Abstract
The preservation of active constituents in Cassia alata through the removal of moisture is crucial in producing a final product with high antioxidant activity. This study aims to determine the influences of various drying methods and drying conditions on the antioxidant activity, volatiles and phytosterols content of C. alata. The drying methods used were convective drying (CD) at 40 °C, 50 °C and 60 °C; freeze drying; vacuum microwave drying (VMD) at 6, 9 and 12 W/g; and two-stage convective pre-drying followed by vacuum microwave finish drying (CPD-VMFD) at 50 °C and 9 W/g. The drying kinetics of C. alata are best described by the thin-layer model (modified Page model). The highest antioxidant activity, TPC and volatile concentration were achieved with CD at 40 °C. GC–MS analysis identified the presence of 51 volatiles, which were mostly present in all samples but with quantitative variation. The dominant volatiles in fresh C. alata are 2-hexenal (60.28 mg 100 g−1 db), 1-hexanol (18.70 mg 100 g−1 db) and salicylic acid (15.05 mg 100 g−1 db). The concentration of phytosterols in fresh sample was 3647.48 mg 100 g−1 db, and the major phytosterols present in fresh and dried samples were β-sitosterol (1162.24 mg 100 g−1 db). CPD-VMFD was effective in ensuring the preservation of higher phytosterol content in comparison with CD at 50 °C. The final recommendation of a suitable drying method to dehydrate C. alata leaves is CD at 40 °C.
Highlights
The majority of the world population has used medicinal plants in some ways as their first source of treatment as remedy for infectious and non-infectious diseases
In the combined method CPD-VMFD, CPD is effective in removing moisture during the initial drying process whilst VMFD assists in the removal of residual moisture, which is strongly bound to the plant cellular structure, thereby shortening
The drying kinetics of C. alata leaves dehydrated using convective drying (CD), vacuum microwave drying (VMD) and CPD-VMFD was best described by the exponential model
Summary
The majority of the world population has used medicinal plants in some ways as their first source of treatment as remedy for infectious and non-infectious diseases. Many of these medicinal plants have been researched and have garnered scientific evidence to be considered and used in general medical practice. A large number of diseases are caused by oxidative stress that can elicit cellular and Molecules 2019, 24, 1625; doi:10.3390/molecules24081625 www.mdpi.com/journal/molecules. Deficiency of antioxidants or overproduction of ROS in the body can cause the disturbance in the equilibrium between ROS formation and elimination, favouring the upsurge of ROS, which results in oxidative stress [1]. Cassia alata (Leguminosae) is a shrub native to Southeast Asia, Northern Australia, Latin America, Fiji and Africa and can be found widespread in tropical regions, cultivated for medicinal purposes [2,3]
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