Low-variable temperature and high humidity thawing improves lamb quality

The effects of a low-variable temperature and high relative humidity thawing method (LVTHRHT) test group, thawing temperature 2°→6°C→2°C, RH>90%) and a conventional air thawing method (control group, thawing temperature 4°C) on the quality of lamb hindquarters were investigated in this paper. The indexes including color, cooking loss, thawing loss, protein content of thawing drip, texture profiles analysis (TPA) of thawed hindquarter and surface hydrophobicity of myofribrillar protein were measured. The microstructures of the transverse section of frozen and thawed samples were observed by scan electric microscopy (SEM). The effects of different thawing methods on the component, aggregation and degradation of myofibrillar protein were studied by SDS-PAGE gel electrophoresis. The results show that LVTHRHT could significantly decrease (P* value, redness a* value, hardness and chewiness. However, there were no significant (P>0.05) effects on yellowness b* value, springiness and gumminess; the results of SDS-PAGE gel electrophoresis. SEM showed that both of the thawing methods could result in aggregation and degradation of myofibrillar protein, and damage the microstructure of muscle. While the microstructure of muscle fiber bundles of control group was damaged more seriously, the air thawing method tore more muscle fiber bundles and exhibited a visibly larger gap between muscle fibers compared to the LVTHRHT. Compared to the most common thawing method (in air at 4°C), there were many advantages of the LVTHRHT method: preventing the loss of the surface water and significantly decreasing thawing loss, cooking loss, nutrition loss (protein); formation of water film to prevent oxidation of meat, retarding the deterioration of lamb quality, and the physicochemical characteristics of the thawed lamb were closer to fresh meat. This new thawing method requires only a slight change to the existing 4°C defrost garage: installing steam pipes to the defrost garage used for increasing the temperature and humidity of the defrost garage to realize high relative humidity thawing. Installing frequency refrigeration fan used for decreasing the temperature of the defrost garage, the combination of hot steam pipes and frequency refrigeration fan could realize LVTHRHT. Besides, installing temperature sensors and humidity sensors to monitor the temperature and humidity of a defrost garage, when temperature was higher than 6°C, the frequency refrigeration fan stared to work until the temperature reached 2°C. When the temperature was lower than 2°C, the hot steam system started to work until the temperature reached 6°C. When the relative humidity was lower than 90%, the hot steam system started to work until the relative humidity reached 90%. Coordination of the two systems would ensure that during the entire thawing process, the temperature was between 2°C and 6°C, and the humidity was greater than 90%. The LVTHRHT could significantly prevent the deterioration of lamb quality, and it was low cost and easy to operate. This research provides a theoretical basis to apply the LVTHRHT method in production and indicants a promising application potential for LVTHRHT in the thawing of frozen meat.