Effect of sodium carbonate solution pretreatment on drying kinetics, antioxidant capacity changes, and final quality of wolfberry (Lycium barbarum) during drying

Wolfberry is an important medicinal and edible plant in China that is difficult to dehydrate owing to its dense pulp and epicuticular wax. Sodium carbonate (SC) pretreatment is an efficient low-cost technology that can help improve the wolfberry drying rate. To determine the effect of SC pretreatment on drying kinetics and quality changes during hot-air drying (AD), wolfberries were dried using AD at different temperatures (40, 50, and 60 °C) with or without SC pretreatment. SC pretreatment was found to increase the effective diffusivity (Deff) and reduce the total drying time by 22-28%. SC pretreatment and low-temperature AD (40 and 50 °C) helped improve wolfberry quality and increased its total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity, carotenoids content, and betaine content by 10-17%, 9-24%, 21-25%, 14-22%, 3-23%, and 17-42%, respectively. Samples dried with or without SC pretreatment showed the same trends, but a different moisture content inflexion point in the drying kinetics and different antioxidant attributes. In all drying processes, the Deff initially increased and then decreased, while the TPC, TFC, and antioxidant capacity initially decreased and then increased.