Effects of Thermal Treatment and Freezing Storage Period on Physicochemical and Nutritional Characteristics of Shiitake Mushrooms

본 연구는 표고의 열처리 방법과 냉동 저장 기간에 따른 이화학적 및 영양학적 특성을 분석하였다. 열수 침지 및 과열 증기로 열처리된 시료를 IQF 처리한 후 함기 및 진공 포장으로 24주 동안 서로 다른 온도에서 냉동 저장하면서 시간에 따른 이화학적 특성을 분석하였다. 색도 분석에서는 열수 침지법이 색변화를 감소시켰고, 함기 포장한 시료와 낮은 온도에서 저장한 시료일수록 밝은 색을 유지하였다. 경도와 pH 측정에서는 과열 증기법이 열수 침지법보다 버섯 특성의 변화가 적게 발생하였으며, 영양학적 측면에서도 과열 증기법이 효율적인 방법이라 판단된다. Freezing is one of the main processes to extend the shelf life of foods. Before freezing, a thermal treatment is normally required to control the food quality. In this study, shiitake mushrooms were heated with boiling water and with superheated steam. After the thermal treatments, the samples were continuously frozen by an individual quick freezing (IQF) process, and put them into air-containing or vacuum packaging. Samples were stored at -12, -18 and $-24^{\circ}C$ for 24 weeks, and their physicochemical properties were determined. The lightness of the samples treated with boiling water and superheated steam was decreased by 12 and 15%, respectively, than that of the control. The hardness of all the samples rapidly increased after heat treatment. The contents of organic acids in the superheated steam treated samples were higher than those in the boiling water treated samples. Therefore, superheated steam treatment of samples may be a candidate thermal treatment to preserve frozen shiitake mushrooms.