The Viscosity Of Homogenate And Myofibrillar Protein Of Tuna And The Correlation Between Viscosity And Quality

Fresh tuna often used as sashimi to eat,but its quality is easy to change,so fast and effective method to evaluate quality is one of the hot topics in the study of tuna.Now physical and chemical indicators,microbiological indicator and sensory indicator are the main method to evaluate quality of fish,while rheological indicator evaluating quality of fish is developing.Correlation between quality of tuna and viscosity of tuna homogenate and myofibril protein are gradually developed in domestic.The viscosity has many influence factors,such as temperature,shear rate,time,pressure,sample preparation,sample composition and additives,etc.Through understanding viscosity characteristics,we confirm the suitable test condition of viscosity to find out the correlation between viscosity and quality.Firstly,we studied some physical and chemical factors on the viscosity of bigeye tuna homogenate,supernatant and myofibril protein.Secondly,we studied the correlation between viscosity of homogenate,supernatant,myofibril protein of bigeye tuna during frozen storage at-18? and-50?and pH,metmyoglobin,Ca2 +-ATPase,K value,sensory evaluation of bigeye tuna during frozen storage at-18? and-50?.Main conclusions are as follows:(1)The viscosity of homogenate and supernatant decreased with the increase of homogeneous time.When homogeneous time is 1,2,3,there was no significant difference between viscosity values of tuna homogenate(p > 0.05).When homogeneous time is 1,2 min,there was no significant difference between the viscosity value of supernatant(p > 0.05).Viscosity of homogenate and supernatant first increased sharply and then kept constant with the increase of the stabilization time.When stabilization time is 60,120 min,there was no significant difference between viscosity values of tuna homogenate(p > 0.05).When stabilization time is 120,180 min,there was no significant difference between viscosity values of tuna supernant(p > 0.05).The viscosity of homogenate and supernatant decreased with the increase of addition of solution.When the ratio of solution to tuna muscle was 9:1 or 10:1,there was no significant difference between viscosity values of tuna supernant(p > 0.05).Viscosity of homogenate and supernatant first increased sharply and then decreased with the increase of the NaCl concentration.The maximum viscosity of homogenate and supernatant were at 1.2 mol/L NaCl;The viscosity of homogenate and supernatant decreased sharply at first,and then increased during the pH change.The minimum viscosity of homogenate was at pH 4.5 ~ 5.The minimum viscosity of supernatant was at pH 5.0 ~ 5.5.When pH was 7.5 or 7.0,there were no significant difference between viscosity of homogenate and supernatant(p > 0.05).Viscosity of homogenate and supernatant decreased with the increase of testing temperature.When testing temperature was 5,7,10 ?,there was no significant difference between viscosity of homogenate(p > 0.05).When testing temperature was 2,5 ?,there was no significant difference between viscosity of supernatant(p > 0.05).The suitable test condition of viscosity of homogenate showed that: homogenization time was 1 min,stabilized for 60 min,the ratio of solution to tuna muscle was 9:1,the concentration of NaCl was 1.2 mol/L,adjusted pH at 7.5,the measurement temperature was at 5 ?.And the suitable test condition of viscosity of supernatant showed that: homogenization time was 1 min,stabilized for 120 min,the ratio of solution to tuna muscle was 9:1,the concentration of NaCl was 1.2 mol/L,adjusted pH at 7.5,the measurement temperature was at 2 ?.(2)The viscosity of bigeye tuna myofibril protein decreased with the increase of temperature in a certain range.When the concentration of myofibril protein was 5 ~ 25 mg/mL,there was a positively correlation between the concentration and viscosity of myofibril protein.When the concentration of myofibril protein was 25 ~ 30 mg/mL,there was a negatively correlation between the concentration and viscosity of myofibril protein.when the concentration of NaCl was 0.6 ~ 1.0 mol/L,there was a positively correlation between the concentration of NaCl and viscosity of myofibril protein.When the concentration of NaCl was 1.0 ~ 1.6 mol/L,there was a negatively correlation between the concentration of NaCl and viscosity of myofibril protein.When the pH was 5 ~ 5.5,the viscosity of myofibril protein viscosity decreased with the increase of Ph.When the pH was 5.5 ~ 7.5,the viscosity of myofibril protein viscosity increased with the increase of p H.The suitable test condition of viscosity of myofibril protein showed that: the measurement temperature was at 5 ?,the concentration of myofibrillar protein was 25 mg/mL,the concentration of NaCl was 1.0 mol/L,adjusted pH at 7.0.(3)The viscosity of homogenate,supernatant,myofibril protein of bigeye tuna decreased during frozen storage at-18?.The pH firstly increased during frozen storage.Metmyoglobin increase during frozen storage.The Ca2 +-ATPase activity reduced during frozen storage.K value increased during frozen storage.The viscosity and biochemical characteristic changed gently during frozen storage at-50?.The viscosity of homogenate had the better correlation with p H value,metmyoglobin,Ca2 +-ATPase,K value and senses of bigeye tuna during frozen storage at-18 ?.The senses of bigeye tuna had the best correlation with viscosity of homogenate,supernatant and myofibril protein of bigeye tuna during frozen storage at-18?.The viscosity of homogenate and myofibril protein of bigeye tuna had the best correlation with pH value,metmyoglobin,Ca2 +-ATPase,K value and senses of bigeye tuna during frozen storage at-50?.The viscosity of homogenate,supernatant and myofibril protein of bigeye tuna during frozen storage at-18 ? and-50 ? was closely correlated to metmyoglobin,Ca2 +-ATPase,K value and senses of bigeye tuna during frozen storage.