INTRODUCTION
Milk is a white liquid produced by the mammary glands of
mammals. It is the primary source of nutrition for young mammals before they
are able to digest other types of food. Early-lactation milk contains
colostrum, which carries the mother's antibodies to the baby and can reduce the
risk of many diseases in the baby. It also contains many other nutrients.
Milk is an emulsion or colloid of butter fat globules within
a water-based fluid that contains dissolved carbohydrates and protein
aggregates with minerals. Because it is produced as a food source for a
neonate, all of its contents provide benefits to the growing young. The
principal requirements of the neonate are energy (lipids, lactose, and
protein), biosynthesis of non-essential amino acids supplied by proteins
(essential amino acids and amino groups), essential fatty acids, vitamins and
inorganic elements, and water.
Generally, fat and protein content of milk are positively
correlated within a population of dairy cattle; however, different breeds of
cattle vary in average component levels. Holsteins have the lowest fat and
protein content, while Jersey and Guernsey breeds have the highest. Because
Holsteins produce more milk, they generally have a higher total yield of fat
and protein than other breeds.
Breed
|
% Fat
|
% Protein
|
F:P
|
Ayrshire
|
3.86
|
3.18
|
1.21
|
Brown Swiss
|
4.04
|
3.38
|
1.20
|
Guernsey
|
4.51
|
3.37
|
1.34
|
Holstein
|
3.65
|
3.06
|
1.19
|
Jersey
|
4.60
|
3.59
|
1.28
|
Average fat and protein content of
milk produced by different breeds.
(F:P -ratio of fat to protein)
(F:P -ratio of fat to protein)
MILK LIPID COMPONENTS
Milk fat can be modified to improve its functionality and
expand its usage for traditional and nontraditional applications. The
triglyceride, diglyceride, monoglyceride, and individual fatty acid components
of milk fat determine functionality. Milk fat functionality is expressed
through crystallization and melting behaviors, surface-active properties, and
nutritional properties.
Methods that are available to modify the functional
properties of milk fat include fractionation by melt crystallization and
supercritical fluid extraction, blending, texturization, interesterification,
and glycerolysis. The selection of modification procedures is often driven by
the requirements of the application.
Modification of selected functionalities can expand the
opportunities for milk fat as nontraditional ingredients in traditional
applications, such as the use of milk fat fractions in chocolate and bakery
products. New applications include the use of intact milk fat and milk fat
fractions in the production of structured lipids, sucrose polyesters, edible
films, emulsifiers, and cosmetics. Other nontraditional functionality
associated with milk lipid components includes the antioxidant and
anticarcinogenic properties of conjugated linoleic acid and the antimicrobial
properties of lauric acid.
The functional attributes that milk fat imparts to a food
system are very dependent upon the application. For example, butter is used for
its shortening properties in cookies to yield a tender crumb, but is used in
pastries for its layering properties, which promotes the characteristic
flakiness of croissants and puff pastry.
The complex chemical composition and broad melting range of
milk fat provide many opportunities for the production of milk fat ingredients
with improved functionality. Modification of milk fat functionality can be
accomplished by a variety of processes, yielding different characteristics in
the finished ingredient. The functional requirements of ingredients based on
milk fat are driven by the needs of the application, which should be of primary
consideration when milk fat is modified.
Applications of Intact Milk Fat Triglycerides
1) Structured Lipids and Medium-Chain Triglycerides
Structured lipids and medium-chain triglycerides are lipid
food ingredients that are increasingly used in high energy foods for people
with special nutritional needs and as frying oils and confectionery and bakery
fats. The desired chemical and physical properties of structured lipids are
dependent upon the final application. Structured lipids and medium-chain
triglycerides are produced by random transesterification of a blend of fatty
acid reservoirs that have been selected for their chemical and physical
properties.
The primary functionality of milk fat in structured lipids
is their use as a reservoir of C8 and C10 fatty acids.
Structured lipids made with blends of milk fat, commercially available
medium-chain triglycerides, and vegetable oils exhibit a range of metabolic and
physical functionalities. The use of milk fat fractions with increased
concentrations of the C8 and C10 fatty acids may increase
the potential value of milk fat as a fatty acid reservoir in the production of
structured lipids.
2) Sucrose Polyesters
Sucrose polyesters are fat substitutes that provide the
flavor and physical functionalities of fat, but that are not absorbed by the
body and provide no caloric value. The flavor and physical properties of
sucrose polyesters are influenced by the fat blend used as the fatty acid
source. Sucrose polyesters are another application of the use of milk fat as a
fatty acid reservoir in the production of structured food ingredients.
Sucrose polyesters are produced by transesterification
reactions between sucrose and fatty acid methyl esters. Sucrose polyesters made
with milk fat have been investigated to a limited extent, and results have
shown that milk fat may be a suitable source for the production of sucrose
polyesters. The physical properties of sucrose polyesters made with milk fat
are dependent upon the properties of the milk fat and, thus, sucrose polyesters
with a range of physical properties may be produced by modification of the
physical properties of the starting milk fat material (e.g., milk fat
fractions).
3) Infant Formulas
The fatty acid and triglyceride composition of current
infant formulas differs from human milk, and an infant formula that more
closely resembles human milk is desirable. Milk fat has been reported to be a
suitable fatty acid reservoir for the production of infant formulas that more closely
resemble human milk fat. Infant formulas are produced by interesterification of
a fat blend selected for its fatty acid composition. The use of an immobilized 1,3-specific
lipase as the catalyst in interesterification reactions allows more accuracy in
creating an infant formula with a fatty acid composition and positional
distribution that is similar to human milk fat.
Applications of Milk Fat Fractions
1) Laminated Pastries
Laminated pastries include croissants, Danish, and puff
pastries. Milk fat, in the form of butter, is commonly used as a roll-in fat
for premium laminated pastries because of its desirable flavor properties. The
roll-in fat is spread or extruded onto the dough surface, and the dough is
folded to form layers of dough separated by layers of fat. The layering process
results in the characteristic flaky texture associated with pastries. The
desired physical attributes of a laminated pastry fat include firmness,
plasticity, and layering properties.
The degree of firmness required is dependent upon the
finished product. For example, a puff pastry is characteristically very flaky
and crisp and requires a fat with a melting point of 38 to 42°C, but a Danish
pastry has a more tender texture and requires a fat with a melting point of 30
to 32°C. Regardless of the final melting point, the fat must be solid enough to
maintain a thin barrier layer between dough layers without melting and becoming
incorporated into the dough, but must be plastic enough to be repeatedly folded
and rolled without cracking.
2) Chocolate
Milk fat is used in chocolate manufacture because it imparts
desirable flavor and textural properties to chocolate, is compatible with cocoa
butter, provides anti bloom properties in dark chocolate, is legally allowed in
chocolate, and is less expensive than cocoa butter. The ability to use more
milk fat to replace some of the cocoa butter in chocolate is limited by the
inhibition of crystallization as the level of incorporation increases.
The use of milk fat results in softening of the product,
which is easily illustrated by the difference in firmness and snap of dark
chocolate compared with those of milk chocolate. Milk fat components inhibit
the crystallization of cocoa butter by two mechanisms: the low melting fraction
dissolves cocoa butter crystals, and the middle melting fraction forms
eutectics with cocoa butter at replacement greater than 30%. The high melting
fraction of milk fat does not cause softening and contributes to the anti bloom
properties associated with milk fat.
The isolation of a high melting milk fat fraction creates a
unique ingredient that improves the desired functionalities of milk fat while
it simultaneously decreases undesired attributes. Blending of fractions offers
further diversity and flexibility to meet the requirements of individual
customers. Milk fat ingredients for use in chocolate are melted prior to
incorporation, and therefore, texturization is not necessary.
3) Edible Films
Edible films are used in the food industry as barriers to
gases and water vapor, as protective coatings for ingredients that are
susceptible for oxidation, as a means of reducing the migration of lipids in
foods or improving the structural integrity of foods, and as packaging
materials. High melting lipids and waxes are often added to edible films to
improve their water vapor properties. Edible films made with high melting milk
fat fractions exhibited good water vapor barrier properties and may also benefit
from the flavor functionality of milk fat. The production of wax monoesters
from milk fat using lipase-catalyzed synthesis is technically feasible. Wax
monoesters made from milk fat may provide good functionality in edible films.
Applications of Milk Fat Monoglycerides and Diglycerides
1) Emulsifiers
Monoglycerides are the most commonly used emulsifiers in
foods. The use of milk fat-based monoglycerides and diglycerides may provide
both emulsification properties and flavor properties to foods. The production of
monoglycerides and diglycerides from milk fat using lipase-catalyzed
glycerolysis has been reported to be feasible. Emulsification properties have
generally been attributed to the monoglyceride component of monoglyceride and
diglyceride mixtures. Monoglyceride and diglyceride mixtures made from butter
oil with concentrations of 50 to 55% monoglycerides have been obtained by
lipase-mediated glycerolysis.
MILK PROTEINS
Major protein components of milk,
Casein
- α-, β-, and К-casein and casein-related compounds, including casomorphine compounds
Soluble Milk Proteins (Whey Proteins)
- α-Lactalbumin
- β-Lactoglobulin
- Bovine serum albumin
- Immunoglobulins
- Lactoferrin
- Lactoperoxidase
NPN
- Polypeptides and proteose-peptones
- Free amino acids
- Urea
- Glyco- and macropeptides
Commercial utilization of individual soluble milk proteins
Component
|
Properties
|
Uses
|
α-Lactalbumin
(with bovine serum albumin and immunoglobulins)
|
Nutrition
|
Infant formula
|
Lactoferrin
|
Antibacterial
|
Infant formula
|
Lactoperoxidase
|
Anticaries
|
Toothpaste
|
Growth factor
|
Stimulates mammalian
cell growth
|
Growth of human skin
and lung cells
|
Possible commercial utilization of individual soluble milk and whey proteins
Component
|
Properties
|
Uses
|
β-Lactoglobulin
|
Gelling
|
·
Restructured meats and fish.
·
Clear sports and dietetic beverages.
|
Immunoglobulin and
bovine serum albumin
|
Solubility and nutrition
Anticancer
Enhanced immunity
|
·
Cancer prevention and treatment.
·
Diets for persons who are. HIV positive, have
AIDS, or otherwise compromised immune systems.
·
Diets for athletes.
|
MILK SUGARS
Natural oligosaccharides exist in milk in very minor
concentrations. These oligosaccharides are not yet commercially available. In a
discussion of milk sugars, lactose cannot be ignored even though it is a major,
not minor, component of milk.
Commercial utilization of selected lactose derivatives
Component
|
Properties
|
Uses
|
Lactulose
|
Bifidobacteria enhancement
Laxative
Oxygen uptake, ammonia reduction in blood
Suppresses ammonia production in intestine
Ammonia reduction in blood
|
Infant formula
Laxatives
Diet for athletes
Drug against chronic portal systemic encephalopathy
Drug against hepatic encephalopathy
|
Lactitol
|
Bifidobacteria enhancement
NoncaIoric sweetener
|
Infant formula
Chewing gum
|
Lactobionic acid
|
Bifidobaeteria enhancement and other health-related uses
|
Various
|
Oligosaccharides
|
Bifidobaeteria enhancement
|
Infant formula, baby foods, other foods (yogurt, etc.)
|
MILK SALTS
Commercial utilization of milk salts
Component
|
Properties
|
Uses
|
Mixture of milk salts recovered
from whey UF permeate
|
Flavor
Nutrition
|
Table salt substitute
Health drinks
|
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