Milk
Trends
Fluid milk and cream consumption has declined
steadily reaching a record low of 200.5 lb in
2005. In 1970, fluid milk and cream
consumption was 275 lb. There has been a
trend to less consumption of whole milk
products to more consumption of lower fat milk
products.
Frozen dairy products, such as ice cream have
been declining since about 1994.
Gross Composition
% by weight
Component
Cow
Water
87.3
Lactose
4.8
Fat
3.7
Protein
3.4
Salts(minerals)
0.7
Nutrients
Milk contains many nutrients: protein,
lactose, fats, vitamins, minerals, and
enzymes
Milk is a complex physiochemical system.
It has particles in:
1. True solution - sugar and salt
2. Colloidal dispersion - protein
3. Globules - fat
Protein
Casein - 80% of total milk protein.
Casein is a phosphoprotein containing
phosphoric acid.
– Coagulates to form a gel
– Coagulates at pH 4.6
– Coagulates at high pH (6.5) with rennet
– Several types of casein - alpha, beta,
gamma, kappa
Whey protein – 20% of total milk protein
– Do not coagulate at pH 4.6
– Do not coagulate with rennet
Proteins
– Lactalbumin - 8% of protein (N)
Water soluble and forms flucculent
precipitate that settles on bottom and sides
of pan when heated.
– Lactoglobulin - 3.5% of protein (N)
Insoluble in water but soluble in dilute
neutral salts. Precipitated by heat.
– Serum albumin and immunoglobulin
Fat
Exists as large globules varying in size
from 0.1-10um in diameter.
Mostly (>95% triglycerides)
Triglycerides = glycerol + fatty acids
Milkfat contains high proportion of short
chain fatty acids (C4-C10)
Butyric acid (C4) is unique to milkfat
Responsible for flavors and aroma
when acted by enzyme lipase.
Carbohydrate (Lactose)
Milk contains lactose or milk sugar.
Lactose = glucose + galactose
Some people exhibit lactose intolerance
and thus milk may give cramping and
diarrhea
Principle source of energy for lactic acid
bacteria.
Bacteria converts lactose to lactic acid
(cheese, yogurt, cultured milk, sour cream)
Vitamins
B1 - thiamine
B2 - riboflavin
B6 - pyridoxine
B12 - cyanocobalamin
niacin
pantothenic acid
Vitamin A, D, E and K (Fat soluble
vitamins)
Minerals and Enzymes
Calcium
Phosphorus
Low in copper and iron
Low levels of sodium, chloride, Magnesium
Plasmin
Lipase
Milk is well buffered by protein and salts
especially phosphates
Pasteurization
Low temperature holding (LTH) - 63 C or
145 F for 30 min.
High temperature short time (HTST) 72 C
or 162 F for 15 sec.
Ultrapasteurization - 138 C or 280 F for
2 or more sec.
Ultra high temperature (UHT) - 138-150C
or 280-302 F for 2-6 sec.
Homogenization
Homogenization
Mechanical treatment of the fat globules in
milk brought about by passing milk under
high pressure through a tiny orifice
Decrease in the average diameter and an
increase in number and surface area
Reduced tendency for creaming of fat
globules
Enhanced stability of homogenized milk
Types of Milk
Fluid
1. Whole - 3.25% butterfat
2. Low-fat - 2% or 1% butterfat
3. Skim or nonfat - fat-free
4. Lactose-free-treated with lactase to
form glucose and galactose
Canned
1. Evaporated - 60% water removed by
heat
2. Sweetened condensed - sugar added
and 1/3 water removed
Dried
1. Spray dried - 2/3 water removed by
vacuum, them sprayed into chamber of
hot air.
2. Foam spray dried - spraying a jet of hot
air into concentrated skim milk.
3. Instant - agglomerated, porous particles
take up liquid quickly.
Filled milks - fat other than milkfat, water, NFMS,
emulsifiers, coloring, and flavoring.
Imitation - no milk products, contain water, corn syrup
solids, sugar, vegetable fat, protein (Na caseinate or
soy protein).
Cultured
1. Yogurt - culture of Lactobacillus
bulgaricus and Streptococcus
thermophilus is used.
2. Buttermilk - Streptococcus lactis.
3. Acidophilus milks - Lactobacillus
acidophilus, balance bacteria in GI tract.
Other dairy products:
1. Cheese
2. Butter
Milk in Food Preparation
Effects of Heating
Lactoglobulin and lactalbumin are
denatured by heat. Increased with acid or
salt. Heat causes the decreased
dispersion of calcium phosphate. Film or
skim forms-coagulated protein,
precipitated salts, and fat globules.
Browning - caramelization and Maillard
reaction
Effects of Acid
Cause coagulation of casein. As pH
decreases from 6.6 to 4.6, colloidally
dispersed casein becomes unstable, adheres
and forms curds. Calcium is lost.
Effects of Enzymes
Rennin clots milk, requires 40-42° C or 104108° F and slightly acid medium.
Effects of Phenolic Compounds and Tannins
cause increased curdling with heat.
Effects of Salts
Salts and NaCl in foods may cause
coagulation of proteins
Creams
Half & Half - 10.5 to 18 % cream
Light or coffee cream - 18 to 30% cream
Light whipping cream - 30 to 36% cream
Heavy whipping cream - 36% or more cream
Sour cream - Streptococcus lactis
Dried cream
Nondairy creamer - corn syrup solids, vegetable
fat, protein (Na caseinate or soy), emulsifier,
salt
Nondairy whipped topping - sugar, vegetable oil
(hydrogenated), Na caseinate, emulsifiers
Whipped Cream
Foam is a dispersion of gas in a liquid.
Foaming agent lowers surface tension
allowing liquid to surround gas. Stabilizing
agent keeps gas separated. In cream,
liquid is the water in cream, gas is air
beaten in, foaming agent is protein where
film of protein surrounds air bubbles, and
fat acts as the stabilizer.
Effects on Whipping Cream
Temperature - cold
Percent of fat
Viscosity
Sugar
Whipped evaporated milk - less fat thus
less stable
Whipped NFDM - less fat thus less
stability, more protein thus more foam
formation or bigger volume
Cheese
Trends
In 2005, Americans consumed 31.4
pounds of cheese per person, 8 times
more than they did in 1909 and more than
twice as much as they did in 1975
More that half (55-65%) of this comes in
commercially manufactured and prepared
foods, such as fast food sandwiches and
packaged snack foods
Pasteurized cows’ milk
310C
Starter (1-2%, v/v):
Rennet (1:15,000)
(CaCl2, 0.02%, w/v)
.
Coagulum
Cut the coagulum
~6mm cubes
Raise temperature : 300C to 37-390
over ~ 30 min
Cook
Cook at 37-390C for ~ 1h
Whey drainage
Cheddaring of the curd
Milling of the curd
pH ~ 5.2
NaCl, (~ 2%, w/w)
Dry salting
Moulding and pressing
Ripening
Cheddar cheese
0.5- 2 years at 6-80C
Cheese Making
Separation of protein in milk begins with acid,
rennin or both which coagulates casein- forms
curds
Acid - added or from souring
Rennin - proteolytic enzyme
Curds are cut, heated, drained of whey, salted,
formed, ripened by molds or bacteria under
temperature and humidity control.
Clear liquid left called whey and contains
proteins, lactose, water soluble vitamins and
some minerals
Nutritive Value
Protein
Fat
Vitamin A
Minerals (Calcium and Phosphorus)
Cheese is high in Na or salt
Types of Cheese
Soft, semihard, hard - moisture content
Unripened or Ripened - physical and chemical
changes in aroma, flavor, texture, and
composition. Sharp or mild. Mold or bacteria
ripened.
Cold pack - mixing varieties of cheese with
added acid, salt, water, coloring and spice.
Processed cheese - blending cheese with heat
and emulsifier.
Processed cheese food and spread - similar to
processed cheese with less cheese and more
milk products plus stabilizers.
Cooking Cheese
Hard cheese softens, then melts at low
temperature. More heat leads to separation of
fat and development of tough rubbery curd
which forms strings and hardens on cooling.
Well ripened cheese and processed cheese
blend better in heated mixtures than mild
natural cheeses and are less likely to produce a
grainy texture and stringiness
Milk sugar causes browning in cheese which is
exposed to dry heat.
Summary
Milk is an essential nutrient
Milk can be used in the manufacture of
various dairy products
Each product has its own characteristic in
terms of sensory properties
Dairy products are used in everyday
cooking and industrially prepared foods
Power Point Authors
Jon Christiano
&
Dr. Jane Ross
The University of Vermont
Foods and Nutrition
Basic Concepts of Food