BLBS102-c04 BLBS102-Simpson March 21, 2012 11:59 Trim: 276mm X 219mm Printer Name: Yet to Come
60 Part 1: Principles/Food AnalysisControl of BrowningEnzymatic browning may cause a decrease in the market value
of food products originating from plants and crustaceans (Kubo
et al. 2000, Perez-Gilabert and Garc ́ıa-Carmona 2000, Subaric
et al. 2001, Yoruk and Marshall 2003, Queiroz et al. 2008).
Processing such as cutting, peeling, and bruising is enough
to cause enzymatic browning. The rate of enzymatic brown-
ing is governed by the active PPO content of the tissues, the
phenolic content of the tissue, and the pH, temperature, and
oxygen availability within the tissue. Table 4.2 gives a list of
procedures and inhibitors that may be employed for controlling
enzymatic browning in foods. A review on conventional and
alternative methods to inactivate PPO has been recently pub-
lished by Queiroz et al. (2008). The inhibition of enzymatic
browning generally proceeds via direct inhibition of the PPO,
nonenzymatic reduction ofo-quinones, and chemical modifica-
tion or removal of phenolic substrates of PPO. Among all these
methods, inhibition of PPO is preferable. According to Marshall
et al. (2000), there are six categories of PPO inhibitors appli-
cable to control enzymatic browning: reducing agents, acidu-
lants, chelating agents, complexing agents, enzyme inhibitors,
and enzyme treatments. Tyrosinase inhibitors from natural and
synthetic sources have been reported by Chang (2009).
Sulfites are the most efficient multifunctional agents in the
control of enzymatic browning of foods. The use of sulfites has
become increasingly restricted because they can produce ad-
verse reaction in some consumers.l-ascorbic and its stereoiso-
mer erythorbic acid have been considered as the best alternative
to sulfite in controlling browning. 4-Hexylresorcinol is also a
good substitute to sulfite. Sulphydryl amino acids such as cys-
teine and reduced glutathione, and inorganic salts like sodium
chloride, kojic acid, and oxalic acid (Pilizota and Subaric 1998,
Son et al. 2000, Burdock et al. 2001, Yoruk and Marshall 2009)
cause an effective decrease in undesirable enzymatic browning
in foods. An equivalent of hypotaurine can be an extract of a
foodstuff that has a high hypotaurine level such clam, oyster,
mussels, squid, octopus, or any combination thereof (Marshall
and Schulbach 2009). The application of this naturally occurring
compound provides a longer-lasting protection from enzymatic
browning in comparison with ascorbic acid or citric acid. On
the other hand, taurine addition may provide nutritional bene-
fits to the supplemented foods because of its health-promoting
properties.
A decrease in enzymatic browning is achieved by the use
of various chelating agents, which either directly form com-
plexes with PPO or react with its substrates. For example,p-
cyclodextrin is an inhibitor that reacts with the copper-containing
prosthetic group of PPO (Pilizota and Subaric 1998). Crown
compounds have potential to reduce the enzymatic browning
caused by catechol oxidase because of their ability to complex
with copper present in its prosthetic group. The inhibition ef-
fect of crown compounds, macrocyclic esters, benzo-18-crown-
6 with sorbic acid, and benzo-18-crown-6 with potassium sor-
bate have been proved for fresh-cut apples (Subaric et al. 2001).
Agro-chemical processes may also be employed for achiev-
ing an effective control of enzymatic browning. In vitro studiesbased on the evaluation of the effect of a range of commonly used
pesticides on the activity of purified quince (Cydonia oblonga
Miller) PPO have indicated that PPO enzyme is competitively
inhibited by pesticides such as benomyl, carbaryl, deltamethrine,
and parathion methyl (Fattouch et al. 2010). Salinity also affects
PPO activity of the fresh-cut vegetables. Increasing salinity con-
ditions may allow fresh-cut vegetables possessing low PPO ac-
tivity, high phenol content and high antioxidant capacity (Chisari
et al. 2010).
Thiol compounds like 2-mercaptoethanol may act as an in-
hibitor of the polymerization ofo-quinone and as a reductant
involved in the conversion ofo-quinone too-dihydroxyphenol
(Negishi and Ozawa 2000).
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 anti-browning agents. Honey
(Chen et al. 2000, Gacche et al. 2009); papaya latex extract (De
Rigal et al. 2001); banana leaf extract either alone or in com-
bination with ascorbic acid and 4-hexylresorcinol (Kaur and
Kapoor 2000); onion juice (Hosoda and Iwahashi 2002); onion
oil (Hosoda et al. 2003); onion extracts (Kim et al. 2005); onion
by-products (residues and surpluses; Roldan et al. 2008); rice
bran extract (Boonsiripiphat and Theerakulkait 2009); solutions
containing citric acid, calcium chloride, and garlic extract (Ihl
et al. 2003); Maillard reaction products (MRPs) obtained by
heating of hexoses in presence of cystein or glutathione (Billaud
et al. 2003, 2004);N-acetylcysteine and glutathione (Rojas-Grau
et al. 2008); resveratrol, a natural ingredient of red wine pos-
sessing several biological activities, and other hydroxystilbene
compounds, including its analogous oxyresveratrol (Kim et al.
2002); and hexanal (Corbo et al. 2000), Brassicacaea process-
ing water (Zocca et al. 2010); and chitosan (Martin-Diana et al.
2009) are some examples of natural inhibitors of PPO. In most
cases, the inhibiting activity of plant extract is due to more than
one component. Moreover, a good control of enzymatic brown-
ing may involve endogenous antioxidants (Mdluli and Owusu-
Apenten 2003).
Regulation of the biosynthesis of polyphenols (Hisaminato
et al. 2001) and the use of commercial glucose oxidase–catalase
enzyme system for oxygen removal (Parpinello et al. 2002) have
been described as essential and effective ways of controlling
enzymatic browning.
Commonly, an effective control of enzymatic browning can
be achieved by a combination of anti-browning agents (Zocca
et al. 2010). A typical combination might consist of a chemical
reducing agent such as ascorbic acid, an acidulant such as citric
acid, and a chelating agent like EDTA (Marshall et al. 2000)
A great emphasis is put on research to develop methods for
preventing enzymatic browning especially in fresh-cut (mini-
mally processed) fruits and vegetables. The most efficient way to
control this problem is the combination of physical and chemical
methods, by avoiding the use of more severe individual treat-
ments, which could harm the appearance and texture of vegeta-
bles. Technological processing, including microwave blanching
either alone or combined with chemical anti-browning agents
(Severini et al. 2001, Premakumar and Khurduya 2002, Yadav
et al. 2008, Guan and Fan 2010); CO 2 treatments (Rocha and