INFLUENCE OF NATURALLY ACID-SOLUBLE PROTEINS FROM BEANS (PHASEOLUS-VULGARIS L.) ON IN-VITRO DIGESTIBILITY DETERMINATION

The in vitro digestibility of bean (Phaseolus vulgaris) protein fracti ons was studied using a pepsin-pancreatin system. Enzymatic hydrolysis was stopped by adding a strong acid and the extent of proteolysis det ermined by measurement of free amino groups in the soluble fraction. T he in vitro digestibility of bean protein fractions was low when in th e native state and was differently affected by denaturation. For phase olin, the main reserve protein, heating caused a significant increase of susceptibility to hydrolysis, whereas heat had no apparent effect o n digestibility of glutelins and albumins (II). For the PIL (protease inhibitor-lectin rich) fraction, which was shown to have a composition similar to total albumins, there was a decrease of digestibility, pro bably associated to disulfide bond formation upon heating. Results of in vitro digestibility were shown to be strongly dependent on the util ization of a sample blank to account for proteins naturally soluble in the acid used to interrupt hydrolysis, which would otherwise be estim ated as digested protein. These proteins are characterized by a high c arbohydrate content, probably responsible for their high solubility an d low digestibility. (C) 1998 Elsevier Science Ltd. All rights reserve d.