Effects Of Different Freezing And Thawing Methods On Quality And Microstructure Of Mutton Sheep Viscera

In this paper,the viscera(heart,liver,lung and kidney)of Inner Mongolia mutton sheep were used as experimental materials.The samples were frozen by different freezing methods(freezing at-20?,freezing at-80? and liquid nitrogen quick freezing),followed by stored at-20? for 120 days.Some indexes were detected and analyzed,such as the nutrient composition,pH,rate of water loss,thiobarbituric acid(TBA)value,volatile base nitrogen(TVB-N)value,colour aberration,sensory index,texture and other characteristics of mutton sheep viscera.Scanning electron microscopy was used to observe the changes of visceral tissue structure in frozen mutton sheep.The samples were thawed by three kinds of methods:natural thawing,ice thawing and microwave thawing.The pH,colour aberration and total bacterial count of samples were determined.Effects of freezing and thawing methods on the eating quality of mutton sheep viscera were comprehensively analyzed.The research results are as follows:(1)The nutrient component of mutton sheep viscera:The contents of water,crude protein,crude fat and crude ash in mutton sheep heart were 72.79%,15.04%,10.05%and 1.71%,respectively.The mutton sheep liver were 76.68%,19.93%,5.79%and 1.84%,separately.The conterparts in mutton sheep lung were 68.75%,13.06%,2.27%and 1.41%,respectively.The four basic nutrient contents of mutton sheep kidney were 74.42%,16.00%,5.62%and 1.66%,respectively.(2)After frozen by different methods,The results showed that there was no significant difference in the above indexes of mutton sheep viscera between liquid nitrogen freezing and-80°C freezing.However,the indexes of the former was significantly better than those of-20“C freezing group.(3)Scanning Electron Microscope(SEM)was used to observe the tissue structure of frozen mutton sheep viscera.It was found that the viscera of mutton sheep treated by liquid nitrogen freezing had compact structure micro aperture,after freezing at-20?,the structure of the sample was more porous and larger with muscle fiber breaking.(4)According to the results of sensory score,pH,TVB-N value,TBA value and other freshness indexes of mutton sheep viscera during the frozen periods show that the viscera of different frozen treated mutton sheep had different freshness indexes during the frozen storage period.However,the visceral freshness of mutton sheep treated with liquid nitrogen freezing met food standards and was better than the other two freezing groups.(5)The color differences,water loss rate,texture and other physical and chemical indexes of mutton sheep viscera were determined.With the extension of frozen storage,The color difference and water loss rate of the mutton sheep after liquid nitrogen treatment changed slowly and was lower than other freezing groups,which was followed by-80? group.During the frozen storage period,the texture of the mutton sheep viscera decreased with the increasing of the storage time,liquid nitrogen group's texture decreased relatively slowly,and maintained well.(6)The viscera of the mutton sheep were thawed separately by natural thawing,ice thawing and microwave thawing.The shearing force,water loss rate,pH,color difference and total number of colonies were determined.The results showed that the microwave thawing was better than the other two thawing methods.Microwave thawing of viscera was time-saving and had minor changes of water loss and pH.Therefore,microwave thawing was more suitable for thawing of viscera of mutton sheep.