Dairy Ingredients for Food Processing

Microbiological Aspects of Dairy Ingredients 69

cream. Pseudomonas spp. can hydrolyze fat

and cause a variety of taints and/or rancidity.

Spoilage of cream by yeasts is well described

in the early literature, especially if the cream

has been sweetened or soured. When sugar

has been added, for example in whipping

cream, yeasts such as Torulopsis sphaerica ,

Torula cremoris , or Candida pseudotropica-

lis can grow and produce a yeasty odor.

Although many yeasts do not ferment lactose

and consequently fail to proliferate or only

grow slowly in cream, a number of species

have been isolated from pasteurized samples

of cream (Fleet 1990 ).

Spores of Bacillus spp. can survive pas-

teurization and other heat treatments applied

to cream. Ready - to - eat foods (e.g., sous

vides ) have become popular in many coun-

tries. Such foods may contain cream and gen-

erally do not receive process treatments to

ensure inactivation of spores. Among the

Bacillus spp. recovered from cream are B.

cereus, which can induce sweet curdling, B.

licheniformis, and B. pumilis, both of which

can grow, albeit slowly, at 8 ° C (Nissen et al.,

2001 ). In addition to spoilage by Bacillus

spp., the risk from B. cereus enterotoxin pro-

duction and the presence of toxigenic strains

of members of the B. subtilis group in cream

and dairy products cannot be dismissed

(Salkinoja – Salonen et al., 1999 ; Nissen et al.,

2001 ).

Butter

Butter is a stable water - in - oil emulsion

derived from cream as its main ingredient.

The term butter is reserved for a product with

a milk fat content of not less than 80% but

less than 90%, a maximum water content of

16%, and a maximum dry nonfat material

content of 2%. For a description of butter -

making processes, see Robinson (2002) and

references therein.

Pasteurization of the cream is the main

critical control point in the butter - making

process. Post pasteurization contamination is

the most likely source of microbial safety and

Creams are also identifi ed through the
heat treatment to which they are subjected.
This has important implications for the safety
and spoilage of cream products and their sub-
sequent use as ingredients. Untreated cream
indicates cream or milk from which it is
derived, which has not been subjected to any
heat treatment. Heat - treated creams include
pasteurized cream, which is subjected to a
temperature not less than 63 ° C for 30 minutes
or longer or above 72 ° C for 155 minutes or
longer; sterilized cream, which is subjected
to a temperature of 108 ° C or higher for 45
minutes or longer in retail containers; and
ultra - high - temperature - treated cream, which
is subjected to a temperature of 140 ° C or
higher for at least two seconds.

Cream Safety

As a consequence of the heat treatments
applied, outbreaks of food poisoning associ-
ated with cream or cream - derived products
are rare. A few minor outbreaks associated
with farm - produced cream have been
reported (Sharp, 1987 ). Risks to public health
may be presented by post heat treatment con-
tamination in the packaging and distribution
chain. Cream products have a longer shelf
life than retail milk and consequently patho-
gens contaminating the product post pasteuri-
zation have the opportunity to proliferate if
temperature abuse occurs.
Escherichia coli 0157 : H7 survived seven
to 35 days in sour cream when inoculated to
contain 10^2 to 10^3 organisms/ml and stored at
4 ° C (Dineen et al., 1998 ). Listeria monocy-
togenes attained populations of 10^6 cfu/ml in
whipping cream after eight days of storage
at 8 ° C (Rosenow and Marth, 1987 ), thus
emphasising the need to avoid post manufac-
turing contamination with such pathogens.

Cream Spoilage

Gram - negative organisms, aerobic spore-
formers, and yeasts are the major groups of
organisms associated with the spoilage of