| Traditional spiced beef has problems of low yield,uncontrollable quality,and high energy consumption,making it unsuitable for industrial production.Studies have shown that the sous-vide process can effectively improve the texture and yield of the product.However,the sous-vide process is time-consuming and the goal of improving production efficiency and saving energy is not fully achieved.Currently,ultrasonic processing technology has been applied to meat processing,which can effectively reduce processing time and ensure product quality.Therefore,the use of new equipment and new methods for quantitative cooking of beef tendon meat and the development of ultrasonic-assisted sous-vide cooking spiced beef products are of practical guidance to solve the problems of traditional spiced beef.This paper systematically investigates the optimization of the process parameters of ultrasonic-assisted sous-vide cooking spiced beef based on the new equipment and the changes in physicochemical quality and flavor during the cooking of spiced beef under the optimal process and explains the mechanism of the changes from the perspective of protein oxidation to provide a theoretical basis for the quality control of the relevant products.Firstly,based on the existing sous-vide cooking spiced beef process,four factors,namely ultrasonic frequency,ultrasonic power,ultrasonic time,and cooking temperature,were selected as the influencing factors in this study.The mathematical models developed were all highly significant yield,shear force,and fuzzy sensory score as the response values for the response surface tests,respectively（P<0.01）.The resulting combined optimal regression equation was:Y=70.30+0.56X1-0.26X2+0.15X3+0.93X40.29X1X2+0.42X1X3-0.32X1X4+0.47X2X3+0.34X2X4+0.17X3X4-2.22X121.63X22-1.69X32-1.77X42.At the same time,the optimal process parameters for ultrasonic-assisted sous-vide cooking of spiced beef were determined in combination with the operability of the actual experiment:ultrasonic frequency of 28 kHz,ultrasonic power of 60 W,ultrasonic time of 37 min,and cooking temperature of 71℃.The results of the validation experiments showed that ultrasonic-assisted sous-vide cooking significantly increased the yield and improved the taste of spiced beef compared to traditional cooking methods（P<0.05）.Secondly,the traditional spiced beef（CT group）and sous-vide cooking spiced beef（SV group）were used as controls to further determine the yield,color,tenderness,textural characteristics,microstructure,pressure loss rate,moisture distribution and organoleptic score during cooking based on the best ultrasonic-assisted sous-vide cooking spiced beef process（USV group）.The results showed that the yield of the USV group decreased gradually with increasing brining time,but was significantly higher than that of the CT group（P<0.05）.At 80 min of cooking,the central temperature of beef with ultrasound-assisted sous-vide cooking spices had reached the set temperature,effectively shortening the processing time.Sous-vide cooking slowed down the oxidation of the spiced beef,while prolonged high-temperature cooking increased the oxidation of myoglobin in the spiced beef,which harmed its color.The results of textural properties,tenderness,and microstructure showed that traditional spiced beef had a loose texture and that ultrasonic-assisted sous-vide cooking of spiced beef was more palatable and tasted better when the cooking time was controlled at 80-100 min.This is also confirmed by the sensory evaluation results.At 40-80 min,the cavitation effect of ultrasound causes the myogenic fibers of the beef to swell and the water-absorbing capacity of the spiced beef to increase,improving the water retention.When the central temperature of the spiced beef stabilized,the continuous cooking destroyed the integrity of the muscle fibers,and the water loss from the spiced beef accelerated,resulting in a reduction in water retention.Gas chromatography-mass spectrometry,electronic nose,and relative odor activity value（ROAV）were used to investigate the changes in volatile flavor substances and their precursors during the cooking of beef with ultrasonic-assisted sous-vide cooking spices.The results showed that ultrasonic-assisted sous-vide cooking could promote the formation of free fatty acids and free amino acids in spiced beef.The USV100 and USV120 groups showed better food value and flavor quality in terms of free fatty acid and free amino acid content and composition.The results of the electronic nose test showed a clear distinction in aroma composition between the different treatment groups,indicating that the volatile odor of spiced beef varied considerably under different cooking methods and cooking times.Among them,hexanal,heptanal,octanal,nonanal,decanal,dodecanal,and eugenol were the key main flavor substances（ROAV≥1.00）common to all treatment groups,while the modified flavor components（0.10≤ROAV<1.00）were mainly composed of alcohols,hydrocarbons,and phenols.The volatile flavor substances were mostly concentrated in the rightmost end of the first principal component and the uppermost end of the second principal component,and the volatile flavor substances were more abundant in the USV80,USV100,and USV120 groups.The ultrasonic-assisted sous-vide cooking was found to promote the degradation of spiced beef proteins and lipids to produce more volatile flavors with low threshold values,which in turn resulted in a richer overall flavor profile.Finally,the effect of ultrasonic-assisted sous-vide cooking on the oxidation and digestive characteristics of spiced beef proteins were investigated,and inter-indicator correlations were modeled by partial least-squares discrimination analysis（PLS-DA）.The results showed that the degree of protein and lipid oxidation in the CT group was significantly higher than that in the USV and SV groups（P<0.05）.The fluorescence intensity of Schiff bases showed that ultrasonic-assisted sous-vide cooking caused intense protein-lipid interactions,which had a beneficial effect on the flavor quality of spiced beef.SDS polypropylene gel electrophoresis and secondary structure results showed that the three cooking methods caused different levels and types of protein cross-linking aggregation,with the CT group losing all protein bands and the SV and USV groups producing more small molecule masses proteins.The synergistic effect of ultrasound and sous-vide cooking weakened the hydrogen bonding that maintains the stability of the α-helix and transformed it into a β-turn and random coil.two-step digestibility was significantly higher in the SV and USV groups than in the CT group（P<0.05）.The two-step digestibility of beef cooked with ultrasound-assisted sous-vide cooking tended to increase and then decrease,thus making the USV80,and USV 100 groups more suitable for consumption in terms of digestion and absorption. |
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