The insignificant changes in gel qualities and protein structure induced by vacuum as well as vacuum-assisted thawing were observed compared with control group. For vacuum thawing, the frozen samples were thawed in a low oxygen environment which exerts reduced effects on microbial reproduction and oxidation reactions. In addition, the insignificant negative impacts on pH and microbial growth in pork and sensory properties of the blocks of Pacific cod were compared between ultrasound thawing and common thawing. For example, the thawing times of mango, edamame and frozen fish induced by ultrasound thawing were reduced by 51–73%, 54.39% and 71%, respectively. Previous studies have reported that the melting speed of ice crystals is faster than that of most common thawing methods, shortening the thawing times of samples. Ultrasound has been verified to function effectively for frozen foods, saving thawing time and improving the qualities of the meat. Scanning electron microscopy images showed that the myofibril arrangements of thawing samples were looser than those of the FM samples with compact and ordered structure, which was proven by the obvious increase in the myofibril gap value of the thawing samples. The decreases in uniform degrees of internal temperature distributions of muscles from the thawing samples were analysed by infrared thermography.
The increases in carbonyl content and TBARS value indicated that proteins and lipids in the thawing samples were oxidized. Changes in quality of the VT and UT samples were less significant than those of the MT samples. The results showed that a significant decrease ( p < 0.05) in quality compared with those of fresh meat (FM) occurred for all of the thawing samples, especially for the MT samples. The effects of vacuum thawing (VT), ultrasound thawing (UT) and microwave thawing (MT) on the quality, protein and lipid oxidation, internal temperature distribution and microstructure of porcine longissimus lumborum were compared.
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