Food Biochemistry and Food Processing

4 Browning Reactions 75

Sulfites are the most efficient multifunctional
agents in the control of enzymatic browning of foods.
The use of sulfites has become increasingly restrict-
ed because they have been considered a cause of
severe reactions in asthmatics. The best alternative
to sulfite in control of browning is L-ascorbic acid or
its stereoisomer erythorbic acid; 4-hexylresorcinol
is also a good substitute for sulfite. Sulfhydryl
amino acids such as cysteine and reduced glu-
tathione, and inorganic salts like sodium chloride,
kojic acid, and oxalic acid (Pilizota and Subaric
1998, Son et al. 2000, Burdock et al. 2001) cause an
effective decrease in undesirable enzymatic brown-
ing in foods. A decrease of enzymatic browning is
achieved by use of various chelating agents, which
either directly form complexes with polyphenol oxi-
dase or react with its substrates. P-cyclodextrin, or
example, is an inhibitor that reacts with the copper-

containing prosthetic group of PPO, forming an in-

clusion complex (Pilizota and Subaric 1998).

Thiol compounds like 2-mercaptoethanol may act

as an inhibitor of the polymerization of o-quinone

and as a reductant involved in the conversion of o-

quinone to o-dihydroxyphenol (Negishi and Ozawa

2000).

Crown compounds have the potential to reduce

the enzymatic browning caused by catechol oxidase

due to their ability to complex with the copper pres-

ent in its prosthetic group. The inhibition effect of

crown compounds, macrocyclic esters, benz18-

crown-6 with sorbic acid, and benz18-crown-6 with

potassium sorbate has been proved for fresh-cut

apples (Subaric et al. 2001).

Because of safety regulations and the consumer’s

demand for natural food additives, much research

has been devoted to the search for natural and safe

Table 4.1.Phenolic Substrates of PPO in Foods

Source Phenolic Substrates

Apple Chlorogenic acid (flesh), catechol, catechin (peel), caffeic acid,

3,4-dihydroxyphenylalanine (DOPA), 3,4-dihydroxy benzoic acid, p-cresol, 4-methyl

catechol, leucocyanidin, p-coumaric acid, flavonol glycosides

Apricot Isochlorogenic acid, caffeic acid, 4-methyl catechol, chlorogenic acid, catechin,

epicatechin, pyrogallol, catechol, flavonols, p-coumaric acid derivatives

Avocado 4-methyl catechol, dopamine, pyrogallol, catechol, chlorogenic acid, caffeic acid, DOPA

Banana 3,4-dihydroxyphenylethylamine (Dopamine), leucodelphinidin, leucocyanidin

Cacao Catechins, leucoanthocyanidins, anthocyanins, complex tannins

Coffee beans Chlorogenic acid, caffeic acid

Eggplant Chlorogenic acid, caffeic acid, coumaric acid, cinnamic acid derivatives

Grape Catechin, chlorogenic acid, catechol, caffeic acid, DOPA, tannins, flavonols,

protocatechuic acid, resorcinol, hydroquinone, phenol

Lettuce Tyrosine, caffeic acid, chlorogenic acid derivatives

Lobster Tyrosine

Mango Dopamine-HCl, 4-methyl catechol, caffeic acid, catechol, catechin, chlorogenic acid,

tyrosine, DOPA, p-cresol

Mushroom Tyrosine, catechol, DOPA, dopamine, adrenaline, noradrenaline

Peach Chlorogenic acid, pyrogallol, 4-methyl catechol, catechol, caffeic acid, gallic acid,

catechin, Dopamine

Pear Chlorogenic acid, catechol, catechin, caffeic acid, DOPA, 3,4-dihydroxy benzoic acid,

p-cresol

Plum Chlorogenic acid, catechin, caffeic acid, catechol, DOPA

Potato Chlorogenic acid, caffeic acid, catechol, DOPA, p-cresol, p-hydroxyphenyl propionic

acid, p-hydroxyphenyl pyruvic acid, m-cresol

Shrimp Tyrosine

Sweet potato Chlorogenic acid, caffeic acid, caffeylamide

Tea Flavanols, catechins, tannins, cinnamic acid derivatives

Source:Reproduced from Marshall et al. 2000.