Characterisation of the Convective Hot-Air Drying and Vacuum Microwave Drying of Cassia alata: Antioxidant Activity, Essential Oil Volatile Composition and Quality Studies

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.

In vitro antimicrobial effects of Myristica fragrans essential oil on foodborne pathogens and its influence on beef quality during refrigerated storage

“…These controversial findings might be related to the changes in the plant climate and locality, and the various solvents used for EOs extraction (El‐Ghorab, Nauman, Anjum, Hussain, & Nadeem, ). Phenolic compounds are generally contributed to the antioxidant activity of plants (Chua et al, ; Goldsmith, Vuong, Stathopoulos, Roach, & Scarlett, ).…”

Hybrid Drying of Murraya koenigii Leaves: Energy Consumption, Antioxidant Capacity, Profiling of Volatile Compounds and Quality Studies

“…This promising trend occurred because the increase in the intensity of the microwave power reduced the total drying time. Hence, the exposure time for high degradative temperature was reduced [20]. In CD, a decreasing trend of volatile content was observed when the hot-air temperature increased from 40 • C (4.687 mg/g dw) to 60 • C (3.420 mg/g dw).…”

“…However, the maintenance and installation cost of MVD for an industrial application are considerably high due to the vacuum pump and the microwave system. Thus, CD can be introduced as a pre-drying step to aid in removing excess moisture from the surface of the material; finally, drying can be finished with MVD to remove internal moisture content by utilising microwave energy [17,20]. In this research, the combined hybrid drying method had reduced the total drying time of CD at 50 • C from 570 min to 138 min (Table 2) and thus reduced the specific energy consumption by 67.3% (kJ/g fw) and 48.9% (kJ/g water).…”

“…The loss of antioxidant capacity was found in the samples dried with thermal drying methods, where the highest loss was found in CD under all conditions and the least loss was found in MVD under all conditions. This result might be caused by thermal antioxidant degradation and oxidative degradation [20]. The intensity of drying methods, such as drying temperature and microwave power was found to influence the antioxidant capacity as the drying temperature increased from 40 • C to 60 • C, the antioxidant capacity reduced from 2.83 ± 0.10 mmol/100 g dw to 2.32 ± 0.31 mmol/100 g dw for ABTS and from 2.17 ± 0.53 mmol/100 g dw to 1.54 ± 0.10 mmol/100 g dw for FRAP.…”

“…The lowest TPC was found in CD at 50 • C with a TPC concentration of 600.49 mg/100 g dw. The lowest retained TPC could be due to the long exposure time to thermal treatment, causing the oxidative degradation of polyphenolic compounds [20]. Increasing drying intensity could decrease the antioxidant capacity and TPC of M. koenigii leaves.…”