The effects of drying conditions on bioactive compounds and antioxidant activity of the Australian maroon bush, Scaevola spinescens

Abstract

Scaevola spinescens is a native Australian plant that has traditionally been used for medical purposes. This study aimed to determine the impact of different drying conditions on the bioactive compound yield and antioxidant activity in dried S. spinescens. The results showed that different drying conditions significantly affected total phenolics, flavonoids, saponins and antioxidant activity. Microwave irradiation at 240 W retained the highest levels of total phenolics (45.82 mg GAE/g), whereas hot air-drying at 110°C and vacuum oven drying at 90°C retained the highest levels of saponins (150.72 mg ESE/g and 146.61 mg ESE/g, respectively) and antioxidant activity. Per kWh of energy consumed, microwave drying at 240 W for 600 s had dramatically higher yields than all other methods tested (~4,700 times more efficient than freeze drying and ~66 times more efficient than hot air or vacuum oven drying), and therefore is recommended for drying S. spinescens. Practical applications Drying is an important step in tea production, and also to prepare starting materials for further processing. However, the drying process can affect the retention of desired compounds and is closely associated with production costs. This study revealed that inappropriate drying conditions can negatively impact the retention of bioactive compounds and antioxidant activity of Scaevola spinescens. Furthermore, we consider recovery yields with respect to power consumed, and found that microwave irradiation at 240 W for 600 s to be the most energy efficient drying method. Microwave irradiation is also the fastest method of drying and can be easily applied to dry S. spinescens on a commercial scale.