RESISTANCE OF THE KIDNEY BEAN RESERVE PROTEIN, PHASEOLIN, TO PROTEOLYSIS IN THE PORCINE DIGESTIVE-TRACT

Phaseolin, the major reserve protein of the seeds of the kidney bean, Phaseolus vulgaris L, was shown to be poorly degraded in the pig small intestine following an initial 7-day exposure to casein-based diets i ncorporating kidney bean meal. Substantial amounts of large polypeptid e fragments, which were recognised by antibodies raised against native phaseolin, were identified in ileal digesta. Little of this immunorea ctivity was detected in the faeces of these animals, suggesting that c omponents of the hindgut microflora were able to degrade these fragmen ts further. Prolonged exposure to dietary kidney beans resulted in an increase in the digestibility of phaseolin, suggesting that the small intestine and/or its microflora may possess significant adaptive capac ity. In-vitro digestion of purified phaseolin by a sequence of pepsin, trypsin and chymotrypsin yielded products which closely resembled tho se isolated from the ileal digesta; analysis suggested that degradatio n of native phaseolin by the major gastrointestinal endopeptidases is restricted to a vulnerable central region of its constituent polypepti des.