Synergistic Effects of Dielectric Barrier Discharge (DBD) Cold Plasma Pretreatment Combined with Microwave Drying on the Physicochemical and Functional Properties of Centella asiatica Leaves

Centella asiatica L. (CA) has garnered substantial attention in both commercial and research domains due to its bioactive compounds, imparting notable functional properties such as antioxidant activity. However, for enhanced shelf life and suitability in food and pharmaceutical applications, proper drying is imperative before utilization. Thus, this study investigated the impact of pretreatments, specifically steam blanching (SB) and cold plasma-activated water (CPAW), on the drying kinetics and quality attributes of CA leaves during microwave drying (MWD). Five semi-empirical models were employed to fit the drying data, and the best-fitted model was determined using the Akaike information criterion (AIC). Subsequently, MWD was optimized through a face-centred central composite design, with microwave power and drying time as independent parameters. The Page and Logarithmic models exhibited the best fit to the drying data, as per AIC with R-2 values ranging from 0.981 to 0.999 and RMSE values from 0.008 to 0.051. Notably, CPAW pretreatment exhibited a more pronounced effect on both drying kinetics and quality parameters compared to SB. Optimal drying conditions were identified as a microwave power of 540 W and a drying time of 6.99 min. This study concludes that microwave drying with CPAW pretreatment is a sustainable method for obtaining dried CA leaves with optimal nutritional qualities, making it relevant from an industrial perspective.