| This paper taking oysters as raw material, extracted the oyster water-soluble protein, saltsoluble protein and insoluble proteins, the effect of different pH,ionic strength,sucroseconcentration and temperture on protein solubility, water, holding capacity, sulphur content,foaming ability and foam stability, emulsification and emulsion stability of oyster protein wereinvestigated, and adopt limited enzymatic hydrolysis method to modificate the oyster protein, inorder to obtain desired functional characteristics, provide a certain basis for the development ofthe oyster protein products. The main results were as follows:1. Protein of oyster meat was separated according to solubility, analyzed the generalcomponents and amino acid composition of each protein component, the molecular weightdistribution was determined by SDS-PAGE. The results showed that the amount of each isolatedprotein fractions: non protein nitrogen0.83%, water-soluble protein37.8%, salt soluble protein31.1%, and insoluble protein26.4%, respectively. It had well-balanced amino acid, the appropriateratio of essential amino acid; essential amino acids and flavor amino acid content were high.SDS-PAGE pattern showed that the samples without mercaptoethanol had protein bands less thanthe samples by mercaptoethanol treatment, in the electrophoresis map of sample treated byβ-mercaptoethanol. The distribution range of water-soluble protein was wide, the molecularweight distribution of water-soluble protein was200-14kDa;salt soluble protein was200-10kDa,apparent bands in the vicinity of200kDa and45kDa, there was obvious paramyosin strip in thevicinity of97kDa; insoluble protein concentrated in the200-29kDa. In the electrophoresis mapof sample treated without β–mercaptoethanol, water soluble protein had a band in116kDa, saltsoluble protein in200kDa and116kDa, insoluble protein in36kDa,29kDa had the proteinbands existed. These results will provide a theoretical basis data for the further development andutilization of the oyster protein.2. The effects of different factors on the solubility of water soluble protein and salt solubleprotein. Results show that the solubility went up after dropping with the increase of pH value,when the water soluble protein at pH=4and salt soluble proteins at pH=6, the solubility of twoprotein fractions reached minimum, which were35.0%and26.9%respectively, had goodsolubility during far away from the isoelectric point. In0-0.6mol/L range of NaCl concentration, the solubility of two protein fractions had a gentle downward trend, however, the solubility had asmall increase between0.6-1mol/L, and the solubility of water-soluble protein was always higherthan that of salt soluble protein. Sucrose concentration has little effect on the solubility of twoprotein fractions, which maintain below40%. The effect of temperature on the solubility of thetwo protein fractions was remarkable, solubility had maximun at60℃.3. The effects of different conditions on the water holding capacity of water soluble proteinand salt soluble protein. The results show that the water holding capacity of two protein fractionsdown first and then up along with the increase of pH value, near the isoelectric point reached aminimum of0.65g/g. The effect of NaCl concentration and sucrose concentration on the waterholding capacity of two proteins was small, when sucrose concentration was up to8%, the waterholding capacity was biggest.4. With the increase of the concentration of the protein, the foamability gradually enhanced,when protein concentration at2%, the foam stability of water soluble protein was highest and hadan advantage over foam stability of salt soluble protein. with the increase of pH, the foamability oftwo protein fractions increased at first and then decreased, reached minimum at pH=5, the foamstability of two protein fractions had been reduced. With the increase of NaCl concentration,foaming ability and foam stability of the protein were on the decline. Instead, with the increase ofsucrose concentration foamability was reduced, and the foam stability had been enhanced.5. The emulsification and emulsion stability of two protein fractions subsequently increasedwith the increase of the protein concentration. The tendency of emulsification and emulsionstability with the different pH was similar to the change between pH value and solubility, whichwas down before they rose, had minimum value near the isoelectric point. With the increase ofNaCl concentration, the emulsification and emulsion stability of the proteins climbed up and thendeclined. Sugar had a promoting effect on the emulsification and emulsion stability of proteins,but when the sucrose concentration was overhigh, the emulsification and emulsion stability had nochange. When temperature was30-50℃, as the temperature rises, the emulsification of watersoluble protein increased, however, emulsion stability reducedr.After50℃the emulsification ofwater soluble protein increased. The emulsification of salt soluble protein was minimum in30℃,with the increase of temperature, emulsion had been increased.6. The contents of total sulphur and active sulphur of water soluble protein were7.736μmol/g,5.892μmol/g.These of salt soluble proteins were4.27μmol/g,3.473μmol/g.7. The Td of water-soluble protein was60℃, the Td of myosin from salt soluble protein was48.1℃, actin Td=95.3℃, there was an endothermic peak at118.9℃in insoluble protein.8. The water-soluble protein, salt-soluble protein and insoluble protein were hydrolyzed by trypsin and alkaline protease, the degree of hydrolysis (DH) under different time was determined,the solubility and emulsifying capacity of protein hydrolysates with different degree of hydrolysiswere investigated. The results showed that the solubility of protein hydrolysates prepared byalkaline protease was better than that trypsin hydrdysattes, the longer hydrolysis time, the higherthe degree of hydrolysis, the better the solubility, but protein emulsification and emulsion stabilityshower a rise first follower by a decline. When the DH reached7%, the emulsification andemulsion stability of water-soluble protein reached maximum, and the emulsifying capacity of saltsoluble protein and the insoluble protein were better in the degree of hydrolysis of5.8%and5.7%,respectively. |
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