电子束辐照对带鱼鱼糜内源性蛋白酶活性及其构象单元的影响

Effect of Electron Beam Irradiation on the Activity and Conformational Unit of Endogenous Proteases from Hairtail Surimi

鱼类内源性蛋白酶是引起鱼糜凝胶劣化的重要因素之一。以不同剂量电子束辐照带鱼鱼糜,测定鱼糜内源性肌原纤维结合型丝氨酸蛋白酶(myofibril-bound serine proteinase,MBSP)和组织蛋白酶L(cathepsin L,Cat-L)活力及其最适反应温度,结合圆二色光谱分析其构象单元变化,探讨电子束辐照对鱼糜内源性MBSP和Cat-L的影响。结果表明:随着辐照剂量的增加,鱼糜MBSP和Cat-L活力降低,当辐照剂量为9 kGy时Cat-L活力下降更为明显;对照组和辐照组鱼糜MBSP的最适温度均为55℃,但3 kGy及9 kGy辐照对Cat-L的最适温度产生影响,使其由55℃降低至45℃;辐照引起鱼糜MBSP和Cat-L分子中的二级结构单元互相转化,导致其构象变化,削弱其降解肌原纤维蛋白的能力。结论:电子束辐照能够影响带鱼鱼糜MBSP和Cat-L的二级结构及活力,减轻二者对肌原纤维蛋白的降解作用,适宜剂量的电子束辐照能有效抑制鱼糜内源性蛋白酶活性,防止凝胶劣化,有利于鱼糜凝胶的形成。

Endogenous proteases in fish are one of the important causes of surimi gel degradation. In this study, to investigate the effect of electron beam (EB) irradiation on endogenous myofibril-bound serine proteinase (MBSP) and cathepsin L (Cat-L) in hairtail surimi, the activity and optimum temperature of both enzymes after being treated with different doses of EB irradiation were determined, and the secondary structure changes were studied by circular dichroism (CD) spectroscopy. The results indicated that the activity of endogenous MBSP and Cat-L decreased with the increase of irradiation dose;especially Cat-L activity decreased significantly at 9 kGy. The optimum temperature of both control and irradiated MBSP was 55 ℃, whereas the optimum temperature of Cat-L decreased from 55 ℃ to 45 ℃ after irradiation at 3 or 9 kGy. EB irradiation resulted in the transformation of secondary structure units in MBSP and Cat-L, thus leading to conformational change and weakening their ability to degrade myofibrillar protein. In conclusion, EB irradiation can affect the secondary structure and activity of endogenous MBSP and Cat-L from hairtail surimi. The appropriate dose of EB irradiation can effectively inhibit the activity of endogenous proteases in surimi, thereby weakening the degradation of myofibrillar protein and consequently facilitating the formation of surimi gel.