Isolation, evaluation of antifungal activity of Lactobacillus spp. against Lasiodiplodia pseudothobromae and Phomopsis mali and study on formula carrier to preserve rambutans at postharvest stage

Based of the isolation result of Lactobacillus spp. from fresh fruits and the traditional fermented produce available in the Mekong River Delta Region, an evaluation on antifungal activity of Lactobacillus spp. against Lasiodiplodia pseudothobromae and Phomopsis mali, which are considered as main agents causing postharvest disease on rambutan fruit was conducted. Results indicated that approximately 98% out of the screened 56 isolates showed inhibitory activity to both Lasiodiplodia pseudothobromae and Phomopsis mali. However, the amount of Lactobacillus spp. which had a strong activity (+++) with a relative inhibitory cycling diameter (GROTERDAN75 mm) as tested under in vitro by using overlaid method was much less (only three isolates). Those three isolates were CC6 (isolated from rambutan (Lactobacillus plantarum); DC2 (from duacai pickle) and DGMC2 (dua gang muoi pickle) (Lactobacillus fermentum), respectively. The objective of this research was to find out Lactobacillus strains combined with carriers, the use in treatment and storage of postharvest of rambutan fruits, helping to maintain quality and prolong shelf life of postharvest life. Chitosan concentrations of 0.01 to 0.05% and carboxymethyl cellulose (CMC) concentrations of 0.5 to 0.75% showed the best density of Lactobacillus fermentum DC2 and Lactobacillus plantarum CC6 in MRS medium. Treating rambutans with a mixture of Lactobacillus plantarum CC6 culture, 0.025% chitosan and 0.5% CMC showed a reduction of of 42.28%; pH of the rambutan juice was 3.28 and dissolved solids of the juice was 17.9 °Brix, efficiently reduced weight loss, remained the fruit peel color, lowered disease rate on postharvest rambutans. After 14 days storage at 13°C the density of Lactobacillus on the peel was 10² CFU cm^‑2.