超声波对不同孔隙率水果冻结特性的影响

为研究超声波对不同孔隙率水果冻结特性的影响，以苹果、梨、哈密瓜为对象，在相同超声频率下，用不同强度超声波辅助浸渍冷冻，用温度记录仪测定冻结时间，分析冻结过程中的温度变化，并对冻融后样品进行滴水损失率、质构、色泽、水分分布以及抗坏血酸含量测定。结果表明：苹果、梨、哈密瓜在0.145 W/cm2的超声强度下浸渍冷冻相变阶段时间分别为21.67、21.33、16.67 s，样品较直接浸渍冷冻处理相变时间显著缩短（P＜0.05）。经不同强度超声辅助浸渍冷冻后的3 种水果与直接浸渍冷冻组相比，滴水损失率均下降，其中苹果因孔隙率小，下降显著（P＜0.05），3 种水果硬度均提高，但与鲜样相比，抗坏血酸含量显著下降（P＜0.05）。相比未超声处理的样品，对孔隙率小的水果进行超声处理更有利于保持产品的品质。

Effect of Ultrasound on Freezing Characteristics of Fruits with Different Porosities

In order to study the effect of ultrasonic on the freezing characteristics of fruits with different porosities, apple, pear, and Hami melon (Cucumis melo var. saccharinus) were allowed to undergo ultrasonic-assisted immersion freezing at the same ultrasonic frequency and different ultrasonic intensities. A temperature recorder was used to measure temperature changes at different freezing time points during the freezing process. The drip loss, texture characteristics, color difference, moisture distribution, and ascorbic acid content of frozen-thawed samples were determined. The results showed that at an ultrasonic intensity of 0.145 W/cm2, the phase-changing times of apple, pear and Hami melon samples were 21.67, 21.33, and 16.67 s, respectively, which were significantly shorter than those of immersion frozen samples (P < 0.05). For each ultrasonic intensity, ultrasonic-assisted immersion freezing led to a decrease in drip loss during thawing compared to direct immersion freezing for all three fruits, especially for apple, which showed a significant decrease due to its low porosity (P < 0.05). Moreover, the hardness of the fruits was increased. Compared with the fresh samples, ascorbic acid contents in the treated samples were decreased significantly (P < 0.05). Compared with the samples without ultrasonic treatment, the fruit samples with smaller porosity maintained better quality under ultrasonic treatment.