The Effect of Lactic Acid Bacteria Fermentation on the Anti-Diabetic Activity of Pumpkin Puree

The purpose of this study was to evaluate the effects of multi-strain lactic acid bacteria (LAB) fermentation on the functional and antidiabetic properties of pumpkin (Cucurbita moschata) puree using integrated physicochemical, biochemical, and cellular analyses. Fermentation induced significant (p < 0.05) physiochemical changes, including a decrease in pH from 6.2 to 6.5 to 3.5-3.6, increased titratable acidity, and higher viable cell counts, indicating active microbial fermentation. Levels of reducing and soluble sugars (glucose, fructose, sucrose, and maltose) decreased significantly due to microbial utilization during fermentation. Fermented pumpkin puree exhibited markedly enhanced antioxidant activity, with DPPH radical scavenging activity increasing from 45% in the control to 83.2%, while ABTS radical scavenging activity increased from 33% to 42%. In vitro enzyme inhibition assays demonstrated enhanced antidiabetic potential, with α-amylase inhibition increasing from 7% to 60% and α-glucosidase inhibition from 10% to 70%. Moreover, glucose uptake in insulin-resistant L6 myotubes was significantly enhanced, indicating improved cellular glucose utilization. HPLC analysis revealed significant enrichment of phenolic compounds, particularly trans-ferulic acid (3894 µg/g), gallic acid (1996 µg/g), and caffeic acid (1894 µg/g), suggesting microbial-mediated release and biotransformation of bound phenolics during fermentation. Correlation analysis showed strong positive relationships among phenolic content, antioxidant activity, and enzyme inhibition. Among the tested LAB strains, Lactobacillus plantarum and Lactobacillus paracasei competitively exhibited the highest functional and anti-diabetic properties. Overall, LAB fermentation effectively enhanced the functional and antidiabetic properties of pumpkin puree.