Hydrolysates of coix seed prolamins (CHPs) have an excellent hypoglycemic effect and can effectively inhibit α-glucosidase, which is the therapeutic target enzyme for type 2 diabetes mellitus. However, its hypoglycemic components and molecular mechanisms remain unclear, and its stability in food processing needs to be explored. In this study, four potential α-glucosidase inhibitory peptides (LFPSNPLA, FPCNPLV, HLPFNPQ, LLPFYPN) were identified and screened from CHPs using LC-MS/MS and virtual screening techniques. The results of molecular docking showed that the four peptides mainly inhibited α-glucosidase activity through hydrogen bonding and hydrophobic interactions, with Pro and Leu in the peptides playing important roles. In addition, CHPs can maintain good activity under high temperatures (40~100 °C) and weakly acidic or weakly alkaline conditions (pH 6.0~8.0). The addition of glucose (at 100 °C) and NaCl increased the inhibitory activity of α-glucosidase in CHPs. The addition of metal ions significantly decreased the inhibitory activity of α-glucosidase by CHPs, and their effects varied in magnitude with Cu²⁺ having the largest effect followed by Zn²⁺, Fe³⁺, K⁺, Mg²⁺, and Ca²⁺. These results further highlight the potential of CHPs as a foodborne hypoglycemic ingredient, providing a theoretical basis for the application of CHPs in the healthy food industry.

The self-assembled structures of coix seeds affected the enzymatic efficiency and doesn't facilitate the release of more active peptides. The influence of heating combined with ultrasound pretreatment (HT + US) on the structure, enzymatic properties and hydrolysates (CHPs) of coix seed prolamin was investigated. Results showed that the structural of coix seed prolamins has changed after HT + US, including increased surface hydrophobicity, reduced α-helix and random coil content, and a decrease in particle size. So that, leads to changes in thermodynamic parameters such as an increase in the reaction rate constant and a decrease in activation energy, enthalpy and enthalpy. The fractions of <1000 Da, degree of hydrolysis and α-glucosidase inhibitory were increased in the HT + US group compared to single pretreatment by 0.68%-17.34%, 12.69%-34.43% and 30.00%-53.46%. The peptide content and α-glucosidase inhibitory activity of CHPs could be maintained at 72.21 % and 57.97 % of the initial raw materials after in vitro digestion. Thus, the findings indicate that HT + US provides a feasible and efficient approach to can effectively enhance the enzymatic hydrolysis efficiency and hypoglycaemic efficacy of CHPs.

Dipeptidyl peptidase-IV (DPP-IV) is a key target for the treatment of type 2 diabetes mellitus. It is possible that peptides that precisely regulate DPP-IV could be released from coix seed prolamins (CSP), but whether this happens has not yet been investigated. We performed the in silico digestion of CSP and predicted the bioactivity, absorption, transport, toxicity, and allergenicity of the resulting peptides. The simulation predicted that 47 non-toxic bioactive peptides would be released. After screening these, we found that 64.58% of them could possess DPP-IV inhibitory activity. The effect of thermal processing on the amino acid composition and structural properties of CSP was determined, and the DPP-IV inhibitory activity of its digestion-derived peptides was also assessed. The results showed that processing could change the flavour of coix seed and the supply of amino acids. After processing, the spatial conformation of CSP changed from ordered to disordered, and the peptide content and the DPP-IV inhibitory activity of its digestion products significantly increased by 19.89–30.91% and 36.84–42.02%, respectively. These results support the hypothesis that processing can change the protein structure and increase the probability that bioactive peptides will be released. They also have important implications for the development of bioactive peptides and the intensive processing of coix seeds.

Previous studies have demonstrated that enzymatically prepared coix seed prolamin hydrolysates (CHPs) contain several bioactive peptides that efficiently inhibit the activity of target enzymes (α-glucosidase and dipeptidyl kinase-IV) in type 2 diabetes mellitus (T2DM). However, the anti-T2DM effects and potential mechanisms of CHPs as a whole in vivo have not yet been systematically explored. Therefore, we evaluated the preventive, therapeutic, and modifying effects of CHPs on T2DM by combining physiological and liver transcriptomics with a T2DM mouse model. The results showed that sustained high-fructose intake led to prediabetic symptoms in mice, with abnormal fluctuations in blood glucose and blood lipid levels. Intervention with CPHs effectively prevented weight loss; regulated abnormal changes in blood glucose; improved impaired glucose tolerance; inhibited the abnormal expression of total cholesterol, triglycerides, and low-density lipoproteins; alleviated insulin resistance; and restored pancreatic islet tissue function in mice fed a high-fructose diet. In addition, we found that CHPs also play a palliative role in the loss of liver function and protect various organ tissues (including the liver, kidneys, pancreas, and heart), and are effective in preventing damage to the liver and pancreatic islet cells. We also found that the intake of CHPs reversed the abnormally altered hepatic gene profile in model mice and identified 381 differentially expressed genes that could serve as key genes for preventing the development of T2DM, which are highly correlated with multiple glycolipid metabolic pathways. We demonstrated that CHPs play a positive role in the normal functioning of the insulin signalling pathway dominated by the IRS-1/PI3K/AKT (insulin receptor substrates-1/phosphoinositide 3-kinase/protein kinase B) pathway. In summary, CHPs can be used as effective food-borne glucose-modifying components of healthy foods.