Investigation on the influence of ultrasonic pretreatment on color, quality and antioxidant attributes of microwave dried Inula viscosa (L.)

Abstract

Impact of various ultrasound pretreatment and microwave drying parameters on the qualitative and antioxidant characteristics of Inula viscosa (L.) was investigated in this study. The leaves of Inula viscosa (L.) were sonicated for 10, 20, and 30 min in an ultrasonic bath (37 kHz, 150 Watts). Microwave drying was done at three distinct times (1, 3, and 5 min) and with three different microwave power levels (100, 180, and 300 Watts). Microwave dried samples were tested for color characteristics (L*, a*, b*), chlorophyll, carotenoid, total phenol, and anti-oxidant content. All dried samples were prepared by infusing them in hot water as tea, and the sensorial properties of teas including odor, color, aroma, and overall acceptability were evaluated by panelists. For 10, 20, and 30 min of ultrasound pretreatment, the L* values of leaves varied from 37.70 to 49.76, 34.97 to 46.25, and 27.88 to 43.34, respectively. The total carotenoid concentration ranged from 0.12 to 0.32 mg/g DW, while the total chlorophyll content was from 0.44 to 0.94 mg/g DW. The antioxidant activity of Inula viscosa (L.) leaves that were dried at 300 Watts for 5 min did not change significantly as a result of ultrasound pretreatment. There was a significant positive correlation between aroma and TPC, as well as between color and overall acceptability. The darkest-colored teas were deemed preferable by the panelists.