Analysis on correlation between change of moisture status and texture during processing of air-dried yak meat

Abstract: The objective of this paper was to research the law of moisture migration, and to investigate the correlation between moisture status and the histological structure and texture during the processing of dried yak meat. The semimembranosus of the healthy and disease-free male yaks when they were from 3 to 4-year-old under natural grazing was selected to remove the fascia and fat on its surface and cut into the strips with cross-section of 2 cm × 2 cm. At the same time, the meat was hung on the wire and kept a distance of 1-2 cm between 2 adjacent pieces of meat in a dark and naturally ventilated place in Xiahe County, Gannan Prefecture, Gansu Province. The temperature was from -10 to -15℃ and the relative humidity was from 50% to 75% there. The samples were collected to analyze the changes of indices during natural drying of 60 d. Moisture ratio of dried yak meat was analyzed by the direct drying. Moisture activity and moisture status were evaluated respectively using the water activity meter and the low field nuclear magnetic resonance (LF-NMR). The change of texture characteristics of dried yak meat was measured by texture analyzer and the histological structure of dried yak meat was observed by hematoxylin eosinstaining. The results showed, during the 60 days of drying, moisture ratio decreased by about 60.27%. The final water activity reached about 0.308 and decreased by about 66.73%. On the 30th day, the peak integral area, which is immobile water content, decreased by about 98.12%, and no peak appeared after 40 days. With the reduction of moisture ratio, myofibril cross-sectional area, muscle fiber diameter and distance between muscle fibers were significantly decreased (P<0.05) respectively by about 42.65%, 67.15% and 61.22%. The hardness, cohesiveness, gumminess and chewiness were significantly increased (P<0.05), and among them, the chewiness that best represents the taste of dried meat increased by 1 229.16 g. However, the springiness and resilience decreased significantly (P<0.05) during the whole process.The change of immobilized water shows a significant negative correlation with changes in hardness, cohesiveness, gumminess, and chewiness，and have a significant positive correlation with springiness and resilience. Moreover, the decrease in distance between muscle fibers, diameter of myofibers and cross-sectional area of myofibers was negatively correlated with changes in hardness, cohesiveness, gumminess, and chewiness significantly, but have a significant positive correlation with changes in springiness and resilience. It shows that the immobile water in yak meat expands and evaporates continuously. It causes the contraction and aggregation of the muscle fiber of yak meat, which leads to the change of its textural properties in the process of natural freezing and drying. The results can provide a reference for the mechanism understanding of moisture migration and product quality control in the processing process of traditionally dried yak meat.