Physical Chemistry of Foods

Irreversibility. The reasoning given above is also an

oversimplification in another sense. Most of the results discussed concern

loss of biological (e.g., enzyme) activity, and the activities then are

determined after cooling to room temperature. It thus concerns an

irreversible change, rather than reversible unfolding. The simplest case

would be

N
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/

ku

kf

U

ki

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FIGURE7.9 Heating times needed (t*) for inactivation (reduction of activity to
about 1%) of the enzymes chymosin (Ch), lipoxygenase (LP), acid phosphatase (AP),
and plasmin (Pl); and for 30%of ovalbumin (OA) andb-lactoglobulin (LG) to
become insoluble. Because of the narrow temperature intervals involved, also plots
versusT, rather than 1/T, can be approximately linear.