Fermentability of resistant starch preparations varies in vitro

Resistant starch has been regarded as a butyrogenic substrate based on in vitro and in vivo studies. However, resistant starch preparation and other physical characteristics may affect its fermentability. Using a batch in vitro fermentation system, short-chain fatty acid (SCFA) production of two preparations of resistant starch (Actistar 11700 and Actistar RT75330) were compared to known fermentable fibres: inulin and partially-hydrolysed guar gum (PHGG). Control fermentation flasks containing no added fibre were run to identify SCFAs produced from remaining substrate in the faecal inoculum. Faecal inoculum was created by pooling faecal samples from 3 healthy humans, who had not taken antibiotics within the previous six months, with distilled water and a reducing solution. Samples from the fermentation were removed at 0, 4, 8, 12, and 24 hours for SCFA analysis by GC-FID. ANOVA was used to determine statistical differences among fibres (n=2) within a time point. 11700 produced significantly greater total SCFA concentrations than RT75330 from 4 to 24 hours. RT75330 was not different than control from 8 to 24 hours. 11700 produced total SCFA concentrations similar to inulin and PHGG at 24 hours. Butyrate production followed a similar pattern, with 11700 producing significantly greater concentrations than RT75330 from 8 to 24 hours. RT75330 produced butyrate concentrations similar to control from 4 to 24 hours, while 11700 produced butyrate concentrations greater than inulin, but lower than PHGG at 12 and 24 hours. These data show that fermentability of resistant starch varies with preparation. SCFA production in this study likely varied due to starch granule conformation. Although starch granule conformation was not assessed, RT75330 likely limited bacterial enzyme accessibility while 11700 (retrograded amylose crystallites) allowed for greater accessibility. Thorough evaluation of physiological effects should precede the introduction of new variations of resistant starch, to ensure that the consumer is not misled.