Dairy Ingredients for Food Processing

59

Chapter 3

Microbiological Aspects of Dairy Ingredients

Michael Rowe and John Donaghy

Milk is a very nutritious medium not only for
humans but, if the extrinsic conditions are
favorable, for microorganisms. The position
of the udder below and proximal to the cow ’ s
rectum means that milk is prone to all of the
spoilage and, more importantly, pathogenic
microfl ora excreted from the animal ’ s gut.
Man has, of necessity, sought means of pre-
serving the nutritious elements of milk,
resulting in a plethora of dairy products, cer-
tainly beyond the scope of this chapter.
Although the need to employ such preserva-
tion methods has diminished in many parts
of the world, the range of dairy products has,
in many respects, been retained because of
the desirable organoleptic properties these
impart either on their own or as ingredients
in other products. It is axiomatic that if used
as an ingredient, although the dairy compo-
nent contributes its own peculiar microfl ora,
the intrinsic and extrinsic characteristics of
the fi nal product largely determine the prod-
uct ’ s spoilage potential and food safety risk.
This chapter confi nes itself to microbial
spoilage and food safety concerns of the
main milk and dairy products used as ingre-
dients. It does not attempt to describe the
microbiological aspects of their production
which are aptly addressed in other chapters
of this book.

Raw Milk

Raw milk can potentially contain a multitu-

dinous range of microfl ora including bacte-

ria, yeasts, molds, prions, and viruses. This

variation encompasses not only the microbial

types but also their population sizes. Random

amplifi ed polymorphic DNA (RAPD) and

subsequent cluster analysis of raw milk

microfl ora indicates that the genetic variabil-

ity among isolates belonging to the same

species is commensurate with the genetic

variability among different species. Such

molecular approaches, based on direct analy-

sis of DNA or RNA and which do not rely on

the prior growth of the microfl ora, have

enabled the dynamics of the raw milk micro-

fl ora and their temporal changes to be eluci-

dated more precisely. However, a list of the

possible microfl ora mainly based on pheno-

typic tests is given in Bramley and McKinnon

(1990) and Oliver et al. (2005) , and a fuller

description of the individual species is given

in Gilmour and Rowe (1990).

The actual microfl ora in any consignment

of raw milk depends chiefl y on the following

factors:

• Cow health and incidence of clinical and
  sub - clinical mastitis


• Cow diet and feeding practices


• Milking procedures and practices


• Milk contact surfaces of equipment


• Sanitation practices


• Husbandry practices (e.g., winter housing
  and summer grazing of cattle)

Dairy Ingredients for Food Processing edited by
Ramesh C. Chandan and Arun Kilara
© 2011 Blackwell Publishing Ltd.