Effect of thermal and ultrasonic pretreatment on enzyme inactivation, color, phenolics and flavonoids contents of infrared freeze-dried rose flower

Abstract

The effects of ultrasound and thermal pretreatment prior to freeze drying combined with infrared on enzyme activity, color changes and antioxidant activities of dried rose flowers were studied. The activities of polyphenol oxidase (PPO) and peroxidase (POD) in rose after ultrasonic pretreatment were significantly decreased than thermal treatments. Ultrasonic pretreatment could improve the color of dried rose flowers. In addition, low-frequency ultrasound pretreatment could significantly improve the content of anthocyanins content and reduce the degradation rate. The antioxidant activity of low-frequency ultrasound pretreatment rose was also higher than that of dried rose flowers by thermal and high-frequency ultrasound pretreatment. However, thermal pretreatment as high temperatures affected the total phenolic content and product quality in different way such as loss of color and nutrients degradation.