Effects of Air Blast Freezing and Microwave Thawing on Physicochemical and Nutritional Properties of Carrots

This study was carried out to observe the effects of various combinations of air blast freezing and microwave thawing on the physicochemical and nutritional properties of carrots. Carrots were cut into 0.5×0.5×5 cm cubes and then frozen at -40C at various freezing rates (0.2, 0.4 or 1.6C/min) until a -12C central temperature in the carrot was reached by using an air blast freezer. Then, the frozen carrots were thawed by using natural air convection and microwaves at 200, 400, and 800 watts. After the thawing treatment, physicochemical properties of the carrots such as pH, thawing loss, hardness, color, morphological images and changes in nutritional compositions were also analyzed. In physicochemical characterization, thawing loss and hardness decreased with increasing the freezing rate. In morphological observation, ice crystal pore sizes in frozen carrots were 0.7, 0.3 and 0.1 mm at 0.2, 0.4 and 1.6C/min, respectively. They significantly decreased as the freezing rate increased. For the nutritional characterizations, the vitamin C and organic acid contents did not differ depending on the freezing rate. The sucrose content was the highest at the 0.2C/min freezing rate. Therefore, we suggest that a faster freezing rate is effective to maintain frozen food quality by minimizing tissue damage and changes in physical properties.