330 Produce Degradation: Reaction Pathways and their Prevention
can reduce the juice release, and when it is followed by immersion in sugar solution
the treatment can also increase the sugar uptake of fruit tissues (Eshtiaghi and Knorr,
1996). Vacuum infusion with cryprotectants (sugar or fruit juice concentrates) and
cryostabilizers (e.g., pectin) prior freezing can reduce ice crystal damage in frozen
fruits by notable reduction of freezable water (Torreggiani and Bertolo, 2001). The
effect is also similar in the dehydrofreezing process. In this process, fruits or vege-
tables are dehydrated to the desired moisture level and then frozen (Spiazzi et al.,
1998). Applications of antifreeze protein can lower the freezing temperature and
retard recrystallization during frozen storage, while ice-nucleation proteins raise the
temperatures of ice nucleation and reduce the degree of supercooling (Li and Lee,
1998). Bacteria-induced ice nucleation has been recognized as a major contributing
factor to frost injury in plant products. The effect of antifreeze protein in fish is also
known, although practical applications are seldom reported. A potential application
of antifreeze protein could be inhibition of recrystallization of ice in ice creams, but
the potential exists for the concept to be developed for a number of agricultural
products.
10.2.3.3.3 Chemoanabiosis
The mechanism of chemoanabiosis is the application of a chemical agent with
antimicrobial effects. Chemosterilation agents, relative to disinfection agents, do not
cause rapid inactivation. They, however, act more through their microbistatic prop-
erties. When they are applied the lag phase of microbial growth is extended.
Chemoanabiosis process may consist of a series of steps (Kyzlink, 1990), including
addition of preservatives, addition of antibiotics (or preparations containing anti-
biotics), addition of natural preservatives (phytoncides), and traditional processing of
food that includes a chemoanabiotic effect (smoking, curing, brining, marinating, etc.).
Preservatives that are used may include various fungicides that are applied after
harvest. Fruits and vegetables to be stored may be treated with one or more fungi-
cides. There are about 20 types of fungicides approved for use on fresh produce
(Eckert and Ogawa, 1990). The list varies from one country to another. Benomyl,
thiabendazol, thiophthanate methyl, and imazalil are more commonly used. In some
countries these products are permitted for use as preservatives by legislation
(Velísˇek, 1999).^ The fungicides are applied by dipping or spraying, through incor-
poration into waxes for surface application on fruits, or in fungicide-impregnated
paper. A number of antimicrobial agents also act as disinfectants, microbistatic
agents, acidulants, and antioxidants^ (Bibek, 1996). Benzoic acid, sorbic acid, para-
bens, and sulfur dioxide are used most frequently for the preservation of fruit and
vegetable products and are permitted in the majority countries.
Benzoic acid is used as an acid or sodium salt at a concentration of 500 to 2000
mg/kg for preservation of acidic products such as beverages, pickles, salad dressings,
and mustard. The undissociated acid is more efficient, but its effectiveness decreases
with increasing pH. Benzoic acid is more effective against yeasts and molds than
against bacteria^ (Bibek, 1996).^ The solubility of benzoic acid is relatively low
(1.8 g/L at 4°C; 2.7 g/L at 18°C; 22 g/L at 100°C). The solubility becomes more
critical when a concentrated solution of sodium benzoate is added to acidic products
or during heat treatment to concentrate and reduce product volume^ (Kyzlink, 1990).