作 者：
王鹏杰;简澍瑜;王辰元;郭慧媛;文鹏程;任发政
单 位：
中国农业大学食品营养与工程学院;教育部功能乳品重点试验室;食品营养与人类健康北京高精尖创新中心
关键词：
蛋白质;粒径;温度;酪蛋白胶束;动态光散射;前处理;冷冻电镜
摘 要：
为了准确评价乳的稳定性和加工性能,探讨不同前处理条件对动态光散射检测酪蛋白胶束粒径的影响,研究了稀释液的种类(超纯水、钙咪唑缓冲液、模拟牛乳超滤液和牛乳超滤液)、稀释液温(4和25℃)和稀释液的放置时间(0~48 h)对脱脂乳中酪蛋白胶束粒径的动态光散射测试结果的影响,并将酪蛋白胶束粒径的动态光散射测试结果与冷冻透射电镜图像中测得的真实结果进行比较。研究发现以超纯水和钙咪唑缓冲液作为脱脂乳稀释液时,部分胶束发生解离,影响测试结果;采用牛乳超滤液及模拟牛乳超滤液作为稀释液时,胶束的微环境没有改变,反映了胶束的真实粒径及分布;放置24 h后,牛乳超滤液及模拟牛乳超滤液将产生颗粒;温度对测试有显著的影响(P<0.05):4℃的样品用25℃的稀释液进行稀释后,动态光散射的计数率和粒径分别增大了16.6%和11.4%;25℃的样品用4℃的稀释液进行稀释后,计数率和粒径分别降低了16.1%和9.8%。结果表明酪蛋白胶束粒径的测试前处理较适宜的条件为:在与样品的温度相同条件下,以配置好后24 h内的模拟牛乳超滤液或牛乳超滤液(10 k Da超滤膜)作为脱脂乳的稀释液进行稀释。通过与冷冻电镜条件下测得的酪蛋白胶束粒径的真值比较,发现该前处理条件下酪蛋白胶束粒径的动态光散射测试结果的相对误差为-5.7%~1.8%,表明该样品前处理方法可用于动态光散射方法快速检测酪蛋白胶束粒径。研究结果为快速、准确地获取酪蛋白胶束的粒径信息,进而准确分析乳的稳定性及加工性能提供参考。
译 名：
Effect of different pre-treatment methods on size determination of casein nanoparticles by dynamic light scattering
作 者：
Wang Pengjjie;Jian Shuyu;Wang Chenyuan;Guo Huiyuan;Wen Pengcheng;Ren Fazheng;College of Food Science and Nutritional Engineering, China Agricultural University;The Innovation Centre of Food Nutrition and Human Health;Key Laboratory of Functional Dairy of Chinese Ministry of Education;Gansu Dairy Industry Productivity Promotion Center;
关键词：
proteins;;particle size;;temperature;;casein nanoparticles;;dynamic light scattering;;pre-treatment;;cryo-transmission electron microscopy
摘 要：
The size and size distribution of casein nanoparticles plays an important role in the functionality and stability of milk. Dynamic light scattering is an effective method of measuring the size and size distribution of casein nanoparticles. But as biomacromolecules, casein nanoparticles are quite sensitive to their microenvironment changes. And therefore, the physicochemical properties of casein nanoparticles could be easily altered in different treatments, resulting in the incorrect size information determined by dynamic light scattering. The object of the present research was to analyze the effect of pre-treatment methods on the size and size distribution of casein nanoparticles determined by dynamic light scattering. The results suggested that when water and calcium imidazole buffer were used as the diluents, the counting rate of the samples was less than 7 ×103 counts/s, indicating there were no particles that could influence the size determination of casein nanoparticles. However, it was also found when water and calcium imidazole buffer were used as the dilution of casein nanoparticles, a significant decrease in the counting rate could be observed. This indicated both water and calcium imidazole buffer could easily alter the microenvironments of casein micelle dispersions, resulting in the partially dissociation of nanoparticles. And thus, the water and calcium imidazole buffer were not suitable for the dilution of casein nanoparticles. When simulated milk ultrafiltrate and milk ultrafiltrate were used as the diluents, it was found that there were no significant changes in the counting rate of the casein micelle dispersions. This indicated the microenvironment of both simulated milk ultrafiltrate and milk ultrafiltrate(10 k Da) was quite similar to that of milk, and thus the casein nanoparticles could not dissociate in both simulated milk ultrafiltrate and milk ultrafiltrate. However, extra particles occurred in both simulated milk ultrafiltrate and milk ultrafiltrate 24 h after their preparation, and therefore they were not suitable for the size measurement of casein nanoparticles under such the situation. Furthermore, it could be observed that the temperature of the diluents could significantly affect the measurement accuracy: when the samples(25℃) were diluted with 4℃ diluents, the counting rate could reduce by 16%; when the samples(4℃) were diluted with 25℃ diluents, the counting rate could increase by 10%. Based on the conclusion obtained above, it was suggested that the best pre-treatment methods for the size and size distribution of casein nanoparticles by dynamic light scattering were: the temperatures of the samples diluted with simulated milk ultrafiltrate or milk ultrafiltrate(10 k Da) should be similar with the milk samples. Results indicated the size distribution of casein nanoparticles obtained by dynamic light scattering was quite similar with that observed by the cryo-transmission electron microscopy, indicating the pre-treatment methods used could not affect the structural properties of casein nanoparticles in their true microenvironments, and thus permitted us to obtain reliable information of size and size distribution.
