Effects of heat processing on soya bean fatty acids content and the lipoxygenase activity

Abstract

Effects of increased temperatures on the lipoxygenase activity and changes of soya bean fatty acids were observed in the present study. The kernels of soya bean cultivars Bosa and ZPS 015 were subjected to the treatments of extrusion, autoclaving, micronisation and microwave roasting. Depending on the technological processing procedure, the kernels were exposed to temperatures ranging from 60 to 150?C for 25 to 30 seconds during extrusion and for 30 minutes during autoclaving. The temperature that developed in the course of the microwave radiation and autoclaving did not cause statistically significant differences between oil content in heat treated and fresh kernels of soya bean. However, the oil content was higher in soya bean flakes (micronized kernels) and lower in grits than in fresh kernels. The heat treatments resulted in the significant decrease of the linolenic fatty acid content. Depending on the temperature and applied heat treatments, the content of linoleic and oleic fatty acid oscillated. High temperatures caused changes in unsaturated fatty acids with 18 carbon atoms resulting in relative increase of the stearic acid content. The lipoxygenase activity decreased in correlation with increased temperatures and the time of heating. The maximum drop of the activity was observed after kernel exposure to the extrusion and micronisation processes at the temperature of 100oC. However, a significant lipoxygenase activity increase was recorded in both studied cultivars after one-minute microwave heating, i.e. at the temperature about 60?C. A further temperature increase led to a gradual denaturation of the enzyme and therefore to its decreased activity.U ovom radu prikazani su rezultati promene aktivnosti lipoksigenaze 1 i sadrzaja masnih kiselina u sojinom zrnu pod uticajem povisene temperature. Zrno soje sorte Bosa i ZPS 015 bilo je podvrgnuto tretmanima suve i vlazne ekstruzije, autoklaviranju, mikronizaciji i przenju u mikrotalasnoj peci. U zavisnosti od tehnoloskog tretmana prerade zrno je bilo izlozeno dejstvu povisene temperature od 60 do 150?C u trajanju od svega 25 do 30 sekundi pri ekstruziji do 30 minuta pri autoklaviranju. Povisena temperatura tokom mikrotalasnog przenja i autoklaviranja nije uticala na sadrzaj ulja u sojinom zrnu. Medjutim, u sojinim flekicama sadrzaj ulja bio je visi, a u grizu nizi od sadrzaja u sirovom sojinom zrnu. Primenjeni termicki tretmani prerade uticali su na znacajno smanjenje sadrzaja linolenske kiseline u ulju sojinog zrna. U zavisnosti od temperature, kao i vrste termickog tretmana sadrzaj linolne i oleinske kiseline u preradjenom sojinom zrnu je varirao. Povisena temperatura uslovila je promene nezasicenih masnih kiselina sa 18 ugljenikovih atoma rezultirajuci povecanje sadrzaja stearinske kiseline. Prema nasim rezultatima aktivnost lipoksiganaze je opadala sa povecanjem temperature i produzenjem tretmana prerade. Maksimalan pad aktivnosti lipoksigenaze utvrdjen je vec nakon izlaganja zrna temperaturi od 100oC tokom ekstruzije i mikronizacije. Medjutim, nakom jednog minuta przenja zrna u mikrotalasnoj peci (60?C) aktivnost lipoksigenaze je bila visa u odnosu na aktivnost u sirovom zrnu. Daljim produzenjem tretmana, a time i povecanjem temperature doslo je do postepene denaturacije enzima i smanjenja aktivnosti. PR Projekat Ministarstva nauke Republike Srbije, br. TR-20114