Changes in chemical composition of rapeseed meal during storage, influencing nutritional value of its protein and lipid fractions

Abstract

The aim of the study was to analyse the quality changes in rapeseed meal (RSM) in the presence of oxygen and water vapour at elevated temperature. The chemical composition of fresh and after storage (30 days at 40 °C and 80% relative humidity) samples of RSM was determined. In comparison with fresh samples significant differences in the meal after storage in the content of true protein (35.7 vs 37.5% DM), crude fat (6.8 vs 7.5% DM), crude fibre (11.5 vs 10.6% DM), methionine (7.7 vs 8.2 g · kg-1 DM), cysteine (8.2 vs 8.9 g · kg-1 DM) and arginine, histidine, aspartic acid, glutamic acid, tannic acid and phytic phosphorus were observed. After storage, the content of butyric, caproic, caprylic and palmitoleic acids increased, while concentration of lauric, stearic and oleic acids decreased. Proportion of saturated fatty acids in total fatty acids raised (19.7 vs 14.3%) and that of unsaturated fatty acids declined (80.3 vs 85.7%). The storage had influence on acid and peroxide values of oil, increasing them to 20.9 mg KOH · g-1 and 27.08 meq · kg-1, respectively. No significant differences in the content of starch, sugar, some amino acids (including lysine) and polyunsaturated fatty acids in fresh and post-storage meal were noticed. Aflatoxins B1, B2, G1, G2 and ochratoxin A were not detected after storage. It can be concluded that storage conditions affect adversely the quality of RSM having the moisture content only slightly above the recommendation (12.7 vs 12.5%) and simultaneously changing significantly its protein and lipid profiles.