Solubilisation of Mixed Linkage (1→3), (1→4)β-D-glucans From Barley: Effects of Cooking and Digestion

The extractability behaviour of mixed linkage β-glucans from barley has been assessed during cooking and under different regimens used for fibre isolation. Whilst β-glucan extractability increased to around 50% during cooking, from around 30% in the raw flour, methods used for NSP isolation resulted in even greater extractability (>60%). Enzymic 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 β-glucan to a level similar to that found in ileal effluent from patients fed an acute barley-based diet. This is consistent with the presence of mixed linkage β-glucans as proteoglycan complexes in barley. The extractability of β-glucans measuredin vivowas significantly higher (P<0·001) than that measured in the original barley but without protease treatment. Thus, not only do «unextractable» β-glucans 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 implications 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 source.