EFFECTS OF DIFFERENT FREEZING RATES AND THAWING RATES ON THE MANUFACTURING PROPERTIES AND STRUCTURE OF PORK

ABSTRACT

Uniform design was adopted, and three factors, i.e., freezing rates with two levels, thawing rates with six levels and individual (six pork M. Longissimus dorsi from three pigs), were investigated. After thawing, thaw loss (TL), cook loss (CL), water-holding capacity (pressing loss) and protein solubility were measured. Structure was also viewed using transmission electron micrographs and scanning electron micrographs. The results showed that freezing rates, thawing rates and individual significantly affected TL and CL. Eliminating the effects of fixed factors of different individuals, the effects of thawing rates and freezing rates on TL and CL were nonlinear. Significant interactions between freezing rates and thawing rates on both TL and CL were observed. Water-holding capacity was correlated to different animals and was independent of freezing rates and thawing rates. Thawing rates and animal had some effects on total protein solubility (TPS) and myofibrillar protein solubility (MPS); however, freezing rates had almost no effects on them. Considering the CL, TL, TPS and MPS comprehensively, fast freezing rate and slower thawing rates (0.75 cm/h) were the optimal combination. Scanning electron micrograms of meat frozen at different freezing rates showed that ice crystals formed at different sizes and distribution. Slow freezing rates resulted in intercellular ice crystals, while quick freezing rates resulted in intracellular ice crystals. Freezing and thawing processing had some negative effects on the structure of meat. Thawed meat showed a reduction in the density of the Z-disks, and the overall integrity of the myofibril was lost; the quicker the thawing rates were, the more severe the disruption of the myofibril.

PRACTICAL APPLICATIONS

The freezing of meat has been widely used as an economically favorable way of storage, and generally, frozen meat should be thawed before it is used in the subsequent production. However, freezing procedures, frozen storage and the thawing procedures could affect meat quality attributes such as thaw loss, color and tenderness. Although there are many different methods of thawing, air thawing and water thawing are still the methods widely used in the food industry, especially in China, for its priority in price and convenience. Therefore, experiments were carried out to research the effect of freezing rate and thawing rate, which were similar to the present practice of the food industry in China. We found that fast freezing and low thawing were the optimal combination, which can decrease thaw loss, cook loss and pressing loss, and can maintain the functional properties of frozen pork meat. The result of our research was operable and very useful for both the food industry and the consumers to control the quality of frozen meat and to enhance the eating quality and the monetary value.