Effect of air exposed storage on quality deterioration and microbial succession of traditional Sichuan Paocai

In this study, quality and microbial properties of paocai stored in air exposed (AE group) condition were studied and compared with the water sealed control (CT) group during 16 days of storage. Results showed that pellicles produced on brine surfaces in the day 4 and mold colonies showed on the pellicles in the day 8 in AE group. Plate counts of yeasts rose rapidly after air exposure, followed by increasing of mold count after day 12. High throughput sequencing revealed a rapid growth of aerobic fungi. After 8 days, Pichia spp. dominated the cover brine. Penicillium, Fusarium and Serratia increased in the day 16. Firmness of paocai in AE group decreased significantly during storage. Links among cells of paocai weakened and cell walls were damaged in AE group after 16 days of storage. Total pectin content, molecular mass of water soluble pectin and sodium carbonate soluble pectin fractions also decreased in AE group. Air exposure promoted the growth of aerobic microbes in cover brine. These pellicles forming Pichia species may hydrolyze pectin of paocai or promoted the growth of mold and other harmful microbes, which was responsible for the paocai spoilage characterized by firmness loss.