Effects of lactic acid bacteria fermentation on chemical compounds, antioxidant capacities and hypoglycemic properties of pumpkin juice

The purpose of this research was to screen strains to ferment pumpkin juice with excellent flavor and biological activities by the comparison of 5 species of lactic acid bacteria (LAB) strains, namely Lacticaseibacillus casei (Lc), Lactiplantibacillus plantarum (Lp), Lactobacillus acidophilus (La), Lactobacillus helveticus (Lh) and Lacticaseibacillus paracasei (Lpc). The pumpkin juice inoculated with LAB was fermented at 37 °C for 48 h. Viable cell counts were all above 7.92 log CFU/mL, implicating that pumpkin juice was a favorable matrix for LAB. The contents of reducing sugars and total sugars contents obviously declined at the end of fermentation. LAB strains utilized mainly fructose, surcose and glucose for fermentation. Lpc fermented pumpkin juice showed the most abundant organic acid. Furthermore, the strongest DPPH and hydroxyl radical scavenging capacities were observed in Lp, La and Lh, which were positively associated with vanillic acid and sinapic acid contents. There were 30 new volatile compounds that appeared after fermentation, including 8 of ketones and alcohols, 5 esters and so on. The highest sensory scores could be found in La and Lh primarily due to their rich volatile compounds. LAB fermentation was beneficial to inhibiting α-glucosidase and α-amylase activities. In conclusion, La and Lh were more suitable to develop into a functional beverage with pleasant flavor.