关键词: 苹果片, 射频加热, 理化性质, 微观结构

Abstract:

Heating and blanching is an important process in apple and even fruit and vegetable processing industry. A pilot scale radio frequency (RF) heating system was used to heat apple slices under different gaps, to test heating curves and their uniformity, color, texture, activity of polyphenol oxidase (PPO) and weight changes. Micro-structure of apple slices was observed by scanning electron microscope (SEM) to reveal the mechanism of physical and chemical property changes in the process of RF blanching. The results indicated that the heating speed was the fastest at gap of 115 mm and the lowest at 125 mm. For temperature to raise from 22℃ to 95℃ 95 s and 140 s were needed, respectively. The temperature of apple slices was higher in the middle than the edges. The relative enzyme activity of PPO by RF blanching was due to the heating temperature and endurance time. With the increase of blanching temperature, the color-protecting effect became better, while the hardness of apple slices decreased. The cell damage degree of apple slices increased with the increase of temperature. The cell destruction of apple slices was smaller when temperature rose faster. The best RF heating conditions for apple slices was at the gap of 105 mm for 101 s.

Key words: apple slices, radio frequency heating, physicochemical property, microstructure