Objective The aim of this study was to investigate the effects of lactic acid bacteria complex fermentation on the basic composition, probiotic activity and in vitro digestion characteristics of longan pulp, so as to provide a theoretical basis for the development of functional longan products.

Method Longan pulp was fermented by a combination of Lactobacillus plantarum, L. fermentum and L. casei. Unfermented longan pulp was used as the control. The influences in the content of basic components of the pulp, the viable count of probiotics, the content of various components before and after gastrointestinal digestion, the digestibility, the content of components before and after dialysis and the dialysis retention rate were analyzed.

Result Longan pulp was mainly composed of carbohydrates, with a proportion of 67.8%. Small amounts of protein and fat were also contained, accounting for 5.32% and 0.86% respectively. After fermentation, the contents of polysaccharides and free sugars in longan pulp decreased by 6.03% and 4.27% respectively, while the protein content was increased by 24.2%. The probiotic activity experiment found that the fermented longan pulp could better promote the proliferation of L. fermentum, Leuconostoc mesenteroides, Bifidobacterium adolescentis, B. infantis, and B. longum. The average proliferation amount increased by 0.12-0.21 lg CFU/mL within 24 and 48 h. The results of the in vitro simulated digestion show that lactic acid bacteria fermentation significantly improves the digestibility of polysaccharides and proteins in longan pulp during the gastrointestinal digestion stage. The digestibility of polysaccharides and proteins in the gastric stage increased by 0.87% and 3.83% respectively, and in the intestinal stage, the digestibility of polysaccharides and proteins increased by 0.88% and 4.98% respectively. By using dialysis to simulate intestinal absorption, it was found that after lactic acid bacteria fermentation, the contents of absorbable polysaccharides, proteins, fructose, and glucose in longan pulp increased by 2.99%, 8.34%, 0.11%, and 0.28% respectively.

Conclusion After being fermented by lactic acid bacteria, the longan pulp not only has a reduced sugar content but also exhibits better probiotic activities and in vitro digestion characteristics. Therefore, lactic acid bacteria fermentation is suitable for the development of high-activity longan products.