Research And Application Of Identification Technique For Dried Shark Fin Products

Shark fin dried products, which are mainly made by dried fins of sharks and have very high medical and medicinal value, are deeply loved by consumers. Unfortunately, there is a potential for those dishonest traders in the shark fin dried products market to attempt to make money by passing off the cheaper product as the more expensive one, resulting in extremely widespread of counterfeit shark fin dried products, consequently, not only influence market order, but also damage consumers rights and interests. As the identification of shark fin dried products mainly depends on the experience, such as color and luster, texture, and appearance, which exist subjectivity and uncertainty, in this work, several techniques, including genomics analysis, infrared spectroscopy (IR) fingerprint analysis, scanning electron microscopy (SEM) microstructure analysis, stable isotope ratio analysis, amino acid content analysis, metallic element analysis and the polysaccharide composition analysis, were used to scientifically and accurately identify the authenticity of shark fin dried products. A basic strategy for identification of shark fin dried products, which contains the core technique of DNA identification method and the assisted-confirmation techniques (including other identification methods), was formed. The developed strategy could provide technical support for consumer recognition and government supervision.(1) PCR method. The shark specific primer was designed based on cytochrome oxidase subunit I (COI) gene of shark mitochondria, the amplification length was 228 bp and DNA in shark fin dried products was extracted by using phenol-chloroform extraction method. The results indicated that favorable generality and specificity of designed primers were obtained. The pretreatment method, DNA extraction method and PCR detection method can be applied to the shark composition detection identification with the sensitivity of 0.1% (m/m) in shark fin dried products and even other food. Combined with reverse validation using specific primers of plant, this method can correctly identify the authenticity of shark fin dried products.(2) SEM method. The ultra-structural morphology features of shark fin dried products’ outer surface, cross-section and shark fins needle were investigated by SEM, and the results showed that the morphology structure of real shark fins displayed different levels of difference with those of fake shark fins, thus the typical morphology structure can be used to clearly distinguish the fake shark fin dried products from the real ones. This method is simple, fast and intuitive, and most importantly, can make up the defect of PCR method.(3) ATR-FTIR method. The infrared spectrograms of different kinds of shark fin dried products were obtained using ATR-FTIR method, the results indicated that the infrared spectrograms of the same samples had good stability, and there was obvious difference in infrared spectrograms of true and false shark fin dried products, which mainly presented in the differences of protein amide I and II peaks (1650 cm-1,1544 cm-1) and polysaccharide skeleton peak (1050 cm-1). The differences in infrared spectrograms and Apro/Apol values could be adopted in undamaged identification of shark fin dried products.(4) Element analyzer- isotope ratio mass spectrometry (EA-IRMS) method. The δ13C and δ15N values of different kinds of shark fin dried products were determined by EA-IRMS, and the results indicated that the δ13C and δ15N values of real shark fins products ranged from-16.553‰ to -11.065‰ and 8.803‰ to 19.122%o, respectively, while δ13C values of some artificial shark fin dried products and δ15N values of some fake shark fin dried products were in the range of δ13C and δ15N values of real shark fin dried products, resulting in the consequence that real shark fin dried products cannot be effectively distinguished from false shark fin dried products by only carbon isotope ratio or nitrogen isotope ratio. However, the authenticity of shark fin dried products could be effectively identified through comprehensive evaluation of two-dimensional elements indexes.(5) Determination of amino acid contents in shark fin dried products.18 kinds of amino acids contents were determined using amino acid analyzer and ultra high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) after acid hydrolysis of samples. The results showed that there were differences within 10 kinds amino acids (Including aspartic acid, threonine, histidine, tyrosine, leucine, arginine, proline, glycine, alanine, lysine), and the authenticity of shark fin dried products could be identified according to the scope of this difference.(6) Metallic elements analysis of shark fin dried products.23 kinds of metallic elements contents were determined by inductively coupled plasma-mass spectrometry (ICP-MS) and the differences of metallic elements contents were analyzed. The results showed that metallic elements analysis could only be an assisted-method for the identification of shark fin dried products.(7) Polysaccharide components analysis of the shark fin dried products.5 kinds of monosaccharide and disaccharide and 2 kinds of uronic acid were determined using pre-column high performance liquid chromatography (HPLC) method after the enzymolysis of samples by papaya protease and amylase enzyme. This method could be used to quickly identify the artificial shark fin dried products by the differences of polysaccharide composition. However, the fake shark fin dried products could not be distinguished from real shark fin dried products by using this method, fortunately, this kind shark fin dried product could be identified by other methods in this study.(8) 5 kinds of amino acids,8 kinds of metallic elements, and δ13C and δ15N values values were selected to establish evaluation model of shark fin dried products based on the principal component analysis (PCA) method. Under this model, the synthetical scores of really shark fin samples, fake shark fin samples and artificial shark fin samples ranged from 71.9498 to 564.9416,607.9568 to 644.1284 and 648.014 to 798.5972, respectively, which can effectively identify the authenticity of a shark fin dried products.