Abstract: The aim of this study was to evaluate the changes in microbial and physicochemical characteristics (acidity, pH, VC and organic acid contents and color) during the fermentation of the fruit juice of Citrus paradisi cv. Changshan Huyou by either Lactobacillus plantarum L1 or Lactobacillus fermentum L2. Besides, we also examined the effect of different Lactobacillus strains on the contents of total phenol, total flavonoids and antioxidant activity of fermented Huyou juice. Results indicated that the two lactic acid bacteria grew rapidly in Huyou juice and attained a viable bacterial population of 108 CFU/mL. During their growth, the pH decreased significantly whereas the acidity and VC content greatly increased. In addition, significant changes were observed in the color parameters; L* value decreased whereas a* and b* values increased. The contents of organic acids also changed considerably; the contents of tartaric acid, citric acid, acetic acid and lactic acid increased significantly, whereas the opposite was observed for oxalic acid, malic acid and succinic acid. Acetic acid, lactic acid and malic acid were changed most obviously among all organic acids. The antioxidant activity of the fermented fruit juice was greatly higher than that of the unfermented control; the scavenging capacity against DPPH, superoxide anion and hydroxy radicals were increased by 4.3%, 15.9% and 0.7%, respectively. The contents of total phenol and total flavonoids increased after fermentation. The quality and antioxidant activity were improved significantly by fermentation with the two lactic acid bacteria. This study can provide the theoretical basis for probiotic fermentation of Huyou juice and for the development of probiotic fermented fruit juice.

Key words: lactic acid bacteria, Huyou juice, quality characteristics, antioxidant activity