Dairy Ingredients for Food Processing

Microbiological Aspects of Dairy Ingredients 89

tion, evaporation, homogenization (optional),

drying, and packaging. From the microbio-

logical standpoint, the quality of the raw milk

used and the heat processes applied, evapora-

tion, drying, and prevention of post process-

ing contamination are most important for the

microbiological safety of milk powders. Milk

streams are given a heat treatment prior to

concentration. This preheating eliminates

pathogenic bacteria and saprophytic microor-

ganisms and inactivates enzymes such as

lipases. Heat treatments are generally 88 ° C

to 95 ° C for 15 to 30 seconds, although in the

separation of whole milk into skim milk and

cream, the former may be subjected to

defi ned heat treatments: low heat, 72 ° C for

15 seconds; medium heat, 75 ° C for 1 to 3

minutes; and high heat, 85 ° C for 30 minutes

or 90 ° C for 10 minutes or 120 ° C to 135 ° C

for 1 to 2 minutes (Augustin and Clarke,

2008 ).

The milk stream is generally thermally

concentrated but may be concentrated through

membranes (ultrafi ltration or diafi ltration).

Residence time and temperature exposure are

generally less than 60 seconds and lower than

72 ° C, respectively, during thermal concentra-

tion, a process which should further enhance

the microbiological quality of the milk

powder. In some evaporation plants the milk

stream is heated to between 140 ° C and

150 ° C, resulting in a product with high

microbiological quality. Such products are

used as ingredients in baby food manufac-

ture. Spray - drying is the most commonly

applied method of drying evaporated milk.

Evaporated milk is atomized into fi ne drop-

lets and exposed to a hot stream in the drying

chamber. Milk particles may be heated to

65 ° C to 75 ° C during these processes.

Dried Milk Powder Safety

The principal foodborne pathogens associ-

ated with dried milk powders are Salmonella

spp., Staph. aureus , Bacillus spp., Cronobacter

sakasakai, and Clostridium spp.; outbreaks

sists of seeding cooled (approximately 30 ° C)
milk with fi ne lactose crystals to induce for-
mation of numerous small crystals rather
than fewer larger ones. Microbial lethality
depends on the forewarming stage and super-
heating phase, if used, while microbial stabil-
ity of the resultant SCM depends on lowering
the a w and binding available water by the
added sugar. The containers used are usually
cans, which are treated along with the lids by
gas fl ames, superheated steam, or ultraviolet
radiation.
Absence of air in the cans by proper fi lling
inhibits the growth of aerobic microorgan-
isms, particularly molds, yeasts (e.g.,
Torulopisis spp.), and micrococci, which can
tolerate high osmotic pressures (although
they should have been killed at the fore-
warming stage). Heat - stable proteolytic and
lipolytic enzymes elaborated by psychrotro-
phic bacteria at the raw milk stage also can
cause spoilage.

Dried Milk Powders

Milk powders are produced by the dehydra-
tion of liquid milk streams or fractions of
dairy streams. Consequently, there is a variety
of powders available to the recombined dairy
industry and as ingredients to the dairy and
other food industries. Among the dried
powder products available are: full - cream
milk powder, skim - milk powder, whey and
whey protein concentrate powders, milk
protein/caseinate powders, buttermilk pow-
ders, and cream powders. Further tailor - made
powder ingredients are commonly produced
for specifi c products, which benefi t from
functional, textural, and nutritive qualities
of the milk - based product. Among the indus-
tries using dried milk - based powders are
dairy, confectionary, infant formula, and
manufactured - food industries, where they are
used in coatings, soups, sauces, and ready - to -
eat meals.
The key steps in milk powder production
are milk clarifi cation, cooling, standardiza-