Biochemical approach of protein digestion in chickens

International audienc

Characterisation and foaming properties of hydrolysates derived from rapeseed isolate

Two hydrolysis methods used to obtain rapeseed isolate derivates were compared: chemical hydrolysis performed under alkaline conditions and pepsic proteolysis performed under acidic conditions. The mean molecular weights obtained for the hydrolysates varied from 26 to 2.5 kDa, depending on the level of hydrolysis. Further characterisation showed that, at the same level of hydrolysis, the chemical hydrolysates differed by their charges and hydrophobicity from those derived from enzymatic digestion. Analysis of the foaming properties showed, for both cases, that a limited degree of hydrolysis, around 3%, was sufficient to optimise the foaming properties of the isolate despite the different physicochemical properties of the peptides generated. The study of foaming properties at basic, neutral and acidic pHs showed that the hydrolysate solutions yielded dense foams which drained slowly and which maintained a very stable volume under the three pH conditions tested

Impact of Particle Size Reduction and Carbohydrate-Hydrolyzing Enzyme Treatment on Protein Recovery from Rapeseed (Brassica rapa L.) Press Cake

The aims were to assess how particle size reduction and carbohydrate-hydrolyzing enzyme treatment influence protein recovery from rapeseed cold-pressed cake and to determine the effect of these pretreatments in protein extraction procedures varying in ionic strength, pH, and total solid content. Defatted press cake (median particle size 600 µm) was milled to 21-164 µm and 7 µm median particle sizes by pin disc milling and air-flow milling, respectively. The milled press cake samples were treated with a carbohydrate-hydrolyzing enzyme preparation, after which proteins were extracted in saline (pH 6) or alkaline (pH 12) buffer at 5 % solid content, or in water at 20 % solid content. Particle size reduction of the press cake did not influence enzyme action or protein yield, suggesting that protein release from the press cake is not physically limited by cell walls or internal cell structures. As an exception, protein release from the aleuronic cells appeared to be hindered by intact cell walls. Enzyme treatment improved protein recovery, more substantially when the extraction was carried out in water at 20 % solid content than in saline or alkaline conditions at 5 % solid content. The enzyme mediated its positive effect most probably by reducing the water holding capacity of the press cake, thereby facilitating solid-liquid separation, and releasing anionic compounds which improved protein solubility through electrostatic stabilization. The results suggest that carbohydrate-hydrolyzing enzymes are beneficial for rapeseed protein extraction at reduced water content or when no salt or alkali is added to increase protein solubility