The initial physicochemical properties of different lotus roots were studied with the aim to evaluate their influence on freezing suitability. Six physicochemical properties indicators (starch content, whiteness index, maximum diameter, protein amount, titratable acidity and vitamin C) of lotus root were determined by principal component analysis. It was observed from the experimental results that the initial physicochemical properties of lotus root can directly affect the freezing suitability in terms of initial freezing temperature, transition phase time, total freezing time, relative firmness and drip loss. Correlation analysis suggested that relative firmness increases in proportion to starch content, and initial freezing temperature and drip loss are inversely proportional to the starch content. Compared to immersion freezing, power ultrasound can significantly improve the freezing rate and relative firmness but decrease drip loss. These results suggested that high quality frozen lotus root can be achieved via appropriately selecting high starch content lotus root and using ultrasound-assisted immersion freezing.
The effect of ultrasound pretreatment at various power (360 W, 600 W and 960 W, frequency 20 kHz) on the glass transition temperature of freeze dried pear (Pyrus pyrifolia) has been studied. DMA temperature plots were divided into four sections (A - glassy region, B - transition region, C - Rubbery plateau region and D - terminal region) with the aim to analyze their properties changed with sonication. Under the same freeze drying condition, with the increase in ultrasonic power, dried pear showed higher glass transition in terms of storage modulus, loss modulus and loss tangent peak. Also a decrease in a