| Goose liver contains a high amount of proteins,approximately 20%of the liver weight,which is considered as being of high quality protein source for human.While,this potential protein source is often neglected as human food due to the limited consumer acceptability owning to its odour,taste and colour.In light of the intractable growth of human population and dwindling supply of food resources,the food industry has been prompted to explore all of the possible sources of protein to meet human nutritional demands.So,to develop the edible value of goose liver is of practical significance.Isoelectric solubilisation/precipitation process(ISP)is a practical technology to recover edible proteins,especially used in low valued animal products.It advantages of high extraction efficiency,low cost,safety and non-pollution.But currently,there is few research regarding the goose liver proteins extraction.Hence,in this paper,we apllied the ISP process to goose liver proteins extraction,and investigated the composition and molecular properties of proteins revoverd by different pH conditions.Then the functional properties of ISP-recovered proteins were studied.For the sake of providing theoretical basis and technical support for the use of goose liver proteins in the food industry.The results were as follows:1.Extraction of goose liver proteins and molecular properties.Based on the goose liver solubility profile under different pH conditions,acid-(pH 2.0,2.5 and 3.0)and alkali-(pH 11.0,11.5 and 12.0)pH values were selected for the protein solubilisation and pH 5.5 was selected for protein precipitation.The protein recovery was in the range of 58.4%?79.0%.Ash,fat and pigment in the raw material could be efficiently reduced.pH 3.0,11.0 and 11.5 treatments had no adverse effects on the amino acids content(P>0.05).Different pH conditions had various effects on composition and structure of ISP-recovered goose liver proteins.SDS-PAGE indicated that high molecular weight proteins(100?250 kDa)were degraded during acid process,while few changes occurred regarding the protein profiles after alkali process.The study on structure of ISP-recovered proteins showed that,the content of both active sulfhydryl and surface hydrophobic groups was increased in ISP treatments(P<0.05).The acid-proteins had higher surface hydrophobicity but less active sulfhydryl groups than alkali-proteins(P<0.05).Compared to the control,acid proteins had significantly decreased ?-helix and ?-fold(P<0.05),as with an increase in irregular curl(P<0.05).The alkali-proteins exhibited less ?-helix but more ?-folded fraction than control(P<0.05).2.Gelation properties of goose liver proteins recovered by ISP process.This study focused on the gelation properties of goose liver proteins recovered by ISP process.Goose liver paste was set as the control.The results indicated that,the lowest cooking loss and centrifugation loss were found in pH 11.0-gels,which were significantly lower than the control(P<0.05).While acid conditions debilitated water holding ability of proteins.For pH 11.0-gels,there was more free water(T22)converted into immobilized water(T21).The decreased T2 relaxation time indicated the enhacement of binding force between water and proteins.While for acid-gels,increased free water fraction indicated that water was weakly bound to the macromolecules and was highly mobile.Rheological tests showed that,proteins produced by alkali process formed more visoelastic gels than control.pH 11.0 and 11.5 treatments strengthened the hardness of gels,and had a significantly positive influence on elasticity(P<0.05).These gels showed a compacted and uniformed microstructure.In contrast,acid treatments exerted an adverse effect on textural properties of the gels,with a soft and brittle texture,exhibiting a coarse appearance and irregularly shaped of protein aggregates.Taken together,gels produced by alkali process had better water holding ability and texture than those by acid process.Proteins isolated by pH 11.0 had optimal gelation properties.3.The emulsion properties of goose liver proteins extracted by ISP process.The emulsion properties of goose liver proteins recovered by ISP process were studied.Goose liver paste was set as the control.The ISP-recovered proteins and liver paste emulsified with soybean oil,respectively,to produce the emulsion system.The results demonstrated that proteins recovered by pH 11.0 had higher emulsifying activity index(EAI),emulsifying stability index(ESI)and emulsifying viscosity than control(P<0.05).Smaller,spherical droplets uniformly distributed in emulsion system.While the acid-proteins had decreased EAI and ESI,of which the emulsion droplets were larger,with irregular shape and uneven distribution.Flocculation phenomenon between the droplets presented in pH 2.0 and 2.5 emulsion.Compared to the control,acid treatments had lower p-sheet(P<0.05),indicating the weak interactions between proteins,in accordance with deteriorative emulsifying properties.In contrast,the increased ?-sheet fraction(P<0.05)for alkali treatments favored more stable emulsion.In conclusion,ISP process is feasible for goose liver proteins extracrion.pH 11.0 treatment had best gelation and emulsifying properties.This study could serve as a practical basis for the use of goose liver proteins in food industry. |
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