PROTEIN QUALITY EVALUATIONS OF COMMERCIAL RAPESEED MEALS BY CHEMICAL AND BIOLOGICAL ASSAYS

Abstract

Fourteen commercial rapeseed meals (RSM), selected from a total of 63 samples received from six rapeseed processing plants, and one sample of soybean meal (SBM) were tested for protein quality in a chick growth trial. The RSM studied consisted of six pairs, of which each pair of meals represented the meals with the highest and lowest protein solubilities in 0.2% KOH solution among samples received from each plant and one pair of RSM selected in a similar manner from among a second set of RSM samples supplied by one of the processing plants. The protein solubilities of the RSM used in the growth trial ranged from 33.9 to 72.6%. However, the protein quality of the same meals determined biologically by the total protein efficiency (TPE) method were not significantly different (P < 0.05). The TPE values of the RSM varied from 2.57 to 2.71 and were not significantly different from that of soybeam meal (2.65). These results indicate that determination of protein solubility of RSM in 0.2% KOH solution is not a suitable laboratory method of predicting the protein quality of commercial RSM. Other analyses performed on the RSM samples included determination of basic amino acid composition, available lysine content and dye-binding capacity of protein (DBCP) with Acid Orange 12. Of these analyses, only the DBCP values of the meals were found to be significant (P < 0.05) correlated with the TPE values.