三疣梭子蟹可食用部位镉组分的逐级提取及分子质量分布特征

不同赋存形态镉的提取分离对于海洋食品的安全性评估分析具有至关重要的作用。本文以三疣梭子蟹为样品,利用Tris-HCl、盐酸、碱性蛋白酶等方法对其可食部位镉进行了分离提取,并借助超滤、透析等方式对Tris-HCl提取物进行了分离、测定以分析其中的镉形态分布特征。结果表明,Tris-HCl具备较好的提取效果,对于肝胰腺、性腺等部位的镉提取率高达90%,但是肌肉组织仍有37%的非游离态镉存在,经碱性蛋白酶处理后可有效溶出;对于Tris-HCl提取物的超滤透析结果显示,分子质量>10 kDa的镉复合物占比最高,可能是金属硫蛋白以外的其它蛋白或多糖、脂类等与镉形成大分子复合物;同时<500 Da的镉组分约占4%~25%,可能包括离子态镉、氨基酸-镉等小分子镉组分。以上结果表明,镉在梭子蟹等海洋生物中的蓄积和代谢过程,除金属硫蛋白所介导的途径之外可能另有其它机制,而且其实际危害程度可能与之前基于总镉(假设全部为离子态)的评估结论存在差异。

Sequential Extraction of Cadmium in Edible Parts of Portunus trituberculatus and the Molecular Weight Distribution

Extraction and isolation of different cadmium complex from aquatic products are essential for the purpose of safety evaluation and analysis. In this study, the methods involving Tris-HCl, HCl and alkali protease for extraction of cadmium in edible tissues of Portunus trituberculatus were investigated and compared precisely, and coupled with ultrafiltration and dialysis, cadmium complexes with peculiar molecular weights distribution were also isolated. The results indicated that Tris-HCl soluble cadmium contributed most of the total cadmium, especially in gonad and hepatopancre with extraction efficiency of 90% or more. However, about 37% of the cadmium in muscle need alkaline protease treatment for effective dissolution due to its strong binding with tissues. Additionally, the complex with molecular weight>10 kDa accounted for the highest percentage of total cadmium in Tris-HCl extraction, which indicated the possibility of significant conjugation of cadmium with various proteins, lipids and polysaccharide, other than metallothionine-Cd. Besides, cadmium complex with molecular weight lower than 500 Da accounted for about 4%~25% of Tris-HCl extracted cadmium, maybe consisting of free Cd2+ and the cadmium-cysteine or-glutathione complex. These results exhibited that other mechanism, differed with metallothionine-induced pathway, for the accumulation and metabolism of cadmium in marine animals existed. Meanwhile, considering the large percentage of cadmium complex, the risk analysis based on the traditional total cadmium maybe much overestimated.