Effect Of Different Thawing Methods On The Textural Properties Of Frozen Instant Sea Cucumbers

Sea cucumbers have become one of the popular marine foods in China due to their high content of bioactive components.However,fresh sea cucumbers were easy to autolyse after capture,so most of them will be sold as processed products.The dried sea cucumbers made by traditional methods are complicated to rehydrate,and frozen instant sea cucumbers had become popular in recent years due to their convenience and better texture.In order to investigated the changes in the textural properties of frozen instant sea cucumbers under different thawing methods,this paper investigated the macroscopic evaluation of the thawing efficiency,thawing loss,cooking loss,water holding capacity and textural sensory properties of frozen instant sea cucumbers（Stichopus japonicus）under four different thawing methods（cold air thawing,air thawing,water immersion thawing and ultrasonic assisted water immersion thawing）.Then,based on the sensory aspect of texture,the texture characteristics were taken as the entry point,and the texture characteristics of thawed instant sea cucumbers were evaluated objectively using texture meters（TPA mode,shear mode,stress relaxation mode）and rheometers,and a correlation analysis was made with the organoleptic evaluation to determine the indicators that represent the qualitative characteristics and play a decisive role.Finally,the analysis of the causes influencing the differences in the conformational properties of different thawing methods from the microscopic point of view of microstructure,moisture distribution,protein traits and protein conformation were explained and correlation analyses were made to provide novel research directions for the conformational evaluation of aquatic frozen quality and provides practical guidance for consumers in the aftermarket.The results of the study are as follows:（1）Effect of different thawing methods on the physicochemical properties of frozen instant sea cucumbers.Different thawed samples were found to have the best quality and the longest thawing time（414.9 min）after cold air thawing.The samples thawed by ultrasound-assisted water were second only to cold air thawing,but the thawing time was significantly shorter（11.3 min）and mostly performed better than air and immersion thawing,with no significant difference from immersion thawing only in thawing loss,water holding capacity and total sensory score of texture（P>0.05）.Compared to the first three methods,air thawing had a greater impact on the quality of the thawed samples than the first three methods,as they significantly reduced the hardness,springiness and water holding capacity of the samples（P<0.05）,while thawing loss and cooking loss increased significantly（P<0.05）.Frozen instant sea cucumbers after high temperature and pressure treatment had 3.15%higher moisture than fresh sea cucumbers,while protein,fat and ash were 0.45%,0.15%and 1.2%lower than fresh sea cucumbers,while collagen content was similar to fresh sea cucumbers,both accounting for about 70%.（2）The correlation between the texture characteristics of frozen instant sea cucumbers by different thawing methods was investigated.11 instrumental parameters and 3 sensory evaluation parameters of the four thawing groups were significantly different（P<0.05）,among which the hardness,elasticity and viscosity parameters of the cold air thawing group were greater than those of the other thawing groups,followed by the ultrasound-assisted water immersion thawing group.The correlation between the 11 instrumental test indicators was high（r≥0.800）,except for TPA cohesion and TPA elasticity,longitudinal shear,coefficient of adhesionη,energy storage modulus G′and loss modulus G″.There was also a correlation（r=0.577-0.994）between the instrumental test indicators and the sensory evaluation indicators,whose hardness,elasticity and viscosity indicators were suitable to be expressed as TPA hardness,modulus of elasticity E₁and modulus of loss G″respectively.Principal component analysis revealed that the cold air thawing group with the highest total sensory evaluation score tended to be in the positive direction of principal components1 and 2,and which could be simultaneously better explained by TPA cohesion,TPA hardness,transverse shear and modulus of elasticity E₁.（3）The causes of the differences in the texture of frozen instant sea cucumbers due to different thawing methods.The cold air thawing group performed best in terms of microstructure,water distribution,protein properties and conformation.Ultrasonic-assisted immersion thawing was second only to cold air thawing and did not differ significantly from immersion thawing only in terms of free water relaxation time and protein tertiary structure（P>0.05）.Compared with the previous two methods,air thawing and immersion thawing damaged the texture of instant sea cucumbers more,as they significantly reduced the side chain structure,surface hydrophobicity,maximum denaturation temperature andα-helix of the samples（P<0.05）,while pore size,relative free water content andβ-folding increased significantly（P<0.05）.The PCA analysis also revealed that the frozen sea cucumber samples thawed by cold air and ultrasound-assisted immersion thawing had better structural properties than those thawed by air and immersion.PLS analysis found that higher higherα-helix fractions had higher hardness properties,similarly T_maxshowed a higher positive correlation with transverse shear and P₂₂with cohesion,in contrast P₂₃,T₂₃andβ-sheet showed a higher negative correlation with the textural property index.VIP analysis found that P₂₂,α-helix and T_maxwere very useful for predicting hardness and elasticity,while T₂₁and irregular curl were important variables for differentiating viscosity and tenderness,and P₂₂,P₂₃,T_max,α-helix andβ-sheet were useful for predicting four key textural indicators of frozen instant sea cucumbers,namely TPA hardness,TPA cohesion,transverse shear and E₁.