Study On The Retention Of Pigments And Recognization Of Authenticity Of Rainbow Trout

The illegal use of industrial dyes on some agricultural production is universal in China. Industrialdyes can produce a bright color, besides they can lead to a high toxic, carcinogenic, teratogenic,mutgenic dye residues on agricultural products. Customers pay more and more attention to the safety ofagricultural products. The abuse of food raw material such as industrial pigment and synthetic pigmentbrought greatly challenge to the food. It is necessary to set up a variety of detection technologypreventing the illegal behavior of food additives.Using the dying Rainbow trout as Salmon can be easily found in the newspapers. The price ofSalmon can be two times higher than it of Rainbow trout. Some farmers added the industrial dyes andhighly dose of pigments to the feed. Then they can make the Rainbow trout into red. When thecustomers eat these counterfeit Salmon, they may get ill and even the cancer.This paper focus on the retention of canthaxanthin, astaxanthin and rhodamineB, the δ¹³C、δ¹⁵Nvalues of the crude protrin, the histological features of the muscle, carried out several kinds of methodsto recognize the Rainbow trout. The main contents and results are as follows:（1）By using different levels of pigments （0⁸0mg/kg） to feed the Rainbow trout for8weeks, thebasic ration can meet the requirements of Rainbow trout, through all periods of the feeding experiments,no sickness or death was found. The speed of the body weight gain was similar among all the treatments.The pigments, astaxanthin and canthaxanthin, can change the color of muscle from cyan to orange in6weeks, the color of the Rainbow trout muscles can reach the same level of Salmon, and the color waspositively correlated with the volume of addition, after removing the pigments from the basic ration, theRSF and a*value were also decline. RhodamineB did not have the function to change the color ofmuscle.（2）Through the optimization of the instrument parameters, composition of mobile phases andsample extraction, the HPLC method was developed for the determination of canthaxanthin, astaxanthinand rhodamineB. The results showed that: after6weeks of feeding the RSF could reach to25and a*to6.0. Using the above-mentioned method, the recoveries of astaxanthin, canthaxanthin and rhodamineBwere in the range of87.1%⁹0.5%,88.6%⁹4.9%,87.8%⁹2.2%respectively, and the relative standarddeviation was from1.39%to5.60%, the detection limits were0.001mg/kg、0.001mg/kg and0.0008mg/kg respectively. The retention of astaxanthin was3.6%（2wks）,5.5%（4wks）,7.2%（6wks）, andcanthaxanthin was2.6%（2wks）,4.3%（4wks）,6.4%（6wks） respectively. This method can be used todistinguish the Rainbow trout and Salmon through the kind and content of pigments in the fishes.（3）Through the study of δ¹³C、δ¹⁵N values of Rainbow trout muscle and basic ration, ancorrelativity was established between the muscle and the content of corn, fish meal in the feed. Thecorrelation index can reach to0.989and0.985respectively. The basic rations of the Rainbow trout andSalmon were different, measuring the δ¹³C、δ¹⁵N values can be a method to distinguish the Rainbowtrout and Salmon. （4）Through the study of the histological features, an order was found: with the increasing of thebody weight, the muscle fiber density decreased and the muscle fiber diameter increased. No apparenteffect on the muscle fiber diameter was found among the treatments with pigments. While the musclefiber density of the astaxanthin40mg/kg was greater than the fiber density of the astaxanthin80mg/kg,the same rule was also in the treatments of canthaxanthin and rhodamineB. The protein level of basicration can also influence the muscle fiber. With the increasing of protein level of basic ration, themuscle fiber density decreased and the muscle fiber diameter increased. When the muscle fiber diameterof the Rainbow trout and Salmon reached the same, the muscle fiber density of Salmon was muchsmaller. This method can be used to distinguish the Rainbow trout and Salmon.