低温高湿变温解冻库的研制与应用

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

为解决现有冻肉解冻库解冻速率慢、营养流失大、解冻过程氧化劣变严重等问题，研制了一种新型的低温高湿变温解冻库，该解冻库由绝热库体、蒸汽加热加湿系统、变频制冷系统和控制系统组成。通过各系统的协调运作，使库内温度始终维持在2-8℃，相对湿度始终保持在90％以上，从而实现冻肉解冻过程中的有效保鲜。同时通过低温高湿变温解冻库解冻20t冷冻牛肉的加热负荷、制冷负荷、加湿蒸汽量及总蒸汽量等工艺参数的优化计算，研制出用于冷冻肉解冻的20t低温高湿变温解冻库，并进行了生产验证试验，比较分析了该解冻库与常规4℃解冻库对解冻牛肉品质的影响。结果表明，该低温高湿变温解冻库解冻入库平均温度为-18℃的20t冷冻牛肉耗时约12h，加热负荷为95．94kw，制冷负荷为18．77kW，加湿蒸汽量为8．78g／s，需要总蒸汽量为49．19g／s；与常规4℃解冻库相比，低温高湿变温解冻库解冻汁液流失率、汁液蛋白含量及解冻牛肉蒸煮损失率分别显著降低了44．17％，21．61％及20．30％，解冻牛肉肌红蛋白含量显著增加了41．04％，高铁肌红蛋白含量显著降低了58．69％，硬度及咀嚼性分别显著增加了39．86N及15．11N，实现了冷冻牛肉的保鲜解冻。该研究为低温高湿变温解冻库的研制提供了参考，有利于解决冷冻肉解冻过程中的品质劣变问题。

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 coifs, 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 frequeficy 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.