微生物法测定乳清蛋白粉类样品中的叶酸含量

目的 建立微生物法测定乳清蛋白粉类样品中叶酸含量的分析方法。方法 利用叶酸标准品制作叶酸标准曲线。将样品进行超声处理得到样品溶液。向试管中加入等体积的培养基和不同体积的样液,稀释至10mL,得到样品待测液。样品待测液和叶酸标准曲线溶液灭菌后,加入鼠李糖乳杆菌(Lactobacillus casei spp.rhamnosus)CICC 6224菌悬液进行培养,将培养物混匀后测其吸光度值,根据标准曲线计算相应的叶酸含量,并进行方法的空白试验、检出限、精密度、重复性、稳定性及回收率试验。结果 在0.1010~1.0103ng/mL范围内,叶酸标准曲线呈现良好的线性,相关系数R_²=0.99373,符合GB/T27404-2008《实验室质量控制规范》的要求,该方法的相对标准偏差(relative standard deviation,RSD)为3.8%(n=6),平均回收率为102.5%(n=9)。结论 该方法稳定准确,适合用于测定乳清蛋白粉类样品中的叶酸含量。

Determination of folic acid in whey protein powder samples by microbiological method

Objective To establish a method for content determination of folic acid in whey protein powder samples by microbiological method. Methods Folic acid standard curve was made from folic acid standard. The sample was sonicated to obtain the sample solution. In the test tube, equal volume medium and different volume sample solution were added and diluted to 10 mL to obtain the sample solution to be tested. Sample solution to be tested and folic acid standard curve solution were sterilized, then the suspension of Lactobacillus casei spp. rhamnosus CICC6224 bacteria was added to culture, the absorbance value of the culture was measured after mixing the corresponding folic acid content was calculated according to the standard curve, and the blank test, limit of detection, degree of precision, repeatability, stability and recoveries of the method were carried out. Results The standard curve of folic acid was well linear in the range of 0.1010~1.0103 ng/mL, and the correlation of coefficient r2=0.99373, which was in line with the requirements of GB/T 27404-2008 laboratory quality control code. The relative standard deviation of the method was 3.8% (n=6), and the recoveries was 102.5% (n=3). Conclusion The method is stable and accurate, which is suitable for content determination of folic acid in whey protein powder samples.