Maintaining processing quality and histological structure of yak rumen smooth muscle by proper heating temperature

Abstract: Smooth muscle is a category of muscle tissue, and is widely distributed in blood vessels, stomach, intestines and other internal organs. Smooth muscle has wealthy nutritional value, special flavor and texture. Smooth muscle included in animal organs can be cooked to special dishes in lots of Asian countries. However, smooth muscle is treated as by-product and little as valuable muscle compared to skeletal muscle. In order to meet consumers' demand for new valuable food resource and high edible quality, we investigated the processing quality and histological structure change of yak rumen smooth muscle under different temperatures. The yak rumens were picked from a commercial abattoir, and the yaks were aged 36-38 months, had the same feeding background, and were slaughtered by conventional slaughtering method. The rumens were obtained, vacuum packaged and transported to the laboratory at (3±1) ℃. The smooth muscle was obtained after removing the villi, mucosa and fat. The yak rumen smooth muscle was cooked at 50, 60, 70, 80, 90, 100 °C for 60 min, respectively. And the cooking loss, heat shrinkage rate, Warner-Bratzler shear force (WBSF), collagen content and histological structure of yak rumen smooth muscle were evaluated. The results showed that cooking temperature had significant effect on WBSF, cooking loss, heat shrink rate, collagen content and histological structure. As the increasing of cooking temperature, the cooking loss value and heat shrinkage rate significantly increased (P<0.05); the initial cooking loss value of yak rumen smooth muscle was 9.93%±1.71% and then increased to 34.93%±3.06%; the heat shrinkage rate increased by 306.78%, from 10.18%±0.64% to 41.41%±1.64%. However, WBSF and collagen content significantly decreased (P<0.05) with the increase of cooking temperature; the value of WBSF from (116.62±0.78) N to (61.74±1.67) N; the content of collagen decreased by 57.49%, from (72.87±1.97) to (30.98±1.91) mg/g. The histological structure indicated that with the increasing of cooking temperature, the muscle fiber diameter of yak rumen smooth muscle and the crack between smooth muscle fiber changed from big to small, but the thickness of the primary and secondary perimysium changed from small to big. The muscle fiber diameter of the yak smooth muscle decreased from (131.13±13.94) μm to (78.13±6.51) μm; but the thickness of the primary and secondary perimysium increased by 306.59% and 60.71%, respectively. From the quality and structure change of yak rumen smooth muscle under different temperatures, the yak rumen smooth muscle processing quality decreased with the increase of temperature, and the histological structure shrank with the increase of temperature. In order to satisfy the needs of consumers, food industry and institute should pay more attention to cooking temperature, and should choose suitable cooking style to different products which focuse on different consumers. In summary, we suggest the yak rumen smooth muscle is cooked at 80-90 ℃ for 60 min, and the product will have satisfying processing quality and shape. The result will provide technical reference for the processing of by-products which include smooth muscle.