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2. Food Chemical Codex II (1972) Washington DC: National Academy Press.
3. Houben-Weyl Methoden der organischen chemie (1952), Band VIII-Sauerstoffverbindungen III, pp. 98–100.
4. Reaction of apple pectin with ammonia;Kratchanov;International Journal of Food Science and Technology,1989
5. Kratchanov, Ch. r., Kratchanova, M., Huyghebaert, A., Pavlova, E., & Ratcheva, L (1998) On the chemical degradation of pectic substances during processing and storage of fruit and vegetables. Lecture in Anniversary scientific conference Progress in Food Science, Engineering and Technology (45 years Higher Institute of Food and Flavour Industries), 14-16.05.1998, Plovdiv, Bulgaria. Proceedings—Abstracts of Scientific works of HIFFI, Plovdiv, pp. 4–5 (in Bulgarian).