Food Biochemistry and Food Processing (2 edition)

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3 Enzymes in Food Analysis 45

Table 3.2.(Continued)

Food Component Enzymes Involved Commercial Kit Reference

Other Components

Citric acid Citrate lyase Wiseman 1981, Mello and

Kubota 2002,

Prodromidis and

Karayannis 2002, Cock

et al. 2009

Catechol/polyphenols Polyphenol oxidase, tyrosinase

Oxalate Oxalate oxidase

Lactate Transaminase, lactate dehydrogenase

Aspartame Carboxyl esterase, alcohol oxidase,

aspartase, carboxypeptidase,

chymotrypsin, glutamate oxidase

Alcohol Alcohol dehydrogenase Megazyme International Wiseman 1981, Mello and

Kubota 2002, Cock et al.

2009

Ascorbic acid Ascorbic acid oxidase Megazyme International

Xylitol Alkaline phosphatase (ELISA) Sreenath and Venkatesh

2010

enzyme reactor (Matsumoto et al. 1988). In the analysis of wine

components, Zeravik et al. (2009) have discussed the use of (a)

PQQ-bound dehydrogenases for the determination of glucose,

alcohol, and glycerol; (b) tyrosinase, laccase, and peroxidase for

phenolic compounds; and (c) sulfite oxidase for sulfite content.

For analysis of starch, a complex polysaccharide, the under-

lying principles of starch liquefaction and saccharification are

utilized. Theα-amylases hydrolyze starch, releasing maltose

units and limit dextrin. This is characterized by viscosity re-

duction or what is more commonly referred to by the starch

industry as liquefaction. Further treatment with pullulanase and

amyloglucosidases (glucoamylases) results in hydrolysis of the

maltose units and limit dextrin, ultimately producing glucose

units that are subsequently analyzed by some of the methods

discussed earlier. Figure 3.5 illustrates the salient features of the

amylase, pullulanase, and amyloglucosidase reaction. Analyses

of other polysaccharides have been conducted in similar fashion

by initial breakdown to simpler sugars using different carbo-

hydrases depending on the nature of the substrate. Dextranases

have been used for dextrans, cellulases for cellulose, hemicel-

lulases for hemicelluloses in dietary fiber, and pectinases and

polygalacturonases for polysaccharides in soy sauce and other

plant-based foods (Wiseman 1981). Table 3.2 provides a list of

some of the enzymatic methods for food component analysis

along with some of the commercially available test kits.

Other Food Components

Alcohol

Alcohol (ethanol) content in beer, wine, and other alcoholic bev-

erages is a very important quality attribute and is also required

for regulatory classification. The NAD-dependent alcohol de-

hydrogenase is widely used for analysis of alcohol content in

foods and alcoholic beverages. The enzyme catalyzes oxida-

tion of ethanol to acetaldehyde in an equilibrium reaction that

also produces NADH. The reaction is made to proceed in the

forward direction by acetaldehyde reaction with semicarbazine

or hydrazine. The absorbance change resulting from NAD+to

NADH conversion is proportional to alcohol content. Similar

NAD-dependent assays have been used for measuring glycerol

content in foods. Figure 3.6 shows the principle underlying the

method for glycerol analysis.

Cholesterol

Consumption of cholesterol-rich foods and their association

with atherosclerosis, hypertension, and high incidence of other

D-Fructose

Fructos dehydrogenase

2[Fe(CN) 6 ]4– 2e–

Electrode

+400 mV

5-Keto-D-fructose 2[Fe(CN) 6 ]3– 2H+

Figure 3.4.Schematic representation of the principle of fructose sensor based on fructose dehydrogenase.