ABSTRACT
The in vitro prebiotic effects of resistant starch (RS), prepared by different treatments from purple yam, on Bifidobacterium adolescentis (bifidobacteria for short), were investigated. Tolerance tests indicated that bifidobacteria in PDS (prepared by debranching combined with autoclaving) and PDS.H (PDS further treated by double enzyme hydrolysis) media adapted better to simulated upper gastrointestinal conditions (at pH 1.5-3.0 and 0.3% and 1.0% bile acid) than those in GLU (glucose) and DAS (prepared by autoclaving) media. PDS.H, which had the highest digestion resistibility, exhibited significant effects on the OD600 nm value (1.544) and the pH value (4.21) when the carbohydrate concentration was 20 g L-1. Additionally, the exponential growth phase of bifidobacteria was 2 h in the PDS or PDS.H media, whereas it was 4 h in the GLU or DAS media. A higher content of short-chain fatty acids (SCFAs) was obtained in the PDS.H medium. Analysis of the structural features of RS and fermented RS indicated that PDS, especially PDS.H, had a rougher surface and higher crystallinity than DAS. Fermented RS in a simulated large bowel environment showed an eroded surface and decreased crystallinity. All of these findings suggest that RS with a rough surface and perfect crystalline structure could protect bifidobacteria from gastrointestinal conditions and enhance the proliferation of bifidobacteria.