Effects And Mechanism Of Ultrasound-Assited Curing On The Quality Of Beef

Curing processing is the essential step for the production of Chinese traditional sauce spiced beef.For conventional curing treatment,it need one to two days and the low penetration efficiency is the important issue that the most enterprise need to solve.In addition,the safety and the quality of final product could not be negatively influenced if the growth of pathogenic and spoiolage microorganisms could not been controlled effectively during this processing,Recent studies have shown that the rate of mass transfer,the water retention and the tenderness of meat could be accelerated and improved with ultrasound assisted curing processing and the inactivation for microorganisms could also be achieved.Thus the application of ultrasound to the curing stage of sauce spiced beef processing have potential to be applied for the improvement of production efficiency and product quality and safety.The current study firstly analyzed the effects of ultrasonic intensity and salt concentration for the diffusion coefficient of NaCl and moisture which improved the kinetics of mass transfer during ultrasonic assisted curing.Secondly,we evaluated the effects of ultrasound intensity on the edible quality and nutritional quality of beef after the curing procedure.Based on the results above,we studied the ultrasound treatment for the degradation,structure and oxidative modification of myofibril protein.As for the microbiology the present study utilized the common pathogenic and spoilage bacteria in beef like Escherichia coli 0157:H7 and Bacillus cereus to evaluate the influence of ultrasound treatment on the number of living bacterium in brining and beef.The Weibull frequency distribution model of Escherichia coli 0157:H7 and Bacillus cereus was established for the ultrasound sterilization in brining.Therefore,this dissertation discussed the mechanism of ultrasound assisted curing processing for the structure modification of myofibril protein and microorganisms inactivation.The main results of this study are as follows:1.The analysis of mass transfer kinetics for the ultrasound assisted curingThe calorimetry was used to evaluate the ultrasound energy efficiency which showed that the ultrasonic power with 150,200,250,200 W were corresponded to the ultrasound intensity at 2.39,6.23,11.32,20.96 W cm-2,respectively.Based on this measurement,we analyzed the effects of ultrasound intensity and salt concentration on the content of NaCl and water in beef.The studies revealed that,compared with the static brining treatment,the content of NaCl and water in beef were increased significantly with the ultrasound intensity and treatment time.The time of the curing processing could be shortened by 20%and the concentration of NaCl in brining could be reduced by 15 to 20%.When the ultrasound intensity was between 2.39 to 20.96 W cm-2,the salt and water content in beef was positively related to the ultrasound intensity.The Fick's second law was employed to establish the diffusion mathematical model for the ultrasound intensity or salt concentration in brining.The NaCl and moisture content in beef at different processing time could be calculated accurately by the established models.In addition,the percentage of explained variance(%VAR)for both ultrasound intensity and salt concentration in brining were greater than 95%.These results indicate that the proposed diffusion model for NaCl and moisture had good fitness and could describe the brining process adequately.These models could be used for the prediction of NaCl and water content in beef during the industrial production.On the other hand,there existed an exponential relationship between ultrasound intensity and diffusion coefficient at the same salt concentration with the correlation coefficients being greater than 0.98.These results indicated that,together with the model of Fick's second law above,the content of NaCl and moisture in beef could be calculated at other ultrasound intensity.Taking the factor of ultrasound intensity and salt concentration into consideration,the intensity of ultrasound was more advantageous for NaCl and moisture diffusion coefficient while the influence of salt concentration was less.2.Effect of ultrasound treatment on the quality of beef during curing processingThe eating quality and nutritional quality were employed to analyze the influence of ultrasound assisted curing treatment for the beef quality.Previous analysis have shown that the ultrasound intensity had a greater effect on the rate of mass transfer.The increased rate of NaCl and water penetration in beef might result in a remarkable quality changes.Therefore,in this chapter,we evaluated the effect of ultrasound intensity on the meat quality changes during curing processing.The results confirmed that the ultrasound assisted curing treatment could improve the tenderness,the texture properties and the water holding capacity of meat,which were helpful for the improvement of the edible quality of sauce spiced beef products.The observations of transmission electron microscope(TEM)showed that the myofibrils were ruptured along with the Z-line and M-line leading to the wider space between myofibrils as the ultrasound intensity increase.The illustration of ultrastructure of myofibril demonstrated that ultrasound treatment could destroy the structure of myofiber which could further affect the meat quality.As for the color of beef,the value of lightness(L*)could be increased by all ultrasound intensity treatment.With the short processing time,the redness(a*)of beef could increase while the longer treatment time could induce the decrease of this values.Considering the nutritional quality,ultrasound assisted curing processing caused the loss of essential amino acids and unsaturated fatty acids.3.Effects of ultrasound treatment on the degradation and structure changes of myofibrillar protein during curing processingThe results of TEM observation showed that the ultrasound assisted curing treatment could induce the changes of myofibril structure.Thus we continued to analyze the effects of ultrasound treatment on myofibril protein degradation.Results showed that ultrasound assisted curing treatment could increase the myofibril fragmentation index and promote the degradation of desmin and troponin-T protein.These phenomena could explain the improvement of tenderness and water retention of beef after ultrasound treatment.LF-NMR analysis showed that the ultrasound assisted curing had no significant effects on the T2b value of myofibril while reduced the ratio of bound water(P2b),indicating that ultrasound might result in the structure changes of myofibril protein.In addition,the mobility of capillary water(T21)could be affected by ultrasound treatment significantly.Meanwhile,the proportion of the mobility of capillary water(P21)increased after the application of ultrasound.The results above could emphasize the improvement of the water holding capacity of beef after ultrasound treatment.As for the structure of myofibril protein,the ultrasound assisted curing treatment could induce the increase in the protein surface hydrophobicity and ?-sheets while decreases in a-helix structures.4.Effects of ultrasound treatment on the oxidation modification of myofibrillar protein during curing processingFor the evaluation of oxidation effect of ultrasound,we determined the concentration of hydrogen peroxide in brining during the process of ultrasonic assisted curing.Results showed that a marked increase of H2O2 amounts in the liquid with the increase of ultrasound intensity and treating time.According to the measurement of TBARS,the ultrasound application could improve the extent of lipid oxidation of beef.The results could explain the decreased content of unsaturated fatty acid after ultrasonic treatment.The increased carbonyl group and decreased total sulfydryl content revealed that ultrasound assisted curing could promote the extent of myofibril protein oxidation.However,the content of free sulfhydryl was increased with ultrasound intensity and treatment time.These results suggested that the protein oxidation was accompanied with the change of protein structure during the ultrasound treatment.On the other hand,according to results of the non-reducing SDS-PAGE and Nano LC-ESI-MS/MS analysis,the content of protein polymerization was increased with the ultrasound intensity and the polymers were mainly formed by the MHC through the covalent disulfide bond after the ultrasound treatment.The results could further confirm that the ultrasonic treatment could induce the myofibril protein oxidation.5.The establishment and the application of the microorganism inactivation model for the ultrasound assist bacterial sterilizationThe current study analyzed the effects of ultrasound intensity on the number of Escherichia coli 0157:H7 and Bacillus cereus in the brining and beef.The results showed that,for the Escherichia coli 0157:H7,both the ultrasound and static brining treatment could reduce the number of living bacteria significantly in the brining.As for the Bacillus cereus,only the ultrasonic intensity was higher than 6.23 W cm-2 could achieve the effect of cell inactivation.The counting number of the living microorganisms in beef indicated that the static brining and ultrasound treatment with low intensity could promote the penetration of Escherichia coli 0157:H7 and Bacillus cereus into the beef.When the higher intensity of ultrasound applied,the short processing time could improve the number of microbial populations in beef while the long processing time could reduce the number of number of bacterium in beef.In addition,the present study utilized the Weibull frequency distribution equation to establish the model for the Escherichia coli 0157:H7 and Bacillus cereus in brining.Good fitness of Weibull model was obtained with the distinct shape of curves between two microorganisms which could describe the microorganism inactivation by ultrasound adequately in salt solution.Moreover,the particle size distribution measurement for the Escherichia coli 0157:H7 and Bacillus cereus revealed that,bacterial cells after ultrasound treatment could lead to a small volume distribution at low sizes(50?200 nm while the area of the main peak was decreased and moved to the low sizes range.In addition,the fluorescence assay of the two bacterial revealed that ultrasound treatment could lead to the damage of the integrity of cell membrane.The number of damaged cells were increased with the ultrasound intensity and treatment time.These results demonstrated that ultrasonic treatment could lead to the membrane damaged and fragmented of the bacteria,which further confirmed the effects of inactivation due to the ultrasound assisted curing treatment.