Dairy Processing - January/February 2023 - 32

FORMULATIONS
Wash. " The amount of moisture in a product also influences
nutritional content and labeling requirements. "
The water content of food is expressed as a percent;
however, this number does not reflect how the water exists
in the food. Formulators must consider all four forms of
water - bulk, capillary, physically bound and chemically
bound - when trying to manage moisture. This takes into
consideration water activity, which describes the energy
status or the escaping tendency of the water in the food
matrix. Water activity is a thermodynamic concept expressed
as a ratio of the vapor pressure of water in a food to the vapor
pressure of free water at the same temperature. It indicates
how tightly water is bound in a food matrix.
Why does this matter? Water activity predicts safety and
stability with respect to microbial growth, chemical and
biochemical reaction rates, and various physical properties.
" If you understand how water activity works, you will be
able to develop products that are stable and desirable to the
consumer and can predict and prevent potential problems, "
Galloway said. " There is a
relationship between water
activity and moisture content,
but it is unique to each product
and formulation. "
This relationship is explained
by moisture sorption isotherms. These
graphs allow for modeling of best formulations, in terms
of quality and safety. They also allow for predictions of
temperature abuse and shelf life.
Water activity is often described in terms of the amount of
bound water and free water. Although these terms make the
concept of water activity somewhat easier to conceptualize,
the reality is that all water in food is somewhat bound;
after all, it is contained in the food. Thus, water activity is a
measure of how tightly water is bound and relates to the work
required to remove water from the system.
" Differences in water activity dictate how water will
move, " between components in a food matrix, between
microorganisms and a food matrix, etc., Galloway said.
Most foods have a water activity above 0.95 and that
will provide sufficient moisture to support the growth of
bacteria, yeasts and mold, according to the US Food and
Drug Administration (FDA), Washington, DC. The amount of
available moisture can be reduced to a point that will inhibit
the growth of the microorganisms.
One way to do this is with the addition of sucrose or
sodium. These ingredients associate with the water in a food
system, making the water unavailable to microorganisms.
Like humans, microorganisms require water to thrive and
proliferate. A water product activity of 0.85 is enough to
inhibit the growth of dangerous bacteria.
Listeria monocytogenes is a common contaminant in the
dairy environment, both on the farm and in the processing
32 JAN-FEB 2023 | DAIRYPROCESSING.COM
Milk has a typical
moisture content
of about 87%,
whereas cheddar
is about 38%.
Center for Dairy
Research
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Dairy Processing - January/February 2023

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