Dry Milk Ingredients 143a microbiologically stable product, the micro-
bial quality of the raw milk infl uences the
shelf - stability of the powder and it is essen-
tial to use good - quality milk to manufacture
powders.Preheating
Milk streams are given a heat treatment prior
to concentration, which is essential to obtain
dry milk products with good microbiological
quality. The heat treatments applied to skim
milk vary, ranging from a low heat (typically
72 ° C [161.6 ° F] for 15 seconds), to medium
heat (75 ° C [167 ° F] for 1 to 3 minutes, 85 ° C
to 105 ° C [185 ° F to 221 ° F] for 1 to 2 minutes),
to high heat (85 ° C [185 ° F] for 30 minutes,
90 ° C [194 ° F] for 10 minutes, 120 ° C to 135 ° C
[248 ° F to 275 ° F] for 1 to 2 minutes).
The preheat treatments are also used to
achieve a desired level of denaturation of the
whey proteins. The heat treatment applied
prior to concentration is the prime determi-
nant of the extent of whey protein denatur-
ation during skim milk powder manufacture,
because minimal heat damage occurs during
the concentration and drying stage (Singh
and Newstead, 1992 ). The extent of whey
protein denaturation has a signifi cant infl u-
ence on the physical functionality of the milk
powder in its end use, which has led to the
development of a range of indices for clas-
sifying skim milk powders based on heat
treatment.
The whey protein nitrogen index (WPNI)
has traditionally been used as the indicator of
the heat treatment used in skim milk powder
manufacture (Table 6.2 ). However seasonal
and other natural variations in the protein
composition (i.e. whey protein and casein
content) of the raw milk supply can affect the
WPNI data. Specifi cally, a fi xed heat treat-
ment can result in different extents of whey
protein denaturation in milk when there are
differences in the amount of whey protein in
the raw milk or a change in the ratio of
casein:whey protein (Jensen, 1990 ).their required compositional specifi cations.
Traditionally, skim milk powder has been
defi ned as the product resulting from the
removal of fat and water in milk that contains
not more than 5% moisture and 1.5% fat.
This defi nition requires the lactose, milk pro-
teins, and milk minerals to be in the same
relative proportion as in the fresh milk
(ADPI, 2002 ).
With the advent of legislation that allows
for standardization of skim milk powder,
some specifi cations now stipulate a level for
the minimum protein content. Milk products
that can be used for standardizing the protein
content of milk include (Codex Alimentarius,
1999 ):
- Milk retentate, obtained by concentrating
milk, partly skimmed milk, or skim milk
by ultrafi ltration; - Milk permeate, obtained by using ultrafi l-
tration to remove milk proteins and milk
fat from milk, partly skimmed milk, or
skim milk - Lactose
Incorporating protein content into the
specifi cations for milk powders is a logical
extension of traditional milk powder specifi -
cations because protein has a major infl uence
on the attributes of the milk powder in many
applications. Full - cream is standardized to
a desired solids - not - fat (SNF) : fat ratio to
obtain powder that meets a minimum of 26%
milk fat. Buttermilk powder is obtained by
drying buttermilk, a by - product of butter
manufacture. It should have a minimum
protein content of 30% and a fat content
greater than 4.5% (ADPI, 2002 ). One of the
distinguishing features of buttermilk powder
compared to skim and full - cream milk
powders is its high amount of phospholipids.
Buttermilk powder also has a stronger dairy
fl avor.
Specifi cations for dry milk products,
including some additional quality factors, are
given in Table 6.1. Although milk powder is