Evaluation of the changes in physicochemical and functional characteristics of leaves of Solanum nigrum under different drying methods

• Drying treatment affects chlorophyll levels of Solanum nigrum leaves. • The methanolic extracts are rich in polyphenols, flavonoids and antioxidants. • Recirculatory air drying extracts have high free radical scavenging activity. • Recirculatory air drying compared other processes had better hydration property. The aim of this study was to quantify and understand the changes in the functional properties and hydration quality of Solanum nigrum (SN) leaves among different drying treatments. It was then compared with the traditional method of shade drying besides freeze-drying, to assess and compare the effect of heat sensitisation across the different treatments. The functional quality assessed were chlorophyll, polyphenolics, flavonoids content and the respective antioxidant activity. The water retention capacity, swelling capacity and rehydration ratio were also studied. The LC-MS results showed that the leaf powder retained significant levels of phenolic and flavonoid. Freeze-drying (FD) samples were observed to have 6.73±0.01 mM equivalence α-Tocopherol/g of dry sample as the highest levels of antioxidant capacity, followed by Recirculatory air-drying (RAD) (65°C) and Microwave oven drying (MOD) (7 W/g) treatment with 6.56±0.08 and 6.47±0.08 mmol mM equivalence α-Tocopherol/g. The water retention capacity (WRC) results show that 45°C RAD had the best water retention capability (9.8±0.04 g of water retained/g dry wt.) It can be concluded that 65°C RAD treated the leaves retained significant levels of functional components present in the leaves compared to the other drying treatments.