Synbiotics are combinations of probiotics and prebiotics. It has been shown to be beneficial to aquatic animals. In this study, Lactobacillus rhamnosus was cultured with different prebiotics as the sole carbon source, including inulin, acanthopanax senticosus polysaccharide (ASPS), chitosan oligosaccharide (COS), saposhnikovia divaricata polysaccharide (SDP), polysaccharide of atractylodes macrocephala koidz (PAMK), astragalus polysaccharides (APS), Yu-Ping-Feng polysaccharide (YPFP), xylooligosaccharides (XOS) and mannose (MAN). Screening and gradient experiments revealed that the suitable prebiotics and concentrations were: 2 % MAN, 3 % APS, 3 % YPFP, 4 % PAMK, 3 % SDP. L. rhamnosus (108 CFU/mL) and suitable prebiotics were inoculated into the media supplemented with the intestinal chyme of Macrobrachium rosenbergii. Based on the preliminary screening experiment with the gradients. The in vitro fermentation experiment comprised seven groups: a control group (CT); L. rhamnosus group (LGG); L. rhamnosus + 2 % MAN group (LGG+MAN); L. rhamnosus + 3 % APS group (LGG+APS); L. rhamnosus + 3 % YPFP group (LGG+YPFP); L. rhamnosus + 4 % PAMK group (LGG+PAMK); L. rhamnosus + 3 % SDP group (LGG+SDP). The in vitro fermentation results revealed that the amylase activity was significantly increased in LGG+PAMK, LGG+SDP and LGG+APS groups than in the CT group (P<0.05). The LGG+MAN group showed the highest protease activity (P<0.05), while the activity of lipase was significantly greater in the LGG and LGG+YPFP groups than in the CT group (P<0.05). Moreover, the acetic acid and valeric acid contents were significantly increased in the LGG+PAMK, LGG+YPFP and LGG+SDP groups than in the CT and LGG groups (P<0.05). Additionally, the LGG+APS, LGG+PAMK, LGG+YPFP and LGG+SDP treatments significantly decreased the abundance of Aeromonas (P<0.05). Lactobacillus was more abundant in the LGG+YPFP group than in the other groups (P<0.05). In general, based on in vitro fermentation of M. rosenbergii intestine, the combination of L. rhamnosus with 3 % YPFP is the optimal synbiotic for the prawn.
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