2018年11月5日
Epimerization and decomposition of kojibiose and sophorose by heat treatment under neutral pH conditions
Journal of Applied Glycoscience
- 巻
- 66
- 号
- 1
- 開始ページ
- 1
- 終了ページ
- 9
- 記述言語
- 英語
- 掲載種別
- 研究論文(学術雑誌)
- DOI
- 10.5458/jag.jag.JAG-2018_0002
We evaluated the stabilities of kojibiose and sophorose when heated under neutral pH conditions. Kojibiose and sophorose epimerized at the C-2 position of glucose on the reducing end, resulting in the production of 2-O-α-D-glucopyranosyl-D-mannose and 2-O-β-D-glucopyranosyl-D-mannose, respectively. Under weak alkaline conditions, kojibiose was decomposed due to heating into its mono-dehydrated derivatives, including 3-deoxy-2,3-unsaturated compounds and bicyclic 3,6-anhydro compounds. Following these experiments, we propose a kinetic model for the epimerization and decomposition of kojibiose and sophorose by heat treatment under neutral pH and alkaline conditions. The proposed model shows a good fit with the experimental data collected in this study. The rate constants of a reversible epimerization of kojibiose at pH 7.5 and 90 °C were (1.6 ± 0.1) × 10−5 s−1 and (3.2 ± 0.2) × 10−5 s−1 for the forward and reverse reactions, respectively, and were almost identical to those [(1.5 ± 0.1) × 10−5 s−1 and (3.5 ± 0.4) × 10−5 s−1] of sophorose. The rate constant of the decomposition reaction for kojibiose was (4.7 ± 1.1) × 10−7 s−1 whereas that for sophorose [(3.7 ± 0.2) × 10−6 s−1] was about ten times higher. The epimerization reaction was not significantly affected by the variation in the buffer except for a borate buffer, and depended instead upon the pH value (concentration of hydroxide ions), indicating that epimerization occurred as a function of the hydroxide ion. These instabilities are an extension of the neutral pH conditions for keto-enol tautomerization that are often observed under strong alkaline conditions.
- リンク情報
- ID情報
-
- DOI : 10.5458/jag.jag.JAG-2018_0002
- ORCIDのPut Code : 50229922