Effect of fractionated lotus seed resistant starch on proliferation of Bifidobacterium longum and Lactobacillus delbrueckii subsp. bulgaricus and its structural changes following fermentation

•The fractions, especially LRS3-20%, promoted the proliferation of the probiotics.•B. longum produced large acetic acid, while L. delbrueckii produced lactic acid.•RS enhanced the tolerance of probiotics to adverse gastrointestinal media.•The fractions underwent structural changes after fermentation by ESEM, XRD, FT-IR.•The changes were related to original structures and utilisation by the probiotics. The aim of this study was to investigate the proliferation effect of fractionated lotus seed resistant starch (LRS3-20%, LRS3-30%) and the structural changes following fermentation. Fractionated lotus seed resistant starch, especially LRS3-20%, promoted the proliferation of these probiotics, and Bifidobacterium longum produced large quantities of acetic acid, while Lactobacillus delbrueckii subsp. bulgaricus produced lactic acid. Additionally, the probiotics with lotus seed resistant starch (LRS3) and LRS3-20% survived more successfully in simulated gastrointestinal solutions compared to glucose, LRS3-30% and high amylose maize starch, but LRS3 and LRS3-20% differed in their abilities to enhance the tolerance to acidic buffer, bile acid and simulated gastric juice. Furthermore, after fermentation, fractionated lotus seed resistant starch displayed a loose, rough surface. The crystalline and double helical structure increased as the amount of amorphous and sub-crystalline structure reduced following fermentation. Interestingly, structural changes were correlated with the original structures and utilisation by the probiotics.