Unlike in the case of biotransformation, in de novo synthesis no specific precursors are needed in the medium. Products formed by using different micro-organisms include lactones, esters, and oxygenated terpenes (Table 3; Schindler and Schmid 1982; Scharpf et al. 1986).
The fruity flavor and aroma compounds produced by de novo synthesis depend on the media constituents like glucose, amino acids, and salts (Quehl and Ruttloff 1992). In the de novo synthesis category most of the experiments carried out till now, were only on a laboratory scale, and the product yields were found to be low. However, they have helped in the study of the enzyme systems involved, and of their reaction pathways during the synthesis. Sarris and Latrasse (1985) demonstrated when Fusarium poae was grown on a solid malt medium till sporulation, it produced a lactone with a peach-like aroma; but under insufficient aeration 2-methylbutanol and 3-methylbutanol were produced. T. viride on a simple growth medium generated a strong coconut aroma of 6-pentyl-2 pyrone (Welsh et al. 1989).
Composition of the medium and age of culture generally influence the formation of flavoring compounds in de novo synthesis. For instance, an intense banana aroma was formed by Ceratocystis fimbriata when the growth medium was supplemented with several nutrients (Christen and Rainbault 1991). Similarly, Lee et al. (1999) also reported formation of g-decalactone, in an optimized immobilized culture of Sporidiobolus salmonicolor.
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