https://blog.gongquiz.com/2022/07/02/%ec%8b%9c%ed%8a%b8%eb%a5%b4%ec%82%b0citric-acid%ec%9d%80-%eb%aa%87-%ea%b0%9c%ec%9d%98-%ec%b9%b4%eb%b3%b5%ec%8b%a4carboxyl-%ec%9e%91%ec%9a%a9%ea%b8%b0%eb%a5%bc-%ea%b0%96%ea%b3%a0-%ec%9e%88%eb%8a%94/