazards model. Results During the follow-up period, there were 265 total deaths, 40 cardiovascular deaths and 90 cancer-related deaths. Kaplan–Meier analysis showed that the total mortality in high/moderate/low yogurt intake and moderate/low milk intake groups was lower than that in none group (log-rank, P < 0.01). In the multivariate Cox proportional hazard analysis adjusted for possible confounders, the hazard ratio (HR) for total mortality significantly decreased in high/moderate yogurt intake group (HR: 0.62, 95% confidence interval [CI]: 0.42–0.91 for high intake, HR: 0.70, 95%CI: 0.49–0.99 for moderate intake) and moderate milk intake group (HR: 0.67, 95% CI: 0.46–0.97) compared with the none yogurt and milk intake groups. A similar association was observed for cancer-related mortality, but not for cardiovascular mortality. Conclusions Our study showed that yogurt and milk intake was independently associated with a decrease in total and cancer-related mortalities in the Japanese population.
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Tüm memeli sütlerinde farklı miktarlarda bulunan insülin benzeri büyüme faktörü (IGF-1) yenidoğan için büyüme gen sinyalizasyon sisteminin başlıca düzenleyicisidir. Önemli bir anabolik hormon olan IGF-1’in temel biyolojik fonksiyonları hücre metabolizmasının düzenlenmesi, büyüme, hücre çoğalması ve programlı hücre ölümüdür. Serumdaki IGF-1’in seviyesi ile insan sağlığı üzerine olumlu ve olumsuz etkilerini veya hastalık risklerini ortaya koyan çalışmalar bulunmaktadır. Serum IGF-1 seviyesindeki azalma, kalp-damar hastalıkları, kalp otofaji, hipertansiyon, sarkopeni, sinir sistemi hastalıkları ve tip 2 diyabet riskleri ile ilişkilendirilirken, yüksek IGF-1 miktarı prostat, menopoz öncesi meme ve kolerektal kanserlerle ve yaşam süresinin kısalmasıyla bağlantılı bulunmaktadır. IGF-1’in Alzheimer, demans, Parkinson hastalıklarından koruyucu etkisi olduğu bilinmektedir. Sistematik derlemeler ve meta analiz çalışmaları incelendiğinde, süt tüketiminin IGF-1 seviyesi ve sağlık üzerine etkileri ile ilgili daha tutarlı sonuçlar elde etmek için daha fazla çalışmaya ihtiyaç olduğu anlaşılmaktadır. Ayrıca sütteki IGF-1’in miktar olarak ve moleküler düzeyde, süte uygulanan ısısal olan veya olmayan işlemlerden ve sindirimden nasıl etkilendiğine dair çalışmalar yetersizdir.
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The current study was planned to prepare the camel milk yogurt (CMY) collected from different ecological zones of Punjab province (Pakistan).CMY was prepared with the addition of stabilizers and stored for 21 days at refrigeration temperature to evaluate the effect on physicochemical (pH, titratable acidity, total solids, fat, solids not fat, crude protein, ash, minerals, fatty acids, insulin, organic acids), rheological (viscosity, syneresis, color, textural, water holding capacity) and organoleptic characteristics (color, body & texture, flavor, appearance, mouth feel, overall acceptability). The overall comparison of CMY composition for 21 days storage exhibited that all the parameters, except acidity, had maximum components at the start of storage study and decreased gradually throughout the storage span. The data regarding rheological properties of CMY showed that viscosity, water holding capacity and texture was high on the start of storage period that gradually decreased during storage in comparison to syneresis that increased throughout the storage span. A significant effect of the source of camel milk was also observed on the insulin content of yogurt. The mean values of the sensory parameters depicted highly significant (P<0.01) effect for the sources of camel milk yogurt and storage days.
Milk is a nutrient-rich food with various micronutrients and bioactive components that are affected by heat treatment depending on time-temperature norm. Pasteurisation and short time ultra high temperature treatments do not cause significant changes in most micronutrients; however, intensive heat treatments such as in-bottle sterilisation can cause severe degradation of water-soluble vitamins, essential fatty acids and hormones. Exposure of heat-treated milk to light and oxygen has a more destructive effect on oxygen-sensitive micronutrients, unsaturated fatty acids and most vitamins than heat treatment itself. Therefore, losses during evaporation and drying processes can be significant and should be considered in evaluating the nutritional value of milk. Moreover, packaging material, storage temperature and duration also contribute to the losses. Application of severe heat may also cause minor losses in minerals due to precipitation in processing lines. An integral approach is recommended for retention of the nutritional value of raw milk in processed milk products.
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Fortification of milk with micronutrients play a major role in releaving nutritional deficiency problems in humans. It can improve the palatability and sensory of the products. The studies prove that wide use of fortified milk products in the world improve the health condition of people in geographically specific areas. In this review article fortification of milk and milk products with addition of iron, iodine, vitamins, fish oil, probiotic, conjugated linoleic acid, casinate and fiber fortification discussed below.
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Currently, there are no truly effective therapies for the treatment of chemotherapy-induced intestinal mucositis, a debilitating side effect with a pathophysiology common to many chemotherapy regimens. We tested the efficacy of a growth factor extract derived from cheese whey against experimental intestinal mucositis in rats. Rats were subcutaneously injected with the chemotherapeutic drug methotrexate on d 1, 2 and 3 to induce severe damage in the small bowel and bacterial translocation across the gut. Whey extract (15 to 514 mg/d) was given orally for 5–12 d, starting on d 1. Controls were fed an isonitrogenous diet. Histological indices of villus and crypt integrity were utilized to assess potential efficacy of the extract. Administration of the whey extract for 5 d increased the villus surface length indices in the jejunum and ileum by 52% and 56%, respectively (P < 0.001) compared with controls not receiving the whey extract. The crypt area index was 64% greater (P < 0.001) in the jejunum, but not significantly greater in the duodenum or ileum compared with controls not receiving whey extract. Similarly, sucrase activity was significantly higher in the ileum (P < 0.001) but not significantly elevated in the jejunum, whereas bacterial translocation (incidence and number of colonies) was significantly reduced compared with controls not receiving whey extract. We conclude that oral whey growth factor extract reduces methotrexate-induced damage in the small bowel, which suggests clinical applications for the treatment of intestinal mucositis.
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Concentrations of IGF-I and IGF-II, and IGF binding proteins (IGFBP) in serum and mammary gland secretions were surveyed during the dry period and early lactation of 30 Holstein cows. Although there was a threefold drop in the concentration of IGF-I in serum from the last week of the dry period to parturition (81 +/- 7 to 24 +/- 3 ng/ml, P less than .01), there was no significant change in serum IGF-II concentration during this period (150 +/- 17 vs 173 +/- 13 ng/ml, P greater than .05). Furthermore, a 57% increase in serum IGF-I was observed from the last week of lactation to the second week of drying off (100 +/- 5 to 157 +/- 8 ng/ml, P less than .05). Changes in serum IGF-II were not observed (126 +/- 11 vs 150 +/- 10 ng/ml, respectively; P greater than .05). Although IGF-I, IGF-II, and IGFBP concentrations in mammary secretions peaked 2 wk before parturition (2.95 +/- 1.1, 1.83 +/- .6, and 7.27 +/- .76 micrograms/ml, respectively), total output/quarter was highest in colostrum (394 +/- 119, 295 +/- 132, and 2,680 +/- 1,967 micrograms/quarter, respectively). Weekly milking of two individual quarters during the dry period did not affect (P greater than .05) IGF-I or IGF-II concentration (ng/ml) or total output (microgram/quarter) and milk yield in colostrum and milk (2 wk and 7 wk) compared with the ipsilateral quarter. The data support the hypothesis that IGF-I may be transported by the mammary gland epithelium. Furthermore, the secretion mechanisms of IGF-I, IGF-II, and IGFBP by the gland may be related to each other.
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To establish the naturally occurring range of insulin-like growth factor-I concentrations in bovine milk, samples from individual cows (n = 409) managed on five Missouri dairy herds were assayed. Parity, stage of lactation, and farm affected milk insulin-like growth factor-I concentration. Milk insulin-like growth factor-I concentration was higher in early lactation than mid and late lactation with concentrations in multiparous cows exceeding those in primiparous cows. Insulin-like growth factor-I concentration was negatively correlated to milk production the day of sample collection (r = -.15) and not correlated to predicted 305-d milk yields. Unprocessed bulk tank milk samples (n = 100) from a commercial processing plant had a mean concentration of insulin-like growth factor-I in milk of 4.32 ng/ml with a range of 1.27 to 8.10 ng/ml. This distribution was similar to the range detected in samples from individual cows, but values were lower than those reported for human milk. Concentration of insulin-like growth factor-I in milk was not altered by pasteurization (at 79 degrees C for 45 s). However, insulin-like growth factor-I was undetectable in milk heated to temperatures (121 degrees C for 5 min) required for infant formula preparation or in commercially available infant formula. These data indicated that insulin-like growth factor-I is a normal but quantitatively variable component of bovine milk that is not destroyed by pasteurization but is undetectable in infant formula. Concentration of insulin-like growth factor-I in bovine milk is lower than concentrations reported for human milk yet similar to those reported for human saliva.(ABSTRACT TRUNCATED AT 250 WORDS)
The objective of this study was to determine whether supplemental glutamine (alanylglutamine dipeptide) is effective in preventing small intestinal mucosal atrophy associated with total parenteral nutrition and whether it affects the growth of other organs in neonatal pigs. We compared organ growth, intestinal enzyme activity, and plasma nitrogen metabolites in 4-day-old pigs randomly selected to receive total parenteral nutrition supplemented with 0 g, 2.0 g, or 4.5 g of glutamine per deciliter for a total amino acid intake of either 11 or 25 g-kg⁻¹d⁻¹ for 7 days. Glutamine supplementation increased (60% to 100%) plasma concentrations of glutamine, urea nitrogen, ammonia, and both jejunal villus height and surface area, but it did not significantly affect jejunal mucosal protein and DNA masses or the relative growth of liver, kidneys, and brain. No histologic evidence of tissue toxicity was found. Supplementing large amounts of glutamine (alanylglutamine dipeptide) did not completely prevent total parenteral nutrition-associated intestinal mucosal atrophy but did improve villus morphology without affecting vital organ growth or histology. (Journal of Parenteral and Enteral Nutrition 18:313-319, 1994)
Lactic acid bacteria (LAB) constitute a group of gram-positive bacteria united by a constellation of morphological, metabolic, and physiological characteristics. The general description of the bacteria included in the group is gram-positive, nonsporing, nonrespiring cocci or rods, which produce lactic acid as the major end product during the fermentation of carbohydrates. The LAB term is intimately associated with bacteria involved in food and feed fermentation, including related bacteria normally associated with the (healthy) mucosal surfaces of humans and animals. The boundaries of the group have been subject to some controversy, but historically the genera Lactobacillus, Leuconostoc, Pediococcus, and Streptococcus form the core of the group. Taxonomic revisions of these genera and the description of new genera mean that LAB could, in their broad physiological definition, comprise around 20 genera. However, from a practical, food-technology point of view, the following genera are considered the principal LAB: Aerococcus, Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus, and Weissella. The genus Bifidobacterium, often considered in the same context as the genuine lactic acid bacteria and sharing some of their typical features, is phylogenetically unrelated and has a unique mode of sugar fermentation. The classification of lactic acid bacteria into different genera is largely based on morphology, mode of glucose fermentation, growth at different temperatures, configuration of the lactic acid produced, ability to grow at high salt concentrations, and acid or alkaline tolerance. Chemotaxonomic markers such as fatty acid composition and constituents of the cell wall are also used in classification. In addition, the present taxonomy relies partly on true phylogenetic relationships, which have been revealed by extensive work on determining rRNA sequences. Some of the newly described genera are most easily determined with oligonucleotide probes, polymerase chain reaction (PCR)–based technologies using these sequences, or direct sequencing of the 16S rRNA gene. Most genera in the group form phylogenetically distinct groups, but for some, in particular Lactobacillus and Pediococcus, the phylogenetic clusters do not correlate with the current classification based on phenotypic characters. New tools for classification and identification of LAB are currently replacing and/or complementing the traditional phenotype-based methodologies. The most promising for routine use are 16S rRNA gene sequencing, PCR-based fingerprinting techniques and soluble protein patterns.
In colostrum collected 0–80 h postpartum the contents of immunoglobulins (Igs), transforming growth factor beta-2 (TGF-β2), insulin-like growth factor-1 (IGF-1) and growth hormone (GH) were analysed. Colostrum initially contained 90 mg mL−1 IgG1, 2.8 mg mL−1 IgG2, 1.6 mg mL−1 IgA, 4.5 mg mL−1 IgM, and these concentrations declined by 92%, 87%, 93% and 84%, respectively, in the samples collected later. Of the growth factors, colostrum initially contained 289–310 ng mL−1 TGF-β2 and the concentration diminished to 66 ng mL−1. The content of IGF-1 and GH postpartum decreased from 870 to 150 ng mL−1, and from 0.17 to <0.03 ng mL−1, respectively. Heat treatment and freeze-drying of colostral whey decreased the content of Igs to 75%, while the contents of IGF-1 and TGF-β2 were unaffected. A similar processing, including filtration steps reduced also the IGF-1 and TGF-β2 by 25%. IgM seems to be the most sensitive of the Igs to processing.
IGF-I and -II are peptide growth factors that may be important contributors to the growth-promoting properties associated with milk. IGF in extracellular fluids, including serum and milk, are carried by specific high-affinity binding proteins (IGFBP). In this study, the levels of IGF-I and -II in rat serum and milk were quantified by specific RIA, and the IGFBP were characterized using Western ligand blotting and autoradiography throughout lactation. The levels of IGF-I in both milk and maternal serum decreased during lactation. Serum IGF-I decreased from 743 +/- 187 micrograms/L on d 1 to 391 +/- 106 (mean +/- SD) on d 21 of lactation, and milk IGF-I levels fell from 30 +/- 10 to 13 +/- 8 micrograms/L. Levels of IGF-II in serum and milk were much lower than IGF-I, and were unaffected by lactation. In maternal serum, several IGFBP were identified: IGFBP-3, which migrates as four glycosylated bands with apparent Mr from 38 to 42 kD and one to two nonglycosylated bands with apparent Mr of 28 to 29 kD, and an IGFBP with an apparent Mr of 24 kD. In milk, IGFBP-3, the 24-kD binding protein, and a third IGFBP with an apparent Mr of 29 kD were identified. Treatment of milk and serum with Endoglycosidase F reduced the four glycosylated IGFBP-3 bands (38-42 kD) to two bands with apparent Mr of 35 and 32 kD. In rat milk, but not adult rat serum, the IGFBP with an apparent Mr of 29 kD was immunoprecipitable by an antibody that recognizes IGFBP-2.(ABSTRACT TRUNCATED AT 250 WORDS)
Scientists in the Food and Drug Administration (FDA), after reviewing the scientific literature and evaluating studies conducted by pharmaceutical companies, have concluded that the use of recombinant bovine growth hormone (rbGH) in dairy cattle presents no increased health risk to consumers. Bovine GH is not biologically active in humans, and oral toxicity studies have demonstrated that rbGH is not orally active in rats, a species responsive to parenterally administered bGH. Recombinant bGH treatment produces an increase in the concentration of insulin-like growth factor-I (IGF-I) in cow's milk. However, oral toxicity studies have shown that bovine IGF-I lacks oral activity in rats. Additionally, the concentration of IGF-I in milk of rbGH-treated cows is within the normal physiological range found in human breast milk, and IGF-I is denatured under conditions used to process cow's milk for infant formula. On the basis of estimates of the amount of protein absorbed intact in humans and the concentration of IGF-I in cow's milk during rbGH treatment, biologically significant levels of intact IGF-I would not be absorbed.