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Power ultrasound, which can enhance nucleation rate and crystal growth rate, can also affect the physico-chemical properties of immersion frozen products. In this study, the influence of slow freezing (SF), immersion freezing (IF) and ultrasound-assisted freezing (UAF) on physico-chemical properties and volatile compounds of red radish was investigated. Results showed that ultrasound application significantly improved the freezing rate; the freezing time of ultrasound application at 0.26 W/cm(2) was shorten by 14% and 90%, compared to IF and SF, respectively. UAF products showed significant (p<0.05) reduction in drip loss and phytonutrients (anthocyanins, vitamin C and phenolics) loss. Compared to SF products, IF and UAF products showed better textural preservation and higher calcium content. The radish tissues exhibited better cellular structures under ultrasonic power intensities of 0.17 and 0.26 W/cm(2) with less cell separation and disruption. Volatile compound data revealed that radish aromatic profile was also affected in the freezing process., (Copyright © 2015 Elsevier B.V. All rights reserved.)

To reduce the size of ice crystals in mushroom ( Agaricus bisporus ) contact ultrasound (300 W, 20 kHz) was applied during freezing and frozen storage. Stereomicroscopy was used to observe the ice crystal morphology, and DSC and NMR spectroscopy were performed to evaluate the water states in the samples. Results indicated that ultrasound irradiation initiated the nucleation of ice and reduced the mean size of ice crystals during freezing and frozen storage, and therefore improved the frozen product quality compared to the control samples. Most of the ice crystals in the ultrasound assisted frozen (UAF) samples were in the size range of 0–80 microns while that for the control samples were in the size range of 50–180 microns. SEM photos also proved that due to the application of ultrasound, the sizes of the ice crystals was reduced. This micro-scale information on the documentation of ice crystals will assist in understanding the ice crystal growth phenomena in an ultrasound assisted freezing process. [ABSTRACT FROM AUTHOR]

Abstract: The application of power ultrasound during immersion freezing significantly (P < 0.05) affected freezing rate of mushrooms. Ultrasound at 0.39 W cm−2 (20 kHz) reduced nucleation time by 24%, 53% and 34% in Lentinula edodes, Agaricus bisporus and Pleurotus eryngii respectively. Drip losses during the thawing process were found to be 10% less compared to control samples. Whiteness index increased when ultrasound intensity was higher than 0.27 W cm−2 (20 kHz) in L. edodes and P. eryngii whereas, ultrasound at 0.39 W cm−2 (20 kHz) showed the highest chroma value with lower yellowness and browning indices. Ultrasound at 0.39 W cm−2 (20 kHz) resulted in the highest textural hardness values in all the three mushroom varieties. Polyphenol oxidase and peroxidase enzyme activities were also significantly (P < 0.05) reduced with the increase in ultrasound power during ultrasound-assisted freezing (UAF). These results indicated that UAF can be a suitable technology for industrial freezing of mushroom. [Copyright &y& Elsevier]

In this study, the effect of ultrasound irradiation temperature and ultrasound intensity on the freezing and nucleation in strawberry samples was studied. The application of ultrasound irradiation at different temperatures was able to induce nucleation at lower degree of supercooling compared to the control samples. The achieved degree of supercooling in the ultrasound irradiated strawberries was linearly correlated to the ultrasound irradiation temperature. At the ultrasound irradiation temperature of −1.6 °C, the characteristic freezing time (CFT) was significantly shorter than that in the control sample ( p < 0.05). The application of ultrasound at higher intensities was found to effectively shorten the CFT. The degree of supercooling in ultrasound irradiated samples was not linearly correlated to ultrasound intensity. In conclusion, the combination of ultrasound irradiation temperature and intensity can be effective in controlling nucleation and freezing processes of perishable fruits such as strawberry. [ABSTRACT FROM AUTHOR]