| Sashimi fish is a type of fish that can be eaten raw.They are deeply loved by consumers because of their delicious taste and rich nutrition.At present,there are many studies on sashimi fish,but because the process of sashimi fish from fishing to prepare sashimi fillets needs several key preparation,there are many factors that affect its final quality,and the research on its process control is not comprehensive.Based on the above problems,this study separately analyzed the moisture change of sashimi during storage,the effect of thawing method on the quality of sashimi during processing,the non-destructive fast inspection technology for the freshness of sashimi fillets during the sale process and the volatile flavor components of sashimi fillets at different freshness.The specific research results are as follows:(1)Low-field nuclear magnetic resonance technology and HE staining were used to study the water state and migration of sashimi fish at different temperatures and different storage periods.The results show that:in the low temperature storage(LTS;-18?storage for180 days),ultra-low temperature storage(ULTS;-78?storage for 180 days)and variable temperature storage(VTS;the central temperature of sashimi was rapidly reduced to-18?at-78?,and then quickly transferred to-18?for 180 days)sashimi fish in the three different temperature storage processes,there are three different states of water groups:bound water,non-flowing water and free water.During the storage period of 0-24 weeks,the relative content of non-flowing water and free water in LTS,ULTS and VTS changed significantly with the storage time(P<0.05).Among them,the relative content of non-flowing water in LTS,ULTS,and VTS decreased from 91.63%,93.73%,92.36%to 61.18%,81.34%,72.40%.And the relative content of free water increased from 3.45%,1.74%,3.12 to 34.36%,14.28%,23.23%,but the relative content of bound water was in the range of 4.3%to 5.0%in the three storage processes,and the fluctuation range was small.The moisture distribution in the three storage processes changed from a uniform distribution at the initial stage of storage to a migration from the inside to the outside,and then restored to a uniform state in the later stage of the storage.In addition,the sashimi fish in ULTS and VTS have the shortest time to pass through the maximum ice crystal formation zone,both are 29 minutes,which is more conducive to the rapid freezing of sashimi fish.Combined with the results of HE staining,it can be seen that in ULTS,the ice crystals formed in the sashimi fish have the smallest size and cause less mechanical damage to the muscle fibers,which is beneficial to the integrity of the muscle fibers and the maintenance of the water holding capacity in the system,and the amount of water migration is less.(2)The effects of room temperature air thawing,refrigerator thawing,water bath thawing and microwave thawing on the sensory,thawing loss,whiteness,TVC,TVB-N,microstructure,texture characteristics,water migration and volatile odor characteristics of sashimi fillets were explored.The results showed that the sensory evaluation score of RT's sashimi fillet was 24.85,which had the best sensory characteristics among the four thawing methods,and its microstructure and organization were the least damaged.The thawing loss of WBT is 6.05%,which is significantly lower than the other three thawing methods(P?0.05),and it is conducive to the retention of moisture in sashimi fillets.Its freshness index TVB-N value is 11.76 mg/100 g,which is only higher than MT,which can effectively alleviate the decrease in freshness of sashimi fillets during the thawing process.The whiteness,TVC and TVB-N of MT are 44.54,2.88 lg CFU/g,10.74 mg/100 g,respectively,which are better than the other three thawing methods.It can effectively inhibit the color change during the thawing process,the growth of microorganisms,and alleviate the production of ammonia and amines in the sashimi fillets.However,at the same time,the uneven heating of the sashimi fillets by microwave thawing leads to obvious partial ripening,which is poor in terms of sensory and texture.For RTAT,it is inferior to other thawing methods in all thawing quality indicators,and it is not suitable for thawing sashimi fillets.Therefore,choosing WBT is more conducive to ensuring the thawing quality of sashimi fillets and avoiding adverse changes in sashimi fillets during thawing to the greatest extent.(3)Compared with the classic freshness TVB-N detection index,the NIR non-destructive detection technology was used to establish freshness exploration and found that the use of 1 000?1 800 nm spectrum can realize the qualitative classification of different freshness of sashimi fillets.The results show that the classification accuracy rate of fresh and spoiled sashimi fillets is 90.91%,while the classification accuracy rate of sub-fresh sashimi fillets is 100%,and the overall classification accuracy rate is 93.33%.Using PLS to establish a quantitative analysis model for the TVB-N value of sashimi fillets,the results show that the SEC and SECV values of the model obtained after SNV pretreatment are the smallest,and the values of R_C and R_P are both greater than 0.95 and better than those without pretreatment methods.The performance of the model is optimized,and the accuracy of the prediction is effectively improved.Under this model,the predicted value of TVB-N is in good agreement with the true value.In addition,in external verification,the model's average deviation of the TVB-N prediction for the sample was 0.16,and the predicted value and the true value showed a very significant correlation(P<0.01),and the correlation coefficient was 0.969.Therefore,the use of near-infrared spectroscopy technology can quickly realize the qualitative classification of different freshness of sashimi fillets and the quantitative detection of TVB-N value in the process of sale,and both have high accuracy.(4)The SPME-GC-MS technology was used to compare the volatile flavor components and contents of three different freshness sashimi fish fillets.And the non-destructive testing technology based on the electronic nose to quickly identify the freshness level is explored.It was found that in three different freshness sashimi fillets,a total of 88 volatile flavor components in 6 categories were detected,including 47 hydrocarbons,11 alcohols,14aldehydes,1 acid,4 ketones,and 11 esters.However,the volatile flavor components contained in sashimi fillets of different freshness are very different.Among them,aldehyde compounds characterize the flavor of fresh sashimi to a certain extent,while alcohol compounds explain the flavor of spoiled sashimi.Radar fingerprint analysis,load analysis,PCA and LDA analysis are performed on the odor characteristics of fresh,sub-fresh and spoiled sashimi fillets with the response signal of the electronic nose.The results show that the changes of nitrogen oxides,alkanes,sulfides,alcohols and other aromatic compounds play a major role in distinguishing the volatile odor of sashimi,which further verified the results of SPME-GC-MS analysis of volatile flavors of sashimi fillets with different freshness.At the same time,it is proved that the electronic nose combined with PCA and LDA can achieve rapid and non-destructive freshness classification of sashimi based on volatile flavor characteristics,which provides a new idea for its non-destructive and fast freshness inspection technology. |
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