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Food products from corn germ: enzyme activity and oil stability

Gardner, H.W., Inglett, G.E.
Journal of food science 1971 v.36 no.4 pp. 645
corn germ, enzyme inactivation, peroxidase, cooking, inactivation temperature, flakes, triacylglycerol lipase, lipoxygenase, isomerases, corn oil, lipid peroxidation, rancidity, peroxide value, enzyme activity, postharvest treatment, oxidative stability
Full-fat corn germ was cooked by heated rolls at roll temp. in the range 99-204°C. Resulting flakes were examined for peroxidase, lipase, lipoxygenase (formerly lipoxidase) and linoleic acid-hydroperoxide-isomerase activity. Stability of the oil in germ flakes was also investigated. Amount of enzyme activity found in corn germ before roll-cooking was depended on the post-harvest history of the corn. After picker-sheller harvest, drying the grain in heated air significantly inactivated enzymes. Cooking the germ by heated rolls at temp. of 124^374C and above completed inactivation of all enzymes studies except peroxidase. Residual amounts of peroxidase activity remained in almost all samples. Oil in heated germ was resistant to hydrolytic rancidity when stored under N2 at a RH as high as 75%. If the germ was stored in air at 75% RH, mould developed on many of the samples. Oxidative rancidity, as measured by the peroxide value of extracted oil, increased to ~20-40 m-equiv. peroxide/kg oil after 170 days storage only in samples heated at or above 124°C. Low peroxide values (1.5-6 m-equiv. peroxide/kg oil) of oil from relatively unprocessed germ were postulated to result from the action of linoleic acid-hydroperoxide-isomerase. This enzyme catalyses conversion of hydroperoxide to products not measured by peroxide value.