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

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.

Protein digestive dynamics of meat and bone meals in broiler chickens

This study determined the variations in protein digestibilities and digestion rates in broiler chickens offered diets containing 7 different meat and bone meals(MBM).A total of 252 male Ross 308 broiler chickens were offered 7 atypical diets largely based on maize and MBM from 24 to 28 d post-hatch.Each experimental diet was offered to 6 replicates with 6 birds per replicate cage.Excreta were collected in their entirety from 25 to 27 d post-hatch and on 28 d post-hatch.Digesta samples were collected from the proximal jejunum,distal jejunum,proximal ileum and distal ileum.Apparent digestibilities of protein were determined in each segment and apparent digestibilities of amino acids were measured in the distal ileum.There were significant differences in apparent protein digestibility coefficients in the proximal jejunum(P=0.006),where broiler chickens offered the high ash beef meal(diet 7)generated the lowest protein digestibility in the proximal jejunum(0.318).Similarly,there were significant differences in apparent digestibility coefficients in the distal jejunum(P<0.001)and distal ileum(P<0.001)but not in the proximal ileum.More pronounced differences were found in the disappearance rate of protein and there were significant differences in all 4 segments of the small intestine(P<0.001).Broiler chickens offered the high ash beef meal had the lowest protein disappearance rate(P<0.001).No difference was observed in the predicted protein digestion rate(P=0.486)but chickens offered the high ash beef meal had the lowest potential digestible protein(0.662,P=0.034)whereas the highest potential digestible protein(0.739)was detected in diet 5(containing a beef meal).This study contributed to the establishment of a preliminary database to include digestion rates of starch and protein into practical diet formulation.