Source Tracing In Sea Cucumber Using Stable Isotope Technology

Source tracing analysis of food can provide technical verification for market regulation and protect geographical indication brand,and sea cucumber from different origins has different prices commercially,and unscrupulous businessmen,driven by the benefit,will falsify the information of sea cucumber origin to obtain higher profits,so that the construction,accumulation,and improvement of a traceability database for sea cucumber origin has become a common focus of concern for sea cucumber consumers,industry practitioners,and regulatory agencies.Development of a low-cost and highly stable technique for source tracing analysis of the sea cucumber origin is highly desirable for practical application,based on optimization of experimental conditions for detection of carbon and nitrogen isotopes in sea cucumbers by EA-IRMS and for detection of strontium and lead isotopes in sea cucumbers by ICP-MS.The data were subjected to differential analysis,and a discriminant model was established for bottom seeding sea cucumbers by combining principal component analysis and discriminant analysis among the three production areas:Jinzhou,Yantai and Xiapu.The main findings of the paper are as follows:（1）Sea cucumber samplesδ¹⁵N ranged from 7.89‰to 10.45‰,δ¹³C ranged from-20.31‰～-16.13‰.Between three regionsδ¹³C andδ¹⁵N all presented significant differences.Sea cucumber body wall and longitudinal muscleδ¹³C andδ¹⁵N was highly significantly associated.No significant fractionation effects occurred on stable isotope ratios of body wall to longitudinal muscle.When the body wall,longitudinal muscle and respiratory tree were used to discriminate,the correct rate was higher,all of them could reach more than 95%,while the digestive tract was used to discriminate relatively lower,Jinzhou and Yantai had some false judgments.（2）An accurate analytical method for the ratio of lead isotopes in sea cucumbers was established by ICP-MS.Based on the low amount of Pb in sea cucumber,the total Pb content in the digestion solution was adjusted to 5-20μg/L,followed by 10μg/L of lead isotope standards for cross determination,allowing precise correction for mass discrimination effects.The measurement precision of ²⁰⁴Pb/²⁰⁶Pb,²⁰⁷Pb/²⁰⁶Pb,and ²⁰⁸Pb/²⁰⁶Pb was less than0.1%,and the present method showed good repeatability,accuracy,and stability.Using the discriminant function built from lead isotopes alone for origin of sea cucumbers,the discriminant accuracy of body wall was the best,with 92.0%and 90.0%in initial and cross validation,respectively,and that of digestive tract was the worst,with 80.7%and 79.3%in initial and cross validation,respectively.The discrimination correct rates of the longitudinal muscle and respiratory tree were slightly smaller than those of the body wall,and were also all above 90.0%（3）An analytical method based on ICP-MS technique for the determination of isotopic ratios of strontium in aquatic products was developed.The results indicate that adjusting the total strontium concentration in the sample solution between 70-100μg/L,and 80μg/L standards were cross measured to accurately correct for mass discrimination effects.The precisions of the methods ⁸⁴Sr/⁸⁶Sr,⁸⁷Sr/⁸⁶Sr,and ⁸⁸Sr/⁸⁶Sr were less than 0.1%and showed good repeatability,accuracy,and stability.When we determined the strontium isotopes of sea cucumber samples from three locations（Jinzhou,Yantai and Xiapu）,we determined that the total strontium content as well as the isotope ratios of sea cucumber samples from different origins showed marked geographical variations,but the results of both principal component analysis and discriminant analysis were unsatisfactory,and none of the four organizations could distinguish the samples from the three locations with less than 80%overall discrimination correct.But Jinzhou’s sample was able to be effectively differentiated from the other two regions in the discriminant analysis of the 4 tissues,and the correct rates in both initial and cross validation were above 90%.（4）Correlation analysis using Pearson’s correlation coefficient was performed on eight isotopic indexes from the body wall,longitudinal muscle,respiratory tree,and digestive tract of sea cucumber,which showed strong correlations between isotopic indexes of each tissue.Overall,positive correlations were found between lead isotopes and with carbon and nitrogen isotopes,whereas negative correlations were found between strontium isotopes and lead isotopes as well as between carbon and nitrogen isotopes.Using principal component analysis to convert the information from 8 to 2 dimensions,the characteristic isotopes of body wall were found to be ²⁰⁴Pb/²⁰⁶Pb,²⁰⁷Pb/²⁰⁶Pb,δ¹⁵N.A total of fourδ¹³C,one by one discriminant analysis using these four indexes resulted in a discriminant function with 98.0%correct initial validation and 97.3%correct cross validation.The characteristic isotopes of the longitudinal muscles and respiratory tree were ²⁰⁷Pb/²⁰⁶Pb,δ¹⁵N,δ¹³C.After discriminant analysis one by one,resulted in discriminant functions with correct rates of 96.7%and93.3%,respectively.While the gastrointestinal ²⁰⁷Pb/²⁰⁶Pb,δ¹⁵N,δ¹³C signature isotopes,when discriminant analysis was performed one by one,δ¹⁵N was eliminated again,and finally the obtained initial and cross validation correct rates of the discriminant function were only 82.7%and 81.7%.