In vitro fermentability of inulin and fructo‐oligosaccharides (FOS) is dependent on chain length

Abstract

Inulin and FOS are isolated from chickory root and Jerusalem artichoke for use as dietary supplements and are also consumed naturally from wheat, onions, and bananas. Inulin and FOS exert beneficial physiological effects such as fermentability, enhanced mineral absorption, improved colonic health, and improved colonic microflora. This study investigated the in vitro batch fermentability of six chain lengths of inulin and FOS (degree of polymerization (dp) 2- >20) using human fecal inoculum generated from 3 donors, as described by McBurney (1987). Samples were removed at 0, 4, 8, 12, and 24 hours, and total short-chain fatty acid (SCFA), acetate, propionate, and butyrate were measured by gas chromatography. SCFA concentrations were compared using the SAS statistical software package. For all SCFAs, individual sample chain length did not follow a clear trend with fermentability. When grouped as FOS (chain lengths <10) versus inulin (chain lengths >10), statistical differences emerged in fermentability. Total SCFA and acetate concentrations peaked at 4 hours for FOS samples, while inulin samples increased over the course of 24 hours. Propionate production by FOS was significantly greater than inulin at 12 hours. Butyrate production was significantly lower for long chain inulin (dp>20) compared to all other samples at 24 hours. Chain length has shown to be an important factor in pace of fermentation, with short chains fermenting quicker than longer chains. Long chain length resulted in low butyrate production, perhaps limiting its use for improved colonic epithelium health. Clinical studies should be conducted to determine if the in vitro fermentability transfers in vivo.