Lipoxygenase and lipid oxidation in foods - Oxidation in Foods and Beverages and Antioxidant Applications - page 116

was retained after drum-drying. This extensive destruction of vitamin E may be
due to lipid degradation catalyzed by LOXs. When LOX was heat-inactivated by
a low moisture processes, vitamin E retention was greatly improved (Hakansson
and Jagerstad, 1990).
Cereal products such as wheat flour undergo fast oxidation and generate
bitter and rancid flavors once the raw materials are mixed with water. Heat
processing can easily deactivate the LOX, especially in the presence of a high
moisture content (64 ëC at 12% moisture and 103 ëC at 8% moisture) (Frankel,
1998). The endogenous tocopherols in plant materials play an important role in
preventing lipid oxidation. Synthetic BHA and TBHQ and natural phenolic
extracts are effective in extending the shelf life of dry cereal products.
Inactivation of enzymes by heat generated from radiofrequency (RF) electric
fields was also investigated for inactivating LOX (Manzocco et al., 2008). The
effect of increasing RF on the activity of polyphenoloxidase and LOX was tested
in model systems and in apple products. The treatments efficiently inactivated
both enzymes because RF generated thermal effect that denatured the enzymes.
RF also allowed apples to be adequately blanched and produced a puree quality
equivalent to that obtained by traditional blanching.
5.4.3 Irradiation
Gamma-irradiation of buckwheat seeds at 4±6 kGy resulted in a significant
reduction in LOX activity, achieving 22±43% activity of the untreated control
(Henderson and Eskin, 1990). The authors suggested that heating is more
efficient and effective way to eliminate LOX than irradiation.
5.4.4 Pressure change
LOX inactivation by pressurization-depressurization may be possible. In an
Indian patent (Mukhopadhyay and Chakraborty, 2007), supercritical CO 2 treat-
ment of legumes and cereals was shown to inactivate LOX, lipase and trypsin
inhibitor by using a sequential processing protocol that involves a pressuriza-
tion-depressurization at temperature of 35±60 ëC, pressure of 7±15MPa, and
treatment time of 15±90min. This process produced final products without
beany flavor, trypsin inhibitor, and lipase activity.
5.4.5 Endogenous antioxidant systems
The endogenous antioxidants in muscle include -tocopherol, ubiquinone,
ascorbate, histidine-dipeptide, and enzymes such as superoxide dismutase
(converts superoxide anion to hydrogen peroxide), catalase (convert hydrogen
peroxide to water and oxygen), glutathione peroxidase (converts hydroperoxides
to alcohols). Glutathion can reduce the lipid oxidation initiator ferryl myoglobin
to metmyoglobin, reducing its LOX-like activity. Lipid oxidation in meat can be
accelerated by the depletion of glutathione peroxidase and glutathione
transferase, which decompose hydroperoxides.