SOLUBILIZATION OF MIXED LINKAGE (1-]3),(1-]4)BETA-D-GLUCANS FROM BARLEY - EFFECTS OF COOKING AND DIGESTION

The extractability behaviour of mixed linkage beta-glucans from barley has been assessed during cooking and under different regimens used fo r fibre isolation. Whilst beta-glucan extractability increased to arou nd 50% during cooking, from around 30% in the raw flour, methods used for NSP isolation resulted in even greater extractability (>60%). Enzy mic rather than chemical treatments were more important in accounting for the increased extractability. Endogenous proteases from the small intestine were shown to be capable of enhancing the extractability of the beta-glucan to a level similar to that found in ileal effluent fro m patients fed an acute barley-based diet. This is consistent with the presence of mixed linkage beta-glucans as proteoglycan complexes in b arley. The extractability of beta-glucans measured in vivo was signifi cantly higher (P < 0.001) than that measured in the original barley bu t without protease treatment. Thus, not only do 'unextractable' beta-g lucans from barley have the potential to behave as a source of soluble NSP but the fibre matrix can be modified during transit in the upper gut. Hence the amount of soluble fibre present during gut transit can differ significantly from that measured in foods. This has implication s for assessing the mechanism(s) involved in determining the response to fibre in the diet. It is important to take account of modifications to the fibre matrix when assessing the dietary response to a fibre so urce. (C) 1997 Academic Press Limited.