Microbial Transformation of Citral by Aspergillus niger-PTCC 5011 and Study of the Pathways Involved

Esmaeili A., Rohany S., Safaiyan S., Amir Z.S. (2011): Microbial transformation of citral by Aspergillus niger-PTCC 5011 and study of the pathways involved. Czech J. Food Sci., 29: 610–615. Citronellol and hydroxy citronellal are fragrance ingredients used in decorative cosmetics and fine fragrances. They have many applications in flavourings, extracts, foods, and drugs manufacturing. Their use worldwide is in the range exceeding 1000 metric tons per annum. Previous studies investigated the biotransformation of citral by the free cell method and immobilised cell method with Saccharomyces cerevisae. In this research, the microbial transformation of citral by the sporulated surface cultures method with Aspergillus niger-PTCC 5011 was studied. In experiments, A. niger was inoculated on solid media in conical flasks. The transformation took place for the periods of time of 6 days and 15 days. The results were analysed by the theoretical study, Fourier transform infrared spectroscopy, gas chromatography, and gas chromatography-mass spectroscopy. The major compounds produced in 6 days were acetone (26.2%) and hydroxy citronellal (37.0%), while the major compounds after the 15-day period were acetone (15.0%) and citronellol (36.0%). As citronellol has numerous commercial applications, the 15-day biotransformation period was found to be preferable.