The Mechanism Of Plasma-activated Water On The Thermal Aggregation Of Myofibrillar Protein From Silver Carp (Aristichthys Nobilis)

In recent years,the production of surimi products in China has grown rapidly,reaching 1.3342 million tons in 2021.It is well regarded by consumers due to its high protein content,low fat content,and absence of intramuscular spines.The surimi industry’s current development trend is the growth of freshwater fish surimi products.However,the quality of surimi products made from freshwater fish is substandard due to high amounts of endogenous protease,weak antifreeze characteristic of muscle protein,deterioration of gel,and other issues.The quality and three-dimensional gel network of surimi products are both significantly influenced by myofibrillar protein.Therefore,the key to raising the quality of fresh water surimi products is to enhance the gelling characteristics of myofibrillar protein.Plasma is a revolutionary processing method that has the advantages of being inexpensive,easy to use,and residue-free.Although it has been commonly used to sterilize food,there are few studies on how it influence the quality of freshwater fish surimi products.The silver carp,which has a significant annual production in China,was used as the research subject in this study.The effect of plasma activated water with series preparation time on the thermal aggregation behavior of myofibrillar protein was studied（Stage 1:25^oC 30 min;Stage 2:40 ^oC 60 min;Stage 3:40 ^oC 60 min,90 ^oC 30 min）,and the recommended preparation time of plasma activated water was screened.The main research contents and results are as follows:（1）Effect of plasma activated water on heat induced gelling properties of myofibrillar protein.The effects of plasma activated water on the thermal induced gel properties of myofibrillar protein were investigated by using physical property analyzer,colorimeter,rotational Rheometer and laser confocal scanning electron microscope（CLSM）.The results showed that:（ⅰ）The gel strength of myofibrillar protein treated by plasma activated water significantly increased from 15.16 g×mm to 56.05 g×mm（P<0.05）and reached the maximum when the preparation time was 120 s,meanwhile,the water holding capacity（WHC）was significantly increased by 11.72%（P<0.05）;（ii）The time in the‘gel deterioration’stage of myofibrillar protein was cut short by plasma activated water,which also decreased the denaturation temperature and markedly increased the storage modulus（G’）in the‘fish cake’stage;（iii）53.2%ionic bonds between myofibrillar protein molecules were significantly reduced and the hydrophobic interaction was significantly enhanced（P<0.05）by plasma activated water;（iv）As the preparation period for plasma activated water was extended,the cross-linking structure of protein gel became denser and filamentous aggregates appeared in the PAW₁₂₀and PAW₂₄₀.（2）Effects of plasma activated water on physicochemical and structural properties of myofibrillar protein during thermal aggregation.The effects of plasma activated water on the physicochemical and structural properties of myofibrillar protein at different heating stages were analyzed by means of pH meter,Zeta potential meter,particle size meter,Raman spectrometer,sodium dodecyl sulfate polyacrylamide gel electrophoresis meter（SDS-PAGE）,scanning electron microscope（SEM）and atomic force microscope（AFM）.The results showed that:（i）Plasma activated water can promote the aggregation of myofibrillar protein during heating by reducing its pH and weakening the electrostatic repulsion between protein particles;（ii）The unfolding of myofibrillar protein were promoted after treatment with plasma activated water.In Stage 1,about 23.92%of theα-helix were transformed intoβ-sheet and random coil structures,and PAW₆₀has the mostβ-sheet and random coil structures in Stage 3;（iii）After treatment with plasma activated water,the tertiary structure of myofibril protein was changed,and the production of myosin heavy chain（MHC）was promoted and the protein cross-linking was induced in Stage 1;（iv）The 2D,3D images and SEM images of AFM showed that:Plasma activated water promoted the gradual aggregation of myofibrillar proteins from monomers to oligomers in Stage 1;The protein network structure was initially formed,but the degree of aggregation was not high,and the particle size was different in Stage2;The protein gel network structure was dense,the degree of cross-linking of protein aggregates and the height of aggregates increased significantly,and the cross-linked structure of PAW₆₀was more dense and uniform in Stage 3;（v）PAW₁₂₀and PAW₂₄₀form large oligomers in Stage 1,which is not conducive to the formation of protein gel in Stage 2 and Stage 3.（3）The effect of plasma activated water on the thermal aggregation behavior of myofibrillar protein was investigated from the perspective of oxidation.The mechanism of plasma activated water on the thermal aggregation behavior of myofibrillar protein was analyzed from the perspective of oxidation by using ultraviolet spectrophotometer,electrophoresis instrument,amino acid analyzer and other technologies.The results showed that:（i）More sulfhydryl groups of myofibrillar protein were induced to disulfide bonds after treatment by plasma activated water,the content of sulfhydryl groups significantly decreased from 5.90mol/10⁵g protein to 0.51 mol/10⁵g protein and the content of disulfide bonds in supernatant significantly decreased from 1.42 mol/10⁵g protein of PAW₀to 0.03mol/10⁵g protein in Stage 3（P<0.05）;（ii）Plasma activated water oxidation induces tyrosine in myofibrillar protein to form dityrosine;（iii）The recommended preparation time of plasma activated water was 60 s since the more uniform and denser gel structure.