反复冻融的猪肉蛋白对N-亚硝胺形成量的影响

目的:探讨反复冻融的猪肉蛋白对N-亚硝胺形成量的影响。方法:设计两个体外模拟反应系统,模拟反应体系Ⅰ只含有Na NO2,模拟反应体系Ⅱ由二乙胺盐酸盐(DEA·HCl)和Na NO2组成。将反复冻融(0、1、2、3、4、7、10次)造成的不同氧化程度的肌肉蛋白(muscle protein,Mep)、肌浆蛋白(sarcoplasmic protein,SP)和肌原纤维蛋白(myofibrillar protein,MP)分别加入上述两个反应系统发生亚硝化反应,测定N-亚硝基二乙胺(N-nitrosodiethylamine,NDEA)的形成量,同时测定硫代巴比妥酸反应物(thiobarbituric acid reactive substance,TBARS)值、羰基和巯基含量等指标。结果:系统Ⅱ中NDEA的形成量是系统Ⅰ的20~80倍,表明底物DEA·HCl存在对NDEA的形成产生显著影响(P0.05)。反复冻融4次后,3种蛋白的羰基含量显著增加(P0.05),巯基含量显著下降(P0.05),意味着猪肉蛋白均发生了明显的蛋白氧化,其中以SP的氧化速率最快,氧化程度最严重,形成的NDEA量最多,Mep次之,MP氧化程度相对较轻,形成的NDEA量相对较少。结论:反复冻融造成的蛋白氧化促进了NDEA的形成。因而在肉品冻藏过程中应防止温度波动,避免反复冻融引起蛋白氧化,进而控制N-亚硝胺的形成。

Relationship between the Formation of N-Nitrosamine and Proteins in Repeatedly Frozen-Thawed Pork

The purpose of this experiment was to study the relationship between the formation of N-nitrosamine and proteins in repeatedly frozen-thawed pork. Two model reaction systems in vitro were designed. Model system Ⅰ contained NaNO2 only, while model system Ⅱ contained DEA·HCl and NaNO2. Muscle proteins (Mep), sarcoplasmic proteins (SP) and myofibrillar proteins (MP) with different degrees of oxidation from pork subjected to different freeze-thaw cycles (0, 1, 2, 3, 4, 7 and 10 cycles) were added separately to each of the two systems for nitrosation reaction, and the formed N-nitrosodiethylamine (NDEA), thiobarbituric acid reactive substance (TBARS), carbonyl and sulfhydryl were determined. The results revealed that the NDEA formation in model system Ⅱ was 20–80 times higher than in model system Ⅰ, indicating that the substrate DEA·HCl had a significant impact on the formation of NDEA (P < 0.05). After four freezethaw cycles, a significant increase in carbonyl content and a significant decrease in sulfhydryl content were observed for Mep, SP and MP (P < 0.05), suggesting the significant oxidization of all these proteins. Among these proteins, SP were oxidized fastest and to the largest extent to form the most NDEA, followed by Mep, and MP were oxidized to form the least NDEA. Our results demonstrated that repeated freeze-thaw cycles could induce protein oxidization and consequent NDEA formation. Therefore, temperature fluctuation should be controlled during frozen storage of meat.