Julieta Torres

The impact of heating and soaking on the in vitro enzymatic hydrolysis of protein varies in different species of tropical legumes

The effects of different thermal (raw, autoclaving or boiling for 5 and 20min) and soaking (with or without) treatments on the degree of hydrolysis (DH) of protein were investigated for selected legumes (Canavalia brasiliensis; Lablab purpureus; pink, red and white colour hulls Vigna unguiculata). Each legume preparation underwent in vitro simulated gastrointestinal tract digestion comprising either pepsin (120min) or pepsin/pancreatin (120/240min) digestion. The DH was determined based on the amount of free amino groups released. Autoclaving for 5min increased the pepsin/pancreatin DH for all the unsoaked and soaked legumes (+20% to 46% units) except Canavalia, while boiling for 5min only increased DH for two soaked legumes (+12% to 28% units). Extending boiling from 5 to 20min increased the DH for three soaked legumes (+5% to 29% units). In conclusion, autoclaving, in general, extensively increased the sequential pepsin/pancreatin DH, while boiling only increased it for selected legumes.

Characterization of the nutritive value of tropical legume grains as alternative ingredients for small-scale pork producers using in vitro enzymatic hydrolysis and fermentation*

In the tropic, the small-scale pork production is negatively influenced by the low availability of high protein ingredients. The study aimed to compare the protein and starch hydrolysis as well as fibre fermentation of five tropical legume grains (Canavalia brasiliensis, CB; Lablab purpureus, LP; Vigna unguiculata, white WVU; pink PVU and red RVU) and a control (extruded full-fat soybean (SB)), using an in vitro model that simulated digestion in the gastrointestinal tract of pigs. A sequential in vitro hydrolysis was carried out with pepsin (120 min) and pancreatin (240 min) to determine the degree of hydrolysis (DH) of protein and starch. The indigestible residue was fermented in vitro with pig faecal inoculum to compare the modelled kinetics of gas production over 72 h and the production of short-chain fatty acids (SCFA). After 360 min of pepsin-pancreatin hydrolysis, SB and WVU had the highest protein hydrolysis (76% and 66%) and PVU and WVU the highest starch hydrolysis (70% and 64%) (p < 0.01). The in vitro fermentation of the indigestible residue of WVU resulted in the highest (482 ml/g DM; p < 0.001) and CB the lowest (335 ml/g DM) gas production. These data were consistent with the SCFA production. Butyrate, propionate and total SCFA were higher (or tended) for RVU and WVU when compared with CB and SB (p = 0.015-0.085). In conclusion, the high DH of protein and starch as well as the high gas and SCFA production obtained with raw WVU makes it an interesting alternative to SB as a feedstuff for swine nutrition in the tropic. Other legume grains (LP and CB) cannot be used by pigs in their raw form.

In vitro digestion of tropical legume starch is influenced by the combination of heating and soaking treatments

Raw legumes have in general low starch digestion, which limits their use in animal nutrition. This study aimed to determine the effect of different thermal (raw, autoclaving and boiling for 5 and 20 min) and soaking (without or with) treatments on the in vitro degree of hydrolysis (DH) of starch for selected grains of tropical legumes (Canavalia brasiliensis, CB; Lablab purpureus, LP; pink, red and white colour hulls Vigna unguiculata, PVU, RVU and WVU). Indigested residues collected after in vitro sequential pepsin-pancreatin (120–240 min) digestion were used to determine the starch DH and the estimated digestible starch content. The starch content was in general higher when the legumes were treated (e.g. autoclaving increased 28% the starch content of CB). Autoclaving and boiling for 5 min increased the DH for both unsoaked and soaked CB and RVU (+6–16% units), whereas they reduced the DH for unsoaked boiled LP, PVU, WVU and unsoaked autoclaved LP (P 0.05). Similar trends were observed for the estimated digestible starch content, despite the changes in starch content. In conclusion, the effect of soaking and heating treatment combinations on the DH of starch and estimated digestible starch content varied among legumes. Conditions for starch determination may be adapted for legumes.