Development and application of low-variable temperature and high humidity thawing garage

Abstract: Frozen storage is a method widely used for preservation of meat products. However, quality deterioration may occur during the subsequent thawing process, such as flavor deterioration, weight decreasing, juiceless, protein oxidation, tenderness reducing and discoloration. Thawing at a low temperature to avoid notably rising in temperature and excessive dehydration of meat is a useful method to assure meat quality, and a high relative humidity is required to minimize thawing weight loss. Therefore, a low-variable temperature and high humidity thawing garage was developed to improve the quality of thawed meat. This new thawing garage only required slight changes to the existing 4℃ defrost garage including 1) installing heating coils and steam pipes to the defrost garage, which were used for increasing the temperature and humidity of the defrost garage to realize high relative humidity thawing; and 2) installing frequency refrigeration fans, which were used for decreasing the temperature of the defrost garage. The combination of heating coils, hot steam pipes and frequency refrigeration fans could realize low temperature and high humidity thawing. In addition, temperature sensors and humidity sensors to monitor the temperature and humidity of the thawing garage were also installed so that the frequency refrigeration fans started to operate until the temperature decreased to 2℃ when the temperature was higher than 8℃, the hot steam system started to operate until the temperature increased to 8℃ when the temperature was lower than 2℃, and the hot steam system started to operate until the relative humidity increased to 90% when the relative humidity was lower than 90%. The coordination of the two systems could ensure that during the whole of the thawing process the temperature was kept at 2℃~8℃, and the humidity was greater than 90%. The operating performance of the developed thawing garage was also tested based on the evaluation of the main parameters of the thawing garage (heating load, cooling load, humidification steam consumption and total steam consumption) for thawing 20 t frozen beef (average temperature was ?18℃). Subsequently, the effects of the developed low-variable temperature and high humidity thawing garage on beef qualities were compared with the commonly 4℃ defrost garage. The results showed that the heating load, cooling load, humidification steam consumption and total steam consumption for thawing 20 t frozen beef were 95.94 kW, 18.77 kW, 8.78 g/s and 49.19 g/s, respectively. Compared with the commonly 4℃ defrost garage, the thawing loss, protein content of drip, cooking loss of beef decreased by 44.17%, 21.61% and 20.30%, respectively, the content of oxymyoglobin increased by 41.04%, the content of metmyoglobin decreased by 58.69%, and the hardness and chewiness of thawed beef increased by 64.88% and 62.23%, respectively. These results indicated that this developed low-variable temperature and high humidity thawing garage could decrease deterioration of beef quality and realize fresh-keeping thawing for frozen beef. This study could provide valuable information for designing and developing this new low-variable temperature and high humidity thawing garage that could be used for thawing of frozen meat in the meat industry.