Abstract: Different thawing methods, microwave radiation at 500 and 550 W, ultrasonic radiation, and thawing at refrigerated and room temperatures were compared to find the best one to reduce the negative effect of thawing on drip loss, color, functional components and antioxidant activities of quick-frozen mulberry fruits and to shorten the thawing time. The results showed that the time required for microwave thawing was the shortest, which was respectively 0.58 and 0.35 min at 500 and 550 W, while the thawing process took the longest time (305 min) under refrigerated condition. Significant differences were presented in drip loss among different thawing methods; the drip loss after microwave thawing at 500 W was the lowest (1.34%), whereas the highest values was obtained after ultrasonic thawing (9.24%). The content of total phenols (151.66 mg/100 g) and anthocyanins (2.27 mg/g cyanidin-3-O-glucoside, 0.69 mg/g cyanidin-3-O-rutinoside, and 0.047 mg/g pelargonidin-3-glucoside) as well as antioxidant activity in terms of 2,2’-azinobis-(3-ethylbenzthiazoline-6-sulphonate (ABTS) free radical scavenging activity (21.87 μmol Trolox/g), 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity (35.70 μmol Trolox/g) and ferric reducing antioxidant power (FRAP) (27.85 μmol Trolox/g) of mulberry fruits after microwave thawing at 500 W were significantly higher than those of four other thawing methods. In summary, microwave thawing at power 500 W was the most appropriate method for quick-frozen mulberry fruits.

Key words: thaw, drip loss, color, total phenols, anthocyanins, antioxidant activity