PHYSICOCHEMICAL STUDIES USING AMYLOSE AS AN IN-VITRO MODEL FOR RESISTANT STARCH

The effects of hydrolysing amylose gels and films with porcine pancrea tic alpha-amylase were studied in order to construct an in vitro model of resistant starch. Both gels and films proved to be partially resis tant to hydrolysis, their susceptibility decreasing with increasing su bstrate concentration. Storage of gels for 1 day resulted in levels of crystallinity from 6 to 12%. Hydrolysis of these gels produced signif icant increases (from 272 to 557%) in crystallinity in all cases. The amount of resistant material remaining after hydrolysis increased (fro m 33% to 50%)with increasing gel concentration. Storage of amylose gel s for 7 days resulted in levels of crystallinity of 28 to 35%. Hydroly sis of these gels led to increases in crystallinity, but to a lesser e xtent (from 148 to 175%) than before. The amount of resistant material remaining after hydrolysis increased (from 41 to 50%) with increasing gel concentration. Size-exclusion chromatography of resistant materia l from hydrolysed films indicated the presence of a high molecular wei ght component corresponding to undigested amylose, in addition to a lo w molecular weight component corresponding to partially digested amylo se. Chromatograms of resistant material from both gels stored for 1 da y and those stored for 7 days were almost identical and contained only a low molecular weight component with no sign of undigested amylose. X-ray line-broadening analysis showed the average sizes of the crystal lites in the resistant material produced by hydrolysis of gels stored for both 1 day and 7 days to be approximately equal. The ability of th e enzyme to diffuse into its substrate played a major part in the resi stance to hydrolysis of amylose films, but had a much less important r ole in the resistance of gels. Not only crystalline, but also amorphou s portions of amylose gels, were found to be resistant to enzymic hydr olysis. The resistant portion of amylose gels was modelled in vitro wi th a view to explaining the structure of resistant starch in vivo.