Detection of brewed soy sauce adulteration by analyzing levulinic acid with HPLC-UV

• Main Authors: Liu, Chung-Ching, 劉重慶
• Other Authors: Hung, Lang-Bang
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/kf3944

碩士 === 國立臺灣海洋大學 === 食品科學系 === 105 === Soy sauce can be classified by its manufacture process as: acid hydrolyzed vegetable protein (acid-HVP) whuch is made by soybeans hydrolyzed by hydrogen chloride; naturally brewed soy sauce (NBS) which is fermented for several months; blended soy sauce which is prepared as a blend of acid-HVP and NBS. NBS, which is produced according to traditional process does not contain levulinic acid (LV). LV is very stable. It is uneconomically to remove it from the acid-HVP. Therefore, LV is a proper index for determining whether the soy sauce is NBS or not. The purpose of this study is to explore the optimal method for extracting LV from soy sauce by the use of liquid-liquid extraction (LLE) and protein precipitation (PP). Meanwhile, a high performance liquid chromatography (HPLC) method is established for determining the content of LV in soy sauce and detecting whether the commercially available NBS is adulterated with acid-HVP or not. An InertSustain ® C18 column was used for separation. The UV detector wavelength was set at 268 nm. The mobile phase was 0.3% phosphoric acid in water：0.3% phosphoric acid in methanol = 95：5 (v/v). The retention time of LV was 21.17 minutes. The LV content of acid-HVP was extracted with different extraction methods. It was found that performing liquid-liquid extraction for three times by using ethyl acetate as the solvent had the yield of 1243 (± 20) mg/L, while performing protein precipitation method by using zinc acetate and potassium hexacyanoferrate (II) had the yield of 1557 (± 9) mg/L. The PP method had the higher yield and shorter extraction time. Its chromatogram showed less interference peaks than LLE method. Therefore, PP method was used for the later sample analysis. The limit of detection of LV of E brand soy sauce was 1.623 mg/L, and the recovery was 89.04 (± 0.04) to 98.28 (± 0.01)%. In all the samples we investigated, only E brand soy sauce had LV in it.