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FOOD PRODUCTS FROM CORN GERM: ENZYME ACTIVITY AND OIL STABILITY
Published 1971 · Chemistry
SUMMARY Full-fat corn germ was cooked by heated rolls at roll temperatures ranging from 99–204°C. The 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. The amount of enzyme activity found in corn germ before roll-cooking was dependent 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 temperatures of 124°C and above completed inactivation of all the enzymes studied except peroxidase. Residual amounts of peroxidase activity remained in almost all samples. The oil in heated germ was resistant to hydrolytic rancidity when stored under nitrogen at a relative humidity as high as 75%. If the germ was stored in air at 75% relative humidity, mold developed on many of the samples. Oxidative rancidity, as measured by the peroxide value of the extracted oil, increased to about 20–40 meq peroxide/kg oil after 170 days storage only in the samples heated at or above 124°C. Low peroxide values (1.5–6 meq peroxide/kg oil) of oil from relatively unprocessed germ were postulated to result from the action of linoleic acid-hydroperoxide-isomerase. This enzyme catalyzes the conversion of hydroperoxide to products not measured by peroxide values.