Engelhardt U H, Maier H G
Z Lebensm Unters Forsch. 1985 Jul;181(1):20-3. doi: 10.1007/BF01124801.
22 acids in ground roast coffees and instant coffees were determined by GLC of their silyl derivatives (after preseparation by gel electrophoresis) or isotachophoresis. The contribution to the total acidity (which was estimated by titration to pH 8 after cation exchange of the coffee solutions) was calculated for each individual acid. The mentioned acids contribute with 67% (roast coffee) and 72% (instant coffee) to the total acidity. In the first place citric acid (12.2% in roast coffee/10.7% in instant coffee), acetic acid (11.2%/8.8%) and the high molecular weight acids (8%/9%) contribute to the total acidity. Also to be mentioned are the shares of chlorogenic acids (9%/4.8%), formic acid (5.3%/4.6%), quinic acid (4.7%/5.9%), malic acid (3.9%/3%) and phosphoric acid (2.5%/5.2%). A notable difference in the contribution to total acidity between roast and instant coffee was found for phosphoric acid and pyrrolidonecarboxylic acid (0.7%/1.9%). It can be concluded that those two acids are formed or released from e.g. their esters in higher amounts than other acids during the production of instant coffee.
通过气相色谱法测定烘焙咖啡粉和速溶咖啡中的22种酸的硅烷基衍生物（经凝胶电泳预分离后）或等速电泳。计算每种酸对总酸度的贡献（通过对咖啡溶液进行阳离子交换后滴定至pH 8来估算）。上述酸对总酸度的贡献分别为67%（烘焙咖啡）和72%（速溶咖啡）。首先，柠檬酸（烘焙咖啡中为12.2%/速溶咖啡中为10.7%）、乙酸（11.2%/8.8%）和高分子量酸（8%/9%）对总酸度有贡献。还应提及绿原酸（9%/4.8%）、甲酸（5.3%/4.6%）、奎尼酸（4.7%/5.9%）、苹果酸（3.9%/3%）和磷酸（2.5%/5.2%）的占比。发现烘焙咖啡和速溶咖啡在对总酸度的贡献方面，磷酸和吡咯烷酮羧酸存在显著差异（0.7%/1.9%）。可以得出结论，在速溶咖啡生产过程中，这两种酸比其他酸更多地从例如它们的酯中形成或释放出来。
