Abstract: In order to establish an efficient method for the determination of L-carnitine in infant formula for special medical purposes, the spectrophotometric method for the determination of L-carnitine in foods for infants and young children and dairy products specified in the national standard GB 29989—2013 was optimized with respect to standard curve preparation, sample pretreatment and enzyme preparation. The results showed that under the following conditions: using the optimized standard curve, enzyme extraction at a rotation speed of no less than 6 000 r/min, and hydrolysis of 5 g of homogeneous milk powder (accurate to 0.000 1 g) with 0.25 g of α-amylase at 50 ℃ for 30 min, the optimized method exhibited high precision and spiked recovery. This method could overcome the problems encountered in the determination of L-carnitine in infant formula for special medical purposes by the traditional method such as cloudy filtrate, the dark color of prepared samples that could interfere with the determination of absorbance and low spiked recovery, being suitable for the large-scale determination of L-carnitine in amino acid-based infant formula, extensively hydrolyzed protein infant formula and partially hydrolyzed protein infant formula for special medical purposes.

Key words: L-carnitine, spectrophotometry, infant formula for special medical purposes, detection methods, quality control

摘要： 建立一种高效测定特殊医学用途婴儿配方乳粉中左旋肉碱含量的方法。从标准曲线制作、样品前处理、酶制备等方面对GB 29989—2013《食品安全国家标准 婴幼儿食品和乳品中左旋肉碱的测定》方法进行优化。结果表明：采用优化后标准曲线，酶提取转速不小于6 000 r/min，5 g（精确至0.000 1 g）混合均匀的乳粉前处理加入0.25 g α-淀粉酶，在50 ℃条件下水解30 min后制备样液的测定结果精密度高，加标回收率较高；该方法解决了特殊医学用途婴儿配方乳粉中左旋肉碱测定过程中滤液不澄清、制备液颜色较深影响吸光度测定、加标回收率较低的问题，适用于批量测定氨基酸配方、乳蛋白深度水解配方和部分水解配方特殊医学用途婴儿配方乳粉中左旋肉碱含量。

关键词: 左旋肉碱, 分光光度法, 特殊医学用途婴儿配方乳粉, 测定方法, 质量控制