Plantain is a new banana cultivar grown in China, which is rich in resistant starch and dietary fiber. By the China Food and Drug Administration (CFDA) method for the evaluation of assisting blood sugar reduction function, the anti-hyperglycemic activity of plantain was tested. Twenty-four normal rats were arbitrarily allocated into a control group (NC) and a high-dose plantain group (NH), and 48 rats with experimental diabetes mellitus (DM) were randomized into four groups: model control, low- (LP), medium- (MP) and high- (HP)-dose plantain. The effect of plantain on glucolipid metabolism was evaluated by testing blood biochemical indices and hormone levels. Results showed that plantain had no adverse effect on normal rats and alleviates the increase of body mass in normal rats to a certain extent and that plantain intervention alleviated the typical symptoms of diabetes, polydipsia, polyphagia, polyuria and emaciation, decreased blood sugar, and improved glucose tolerance. Compared with the model control group, blood sugar levels were significantly reduced by 10.70%, 10.19% and 13.94% in the low-, middle- and high-dose plantain groups, respectively (P < 0.05). Besides, disorders of glucolipid metabolism were ameliorated. The serum concentrations of triglyceride, total cholesterol, low-density lipoprotein cholesterol and free fatty acid were decreased and so were serum insulin, C-peptide, amylin and glucagon-like peptide-1. Compared with the model control group, insulin levels were decreased by 28.54%, 39.50% and 49.14% in the low-, middle- and high-dose groups, respectively. Therefore, plantain has anti-hyperglycemic activity. It may impact glucolipid metabolism through regulating hormone secretion.

Although banana powder (BP), konjac powder (KP), resistant dextrin (RD), corn starch (CS) and L-carnitine (LC) have been reported for their anti-obesity properties, their effects on the gut microbiota and its metabolites, and the differences in anti-obesity mechanisms related to the gut microbiota are still unknown. In this study, high-throughput sequencing and high performance liquid chromatography (HPLC) were used to detect the gut microbiota profile and the amount of short-chain fatty acids (SCFAs) in the feces of high-fat diet-induced obese rats, respectively. Results showed that the probiotic genera Ruminococcus_2, Coprococcus_2 and Ruminiclostridium_5 were the main bacterial genera in the CS, BP and RD groups, respectively. Spearman correlation analysis and canonical correlation analysis (CCA) demonstrated that glucolipid metabolism parameters were related to changes in the gut microbiota. The relative contributions of soluble dietary fiber-rich diets (konjac powder and resistant dextrin) and insoluble dietary fiber (resistant starch)-rich diets (banana powder and corn starch) to producing SCFAs were equivalent, and greater than that of L-carnitine (LC). The ability of the five materials to promote the growth of probiotics and inhibit the proliferation of harmful bacteria in the gut was in the decreasing order of RD > BP > CS > KP, and the ability to increase fecal SCFAs was in the decreasing order of BP > RD > CS > KP, while LC showed little effect on the gut microbiota or SCFAs. CCA analysis showed that the degree of correlation between glucolipid metabolism parameters and the intestinal microbial community decreased in the following order: blood glucose (GLU) > high-density lipoprotein cholesterol (HDL-C) > total cholesterol (TC) > low-density lipoprotein cholesterol (LDL-C) > triacylglycerol (TG). Spearman correlation analysis showed that Ruminococcus_2 was positively correlated with butyrate content, and Escherichia. Shigella was positively correlated with the contents of acetate, butyrate and total SCFAs.

The composition of phenolics extracted from unripe banana flesh was identified using ultra-high performance liquid chromatography coupled with Q-Exactive Orbitrap mass spectrometry (UPLC-Q-Exactive Orbitrap-MS), and the inhibitory effects of banana polyphenols on α-amylase and α-glucosidase were estimated in vitro. In total, 28 compounds were identified, including 21 polyphenols such as esculetin, hyperoside, and kaempferol-3-O-glucoside, 2 organic acids, 3 ellagitannin metabolites, vanillin and coumarin. In addition, dimethyl ellagic acid and urolithin A were the major chromatographic peaks. Banana polyphenols exhibited excellent inhibitory effects on both α-amylase and α-glucosidase with half maximal inhibitory concentration (IC₅₀) of 0.53 mg/mL and 35.76 µg/mL, respectively. At concentrations of 1.0 mg/mL and 160 µg/mL, the inhibition rates of α-amylase activity and α-glucosidase were (76.25 ± 3.79)% and (92.54 ± 0.69)%, respectively. Therefore, polyphenols may be one of the active ingredients contributing to the antihypoglycemic effect of unripe bananas.