Effects Of Limited Hydrolysis On The Functional Properties Of Protein Isolate From Blue Round Scads(Decapterus Maruadsi)

The protein from marine fish,with high nutritional value for human health,has excellent gelling and emulsifying properties.Therefore,it is regarded as an ideal protein source as food ingredients.However,fish muscle protein is mainly composed of myofibrillar protein which is insoluble in water with low iron strength.That makes it much difficult to be used in food product.Blue round scads is one of the most important economical fishes in Fujian province.In this study,proteins isolate of blue round scads proteins isolate(BPI)were prepared and modified by Alcalase and Flavourzyme,and the mechanisms of the effect of limited enzymatic hydrolysis on the functional properties(solubility,oil holding capacity,emulsifying and foaming properties)were investigated.Moreover,the aggregation behavior and rheological properties of the BPI and pectin composite system as a fat simulant and the effect of the quality characteristics on low-fat mayonnaise were further studied.The main results were showed as follows:Firstly,protein isolate was prepared from the muscle of blue round scads via alkaline isoelectric solubilization/precipitation.The effects of limited enzymatic hydrolysis on the physicochemical and functional properties(solubility,oil holding capacity,emulsifying and foaming properties)of BPI by Alcalase were studied.The results showed that enzymatic hydrolysis could result in significant increase of protein solubility and decrease of molecular weight.With increasing DH,the solubility gradually increased,and DH20 had highest solubility of 98.3%.The surface hydrophobicity of protein hydrolysate increased firstly and then decreased,showing the highest value in DH5.The result was almost consistent with the changes in emulsifying and foaming properties,as well as the oil holding capacity during hydrolysis.After enzymatic hydrolysis,the oil holding capacities of BPHs excepting DH20 were greatly improved comparing with that of control group,while DH5 exhibited the highest value of 3.50 g/g(oil/protein).Next,the enzymatic hydrolysis of protein isolate was carried out using flavourzyme.The effects of DH on the functional properties of protein hydrolysate were investigated as compared with that of hydrolysate by alcalase.The results showed that the molecular weights of protein hydrolysate decreased gradually,along with the increase of protein solubility,with DH increased.The protein solubility reached to the maximum value of 98.0%when DH is 10%.Compared with alcalase,flavourzyme showed a lower hydrolytic efficiency toward protein isolate.The surface hydrophobicity,intrinsic fluorescence and emulsifying showed a similar trends that increased firstly and then decreased as DH increased,in where DH4 possessed the best functionality and had a highest EAI of 93.8±0.6 m~2/g.Compared with control group,DH4 had the smallest particle size and creaming index,indicating the best emulsifying stability.Our results indicated that although flavourzyme has lower hydrolytic efficiency than alcalase,it can release more hydrophobic groups for the interactions between oil/water phases,which therefore result in better emulsifying capacity and stability.Last,blue round scads protein isolate hydrolysates(BPH)were obtained in different DH(6%,8%and 10%)by flavourzyme,and mixed with pectin.Thereafter,the mixture was used as fat replacer instead of 50%fat in mayonnaise to prepared low-fat mayonnaise.The effects of DH on the quality of mayonnaise were investigated.The results showed that apparent viscosity in all samples decreased gradually along with the increase of shear rate that presented a shear thinning phenomenon,indicating the semi-solid emulsion with a fragile network structure.Compared with low-fat mayonnaise,full-fat mayonnaise(FF)has a highest apparent viscosity.Among the groups with different DHs,DH6 presented an apparent viscosity closed to FF group,while DH10 had a similar shear stress to FF.Dynamic viscoelasticity analysis showed that all of groups show a tan?value less than 1,indicating the solid-like behavior.The storage module G'values of low-fat mayonnaise were lower than that of FF group and gradually decreased with DH increased.Compared with FF group,the L*value of low-fat mayonnaise showed the higher value in L*and white,but lower in b*value,while low-fat mayonnaise with DH6 present a similar appearance.Microstructure analysis showed that FF and DH6 showed the smaller and more uniform oil droplets than others.Our results showed that the low-fat mayonnaise with DH6 has the similar appearance and rheological property,indicating the much potential for the application of low-fat mayonnaise as fat replacer.