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.

Tannins are the most abundant phenolic compounds after cellulose, hemicellulose, and lignin. Condensed tannins are one class of tannins with diverse functional activities, such as hemostatic and wound healing, anti-inflammatory and anti-allergic behavior. There is a key research topic in the field of plant polyphenols. Banana peel is one of the main by-products of the banana processing industry, which is usually used as animal feed or directly landfilled with a low utilization rate of the functional components. In fact, banana peel can contain many active ingredients, such as condensed tannins. Previous research has been widely used to optimize the extraction parameters for condensed tannins of banana peel. The structural analysis has been conducted to demonstrate their antioxidant, inhibition of Escherichia coli, and anti-hyperglycemic effects. However, the extracted condensed tannins of banana peel are required for purification. Few purification studies have been carried out at present. In this study, macroporous resins were used to purify the condensed tannins of banana peel. A comparison was made on the static adsorption and desorption performance of six macroporous resins. The most suitable resin was selected in this case. Kinetic models, adsorption isotherm, and thermodynamic parameters were then used to analyze the adsorption properties of macroporous resins. A systematic investigation was implemented to clarify the effects of loading concentration, loading flow rate, and volume on adsorption efficiency, as well as the effects of ethanol concentration, elution flow rate, and volume on desorption efficiency. The results showed that the HP-20 macroporous resin shared a high adsorption rate (87.47%) and desorption rate (84.12%), indicating the best purification for the condensed tannins of banana peel. The adsorption kinetics curve demonstrated that the adsorption capacity of tannin on HP-20 resin sharply increased within the first 4 h, thus reaching the maximum adsorption capacity in 8 h, and then maintaining the stability. The desorption kinetics proved that the desorption was essentially realized within 5 h, with a desorption rate of 92.87%. The adsorption curve was fitted to the pseudo-second-order kinetics (R²=0.997 2). Additionally, the adsorption isotherm experiment confirmed that the adsorption of banana peel condensed tannins by HP-20 resin increased, as the temperature raised. Therefore, the higher temperature was favored to the adsorption. The adsorption isotherms curves were fitted using thermodynamic equations. Freundlich thermodynamic model was suitable for the adsorption behavior of banana peel condensed tannins on HP-20, indicating multilayer sorption on a heterogeneous surface. The K_F of the Freundlich model increased with the increasing temperature, indicating that the higher temperature was favorable for the adsorption. In both the Langmuir and Temkin models, the parameters R_L and K_T were used to predict the adsorption from different perspectives. The computed value of R_L was less than 1, indicating the favorable adsorption of banana peel condensed tannins onto HP-20 resins. Additionally, K_T increased with temperature rising. Consequently, there was a stronger binding energy between condensed tannins and the resin, resulting in a tighter association between them, as temperature increased. Moreover, the thermodynamic parameter was ΔG<0, ΔH=5.13 kJ/mol, ΔS=47.28 J/mol·K. Therefore, the adsorption process was spontaneous and endothermic, with an increased randomness and dominant physisorption. The optimal conditions for purification were determined as the sample concentration of 6 mg/mL, ethanol concentration of 70%, and loading flow rate of 1.5 mL/min, for loading and elution, using volumes of 200 and 120 mL. The purity of banana peel condensed tannins increased from 5.79% to 68.44%. The HP-20 resin and purification conditions were effectively improved for the purity of banana peel condensed tannins.