Effect of steam processing temperature and time on the protein nutritional value of Phaseolus vulgaris beans for swine

Piglets with an average initial weight of 20 kg, fitted with a T-shaped post-valvular caecum (PVTC) cannula were used to determine the effect on apparent ileal digestibility of nitrogen (N) and lysine of inclusion in the diet of beans processed under different conditions. In Experiment 1 the effect of steam heating under atmospheric conditions (102°C) for 20, 40, 60 and 80 min, respectively, was investigated. Experiment 2 comprised six treatments: beans steam heated at 102°C for 60 min; at 119°C for 5 min; at 136°C for 1.5 min and inclusion at 10 and 20% into the piglets' diets, respectively. Intact animals were used to determine faecal digestibility values. Ileal digestibility (ID) of nitrogen of the beans was increased but was similar for beans steam heated at 102°C for periods > 20 min (ID approximately 30%) and those steam heated for 20 min (ID approximately zero: Experiment 1). The effects on the ileal digestibility of lysine also showed a linear plateau relationship although absolute values were higher. Short-term processing at higher temperatures distinctly improved the ileal digestibility of dry matter, N and lysine. Values for ID of beans steam heated at 136°C for 1.5 min were 78% and 76% for N and lysine, respectively (Experiment 2). With the exception of the nitrogen digestibility of diets with beans processed at 102°C, ileal as well as faecal digestibility coefficients of nitrogen and lysine at 20% inclusion level were not different (P > 0.05) from an inclusion of beans at 10%. It is concluded that after elimination of antinutritional factors in beans there still remains a beneficial effect of high-temperature processing on protein/amino acid digestibility