The effects of oven-drying at 50 and 100C, sun-drying and ambient air-drying at 24 ± 1C on the antioxidant properties (AOPs) of mulberry (Morus alba L.) leaves were studied. Except for leaves oven-dried at 50C which showed minimal AOP changes, leaves dried under other conditions resulted in a significant decrease in AOP. Fresh mulberry leaves contained low oxidative enzyme activities (polyphenol oxidase [PPO]: 1.40 ± 0.58 ΔA435/min/g of fresh leaves and peroxidase: 1.59 ± 0.42 ΔA418/min/g of fresh leaves) which were reduced to nonmeasureable or lower values when they were dried at 50, 100C and blanched in boiling water. The major factor causing AOP decrease in thermally treated leaves (oven-drying at 100C and sun-drying) was due to thermal degradation but the decrease in AOP for ambient air-dried leaves was associated with the presence of PPO. Overall, oven-drying at 50C was the most preferred drying method. PRACTICAL APPLICATIONSMulberry with excellent free radical scavenging, antioxidant, anticancer and antihyperglycemic properties has long been used as traditional medicine and health food product. Generally, mulberry leaves are processed and consumed as tea. Drying, which helps preserve the nutrient contents of mulberry leaves, is an important method in mulberry tea processing. In order to exploit mulberry leaves more scientifically and efficiently for commercial purpose, the present study serves as an important work in providing insights into how oxidative enzymes and thermal stability of antioxidants in mulberry leaves affect the antioxidant properties when subjected to different drying conditions. The optimum drying condition found in this study will be beneficial to the tea processing industry.

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The antioxidant and antimicrobial activity of Costus woodsonii was previously investigated in our lab. The present study investigated the cytotoxic activity of different plant parts and to identify the bioactive compound(s). MTT assay showed that among different plant parts, rhizome extract exhibited the strongest activity (IC50 of 48 hr treatment: <75.8 µg/ml) against all cell lines tested. Using C18 column chromatography, the isolated compound from rhizome, which demonstrated potent cytotoxic activity (IC50 ≤ 2.4 ± 0.2 µg/ml) against oral squamous cell carcinoma was shown to be dioscin by HPLC, LCMS‐MS, and NMR analyses. Our findings also showed that dioscin could be a potential treatment for cisplatin‐resistant OSCC and C. woodsonii could serve as a potential commercial source for dioscin. Practical applications Different plant parts of Costus woodsonii have long been used traditionally for medicinal application in water decoction. Nonetheless, the bioactivity study on this plant is scarce. In order to exploit different plant parts of C. woodsonii more scientifically and efficiently for commercial purpose, the present study serves as an important work in understanding the cytotoxic activity of each different parts. This study also provides insight on the effect of extraction solvent on the cytotoxic potential of the selected plant parts. Sequential solvent extraction of rhizome extract followed by fractionation revealed the presence of dioscin, an industrially important steroidal saponin. Overall, this study demonstrated that the rhizome of C. woodsonii may act as a potential source of dioscin.

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