Study On The Effect Of Temperature Fluctuation During Cold Chain Logistics On The Freshness Quality And Odor Characteristics Of Chilled Fresh Pseudosciaena Crocea

Pseudosciaena crocea is the largest mariculture cultured marine fish in China,which is fleshy and fresh taste,rich in proteins,vitamins and trace elements.It’s one of the eight leading export cultured aquatic products with high economic value.The domestic sales of Pseudosciaena crocea are mainly refrigerated cold chain,temperature fluctuations are prone to occur in cold chain transportation,which changes the quality and causes certain economic losses.In this regard,this paper discusses the influence of broken chain temperature fluctuation on the quality of Pseudosciaena crocea,provides a reference basis for the cold chain logistics construction and quality control for Pseudosciaena crocea,and mainly conducts research work in three parts,as follows:Firstly,This study simulated the storage and transportation process of chilled fresh Pseudosciaena crocea under normal cold chain conditions(control group)and interrupted cold chain conditions(three different temperature fluctuation conditions).The freshness indicators,including total volatile base nitrogen(TVB-N),total viable counts(TVC),thiobarbituric acid reactive substance(TBA)value,color difference,K value and texture,were measured at different time points(before and during constant temperature storage after interruption).The results showed that with the increase of temperature fluctuation amplitude,TVC,TVB-N,TBA,and K value all increased to varying degrees.Among them,TVC was more sensitive to temperature fluctuation.The significant changes(p<0.05)of K value and TVB-N mainly occurred in the middle and late stages of storage.When the temperature fluctuation amplitude increased by 4℃,the time for significant changes in K value,TVB-N,and TVC was shortened by 2 days.Although the texture changed due to temperature fluctuation,the difference was not significant(p>0.05)and had a low correlation with other indicators,which could not reflect the quality damage of chilled fresh yellow croaker caused by temperature fluctuation effectively.Subsequently,based on the simulated cold chain conditions in the previous section,we investigated the volatile component changes of yellow croaker and identified the volatile odor components of Pseudosciaena crocea under temperature fluctuation.Preliminary analysis of the volatile components of Pseudosciaena crocea under different cold chain conditions using an electronic nose revealed that temperature fluctuation caused differences in the volatile components such as ammonia,amines,and hydrogen sulfide.Headspace Gas Chromatography Ion Mobility Spectrometry(HS-GC-IMS)and Headspace Solid Phase Micro-extraction Gas Chromatography-mass Spectrometry(HS-SPME-GC-MS)analyses showed that temperature fluctuation led to a decrease in the relative content of aldehydes and an increase in the relative content of ketones in Pseudosciaena crocea.Based on the relative odor activity value,it was found that the contribution of octanal,nonenal and 1-octene-3-ol to the overall odor varied greatly when temperature fluctuation occurred.Combining various chemometric results showed that the changes in the content of 2-pentanone and ethyl acetate were significantly correlated(p < 0.001)with quality changes caused by temperature fluctuation.Finally,we investigated the microbial community structure of Pseudosciaena crocea and its impact on quality changes and odor formation under two different cold chain conditions.High-throughput sequencing revealed that the relative abundance of Ralstonia accounted for more than 45% in the control group,while the relative abundance of Pseudomonas and Aeromonas together accounted for more than 53% in the interrupted group,becoming dominant genera.Linear discriminant analysis effect size(LEf Se)showed that the relative abundance of Cutibacterium,Arenimonas,Chryseobacterium,and Aeromonas significantly differed after temperature fluctuation.Correlation analysis revealed that Pseudomonas and Chryseobacterium were the main genera causing quality changes,while Aeromonas,Ralstonia and Chryseobacterium were the main genera causing odor changes.Predicted bacterial community functions indicated that temperature fluctuation led to an increase in the abundance of energy metabolism,co-factors and vitamins metabolism,nucleotide metabolism,as well as cell processes and signaling pathways.Temperature fluctuation caused significant succession in both microbial community structure and function,with the dominant genera transitioning from Ralstonia to Pseudomonas and Aeromonas.Chryseobacterium,Pseudomonas,Aeromonas,and Ralstonia played important roles in quality changes and characteristic odor formation under temperature fluctuation conditions.