Study On Preparation And Properties Of Protein Isolates From Rabbit By PH-Shifting

Rabbit meat has high nutritive value.China is the world's largest producer of rabbit meat,but the rabbit meat processing industry needs to be developed.And there are few highly processed products of rabbit meat.Protein isolates from animals have high nutritive value,which can be directly processed into food or as nutrient supplement and food additive for food processing.As a source of high quality protein,rabbit meat can be used as raw material to prepare rabbit ptotein isolate.It can enrich the species of rabbit products and improve the economic value of rabbit.pH-shifting,as a new protein extraction technology,has many advantages,such as short extraction time,high recovery rate,little protein denaturation and good safety.It has been widely applied in plant protein and animal protein fild.In this experiment,rabbit meat with high protein content was used as raw material.Firstly,the optimum method of extracting by pH-shifting was established.Futhermore,the effect of pH-shifting on the structure and properties of myofibrillar protein was studied.Then,I studied the properties of protein isolate extracted by pH-shifting,and the best extraction method was determined.Finally,the gel properties of protein isolate was studied.The experiment draws the following conclusions:The protein content of rabbit meat is higher than 20%,which was suitable for the preparation of protein isolate.The best condition of preparaing protein isolate of rabbit meat by pH shifting was determined.Protein isolate of rabbit meat was prepared by solving at pH 3.0 and 12.0 with solid-liquid ratio 1:9?w/v?,and then precipitated at pH5.5.The protein yield was from 59.04%to 62.04%.Moreover,alkali solubilization led to higher yield than acid solubilization.The fat reduction of acid and alkali solubilization were 62.04%and 59.04%.SDS-PAGE analysis showed that,the extraction process could lead to partial degradation or aggregation of rabbit muscle protein,but it did not cause severe denaturation.The pH-shifting can be used in the preparation of protein isolate from rabbit meat.The results showed that:solubility,total sulfhydryl content,emulsifying activity and emulsion stability of myofibrillar protein decreased after treated by pH-shifting.But the surface sulfhydryl content had no significant changes?P<0.01?by acid solubilization.Both acid and alkali solubilization can decrease the content of hydrogen bond.In addition,the two treatments made surface hydrophobicity and turbidity increased.The endogenous fluorescence intensity of myofibrillar protein was reduced by acid and alkali solubilization.After alkali treatment,the intensity of endogenous fluorescence was the lowest,and the degree of red-shift of?_max was the greatest.Morever,pH-shifting also resulted in the decrease of gel strength,water holding capacity,but gel whiteness changed little.Properties of myofibrillar protein had smaller change by acid solubilization.So acid solubilization treatment is more suitable for rabbit protein isolate.The protein content of protein isolates were higher than 90%?dry basis?.But fat?dry basis?and ash content?dry basis?of protein isolate were lower than that of rabbit meat.Protein isolates contained essential amino acids,and retained the characteristics of high lysine content of rabbit meat.The first limiting amino acid is threonine.W_EAA/W_TAAAA are both higher than 40%,and W_EAA/W_NEAAEAA are both higher than 70%.In general,the proportion of protein amino acids is balance.Protein isolate belongs to the source of high quality protein.In physicochemical properties,the protein dissolving curve was similar to the muscle protein but solubility decreased.The total sulfhydryl content and surface sulfhydryl content,but total sulfhydryl content of protein isolate by acid solubilization had a not significant change?P<0.01?.Protein isolates had certain emulsifying activity,emulsifying stability,foaming capacity and foaming stability.They can be used as natural emulsifier or foaming agent in food processing.From the results of sensory evaluation,pH-shifting can deodorize special fishy smell of rabbit meat.The result showed that the kinds and quantities of volatile flavor compounds from protein isolates were significantly reduced?P<0.01?,especially the main volatile flavors such as aldehydes and ketones in rabbit meat.Protein isolates can be further processed into protein products.From the results of protein function and properties,acid solubilization is better than alkali solubilization.Eventhough alkali solubilization led to slightly higher yield than acid solubilization.The optimum process conditions of rabbit surimi prepared by acid protein isolate was:protein isolate?moisture content 79%??blending 5 min?adding 0.3%?w/v?phosphate,2%?w/v?glucose,2.5%?w/v?NaCl?blending 15 min?glues pouring?50?30 min+80?30 min?Quickly cool to room temperature.Adding different types of additives can improve the gel quality of rabbit surimi.TG enzyme can significantly increase the TPA value of rabbit surimi?P<0.01?.The addition of 0.2%TG enzyme increased the whiteness of the surimi significantly?P<0.01?.Besides,TG enzyme can also increase the water holding capacity of the surimi and reduce the loss of cooking.Gel quality of rabbit surimi was improved by adding starch.When starch content was 10%,the rabbit surimi had the best TPA value,water holding capacity and the least cooking loss.However starch had little effect on the whiteness of the surimi.SPI had a negative effect on the whiteness of rabbit surimi.With the increase of SPI addition,the gel hardness,gumminess and chewiness increased at first and then decreased.