Stabilization of bran to inactivate enzyme activity is the most
important factor in rice bran oil extraction. Poor or no stabilization
causes the increase in AV, PV and FFA content and affects the
extraction process, oil quantity and quality. The effects of stabilization
of rice bran by domestic heating on chemical property of coldpressed
RBO are shown in Table 4. Acid value (AV), free fatty acid
(FFA) and peroxide value (PV) were the parameters used for determination
of chemical quality of cold-pressed RBO. Generally, the
content of AV, FFA and PV was positively related to the activity of
enzyme lipase. Acid value can be used for a purity check of oil and
mayhave already started decomposition reactions. Although refined
oils are largely devoid of free fatty acids, considerable amounts may
be present in crude oils. Hydroperoxides are the primary products of
autoxidationwhich in themselves are odorless. Their decomposition
leads to the formation of a wide range of carbonyl compounds,
hydrocarbons, furans and other products that contribute to the stale
flavor of foods and may also be involved in biological oxidation
(Frankel, 1991). The peroxide value (PV) measures the quantity of
peroxides in the oil; these are important intermediates of oxidative
reactions since they decompose via transition metal irradiation and
elevated temperatures to form free radicals (Decker, 1998).