This study aims to reduce the amount of specific energy consumed during the drying of fresh Murraya koenigii leaves by comparing four drying methods: (1) convective hot-air drying (CD; 40, 50 and 60 °C); (2) single-stage microwave-vacuum drying (MVD; 6, 9 and 12 W/g); (3) two-stage convective hot-air pre-drying followed by microwave-vacuum finishing–drying (CPD-MVFD; 50 °C, 9 W/g); and (4) freeze-drying as a control in the analysis sections. The drying kinetics were also modelled using thin-layer models. The quality parameters of dried M. koenigii leaves were measured including total polyphenolic content (TPC), antioxidant capacity (ABTS and FRAP), profiling of volatile compounds, colour analysis and water activity analysis. Results showed that CPD-MVFD effectively reduced the specific energy consumption of CD at 50 °C by 67.3% in terms of kilojoules per gram of fresh weight and 48.9% in terms of kilojoules per gram of water. The modified Page model demonstrated excellent fitting to the empirical data obtained. FD showed promising antioxidant activity. The major contributor of antioxidant capacity was TPC. The volatile compounds profiled by gas chromatography-mass spectrometry, namely, β-phellandrene (31%), α-pinene (19.9%), and sabinene (16%) were identified as the major compounds of dried M. koenigii leaves. Colour analysis showed MVD’s high performance in preserving the colour parameters of M. koenigii leaves under all conditions. The colour parameters were correlated to the antioxidant capacity and TPC. Water activity analysis showed that the water activity of M. koenigii leaves for all drying methods indicating that the conditions were microbiologically and shelf-stable. Pearson correlation showed the colour parameters of the leaves had a strong correlation to TPC. Overall, MVD showed promising energy consumption reduction and recovery in TPC and volatile compounds.

Ziziphus jujube known as red dates are natural flora, are a rich source of antioxidant bioactive compounds and are widely used in making Chinese traditional medicine. However, the optimization of extraction conditions and demonstration of extraction kinetics of red dates remains a gap. Therefore, the main objective of this research was to enhance the antioxidant activity via DPPH, crude extract yield, and TPC by response surface methodology (RSM). Also, mathematical modeling of the TPC extraction kinetics was performed. Single-factor experiments were adopted to identify the preliminary RSM ranges of four extraction parameters such as liquid-solid ratio (10, 20, and 30 ml/g), extraction temperature (50, 60 and 70°C), time (40, 50 and 60min), and ultrasonic power (70, 80 and 90%). The extraction kinetics based on RSM optimized conditions were modeled into six extraction kinetic models. As result, the highest crude extract yield (4.56 g), highest TPC (0.023 g GAE/g extract), and highest antioxidant activity (85.88%) were obtained at 60ºC. The optimum values were liquid-solid ratio 30ml/g, extraction temperature 60°C, time 60 min, and ultrasonic power 70%. The antioxidant activity of red dates after optimization (90.59%) was higher than that of synthetic antioxidants, Butylated Hydroxytoluene (84.71%), and Butylated Hydroxyanisole (77.73%). Furthermore, the best-fitted kinetic model was the second-order kinetic model due to its coefficient of determination (R2) at 0.9849, being the closest to 1 and its root mean square error (RMSE) was the lowest, 0.001028 among other models.