Objective The study was carried out to select the Bacillus suitable for fermentation of fingered citron pulp and develop the probiotic fermented fingered citron soft sweets with living bacteria.

Method Three probiotics of Bacillus subtilis (BS168), Bacillus licheniformis (BL02) and Bacillus coagulans (BC30) were inoculated to fingered citron pulp after sterilization, respectively. The growth curve, nutritional component and antioxidant capacity were determined, and the correlation between the indicators was analyzed. And the survival rate of Bacillus in preparation of soft sweets was explored.

Result The three Bacillus could grow well in the pulp, among them, the BC30 grow best, the viable count of which could reach 8.35 log CFU/g after 48 h fermentation. Fructose, glucose and sucrose contents, and pH value decreased gradually during fermentation, in which BC30 group decreased more. The content of total phenolics decreased during fermentation, and the retention rate of total phenolics of BC30 was 91% after 48 h fermentation. The content of total flavonoids in the pulp fermented by BC30 (105.9 g/kg) was higher than that of the other two Bacillus groups. The scavenging activity of DPPH radical in the fermented fingered citron pulp could be improved by BC30. Compared with unfermented pulp, the scavenging ability of DPPH radical was increased by 7.5% after 48 h fermentation. The results of correlation analysis showed that the scavenging ability of DPPH radical was remarkable significantly positively correlated with viable count of BC30 and had no significant correlation with the contents of total phenolics and flavonoids. The viable count of BC30 was 7.5 log CFU/g in sofe sweets made from the prepared probiotic fermented fingered citron.

Conclusion Among the three Bacillus, BC30 was the most suitable strain for the fermentation of fingered citron, and the fermentation had positive contribution to the improvement of antioxidant capacity, and the number of viable bacteria in the soft sweets developed from BC30 fermented pulp was higher. The study laid a theoretical foundation for the development of the fermented fingered citron soft sweets rich in living bacteria.