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The antifungal effect of metabolites produced by a new strain of Lactiplantibacillus (Lpb.) plantarum LPP703, isolated from naturally fermented yak yogurt, was investigated. The results showed that Lpb. plantarum LPP703 significantly inhibited four fungal species, including Penicillium sp., Rhizopus delemar, Aspergillus flavus, and Aspergillus niger. The metabolites produced after 20 h of Lpb. plantarum LPP703 fermentation showed the highest antifungal activity against Penicillium sp. Compared with the control group, the Lpb. plantarum LPP703 metabolites-treated Penicillium sp. spores were stained red by propidium iodide, indicating that the cell membrane of the fungal spores was damaged. Moreover, the antifungal effect of the Lpb. plantarum LPP703 metabolites on Penicillium sp. was not changed after heating or treatment with various proteases, but showed a sharp decrease when the pH value was regulated to 5.0 or above. The oleamide, trans-cinnamic acid, and citric acid were the three most abundant in the Lpb. plantarum LPP703 metabolites. Molecular docking predicated that the oleamide interacted with the active site of lanosterol 14-alpha-demethylase (CYP51, a crucial enzyme for fungal membrane integrity) through hydrogen bonds and had the lowest docking score, representing the strongest binding affinity to CYP51. Taken together, the metabolites from a new strain of Lpb. plantarum, LPP703, had potent antifungal activity against Penicillium sp., which might be associated with the damage of the active ingredient to fungal membrane integrity. This study indicated that Lpb. plantarum LPP703 and its metabolites might act as biological control agents to prevent fungal growth in the food industry.

Inhibition of dipeptidyl peptidase-4 (DPP-4) is an effective way to control blood glucose in diabetic patients. Tenebrio (T.) molitor is an edible insect containing abundant protein. T. molitor protein-derived peptides can suppress the DPP-4 activity. However, the amino acid sequence and binding mechanism of these DPP-4 inhibitory peptides remain unclear. This study used the flavourzyme for T. molitor protein hydrolysis, identified the released peptides with DPP-4 inhibitory effect, and investigated the binding interactions of these peptides with DPP-4. The results showed that flavourzyme efficiently hydrolyzed the T. molitor protein, as demonstrated by the high degree of hydrolysis, disappearance of protein bands in SDS-PAGE, and changes to protein structure. The 4-h flavourzyme hydrolysates showed a good inhibitory effect on DPP-4 (IC50 value of 1.64 mg/mL). The fragment of 1000–3000 Da accounted for 10.39% of the total peptides, but showed the strongest inhibitory effect on DPP-4. The peptides LPDQWDWR and APPDGGFWEWGD were identified from this fraction, and their IC50 values against DPP-4 were 0.15 and 1.03 mg/mL, respectively. Molecular docking showed that these two peptides interacted with the DPP-4 active site via hydrogen bonding, hydrophobic interactions, salt bridge formation, π-cation interactions, and π-π stacking. Our findings indicated that T. molitor protein-derived peptides could be used as natural DPP-4 inhibitors.