Effects Of The Isoelectric Solubilization/Precipitation Process And NaCl Addition On The Functional Properties Of Chicken Breast Proteins

In conventional meat processing,2-4%NaCl is incorporated into the meat product formulation which is harmful for human's health.If we reduced NaCl addition directly,the texture and water-holding capacity(WHC)of meat product decreased.Therefore,how to reduce NaCl addition in the meat product and maintain its desirable textural and sensory properties becomes a significant problem facing food industry.In the isoelectric solubilization/precipitation(ISP)process,the meat proteins are solubilized at acidic or alkaline pH,and then precipitated by adjusting pH to the isoelectric point and dewatered by centrifugation.The fainal pH of the proteins is adjusted to the neutrality.The ISP process is divided into acid and alkali solubilization isoelectric precipitation(SIP).Currently,there is few research regarding the effects of NaCl addition on the functional properties of heat-induced gels made from chicken breast meat proteins treated by the ISP process(ISPC-gels).Hence,in the first place,we studied the effects of the ISP process on the functional properties of chicken breast meat proteins with low NaCl addition in this paper.Then,the effects of NaCl on gel properties of the ISP-recovered proteins were investigated.The aim of our studies was to provide the theoretical basis and technical support for creating meat product with low NaCl addition.Main contents and results are as follows.1.Effects of pH during the ISP process on gel properties of the muscle proteins from chicken breastThe effects of pH(2.5,3,3.5,11,11.5 and 12)during the ISP process on the yield and amino-acid component of the chicken breast proteins were studied.Additionally,colour,texture and WHC of the ISPC-gels added with 1%NaCl were investigated.Conventionally produced gels added with 2%NaCl served as the control.The results showed that pH had no effect on the protein yield.Besides,there was no significant change in the total content of amino acids and total content of essential amino acids in the ISP-recovered proteins(P>0.05).The ISP process resulted in the decrease of the lightness,redness and yellowness.The ISPC-gels treated at pH 3.5 and 11 had the best textural properties and WHC compared to the other ISPC-gels.In addition,no significance was observed in the textural properties and WHC between the control and the ISPC-gels treated at pH 3.5 and 11(P>0.05).Therefore,the ISP-recovered proteins from chicken breast treated at pH 3.5 and 11 had the highest gel properties.2.Effects of the ISP process on the emulsibility and gel properties of the proteins from chicken breastThe effects of the ISP process on the emulsibility and gel properties of the proteins from chicken breast were studied.The main indexs included texture,emulsion stability,rheological properties,microstructure and sensory qualities.During the ISP process,the chicken breast proteins was solubilized at pH 3.5 and 11 respectively.The ISP-recovered proteins were added with 1%NaCl and 20%back fat.Conventionally produced samples added with 2%NaCl and 20%back fat served as the control.The results suggested that the gel strength and emulsion stability of the proteins treated at pH 11 were similar to those of the control(P>0.05),but higher than those of the samples treated at pH 3.5(P<0.05).Rheological tests showed that the proteins treated at pH 11 formed a more viscoelastic gel than those treated at pH 3.5.There was no significant difference in the storage modulus between the control and the proteins treated at pH 11.The network of the ISPC-gels treated at pH 11 was composed of evenly sized pores,thin cross-linked strands and fat particles,while the microstructure of the ISPC-gels treated at pH 3.5 showed that the proteins aggregated and formed an abundance of bead-like particles which resulted in the decrease of the water-and fat-binding capacities.In addition,compared to the ISPC-gels treated at pH 3.5,the samples treated at pH 11 had more acceptable sensory qualities.Consequently,with 1%NaCl addition,the ISPC-gels treated at pH 11 had good functional properties and sensory qualities.3.Effect of NaCl addition on gel properties of the chicken breast proteins treated by the alkali-SIP processThe effects of NaCl addition(0%,0.5%,1%,1.5%and 2%)on gel properties of the chicken breast proteins treated by the alkali-SIP process were studied in this chapter.Conventionally produced gels with 0%,0.5%,1%,1.5%and 2%NaCl served as the control.The results showed that the proteins treated by the alkali-SIP process had the better flavor than the control.The textural properties and WHC of the gels treated by the conventional process improved with the increase in NaCl addition.However,there was no significant difference in textural properties of the ISPC-gels when NaCl was>1%(P>0.05).In addition,no significant difference was observed in textural properties between the control with 2%NaCl and the ISPC-gels with 1%NaCl.Rheological tests showed that the proteins treated by the alkali-SIP process formed a more viscoelastic gel with the increase of NaCl addition.The ISPC-gels with increased NaCl content exhibited low cooking loss but high centrifugal loss.Low-field nuclear magnetic resonance demonstrated that the amount of free water(T22 component)that was converted into immobilized water(T21 component)in the ISPC-gels increased with NaCl addition in accordance with the decline in cooking loss.However,the increased T21 values at 1.5%and 2%NaCl indicated that water was weakly bound to the macromolecules and was highly mobile.As a result,centrifugal loss increased.Overall,the total water loss,including cooking and centrifugal losses,decreased under 0-1%NaCl addition,but it increased with the increase in NaCl addition to 2%(P<0.05).These results were strongly corroborated by the microstructure images that illustrated the continuous and dense structure of ISPC-gels containing 1%NaCl.This structure had small pores and thin cross-linked strands.Compared to the conventional process,the alkali-SIP process induced more ?-sheets that would increase gel strength of the proteins with low NaCl addition.Prior to heating,NaCl addition had no effect on secondary structure of the proteins treated by the conventional process.However,the ISP-treated proteins with increased NaCl addition exhibited less ?-helixs but more?-sheets(P<0.05),which would weaken the binding strength of water molecule to the macromolecules.In summary,1%NaCl was necessary and enough for the ISP-treated proteins with high functional properties.Hence,the results of this study can be used as a foundation for the application of the ISP process in creating low sodium meat products.