Microwave heating as a tool to enhance antioxidant activity and release soluble conjugates from Feutrell’s Early (citrus mandarin cultivar) peels

The phenolic constituents usually exist in free and covalently bound forms in the plant materials. This study reports the impact of microwave heating on certain phenolic compounds and antioxidant potential assessed by free radical-scavenging and reducing power of citrus peels. Different levels of microwave power (125, 250, 500 W) and heating times (5, 10, 15 min) were applied. The phenolic acids were fractionated into three forms namely; free, glycoside-bound, and ester-bound. Microwave power and heating time significantly increased the content of free phenolic fraction while the content of bound fractions decreased. Increasing microwave power significantly increased the antioxidant activity of heated samples. The microwave heating up to 10 min at 250 W increased the antioxidant activity of the samples but further heating to 15 min exerted an adverse effect. A moderate microwave power and heating time was helpful for improving the antioxidant potential of citrus peels. Practical applications: A very simple method is used in this study to release the bound phenolics and to improve the antioxidant potential of citrus peels, thereby, maximizing the use of fruit byproducts in general and citrus peels in particular. By this way, it can be helpful to decrease the environmental pollution caused by citrus fruit waste products. The use of microwave heating might be helpful for the citrus processing industry to minimize the loss in terms of effluent management. It might be an economical processing technique for the pharmaceutical and functional food sector.