Research On The Molecular Mechanism Of Quality Changes On Sous-vide Hairtail Products During Preparation And Storage

Hairtail(Trichiurus lepturus)is an important economic fish for the southeast coast of China,and it is widely accepted by consumers for the high content of protein and polyunsaturated fatty acids.Nevertheless,hairtail is perishable due to the effects of microorganisms and endogenous enzymes.Through thermal processing,the hairtail could be prepared into a hairtail products,which provides the dual effects of maturation and sterilization,delaying the waste caused by the decomposition of the hairtail.During thermal processing,too mild heating conditions are possibly a risk of insufficient sterilization,while overheating causes the disadvantages in texture denaturation and loss of nutrients for hairtail.Therefore,it is of great significance to optimize the conditions for thermal processing of hairtail and to explore its texture changing mechanism.Among the thermal treating methods,sous-vide cooking has attracted wide attention because it could retain food texture and nutrition to certain extent.Besides,during the preservation of hairtail products,the spoilage caused by the reproduction of microorganisms causes huge losses.The preparation of a chitosan-citrus essential oils microcapsules storage system with biological activity and application to the storage of hairtail products could effectively reduce the waste caused by spoilage.This research focused on the mechanisms of texture changing during the preparation and storage of sous-vide hairtail products in molecular level.By proteomics,texture profile analysis,microstructure analysis,instrumental analysis and chemical analysis methods,the texture maintaining mechanisms of sous-vide hairtail products during the preparation process was clarified,and the mechanisms of protein denaturation and water migration were also explored.The relationship between fatty acid profiles and volatile substances was established,and a novel chitosan-citrus essential oils microcapsules storage system for sous-vide hairtail products was established for prolonging the shelf-life of sous-vide hairtail products,systematically studying its molecular mechanisms to reduce spoilage and retain texture.The main results are as follows(1)Optimization of preparing conditions for sous-vide hairtail products and the law for protein denaturationTexture is one of the key indicators that affect the edible quality of aquatic products The properties of proteins,especially structural proteins,play an important role in texture.Under different heating degrees,the protein produces varying degrees of degradation,which affects the texture of the product.Through microbial residues and instrumental analysis of protein denaturation,it was determined that heating the vacuum-packed hairtail to the core temperature of 68? and maintaining it for 20 minutes is the optimum process condition for preparing sous-vide hairtail products.The stage before the core temperature rises to 68? was named as the heat-up process,and the stage where the temperature maintained at 68? was named as the heating preservation process accordingly.Through various methods including mass spectrometry analysis,electrophoresis analysis,proteomics,the protein changes in the preparation process of sous-vide hairtail products were investigated and compared with the traditional heating method which usually heating hairtail directly to 100?.The results of the texture profile analysis showed that the sous-vide hairtail products had a significantly better texture than traditional heated hairtail(p<0.05),and the changing trend of texture parameters during the heating preservation stage was significantly smaller than that of the heat-up process.During the heat preservation stage,the molecular weight of protein also tended to change smoothly,which was consistent with the results of protein oxidation.The results of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry indicated that the heating preservation process was still accompanied by the decomposition of small molecular proteins and peptides.The proteomics system analysis results showed that some structural proteins were relatively stable at 68? and become enriched due to the denaturation,loss and decomposition of other proteins,which was the key reason for maintaining the texture stability of sous-vide hairtail products during the heat preservation stage.Among them,the most enriched myosin binding protein C(fast type b),keratin(type ? cytoskeletal 13-like),titin-like and myosin heavy chain 1 were identified as differential proteins being able to be maintained during the heat preservation phase of preparing hairtail products by sous-vide cooking,with the concentration folds of 16.7?4.7?3.3 and 2.5,respectively.Myomesin-2,tubulin alpha chain,myosin(heavy chain b),titin(putative)and myosin light chain 1 were the five main structural differential proteins with the most obvious retention of sous-vide hairtail products compared to traditional heating methods,with the concentration folds of 5.1.2.4?2.1.2.0 and 2.0,respectively.Therefore,compared with heating methods,sous-vide hairtail products had better texture by maintaining the key structural proteins The partial denaturation of structural proteins under the mild conditions of sous-vide heating had become the core factor in maintaining the quality of sous-vide hairtail products(2)Study on the mechanisms of protein denaturation and water migration on hairtail during sous-vide cookingThe texture reflects the physical properties related to the tissue structure and state of the food.The texture of sous-vide hairtail products is closely related to the degree of protein denaturation;during the preparation of hairtail products by soud-vide cooking,partial protein denaturation,structural collapse,and water retention was induced.Other properties are affected as well,and the degree of moisture migration changes,which changes the tenderness quality of sous-vide hairtail products and affected its microstructure.Using magnetic resonance imaging and low-field nuclear magnetic resonance atomic dynamics to study the law of water migration during the preparation of sous-vide hairtail products,then combine multi-section microscope image analysis and image digital analysis to explore the relationship between water status and microstructure changes.During the heat-up process of sous-vide cooking,some bound water changed into free water or non-flowing water,and there was no significant change in the state of moisture in the heat preservation process(p>0.05).The ratio of non-flowing water and bound water in the sous-vide hairtail products was significantly higher than that of traditional heated hairtail(p>0.05).During the heating preservation process,the magnetic resonance imaging results reflected that the water evenly distributed in hairtail products,and the water holding capacity was much more stable than that of the traditional heating hairtail.The digital analysis results of the microstructure showed that the cross-sectional area and stretch degree of the microstructure image in the heat-up process showed an upward trend.The cross-sectional area increased from 13.21 ± 0.89 ?m2 to 61.25±8.96 ?m2,and the stretch degree increased from 1.62±0.49 to 8.31±6.02,and they both became stable during the heating preservation process;the microscope imaging analysis results exhibited that the muscle fiber contraction and muscle tissue damage caused by protein degeneration and loss were vital factors that cause the texture changes of the hairtail,and the stability of the microstructure of the hairtail prepared by sous-vide cooking method was consistent with the protein stability at this temperature(3)Identification of characteristic volatile substances for fatty acids and changing mechanisms of hairtail during sous-vide cookingTexture and tenderness focus on the perception of food in the mouth,while the flavour composed of volatile substances tends to stimulate the senses by the taste of food.Together with texture and tenderness,it constitutes perception of food and affects satisfaction for food of most consumers.Hairtail is an aquatic product with rich fatty acids content,and the chemical reaction of temperature-induced fatty acids during sous-vide heating is of great significance to the composition of its volatile components.Gas chromatography-mass spectrometry was used to determine the profile of volatile substances and fatty acids during the preparation of sous-vide hairtail products,and their correlations were analysed.During sous-vide cooking,A total of 15 hydrocarbons such as pristane and pentadecane,12 aldehydes such as benzaldehyde and heptaldehyde,4 alcohols such as 1-octene-3-ol,and 4 aromatics such as m-xylene,2 ketones such as 3,5-octadiene-2-one were identified.Principal component analysis indicated that the volatile components profile of the hairtail at the beginning of the heat-up process has shown great difference from that of the untreated hairtail.From the end of the heat-up process to the completion of the preparation of sous-vide hairtail products,the volatile components were always similar to traditional heated hairtail products,indicating that sous-vide hairtail products exhibited similar flavour to traditional heated hairtail products.Pearson correlation analysis of each volatile component and 8 fatty acids detected in the sous-vide cooking showed that the law of fatty acid changes and multiple volatility substances are similar,which might be due to some of the volatile substances in hairtail were the products of primary oxidation or secondary oxidation of fatty acids Sixteen kinds of volatile substances including pentadecane and benzaldehyde had been identified as characteristic volatile substances of fatty acids.The establishment of a multiple linear regression model based on the relationship between characteristic volatile substances and fatty acid content.Among them,the content of myristic acid,pentadecanoic acid,palmitic acid,oleic acid,eicosapentaenoic acid and docosahexaenoic acid had a good linear relationship with the corresponding characteristic volatile substances,and the judgment probability value reached 0.999 This method provides a new approach to quickly detect the nutritional quality of hairtail fish based on fatty acid content by detecting volatile substances(4)Preparation and characterization of an environmentally friendly storage system based on chitosan-citrus essential oil microcapsules and study on its shelf life extension mechanism for sous-vide hairtail productsFor the prepared sous-vide hairtail products,during the storage process,due to the influence of mild heating temperature and the possibility of the invasion of bacteria,to reduce the risk of quality deterioration,the combination of low-temperature storage technology and preservatives was applied to extend the shelf life of sous-vide hairtail products.Based on ion gelation technology,a storage system based on chitosan-citrus essential oil microcapsules was constructed,which was applied to the storage process of sous-vide hairtail products to extend the shelf life.A series of chitosan-citrus essential oil microcapsules constructed with different emulsifiers were prepared,and their molecular structure was determined by infrared spectroscopy(FI-IR),X-ray diffraction(XRD)and differential calorimetric scanning(DSC)and other instrumental analysis methods.Considering the changes in crystal structure,thermodynamic properties,rheological properties,microstructure and mechanical properties,Tween 60 was selected as the desirable emulsifier,and the prepared chitosan-citrus essential oil microcapsules have the particle size of 289.3 nm,with the embedding rate of 68.1%.It was determined that the chitosan-citrus essential oil microcapsules had good antioxidant biological activity and exhibited desirable inhibitory effects to four common food-borne microorganisms:Staphylococcus aureus,Estherischia coli,Salmonella and Pseudomanas aeruginosa.The chitosan-citrus essential oil microcapsules environmentally friendly storage system was applied to the storage process of sous-vide hairtail products.The result showed that the system could extend the shelf life of sous-vide hairtail products by 15-30 days at 4?.Proteomics research results indicated that the chitosan-citrus essential oil microcapsules storage system could effectively reduce the degradation rate of some structural proteins,thereby maintaining the quality of sous-vide hairtail products.Alpha-actinin-2,myosin heavy chain-1,myosin heavy chain,slow myosin heavy chain 2,myosin light chain 3 skeletal muscle isoform,myosin light chain phosphorylatable fast skeletal muscle b were identified as the differential structural proteins of the chitosan-citrus essential oil microcapsules storage system to maintain fish qualityThis study elaborated the change mechanism of the quality and texture of the sous-vide hairtail products prepared by the sous-vide cooking method during preparation and storage.The results provide theoretical basis for the application of the sous-vide cooking process and expand its application in the industrial production process,providing a novel approach for providing high-quality aquatic products,which can effectively reduce waste in the production and storage of high value aquatic products.