Study On The Effects Of Magnetic Field Treatment On Frozen Pork And Frozen Beef

With the gradual acceleration of economic growth,Chinese consumers' enthusiasm for meat consumption has increased year by year,and the current situation of difficulty in obtaining fresh meat has promoted the development of freezing technology.Magnetic field-assisted freezing technology has attracted much attention because of its good biocompatibility and safety.Studies have shown that food can quickly pass through the maximum ice crystal formation zone during the magnetic field freezing process,thereby forming smaller ice crystals and reducing mechanical damage to cell structure.In this study,the traditional refrigerator was used as a control,the magnetic field(1 mT static magnetic field and 1 mT alternating magnetic field)freezer was used to freeze and thaw pork and beef for 1,3,5,and 7 cycles(freeze at-20? for14 h and thaw at 4? for 10 h as a cycle)and then freeze them for 2,4,6,and 8 weeks,surrounding the water distribution and state,physicochemical properties and sensory quality of pork and beef.The effects of magnetic field on the quality of frozen pork and frozen beef were discussed.The main results were as follows.Firstly,the effects of different magnetic field conditions on the physicochemical properties of freezing-thawing pork and beef were investigated to determine the subsequent freezing storage condition.The indicators included freezing curve,dry consumption rate,drip loss rate,water content,color value and total volatile basic nitrogen(TVB-N)content.The results showed that the freezing points of pork and beef with 1 mT static magnetic field and 1 mT alternating magnetic field decreased,and the phase transition time and overall freezing time were significantly shortened,and the phase transition time of the 1 mT alternating magnetic field group were 66.67%(pork)and 65.00%(beef)shorter than that of the refrigerator group,and the overall freezing time has been shortened by 95 min(pork)and 90 min(beef),respectively.In addition,in the same freezing-thawing cycle,pork and beef under the condition of 1 mT alternating magnetic field always maintained the lowest dry consumption rate,drip loss rate,and higher water content,the second was 1 mT static magnetic field group and the last was traditional refrigerator group.In the same freezing-thawing cycle,pork and beef have the highest L* and a* values(p<0.05)under the condition of 1 mT alternating magnetic field,the b* value had no obvious trend,and the ?E value was the smallest,which indicated that this condition retained better color of meat.Furthermore,the pH difference between the traditional refrigerator group and 1 mT alternating magnetic field group in the same freezing-thawing cycle was small,but magnetic field treatments effectively reduced the increase in TVB-N content of meat after freezing-and-thawing,and retained the freshness of the meat degree.Therefore,based on the above indicators,1 mT alternating magnetic field was selected as the magnetic field condition of the frozen storage experiment(for 8 weeks)and then a batch of pork and beef were frozen in a traditional refrigerator and magnetic field freezer at the same time.The water distribution and state,physicochemical properties and sensory quality of pork and beef were compared under this two conditions.In the frozen storage experiment,the influence of the magnetic field on water condition of frozen pork and beef was first investigated.The indicators included dry consumption rate,drip loss rate,water content,water holding capacity,and moisture distribution status and state.The results showed that frozen pork and beef under the condition of 1 mT alternating magnetic field always maintained lower dry consumption loss rate,drip loss rate,and higher water content and water holding capacity.The magnetic resonance imaging(MRI)images also showed that,compared with traditonal refrigerators,1 mT alternating magnetic field can effectively slow down the migration process of non-flowing water to free water in meat,so that pork and beef retained more water during the same frozen storage period.Secondly,the color value,pH value,TVB-N content,total number of colonies,total number of molds and yeasts,and microstructure of pork and beef were tested to show the effects of magnetic field on the physicochemical properties of frozen pork and beef.The results showed that under the same frozen storage period,the L* and b* values of pork and beef under the condition of 1 mT alternating magnetic field had no obvious trend,but the a* value was significantly higher than that of traditional refrigerator group,and the ?E value was smaller.In the late stages of frozen storage,the pH of the magnetic field group was lower than that of traditional refrigerator group,which slowed down the spoilage of frozen pork and beef.Under the same frozen storage period,the TVB-N content and microbial indicators of traditional refrigerator group were higher than those of 1 mT alternating magnetic field group,and the TVB-N content of beef being frozen for 6 weeks in refrigerator seriously exceeded the limit,reaching 32.99 mg/100 g,which was larger than the TVB-N content of beef being frozen for 8weeks in magnetic field(27.29 mg/100 g).In addition,the muscle structure of the meat in the magnetic field group was clearer,the muscle fibers were more complete and were arranged more closely and orderly.Finally,the analysis of free amino acids(FAA),hydrolyzed amino acids(HAA)and volatile components,electronic nose and sensory evaluation of pork and beef under different frozen storage conditions.The results showed that the total content of FAA of pork and beef frozen under 1 mT alternating magnetic field was significantly reduced,the total content of HAA was significantly increased,and relative content of bitter FAA was reduced.In addition,the volatile components detected in pork and beef were mainly aldehydes and alcohol flavor substances,among which hexanal,heptaldehyde,octanal,nonanal,1-octene-3-ol had major contributions to meat flavor.In the same frozen storage period,the relative content of aldehydes in the 1 mT alternating magnetic field group were less than that of traditonal refrigerator group,and indole,2-pentylamine were only detected in the refrigerator group.In addition,the sensory evaluation and electronic nose analysis results showed that 1 mT alternating magnetic field can improve the color,smell,texture,tissue state and other sensory qualities of pork and beef during frozen storage,and better retained the original flavor of the meat.In conclusion,the application of magnetic field during the freezing process can significantly delay the deterioration of the quality of frozen pork and beef and retain the original physicochemical properties and flavor characteristics of pork and beef to the maximum extent.