Studies on the low temperature infrared heat processing of soybeans and maize

A modified process for the infrared heat processing of oilseeds and cereal grains at relatively low temperatures is put forward. The process which involves an additional holding step and potentials for saving energy was investigated on a pilot plant on the basis of which a design is proposed for industrial applications. The process was used in order to produce full-fat soy flour and maize germ with long shelf life and improved nutritive and organoleptic qualities. Antitrypsin factors, lipoxygenase and lipase could be inactivated with no damage to available lysine. Overheating not only caused damage to available lysine but also made the products more prone to rancidity possibly by causing destruction of natural antioxidants. The process caused protein solubility and dispersibility to fall and starch (in maize germ) to gelatinize. Water absorption of maize germ also increased. In soybeans, urease was found to be a good indicator of the extent of inactivation of antitrypsin factors, while lipoxygenase was found more heat sensitive than urease and antitrypsin factors. For evaluating storage stability, in addition to measuring peroxide value and % free fatty acids, sensory analysis was also carried out.<p>The process was further applied for treating soybeans prior to oil extraction. It was concluded that the quality of the crude oil obtained from the pretreated beans in terms of oxidation products, free fatty acids and nonhydratable phospholipids was such that the alkali treatment step in the refining process could be circumvented. The improved quality of the crude oil was attributed to the inactivation of phospholipase D, lipoxygenase and lipase. The residual defatted flakes showed low levels of trypsin inhibitor activity and could be used directly as food or feed.</p><p>Finally, the involvement of phospholipase D in the hydrolysis of phospholipids and formation of nonhydratable phospholipids in soybeans was elucidated by radio(chemical) methods, as well as thin layer chromatography and densitometry. The presence of an active, soluble form of the enzyme with isoelectric point 4.8 was shown by isoelectric focusing.