Ultrasound and Microwave Assisted Extraction of Phenolic Compounds from Red Onion (Allium Cepa L.) Skin Dried with Infrared Oven

Food industry produces a large amount of onion skin wastes. Due to the high amount of bioactive compounds found in such by-product, developing a method for the recovery of these biological lesions is important to benefit from them as a source of biologically active compounds.  The aims of this research were to compare the two methods, ultrasound and microwave, for extraction the phenolic compounds of red onion skin wastes and also to investigate the drying pre-treatment with conventional or infrared oven. The investigation the total phenolic compounds and anthocyanin content of extracts showed that use of ultrasonic method caused significantly (p < 0.05) enhanced extraction efficacy of phenolic compounds and anthocyanins. Additionally, drying by infrared oven caused significantly (p < 0.05) increase in total phenolic compounds and anthocyanins extraction. The antioxidant activity analysis of extracts showed that antioxidant capacity of samples extracted by ultrasonic method were significantly (p < 0.05) higher than that extracted by microwave method. As a result, the ultrasonic extraction by pretreatment applying infrared oven may be recomended as a suitable technique to extract phenolic compounds found in red onion skins to benefit from the nutritional potential of these biological wastes.