Food Chemistry

2Enzymes..............................................

2.1 Foreword

Enzymes are proteins with powerful catalytic
activity. They are synthesized by biological
cells and in all organisms, they are involved in
chemical reactions related to metabolism. There-
fore, enzyme-catalyzed reactions also proceed
in many foods and thus enhance or deteriorate
food quality. Relevant to this phenomenon
are the ripening of fruits and vegetables, the
aging of meat and dairy products, and the
processing steps involved in the making of
dough from wheat or rye flours and the pro-
duction of alcoholic beverages by fermentation
technology.
Enzyme inactivation or changes in the distribu-
tion patterns of enzymes in subcellular particles
of a tissue can occur during storage or thermal
treatment of food. Since such changes are read-
ily detected by analytical means, enzymes of-
ten serve as suitable indicators for revealing such
treatment of food. Examples are the detection of
pasteurization of milk, beer or honey, and differ-
entiation between fresh and deep frozen meat or
fish.
Enzyme properties are of interest to the food
chemist since enzymes are available in increas-
ing numbers for enzymatic food analysis or
for utilization in industrial food processing.
Examples of both aspects of their use are pro-
vided in this chapter in section 2.6.4 on food
analysis and in section 2.7, which covers food
processing.
Details of enzymes which play a role in food sci-
ence are restricted in this chapter to only those
enzyme properties which are able to provide an
insight into the build-up or functionality of en-

zymes or can contribute to the understanding of
enzyme utilization in food analysis or food pro-
cessing and storage.

2.2 GeneralRemarks,IsolationandNomenclature

2.2.1 Catalysis...............................................

Let us consider the catalysis of an exergonic re-

action:

A

k 1



k− 1

P (2.1)

with a most frequently occurring case in which

the reaction does not proceed spontaneously. Re-

actant A is metastable, since the activation en-

ergy, EA, required to reach the activated transi-

tion state in which chemical bonds are formed or

cleaved in order to yield product P, is exception-

ally high (Fig. 2.1).

The reaction is accelerated by the addition of

a suitable catalyst. It transforms reactant A into

intermediary products (EA and EP in Fig. 2.1),

the transition states of which are at a lower energy

level than the transition state of a noncatalyzed

reaction (A =in Fig. 2.1). The molecules of the

Fig. 2.1.Energy profile of an exergonic reaction

A→P; — without and---withcatalystE

H.-D. Belitz · W. Grosch · P. Schieberle,Food Chemistry 93
© Springer 2009