Effects of brining and standardized drying on the composition, shelf stability, microbial safety and antioxidant status of four wild edible vegetables†

Abstract

Wild edible vegetables (WEVs) are integral for sustained nutrition and livelihood of forest-dwelling tribal communities. Shelf-life enhancement of WEVs is crucial to overcome their perishability and ensure availability. Chemical preservatives are detrimental to their commercial ‘organic’ status, and modern processing technologies are often challenging to be implemented by the marginalized farmers. In this study, four nutritionally important WEVs popularly cultivated, consumed and marketed in the hilly, forest-covered state of Mizoram, India, namely, Solanum aethiopicum (ST), Solanum torvum (TP), Solanum anguivi (TT) and Leucaena leucocephala (JZ), were subjected to brining and drying to enhance their shelf-lives. The drying method was standardized using response surface methodology at 80 °C and 540 minutes, obtaining the lowest moisture content with the highest total phenolic content (TPC) and DPPH radical scavenging activity (DRSA). A strong positive correlation was obtained between TPC and DRSA values of ST (R = 0.738), TP (R = 0.760), TT (R = 0.977) and JZ (R = 0.935). Both brined bottled and dried vacuum-packaged samples were studied over 35 days of storage. Packaged dried samples were stored at room temperature (RT) and under refrigeration (RF). Brined WEVs showed a decrease in moisture and carbohydrate contents. Microbial conversion of sugars to lactic acid was evidenced by lowering pH to below 3.0. Bacterial activity also markedly enhanced TPC, flavonoids and DRSA values by causing free phenolics release and their structural transformation. However, overall microbial population in terms of aerobic coliform bacteria and fungal species were efficiently retarded up to more than 65% by the two treatments. Vacuum-packaged RF samples exhibited lowered microbial metabolism. Pigment degeneration and tissue structure changes were indicated by changed color and hardness. Dried tissue brittleness enhanced the extractability of bioactive compounds. Vacuum-packaging improved antioxidant retention in the processed WEVs.