Physical and chemical changes of rapeseed meal proteins during toasting and their effects on in vitro digestibility

Sergio Salazar-Villanea; Erik M A M Bruininx; Harry Gruppen; Wouter H Hendriks; Patrick Carré; Alain Quinsac; Antonius F B van der Poel

doi:10.1186/s40104-016-0120-x

Physical and chemical changes of rapeseed meal proteins during toasting and their effects on in vitro digestibility

J Anim Sci Biotechnol. 2016 Oct 18:7:62. doi: 10.1186/s40104-016-0120-x. eCollection 2016.

Authors

Sergio Salazar-Villanea¹, Erik M A M Bruininx², Harry Gruppen³, Wouter H Hendriks⁴, Patrick Carré⁵, Alain Quinsac⁶, Antonius F B van der Poel⁴

Affiliations

¹ Wageningen Livestock Research, P.O. Box 338, 6700 AH Wageningen, The Netherlands ; Animal Nutrition Group, Wageningen University & Research, P.O. Box 338, 6700 AH Wageningen, The Netherlands.
² Animal Nutrition Group, Wageningen University & Research, P.O. Box 338, 6700 AH Wageningen, The Netherlands ; Agrifirm Innovation Center, Royal Dutch Agrifirm Group, P.O. Box 20018, 7302 HA Apeldoorn, The Netherlands.
³ Laboratory of Food Chemistry, Wageningen University & Research, P.O. Box 17, 6700 AA Wageningen, The Netherlands.
⁴ Animal Nutrition Group, Wageningen University & Research, P.O. Box 338, 6700 AH Wageningen, The Netherlands.
⁵ CREOL/OLEAD, 11 rue Monge, Parc Industriel, 33600 Pessac, France.
⁶ Terres Inovia, 11 rue Monge, Parc Industriel, 33600 Pessac, France.

Abstract

Background: Toasting during the production of rapeseed meal (RSM) decreases ileal crude protein (CP) and amino acid (AA) digestibility. The mechanisms that determine the decrease in digestibility have not been fully elucidated. A high protein quality, low-denatured, RSM was produced and toasted up to 120 min, with samples taken every 20 min. The aim of this study was to characterize secondary structure and chemical changes of proteins and glucosinolates occurring during toasting of RSM and the effects on its in vitro CP digestibility.

Results: The decrease in protein solubility and the increase of intermolecular β-sheets with increasing toasting time were indications of protein aggregation. The contents of NDF and ADIN increased with increasing toasting time. Contents of arginine, lysine and O-methylisourea reactive lysine (OMIU-RL) linearly decreased with increasing toasting time, with a larger decrease of OMIU-RL than lysine. First-order reactions calculated from the measured parameters show that glucosinolates were degraded faster than lysine, OMIU-RL and arginine and that physical changes to proteins seem to occur before chemical changes during toasting. Despite the drastic physical and chemical changes noticed on the proteins, the coefficient of in vitro CP digestibility ranged from 0.776 to 0.750 and there were no effects on the extent of protein hydrolysis after 120 min. In contrast, the rate of protein hydrolysis linearly decreased with increasing toasting time, which was largely correlated to the decrease in protein solubility, lysine and OMIU-RL observed. Rate of protein hydrolysis was more than 2-fold higher for the untoasted RSM compared to the 120 min toasted material.

Conclusions: Increasing the toasting time for the production of RSM causes physical and chemical changes to the proteins that decrease the rate of protein hydrolysis. The observed decrease in the rate of protein hydrolysis could impact protein digestion and utilization.

Keywords: Hydrolysis rate; In vitro protein digestibility; Rapeseed meal; Reactive lysine; Secondary structure.