Bioactive peptides have been defined as specific protein fragments that have a positive impact on body functions or conditions and may ultimately influence health

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Review
Bioactive peptides in milk
Nashat Dahiyat
The university of Jordan, Food Science and technology, Amman, Jordan
Abstract
The role of proteins as physiologically active components in the diet is being increasingly
acknowledged. Many of the proteins that occur naturally in raw food materials exert their physiological action
either directly or upon enzymatic hydrolysis in vitro or in vivo. In recent years it has been recognized that
dietary proteins provide a rich source of biologically active peptides. Such peptides are inactive within the
sequence of the parent protein and can be released in three ways: (a) through hydrolysis by digestive
enzymes, (b) through hydrolysis by proteolytic microorganisms and (c) through the action of proteolytic enzymes
derived from microorganisms or plants.
© 2013 Ltd. All rights reserved.
Keywords: Milk proteins; Bioactive peptides;; Functionality; Health effects
Contents
5. Bioactive peptides in whey proteins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . … . 7
6.3Effects on the nutrition system. . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . 8
E-mail address: nashatdhiat@yahoo.com/ ndhayyat@aseza.jo (N. Dahiyat)
6.2 Effects on the immune system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... . . .. ..... 8
2.2. Microbial fermentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . .. .. . . 5
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.2. Production of bioactive peptides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... . .. .. 4
3. A fermented milk high in bioactive peptides has a blood pressure –lowering effect . . . .. . .. .. . . . . 6
6.1 Effects on the nervous system. . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........ . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . ........ . . ... . 10
6.Physiological effects of bioactive peptides from milk. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. . ...... . . . .7
2.1. Enzymatic hydrolysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . .4
1. Introduction . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... ... .. ... .. .. . .......... 3
..4. Caseins as source of bioactive peptides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. . 6
8.Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . ...... . . . .... 9
7.Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . ... ....... . . .. . .8

2. 1. Introduction
The role of proteins as physiologically active components in the diet is being
increasingly acknowledged. Many of the proteins that occur naturally in raw food
materials exert their physiological action either directly or upon enzymatic hydrolysis
in vitro or in vivo. In recent years it has been recognized that dietary proteins provide
a rich source of biologically active peptides. Such peptides are inactive within the
sequence of the parent protein and can be released in three ways: (a) through
hydrolysis by digestive enzymes, (b) through hydrolysis by proteolytic
microorganisms and (c) through the action of proteolytic enzymes derived from
microorganisms or plants.
Bioactive peptides have been defined as specific protein fragments that have a
positive impact on body functions or conditions and may ultimately influence health
(Kitts & Weiler, 2003). Upon oral administration, bioactive peptides, may affect the
major body systems namely, the cardiovascular, digestive, immune and nervous
systems (Fig. 1)—depending on their amino acid sequence. For this reason, the
potential of distinct dietary peptide sequences to promote human health by reducing
the risk of chronic diseases or boosting natural immune protection has aroused a lot of
scientific interest over the past few years. These beneficial health effects may be
attributed to numerous known peptide sequences exhibiting, e.g., antimicrobial,
antioxidative, antithrombotic, antihypertensive and immunomodulatory activities.
(FitzGerald & Meisel, 2003).

3. 2. Production of bioactive peptides
biologically active peptides can be produced from precursor milk proteins in
the following ways: (a) enzymatic hydrolysis by digestive enzymes, (b) fermentation
of milk with proteolytic starter cultures, (c) proteolysis by enzymes derived from
microorganisms or plants. In many studies, combination of (a) and (b) or (a) and (c),
has proven effective in generation of short functional peptides (Korhonen & Pihlanto,
2003b). Examples of bioactive peptides produced by the above treatments are given
below.
2.1 Enzymatic hydrolysis
The most common way to produce bioactive peptides is through enzymatic
hydrolysis of whole protein molecules. Many of the known bioactive peptides have
been produced using gastrointestinal enzymes, usually pepsin and trypsin.
Angiotensin-converting enzyme (ACE)-inhibitory peptides and calcium-binding
phosphopeptides (CPPs), for example, are most commonly produced by trypsin
(FitzGerald et al, 2004).
Other digestive enzymes and different enzyme combinations of proteinases
including alcalase, chymotrypsin, pancreatin, pepsin and thermolysin as well as
enzymes from bacterial and fungal sources—have also been utilized to generate
bioactive peptides from various proteins (Kilara & Panyam, 2003).

4. 2.2 Microbial fermentation
Many industrially utilized dairy starter cultures are highly proteolytic.
Bioactive peptides can, thus, be generated by the starter and non-starter bacteria used
in the manufacture of fermented dairy products. The proteolytic system of lactic acid
bacteria (LAB), e.g. Lactococcus lactis, Lactobacillus helveticus and Lb. delbrueckii
ssp. bulgaricus, is already well characterized. This system consists of a cell wall-
bound proteinase and a number of distinct intracellular peptidases, including
endopeptidases, aminopeptidases, tripeptidases and dipeptidases (Christensen
et al, 1999).
Table 1. Examples of bioactive peptides released from milk proteins by various
microorganisms and microbial enzymes
Micro-organisms used
Precursor
proteina
Peptide sequence Bioactivity
Lactobacillus helveticus,
Saccharomyces cerevisiae
b-cn, k-cn Val-Pro-Pro, Ile-Pro-Pro
ACE inhibitory,
antihypertensive
Lb. delbrueckii subsp.
bulgaricus IFO13953
k-cn
Ala-Arg-His-Pro-His-Pro-His-Leu-Ser-
Phe-
Met
Antioxidative
Lb. delbrueckii subsp.
bulgaricus
b-cn
Ser-Lys-Val-Tyr-Pro-Phe-Pro-Gly Pro-
Ile
ACE inhibitory
Lb. helveticus ICM 1004
cellfree
extract
Skim milk
hydrolysate
Val-Pro-Pro, Ile-Pro-Pro ACE inhibitory
aAbbreviations: cn ¼ casein, ACE ¼ angiotensin I-converting enzyme.

5. 2.2.1 A fermented milk high in bioactive peptides has a blood
pressure–lowering effect in hypertensive subjects
Hypertension is a risk factor for cardiovascular diseases, including coronary
heart disease, peripheral arterial disease, and stroke. The renin-angiotensin system is
an important regulator of blood pressure. Therefore, drugs that inhibit the renin-
angiotensin system, either by inhibiting angiotensin-converting enzyme (ACE; EC
3.4.15.1) or by blocking angiotensin (AT1) receptors, are widely used in the treatment
of hypertension. ACE inhibitors have a dual effect on the renin-angiotensin system:
they inhibit the production of the vasoconstrictor angiotensin II and they inhibit the
degradation of the vasodilator bradykinin. In addition, ACE inhibitors have other
beneficial effects in hypertensive patients, for example, in those with cardiac or renal
insufficiency or diabetes. Through fermentation, peptides that have an ACE-
inhibiting and thus a blood pressure–lowering effect can be derived from milk
proteins.
3. Caseins as source of bioactive peptides
Casein is the main proteinaceous component of milk, where it accounts for
ca. 80% of the total protein inventory. Until recently, the main physiological role of
casein in the milk system was widely accepted to be a source of amino acids required
by growth of the neonate. However, the dominant physiological feature of the
casein micelle system has more recently been proven to be the prevention of
pathological calcification of the mammary gland (Holt, 1997). While no specific
physiological property has been proposed for the whole casein system (or its

6. individual fractions, for that matter), various peptides hidden (or inactive) in the
amino-acid sequence have been the subject of increasingly intense studies. Much
work regarding those peptides, which are known to possess bioactivities, is currently
underway regarding their release via selective enzymatic hydrolysis.
4. Bioactive peptides in whey proteins
Two tetrapeptides in the primary structure of whey proteins have potential
opioid activities: Tyr-Gly-Leu-Phe (residues 50-53) from human and bovine α-
lactalbumin and Tyr-Leu-Leu-Phe (residues 102-105) from bovine β- lactoglobulin.
The corresponding amides - named α and β lactorphin, respectively - were
chemically synthesized and their opioid activity was established.
5. Physiological effects of bioactive peptides from milk
5.1 Effects on the nervous system
It is a common belief that falling asleep is easier after drinking a
glass of milk in the evening, and that babies are soothed after breast or bottle
feeding. Recent studies have provided evidence that peptides exist in dairy
products which play an active role in the nervous system; known as opioid peptides,
they can have agonistic or antagonistic activities

7. 5.2 Effects on the immune system
The systems involved in the human body’s defense
against invaders are rather complex; diet is known to play an important role therein.
Research concerning the role of functional peptides in this field is quite recent,
but it already seems very promising. The two main activities are the
immunomodulatory one (i.e. stimulation of the immune system) (Table 4) and the
antimicrobial one (i.e. inhibition of pathogenic bacteria).
5.3 Effects on the nutrition system
Some peptides are able to sequester calcium and other minerals,
hence acting as biocarriers—they are called phosphopeptides glycomacropeptide
(GMP) may also exhibit a number of nutritional features.
6. conclusion
Bioactive peptides are ubiquitous biomolecules widely abundant and easily
obtainable from food proteins. There is no limit therefore to the number of peptides
that can be obtained from a single food protein.
Each of these peptides may present unique structure and biofunctionalities that can
be exploited in the pharmaceutical industry. As research continues to uncover
technologies and means to overcome challenges to the use of peptide therapeutics,
the prospects of

8. food-derived bioactive peptides will likely fuel in the pharmaceutical industry an
exodus from small molecules and biologics to bioactive peptides.
7. Discussion
The potential health benefits of milk protein-derived peptides have been a
subject of growing commercial interest in the context of health-promoting functional
foods. So far, antihypertensive, mineral-binding and anticariogenic peptides have
been most studied for their physiological effects. A few commercial developments
have been launched on the market and this trend is likely to continue alongside with
increasing knowledge about the functionalities of the peptides. The optimal
exploitation of bioactive peptides for human nutrition and health possesses
an exciting scientific and technological challenge, while at the same time offering
potential for commercially successful applications. Bioactive peptides can be
incorporated in the form of ingredients in functional and novel foods, dietary
supplements and even pharmaceuticals with the purpose of delivering specific health
benefits.

9. 8. References
functionality, (945 – 960)
Seppo.L, Jauhiainen.T, Poussa,T, Korpela.R. A fermented milk high in bioactive
peptides has a blood pressure–lowering effect in hypertensive subjects.
Meisel.H, Frister.H, Sehlimme.E (1989). Biologically active peptides in milk
proteins. (267-278).
Sofia V. Silva, F. Caseins as source of bioactive peptides
Pihlanto. A, Korhonen. H . (2011) . Review Bioactive peptides: Production and
Biotechnology
Agyei.D. (2012). Pharmaceutical applications of bioactive peptides.OA