| Aquatic material,with an annual output of around 167 million ton captured and farmed worldwild,is one of the most important protein sources for human comsumption.Proteins from aquatic raw material,as well as low-valued processing by-products,can be recovered by isoelectric solubilization/precipitation(ISP)method.Compared with the traditional surimi processing method,ISP method possesses various advantages in higher material adaptability and product yield,faster processing speed,lower lipid residue,which make it a better method to recover protein from aquatic materials.As so far,researches on processing techniques of ISP,protein nutritional and gel properties of ISP proteins have been wildly reported.However,mass balance and fractins changes during ISP processing were rarely reported.Furthermore,studies on the application of ISP protein in food industry can be barely found.Therefore,this study was carried out to investigate mass balance and fractions changes during protein extraction using ISP method,composition and functional properties of ISP protein,and effects of ISP protein on properties of deep-fried surimi products and krill oil microcapsule.This research may offer both theoretical foundation and technique support for utilization of ISP protein extracted from fish materials in food industries.The results were as follows:1.Mass balance on the fractions(protein,lipid and insoluble)recovered by ISP method from silver carp,Atlantic menhaden and Antarctic krill was studied.Chicken was set as a control.Proportions of protein,lipid and insoluble fractions from silver carp,menhaden,and krill during ISP processing were 28.50～58.53%,0～34.89%and 15.18～24.66%,respectively,while 35.50%,34.23%and 16.63%,respectively,for chicken.Crude protein content of the protein fractions was in the range of 71.86%～89.67%.Protein recovery yield and fat reduction rate were 41.86%～70.07%and 78.21%～97.74%,respectively.The protein recovery yield of chicken and menhaden were higher than the others,and the fat reduction rate of chicken and silver carp were higher than the others.Crude fat content of the lipid fractions from silver carp and chicken were 95.24%and 97.44%,respectively,while there was no lipid fraction collected from menhaden and krill during processing.Crude protein,fat and ash content of the insoluble fractions were 56.49%～61.47%,5.02%～21.81%and 16.79%～35.03%,respectively.Thin layer chromatography(TLC)results showed that triglycerides and membrane phospholipids were the main composition of lipids in the recovered lipid fractions.SDS-PAGE results showed that myosin heavy chain(MHC),actin and tropomyosin β were the main compositions of protein in the recovered protein fractions from sliver carp and chicken,while those proteins from menhaden and krill samples were significantly lower.2.Acid amino compositions,protein pattern,compositions,particle size distribution,Zeta potential,water-retaining capacity,emulsifying capacity and surface hydrophobicity of dorsal muscle,washed surimi protein and ISP protein from silver carp were comparatively studied.The total acid amino concentration of dorsal muscle,washed surimi protein and ISP protein were 19.04,15.87 and 19.28 g/100 g sample,respectively.Glutamic acid,aspartic acid,lysine and leucine were the main amino acids.Protein patterns of ISP protein were similar to that of dorsal muscle,while the protein bands of tropomyosin,troponin and one myosin light chain from washed surimi protein sample were absent.There were a total of 991 confidential peptides confirmed from the dorsal muscle,washed surimi protein and ISP protein.The number of shared proteins of three samples was 137.The number of the differential peptides in dorsal muscle,rinsing surimi protein and ISP protein were 110,22 and 100,respectively.The shared proteins included the myosin heavy chains,actin and tropomyosin and so on,while the lost proteins caused by rinsing method included some myofibriallar proteins,water-soluble proteases and chromoproteins,and the lost proteins caused by ISP method included some myofibriallar proteins and collagen et al.Statistically,the molecular weights of the differential proteins were majorly less than 100 kDa,while pI were distributed mainly in the,range of 5～6.Comparing to the washed surimi protein,particle size of the ISP protein was larger(p<0.05)but less concentrated,water-retaining capacity and emulsion activity index were lower(p<0.05),while emulsion stability index and surface hydrophobicity were higher(p<0.05);Zeta potential was not significantly different(p>0.05).3.Comparative studies in gel properties under high temperature treatment were carried out between washed surimi protein and ISP protein from silver carp.The highest gel strength of the washed protein gels and ISP protein gels were found at 110 and 100℃thermal treatments,respectively.With the increase of treatment time,breaking force and deformation of the washed protein gels and ISP protein gels were significantly decreased(p<0.05).The water-holding capacity of ISP protein gels was not affected by the treatments(p>0.05),while that of washed protein gels was significantly decreased with the increase of heating time(p<0.05).L*and whiteness of the washed protein gels significantly decreased with the increase of treatment time(p<0.05),while those of ISP protein gels showed an opposite trend(p>0.05).Generally,breaking force,WHC,L*and whiteness of the ISP protein gels were lower than those of the washedi protein gels except deformation.4.Three kinds of fish protein powders(Alaska Pollock frozen surimi,SUR;protein isolates extracted using ISP method from silver carp,ISP;sarcoplasmic protein extracted from silver carp,SAR)were obtained and freeze-dried.Effects of coating protein powders on the properties of deep-fried surimi products were studied.The highest L*,b*and a*were owned by SUR,ISP and SAR,respectively(p<0.05).Comparing to the control sample(without coating protein powder),L*of the skin,b*and of both skin and core of the surimi gels coated with ISP after deep-frying were significantly higher(p<0.05),while L*of the core,expressible moisture and the crude fats content of the core was significantly lower(p<0.05),shear force and cook yield were not significantly different.Core structures of the deep-fried gels were not obviously different,while the microstructures of the skin displayed big differences:SAR surface was intact,smooth and thick,while SUR and ISP surfaces were multi-layered,rough with cracks and voids.5.Krill ISP protein was used as wall material in this study.Effects of krill oil/ISP protein ratio on the properties of krill oil microcapsule were investigated.Emulsion stability index of krill oil-ISP protein emulsion was 1.00 regardless of the krill oil/ISP protein ratio.With the increase of the ratio,crude protein,ash content,loading efficiency,encapsulation efficiency and fatty acid concentrations of the krill oil microcapsule were significantly decreased(p<0.05),while crude fat content and loading were sharply increased(p<0.05).The main fatty acids compositions of the krill oil microcapsule were EPA(34.98%～38.05%),C16:0(18.01%～20.46%)and DHA(10.35%～10.53%).Content of saturated,mono-and poly-unsaturated fatty acids of the krill oil microcapsule were 27.81%～31.71%,15.30%～16.48%and 52.99%～55.71%,respectively.Triglycerides and membrane phospholipids,the main lipids compositions of the krill oil microcapsule,were increased with the ratio.Protein bands in the range of 50 kDa～100 kDa,40 kDa and 25 kDa～40 kDa were observed in all samples.Bands intensities were not affacted by the ratio.With the increase of the ratio,raised areas on the surface decrased,particle size increased,and graininess disappeared when the ratio was above 0.2 ml/g. |
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