核桃仁与发酵核桃乳中脂肪酸GC法的甲酯化条件优化及含量测定

本文采用GC-FID测定核桃仁、发酵核桃乳中的脂肪酸。在单因素实验的基础上,以衍生化试剂加入量、超声时间、超声水浴温度为影响因素,峰面积为响应值,运用Box-Benhnken中心组合实验设计原理进行响应面分析,优化了甲酯化反应条件。结果表明,检测核桃仁、发酵核桃乳中脂肪酸甲酯化的适宜条件为:0.5%KOH-甲醇647μL、超声时间5min、超声水浴温度43℃。在该条件下进行甲酯化反应,结合GC-FID检测到9种核桃仁中均含有棕榈酸、硬脂酸、油酸、亚油酸、亚麻酸5种脂肪酸,含量由高到低的顺序为:亚油酸>油酸>亚麻酸>棕榈酸>硬脂酸。用6种乳酸菌发酵的核桃乳,脂肪酸含量的整体变化不显著。 

Methyl esterification conditions optimization and content determination of fatty acids for GC analysis in walnut kernel and fermented walnut milk

The fatty acids of walnut kernel and fermented milk were analyzed by gas chromatography with Flame Ionization Detector ( FID) .The methyl ester reaction conditions were investigated using single factor and response surface methodology based on Box- Benhnken centre design principles. The derivatization reagent addition amount, ultrasound time and ultrasonic water bath temperature were used as affected factors while the total peak area of chromatogram as response value in this study.The results indicated that the optimum conditions for methyl esterification of fatty acids from walnut kernel and walnut milk were obtained as follows: the amount of KOH-methanol 647μL, ultrasound time 5min and ultrasonic water bath temperature 43℃. Under the above conditions, 5 kinds of fatty acids were detected from 9 different walnut kernels, whose contents from high to low in an order of linoleic acid, oleic acid, linolenic acid, palmitic acid, stearic acid.The content of overall change of fatty acids, which was from walnut milk fermented by 6 kinds of lactic acid bacteria, respectively was not significant.