Biotransformation by plant cultures and microorganisms
Biotransformation by plant cultures and microorganisms is a good method based on biotechnology for the preparation of volatile compounds that have shown superior to compounds produced in cell cultures.
In biotransformation, an intermediate compound precursor is incorporated into the culture medium, which is bio-transformed or bio-converted to volatile compounds by enzymatic activities. The efficiency of this method is much higher than those which a precursor is not used in the culture medium. But it should be noted that cheap precursors should be searched and used to produce valuable products [116]. For example, 10 mg/l vanillin was obtained on ferulic acid substrate by cultured Capsicum annuum [139]. Citronellol can be obtained by biotransformation of citronellal by the Peganum harmala [140]. Also The biotransformation of ricinoleic acid by Candida sorbophila can produce up to 40 g/l ץ-decalactone [141].
This method, in addition to positive aspects, also has negative aspects. Such volatiles do not dissolve easily in aqueous medium. There are some solutions to this problem agents facilitating dissolution can be used (above a threshold concentration is inhibited cell growth). Even high concentrations of the product itself can be toxic and inhibitory to cells growth. As a result, continuous addition of substrate at non-harmful concentrations and removal of the product were developed. Among these methods, the pervaporation method [142] and inserting a volatile binder compound is most commonly used. The issue of trapping and isolating volatile compounds produced in the culture medium, has been discussed by Georgiev et al [143] and Ramachandra and Ravishankar [8]. For example, β-cyclodextrins are water-soluble molecules with a hydrophobic interior and hydrophilic exterior that with proper modification, can trap the product in their cavities.