Our previous studies have shown that the nutritional properties of peanut meal after fermentation are markedly improved. In this study, in order to facilitate the further utilisation of peanut meal, we investigated the effects of its fermentation extract by Bacillus natto (FE) on cognitive ability, antioxidant activity of brain and protein expression of hippocampus of ageing rats induced by d-galactose. Seventy-two female sd rats aged 4–5 months were randomly divided into six groups: normal control group, ageing model group, FE low-dose group, FE medium-dose group, FE high-dose group and vitamin E positive control group. Morris water maze (MWM) test was performed to evaluate their effects on learning and memory ability in ageing rats. Superoxide dismutase (SOD) activity and malondialdehyde (MDA) content of brain, HE staining and the expression of γ-aminobutyric acid receptor 1 (GABABR1) and N-methyl-d-aspartic acid 2B receptor in the hippocampus of rats were measured. The results show that FE supplementation can effectively alleviate the decrease of thymus index induced by ageing, decrease the escape latency of MWM by 66·06 %, brain MDA by 28·04 %, hippocampus GABABR1 expression by 7·98 % and increase brain SOD by 63·54 % in ageing model rats. This study provides evidence for its anti-ageing effects and is a research basis for potential nutritional benefits of underutilised food by-products.

Recent studies have demonstrated that the nutritional properties of peanut meal (PM) can be improved after being fermented. The assessment of fermented PM has been reported to be limited to various physical and chemical evaluations in vitro. In the present study, PM was fermented by Bacillus natto to explore the effects of fermented PM extract (FE) on growth performance, learning and memory ability and intestinal microflora in mice. Ninety newly weaned male Kunming (KM) mice were randomly divided into seven groups: normal group (n 20), low-dose FE group (n 10), middle-dose FE group (MFE) (n 10), high-dose FE group (HFE) (n 20), unfermented extraction group (n 10), model group (10) and natural recovery group (10). Learning and memory skills were performed by the Morris water maze (MWM) test, and the variation in gut microbiota (GM) composition was assessed by 16S rDNA amplicon sequencing. The results show that HFE remarkably improved the growth performance in mice. In the MWM test, escape latency was shortened in both MFE and HFE groups, while the percentage of time, distance in target quadrant and the number crossing over the platform were significantly increased in the HFE group. Moreover, the FE played a preventive role in the dysbacteriosis of mice induced by antibiotic and increased the richness and species evenness of GM in mice.