Dairy products and milk-based food ingredients - Natural Food Additives, Ingredients and Flavourings - page 417

The functional properties of casein are exploited in many dairy products and
also make it an interesting substance for food ingredient manufacturers and food
processors. Casein has an isoelectric point of pH 4.6, at which it precipitates: this
is the basis of yogurt production. It has fat emulsifying and water binding
properties, and is heat stable over a wide temperature range.
While casein is the major milk protein, the whey proteins collectively form the
minor milk proteins. They are found in the milk serum. Also termed the serum
proteins, as their name implies they are the proteins lost in cheese whey. Of the
whey proteins, β -lactoglobulin and α -lactalbumin are most abundant (Table 17.3),
followed by bovine serum albumin (BSA), the immunoglobulins and the proteose-
peptone fractions. The functional properties of the calcium-insensitive whey
proteins are of interest to food manufacturers, as they are heat sensitive and can
be made to foam and form gels similarly to egg white.

Lactose
The milk sugar, lactose, is a reducing sugar and the carbohydrate in milk. It
is a disaccharide formed by the condensation of galactose and glucose
(both monosaccharides) through the formation of a β -1-4-glycosidic linkage.
The systematic name for lactose is β - D -galactopyranosyl-(1→4)- D -glucose.
Glucose can take either the α -pyranose or the β -pyranose form, whereas
galactose can take only the β -pyranose form. The result is that lactose can exist in
either of two forms: α -lactose and β -lactose. In solution lactose exhibits the
phenomenon of mutarotation and equilibrium mixtures of α -lactose and β -lactose
occur. Both forms of lactose can be crystallised from supersaturated solutions.
At temperatures below 93.5°C α -lactose predominates. Above 93.5°C, β -lactose
is formed.
As a functional food ingredient, lactose exhibits Maillard browning, a
non-enzymic browning reaction under heat between a carbonyl compound -
the reducing sugar lactose - and an amino acid (Nursten 2005). It will
caramelise and is hygroscopic when crystallised either as amorphous lactose or
predominantly as β -lactose.

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17.3 Dairy products and food additives, ingredients
and fl avourings
Natural food additives, ingredients and fl avourings are important to the
manufacture of many dairy products. Indeed, milk itself is the key natural
ingredient used in the manufacture of dairy products or it is the source of
ingredients used to make milk-based products. Milk is the sole ingredient in liquid
market milk. It is the primary ingredient in, for example, cheese and is the source
of the key ingredients in, for example, butter, cream powder, skimmed milk
powder, casein, etc. This section reviews the principal dairy products and identifi es
the use and function of food additives, ingredients and fl avourings in milk product
manufacture.