Study On The Glass Transition Temperature Of Penaeus Vannamei And Its Frozen Storage Quality Changes

During the freezing process of Penaeus vannamei,different additives are often needed to improve the preservation effect.Traditional additives have more restrictive conditions during the use process,such as high sweetness and calories of sucrose,which affect the flavor of the product;phosphates affect the absorption of minerals.This paper studied the effects of different sugar additives on the quality changes of Penaeus vannamei during frozen storage,explored the related factors affecting the glass transition temperature of shrimp,and studied the relationship between the glass transition temperature and the quality and protein stability of shrimp in frozen storage.In order to have a deeper understanding of the application of thermodynamics in the frozen preservation of shrimps,and reduce the cost of low-temperature storage in industrial production.The method of measuring the glass transition temperature of shrimps is determined by optimizing the annealing temperature,annealing time and heating rate.The initial temperature is 25?and the temperature is constant for 2 min,and the cooling rate is10?/min to-80?,and the constant temperature is 2 min;at 10?/min to 30?,constant temperature for 2 min;then 10?/min to annealing temperature-35?,constant temperature for 30 min;10?/min to-80?,constant temperature for 2 min;heating at 10?/min to30?.The GAB and BET models were used to perform nonlinear regression fitting to confirm the relationship between water activity and moisture content of shrimps.The study found that the BET model is more suitable to describe the water adsorption characteristics of shrimps.Using sodium pyrophosphate,sodium tripolyphosphate,trehalose,seaweed oligosaccharides,carrageenan oligosaccharides as additives,by measuring different concentrations,different soaking time,different freezing storage time,different freezing and thawing times,shrimp Tg',water activity the changes of water content and water content index,studied the effect of sugar additives on the Tg'of Penaeus vannamei,and the relationship between water activity,water content and Tg'.The experimental results show that sugars can effectively increase the Tg'of shrimps.The increase in sugar concentration and the extension of the soaking time can both increase the Tg'.Among them,sodium tripolyphosphate and trehalose have the most significant effects,algin oligosaccharides and pyrophosphate.There is little difference between sodium and carrageenan oligosaccharides.With the increase of sugar concentration and the extension of soaking time,the Tg'of shrimps showed a slow upward trend.As the frozen storage time increased,the Tg'of the shrimp further increased,and the trehalose group reached-52.16? at 90 d.In the process of repeated freezing and thawing,the carbohydrate addition group effectively inhibited the decrease in the moisture content of the shrimp muscles and increased the Tg'of the shrimp.The order of increase was trehalose group,sodium tripolyphosphate group,and seaweed oligosaccharide group.Carrageenan oligosaccharide group,sodium pyrophosphate group.The Tg'of the shrimp is directly proportional to the moisture contentVacuum low-temperature osmosis treatment is used to increase the sugar infiltration rate.Through the determination of thawing loss rate,TPA characteristics,water activity,water content,myofibril protein content,Ca²⁺-ATPase activity and carbonyl content,the effects of different additives have been studied.The effect of frozen storage shrimp quality changes.The experimental results showed that the thawing loss rate,elasticity,hardness,water activity,water content,myofibril protein content,Ca²⁺-ATPase activity,and carbonyl content of Penaeus vannamei changed drastically at the beginning of storage,and gradually became flat at the end of refreezing.The thawing loss rate of the sodium tripolyphosphate group was 3.90%at 90 days,which was significantly lower than that of the distilled water group(12.92%).The trehalose group inhibited the rapid decline of myofibrillar protein content in the early stage of frozen storage,and played a protective effect on the stability of the protein structure.As the osmotic pressure increases and the penetration time increases,the?H,specific heat capacity,moisture content,and water activity of the shrimp decrease,and the Tg increases.Therefore,increasing the osmotic pressure and penetration time helps increase the binding rate of carbohydrate molecules and the system.Through the determination of thermal stability,atomic force microscope imaging,turbidity,endogenous fluorescence,surface hydrophobicity,SDS-PAGE gel electrophoresis and other indicators of the myofibrillar protein of Penaeus vannamei,study the effects of different carbohydrates on frozen shrimp protein the impact of stability.During the freezing process of Penaeus vannamei,myosin and sarcoplasmic protein are poorly thermally stable and prone to heat denaturation.The addition of sodium tripolyphosphate and trehalose can delay the decrease of myosin deformation temperature,and actin is more stable.It can be seen from the atomic force microscope that the myofibrillar protein after adding trehalose is more evenly dispersed after denaturation,and the stability is higher.During the freezing process,the stretch of the myofibrillar protein peptide chain exposes the tryptophan group and the hydrophobic group,causing the endogenous fluorescence intensity to decrease and the surface hydrophobicity to increase.In the relationship of turbidity changes,the turbidity of each group increased significantly after 40?,which was consistent with the denaturation temperature of myosin.The change of bands in SDS-PAGE gel electrophoresis analysis also verified this point.