Food Sci. Biotechnol. 23(4): 1095-1102 (2014) DOI 10.1007/s10068-014-0150-0 Effects of Ultrasound-assisted Thawing on the Quality of Edamames [Glycine max (L.) Merrill] Frozen Using Different Freezing Methods Xin-feng Cheng, Min Zhang, and Benu Adhikari Received May 12, 2013; revised September 11, 2013; accepted September 22, 2013; published online August 31, 2014 © KoSFoST and Springer 2014 Abstract The effects of different freezing and thawing methods on the physicochemical indices and nutritive value of edamame [Glycine max (L.) Merrill] were investigated. Air-blast freezing had less of an impact on the drip loss, color, chlorophyll and ascorbic acid contents, and textural hardness of frozen shelled edamames. Ultrasound-assisted thawing significantly (p<0.05) shortened thawing time, compared to water immersion thawing. Ultrasound-assisted thawing at a 900 W power level showed the best retention of ascorbic acid and chlorophyll, and original hardness, and minimized the drip loss of thawed samples. Ultrasonic assisted thawing at a power level of 1,200 W caused the most pronounced loss of ascorbic acid. A combination of fast air-blast freezing and ultrasound-assisted thawing at a power level of 900 W most effectively retained ascorbic acid and chlorophyll, minimized drip loss, and maintained the textural hardness of shelled edamame samples. Keywords: shelled edamame, ultrasonic-assisted thawing, ascorbic acid, chlorophyll, hardness Introduction Edamame [Glycine max (L.) Merrill] popularly known as ‘vegetable soybean’, is a type of soybean that is harvested at approximately 80% of maturity (1). Compared to mature soybeans, edamame has advantages in sensory attributes, such as a green color, soft texture, large seed size, sweet taste, and less beany flavor (2). In addition, edamame is rich in carbohydrates, proteins, and dietary fiber and offers numerous health benefits, including lower cholesterol levels and reduced risks of cardiovascular disease and cancer (3). However, edamame is a highly perishable product with a short shelf-life (4). Therefore, it is important to find a suitable method to extend the shelf-life and maintain the quality for further commercialization. Freezing is an efficient method that is applied for retaining the valuable sensory attributes and nutritive properties of fresh foods (3). However, some quality deterioration occurs during freezing and frozen storage, especially development of an undesirable odor (5), damage of texture (3), degradation of natural pigments (6) and oxidation of some chemicals (7). The extent of quality loss in frozen foods depends on many factors, including characteristics of the materials to be frozen, the rate of freezing, and the storage temperature. In general, quick freezing is better at retaining the nutritional contents and cell integrity of fruits and vegetables than slow freezing because small ice crystals are formed during quick freezing. In slow freezing, the formation of large, sharp ice crystals causes damage to the delicate organelle and membrane structures of cells. Such cellular damage leads to a high drip loss after thawing (8). Thawing is a necessary process for frozen food before food processing or cooking. The quality of frozen food is more affected by the thawing process because more time is required for thawing than for freezing (9). Moreover, inappropriate thawing may result in serious quality deterioration. For these reasons, a number of studies have examined the merits and demerits of high-pressure (10,11), ohmic (12,13), microwave (9), and ultrasonic thawing methods (14,15). Ultrasonic thawing is being explored as an innovative Xin-feng Cheng, Min Zhang () State Key Laboratory of Food Science and Technology, Jiangnan University, 214122 Wuxi, Jiangsu, China Tel, Fax: +86-0510-85877225 E-mail: min@jiangnan.edu.cn Benu Adhikari School of Applied Sciences, RMIT University, City Campus, Melbourne, VIC 3001, Australia RESEARCH ARTICLE