Effect Of Phosphate On Tilapia Protein And Lipid Oxidation And Quality

Sodium pyrophosphate and mixed phosphates treatment on Tilapia protein and lipid oxidation and flesh quality were evaluated in this paper.Experiments with untreated tilapia fillets as control group, ascorbic acid treatment of tilapia fillets as positive control group, the results are as follows:The carbonyl content of control group, sodium pyrophosphate, mixed phosphate and ascorbic acid treatment group tilapia were 183.2nmol/mg, 167.1nmol/mg,181.2nmol/mg and 178.5nmol/mg after stored for 20 days.The initial and final sulfhydryl content of sodium pyrophosphate treatment group were 65.41 and 50.69 respectively, it’s downward trend lower than the control group,the sulfhydryl content of sodium pyrophosphate treatment group was slightly lower than the untreated group after storage.The disulfide bond content and protein hydrophobicity of sodium pyrophosphate treatment group was significantly lower than control group.Experiments show that sodium pyrophosphate can inhibit the storage process of tilapia protein oxidation effectively, mixed phosphate phosphate mixture of tilapia fillets during storage in the inhibition of protein oxidation was not significant,while no significant effect of mixed phosphate.During storage, the metmyoglobin content of was significantly lower than the control group (80.21%), a* and b* values were lower than the control group,Thus, Phosphate treatment can also inhibit the formation of metmyoglobin from myoglobin oxidation, inhibit fish to be more browning and yellow.Differential scanning calorimetry shows the tilapia muscle actin and myosin heat absorption peak,Thermal denaturation temperature of actin and myosin from Fresh tilapia were:54.4℃ and 84.0℃.their thermal denaturation temperature between 50～57℃and 75～85 ℃ respectively. After sodium pyrophosphate treatment,thermal denaturation temperatures of actin and myosin were between 50～55℃and 81～85℃, after mixed phosphate treatment,thermal denaturation temperature of actin and myosin were between 51～55℃ and 75～80℃.significantly lower than the fresh group.Sodium pyrophosphate can improve the thermal stability of tilapia actin,maintain the thermal stability of myosin.mixed phosphate can reduce thermal stability of tilapia protein.Determination of the two level structure of tilapia proteins by infrared spectrometer, the result shows:a-helix accounted for 44.96%, β-folding accounted for 30.88%, β-angle accounted for 24.16%, random coil accounted for 0%, it showed a stable ordered structure.The contents of a-helix and β-folding of Tilapia proteins after phosphate treatment has decreased,even α-helical structure disappeared, random coil structure appeared.Phosphate treatment can effectively reduce the tilapia fish TBARS value, acid value and peroxide value,in contrast, sodium pyrophosphate can inhibition lipid oxidation in tilapia.Tilapia TBARS value has significant correlation with the change of the protein carbonyl and sulfhydryl content,pearson correlation coefficients were 0.77,0.72,0.70. This indicating lipid oxidation and protein oxidation of tilapia are interdependent.Phosphate treatments can maintain the sensory quality and improved textural qualities.1%,3%and 5%sodium pyrophosphate and 1%and 3%mixed phosphates can maintain the organizational structure of tilapia.Electronic nose can distinguish smell change of different samples,the odour of the untreated samples changed in third days,the odor of the samples after phosphate treatment changes more slowly.Thus, sodium pyrophosphate may inhibit protein and lipid tilapia oxidation, maintaining a good quality tilapia fillets.