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

摘要：

烫漂是苹果乃至果蔬加工业中的一个重要步骤。采用中试型射频加热系统，在不同极板间距下对苹果片进行射频加热，测定射频加热升温曲线和均匀性，测定 颜色、质构、多酚氧化酶（PPO）活性和重量的变化，采用扫描电子显微镜(SEM)观察射频加热过程中苹果片的微观结构，揭示苹果片射频加热烫漂过程中理化 特性变化的机理。结果表明：115 mm时升温速度最快而125 mm下升温最慢，从22℃升到95℃，分别需95 s和140 s；苹果片呈现中间温度高，边缘温度低的现象 。苹果片射频加热的PPO相对酶活是射频加热温度和持续时间的双重作用。随着烫漂温度的升高护色效果变好，苹果片硬度随着烫漂温度的升高而减小。苹果片 细胞破坏程度随着烫漂温度的升高而增大，升温速度越快苹果片细胞破坏越小。苹果片最佳的射频加热条件为极板间距105 mm下加热101 s。

关键词: 苹果片, 射频加热, 理化性质, 微观结构