EFFECTS OF HEAT PROCESSING ON SOYA BEAN FATTY ACIDS CONTENT AND THE LIPOXYGENASE ACTIVITY

Effects of increased temperatures on the lipoxygenase activity andchanges of soya bean fatty acids were observed in the present study. The kernelsof soya bean cultivars Bosa and ZPS 015 were subjected to the treatments ofextrusion, autoclaving, micronisation and microwave roasting. Depending on thetechnological processing procedure, the kernels were exposed to temperaturesranging from 60 to 150oC for 25 to 30 seconds during extrusion and for 30 minutesduring autoclaving. The temperature that developed in the course of the microwaveradiation and autoclaving did not cause statistically significant differences betweenoil content in heat treated and fresh kernels of soya bean. However, the oil contentwas higher in soya bean flakes (micronized kernels) and lower in grits than in freshkernels. The heat treatments resulted in the significant decrease of the linolenic fattyacid content. Depending on the temperature and applied heat treatments, the contentof linoleic and oleic fatty acid oscillated. High temperatures caused changes inunsaturated fatty acids with 18 carbon atoms resulting in relative increase of thestearic acid content. The lipoxygenase activity decreased in correlation witincreased temperatures and the time of heating. The maximum drop of the activitywas observed after kernel exposure to the extrusion and micronisation processes atthe temperature of 100oC. However, a significant lipoxygenase activity increasewas recorded in both studied cultivars after one-minute microwave heating, i.e. atthe temperature about 60oC. A further temperature increase led to a gradualdenaturation of the enzyme and therefore to its decreased activity