Effects of extrusion and traditional processing methods on antinutrients and in vitro digestibility of protein and starch in faba and kidney beans

Abstract

Comparative effects of extrusion cooking and conventional processing methods on protein content and reduction of antinutritional factor (phytic acid, condensed tannins, polyphenols, trypsin, chymotrypsin, α-amylase inhibitors and haemagglutinating activity) levels in Vicia faba and Phaseolus vulgaris seeds were studied. In vitro protein and starch digestibilities were assessed. P. vulgaris seeds showed highest levels of condensed tannins, chymotrypsin and α-amylase inhibitory activities and haemagglutinating activity. Dehulling significantly increased protein content and greatly reduced condensed tannin and polyphenol levels in both legumes. Extrusion was the best method to abolish trypsin, chymotrypsin, α-amylase inhibitors and haemagglutinating activity without modifying protein content. Furthermore, this thermal treatment was most effective in improving protein and starch digestibilities when compared with dehulling, soaking and germination.

Introduction

Food legumes are characterised by a relatively large content of proteins and carbohydrates. In general, pulses also contain significant amounts of crude fibre, lipids, minerals and vitamins.

In recent years, many compounds from food legumes have been shown to cause physiological and biochemical effects, such as pancreas enlargement and growth inhibition in various species of animal (Grant, 1989, Liener, 1989, Guen, Le and Birk, 1993). These compounds include phytic acid, condensed tannins, polyphenols, protease inhibitors (trypsin and chymotrypsin), α-amylase inhibitors and lectins. Moreover, the digestibility of legume protein and legume starch is limited by the presence of antinutrients (Nielsen, 1991, Lajolo, Filho, Menezes, 1991, Yadau, Khetarpaul, 1994) and the utilisation of pulses in both human and animal nutrition is restricted by the presence of the aforementioned factors.

A wide range of processing techniques could improve the protein and starch digestibilities of legumes and therefore their utilisation (Conan and Carre, 1989, Van der Poel, 1990, Gujska and Khan, 1991, Frias, Diaz-Pollan, Hedley and Vidal-Valverde, 1995, Wang, Lewis, Brennan and Westby, 1977, Alonso, Orue and Marzo, 1998). However, it is known that certain treatments, such as heat processing, could produce, in some conditions, physicochemical changes in proteins, starch and in the other components of legume seeds affecting their final nutritional properties (Jeunink and Cheftel, 1979, Della Valle, Quillien and Gueguen, 1994).

The aim of this work was to study the efficiency of processing methods on reduction or elimination of Vicia faba and Phaseolus vulgaris antinutritional factors in order to improve nutritional value of these sources. In addition, the relation of each treatment application to in vitro protein digestibility and, in vitro starch digestibility has been assessed. A special emphasis has been placed on extrusion-cooking as a versatile, quick and efficient method to reduce antinutrients when compared with other traditional processing methods.