Microbiological Aspects of Dairy Ingredients 65been shown to be a safe method for preserv-
ing milk when used according to the Codex
guidelines either alone or in combination
with other approved procedures. It is particu-
larly suitable when technical, economical,
and/or practical reasons do not allow the use
of cooling facilities for maintaining milk
quality (Asaah et al., 2007 ). The lactoperoxi-
dase system elicits antimicrobial activity
against a wide range of microorganisms
including bacteria, yeasts, molds, viruses,
and protozoa. It does not result in any signifi -
cant adverse effects on the physicochemical
or sensory characteristics of raw milk or pro-
cessed dairy products and presents no signifi -
cant toxicological risks. For more information
consult FAO/WHO (2006).
Thermization. Thermization is a heat
treatment less severe than pasteurization,
typically 63 ° C or 65 ° C for 15 to 20 seconds.
It is designed to kill the psychrotroph popula-
tion and, with prompt refrigeration, allow
extended storage at the creamery prior to pro-
cessing (Griffi ths et al., 1986 ). Because the
time - temperature combination cannot reli-
ably destroy M. bovis or C. burnetii , it cannot
be used as a replacement for pasteurization.
Thermization has been shown to result in
higher cheese yields and reduction in off -
fl avor development in both hard and soft
cheeses.
Addition of carbon dioxide. The addition
of carbon dioxide up to a concentration of
30 mM/l has been advocated to inhibit the
psychrotroph population and prolong the safe
storage of raw milk. Higher concentrations
have been shown to lead to protein instabil-
ity. Carbon dioxide has been shown to
prolong the lag and exponential growth
phases of psychrotrophs stored at 10 ° C and
below. It has also been shown to have a dif-
ferential effect on Ps. fl uorescens , the psy-
chrotroph most implicated in spoilage, with
extracellular enzyme production being inhib-
ited to a greater extent than bacterial growth
and fi nal cell numbers. Addition of CO 2 to
approximately 30 mM/l was found to reduceof the raw product unless the refrigerated
storage of raw milk is protracted; however,
its impact can be signifi cant for products
made from that milk.
The psychrotrophic microfl ora, in particu-
lar Pseudomonas spp., can secrete extracel-
lular enzymes (e.g., proteases, lipases, and
phospholipases) in their stationary growth
phases, which may be heat stable and survive
pasteurization. This is even true of ultra - high
temperature (UHT) heat processing in the
case of proteases, subsequently resulting in
spoilage of product. The enzymes may be
produced in the stationary growth phase, as
opposed to constitutively, and bulk milk
arriving at a creamery from a transport
vehicle usually represents a composite of a
number of producers. As a result, a rapid
count, even a rapid count of psychrotrophs if
that were possible, would not give a reliable
indication of the spoilage potential of that
milk.
The majority of the Pseudomonas species
are Ps. fl uorescens and Ps. putida (Dogan
and Boor, 2003 ). Another group of organisms
that may be present in raw milk and have the
potential to spoil dairy products are spore -
forming bacteria, in particular Bacillus spp.
and Paenibacillus spp., and to a lesser extent
Sporosarcinia spp. (Huck et al., 2008 ). The
ability to form endospores gives them the abil-
ity to survive pasteurization and, if the condi-
tions are favorable, to germinate and grow,
causing spoilage.
Various interventions have been proposed
to minimize the spoilage potential of raw
milk and maximize fl exibility in processing,
including activation of the intrinsic lactoper-
oxidase system, thermization, addition of
carbon dioxide, and low temperature (approx-
imately 2 ° C) storage.
Lactoperoxidase. Lactoperoxidase is a
natural antimicrobial system designed to
prevent colonization of the calf ’ s intestinal
tract with pathogenic bacteria. It can be acti-
vated by the addition of potassium thiocya-
nate and hydrogen peroxide. The system has