Effects Of Five Ultrasound-assisted Thawing Methods On The Quality Of Sea Bass(Perca Fluviatilis)

In this experiment,fresh sea bass(Perca fluviatilis)was used as a control.The effects of five thawing treatments(ultrasonic microwave thawing,ultrasonic far-infrared thawing,ultrasonic ohmic thawing,ultrasonic vacuum thawing,and ultrasound thawing)on the quality,myofibrillar proteins and flavor of sea bass were compared.The aim is to solve the problem of uneven thawing and long thawing time of sea bass.1.By the cooking loss rate,thawing loss rate,pH value,TVB-N value,TBARS value,DSC,dynamic rheology and moisture distribution the effects of different thawing methods on the quality of sea bass were studied.The results showed that the thawing loss rate and cooking loss rate were significantly different in different treatments(p<0.05).The thawing loss rate and cooking loss rate of fish by ultrasonic microwave thawing were the lowest.The results of LF-NMR showed that in the samples thawed by ultrasonic microwave,the water migration from intracellular water to free water was less,indicating that the water holding capacity of the thawed by ultrasonic microwave was stronger.The pH values of all thawed samples were not significantly different from fresh samples(p≥0.05)and the TVB-N values were all below 15 mg/100 g,maintaining a high degree of freshness.However,The TBARS values of ultrasonic far-infrared thawing,ultrasonic ohmic thawing,ultrasonic vacuum thawing and ultrasound thawing were significantly increased(p<0.05),indicating a higher degree of lipid oxidation.Ultrasonicmicrowave thawing and ultrasonic far-infrared thawing of sea bass had higher thermal stability,viscoelasticity,and the microstructure was more dense and smooth.But the myofibril bundles were slightly crimped by ultrasonic vacuum thawing,and the fibers by ultrasonic ohmic thawing and ultrasonic thawing had rough surface and loose structure.2.The effects of different thawing methods on the physicochemical properties of myofibrillar protein in sea bass were investigated from protein structure changes,aggregation degree and oxidation degree to preliminarily understand the mechanism of myofibrillar protein denaturation at the molecular level.Raman spectra showed that during thawing,the α-helix structure of myofibrillar protein changed,and partly transformed into random coils,which greatly reduced the tightness and stability of the protein conformation.The ultraviolet absorption spectra and intrinsic fluorescence spectra showed that the ultrasonic microwave thawing could retain the tertiary structure of the protein better.Particle size,Zeta potential and SDS-PAGE were used to analyze the degree of protein aggregation.Compared with fresh samples,the particle size and Zeta potential of all the thawing methods were not significantly different(p≥0.05).The electrophoretic band of ultrasonic microwave thawing was the closest to the fresh sample,which indicated that the degradation degree of proteins was lower.During thawing,active sulfhydryl groups were gradually oxidized into disulfide bonds.The protein polymerized with each other through hydrophobic interactions and disulfide bonds.Myofibrillar proteins aggregated and denatured,and the total sulfhydryl content of ultrasound thawing significantly decreased(p<0.05),indicating a high degree of protein oxidation.3.Electronic nose,electronic tongue and HS-SPME GC-MS are effective means to analyze the flavor change of sea bass during thawing.61 volatile substances were detected by GC-MS,mainly aldehydes,alcohols,and hydrocarbons.After thawing,the types and total contents of volatile components in fish decreased to different degrees.After ultrasonic microwave thawing,thecontent of aldehydes in fish was close to that of fresh fish,and the content of aldehydes decreased the most after ultrasonic thawing.Based on principal component analysis of taste properties and flavor patterns,the electronic tongue and electronic nose showed the potential as a screening tool.The results showed that the umami of fish was selected as having the strongest taste characteristics after ultrasonic microwave thawing.Compared with fresh fish,the smell and taste of the fish after thawed by ultrasound fluctuated greatly.