The occurrence of styrene in food may be an important aroma defect (celluloid odour), even at very low concentrations (Miltz et al. 1980) causing consumer rejection and is therefore a problem for the food industry. We examined the biosynthetic pathway leading to styrene formation by Penicillium camemberti using labelled compounds. As styrene is strongly hydrophobic and volatile, we first had to develop a continuous extraction process. Using resins XAD2 it was reasonable to suspect phenylalanine (Phe) as the precursor. The addition of Phe marked with 13C on the ring provokes the accumulation of labelled styrene. The enzyme activities involved were also tentatively measured. Styrene appears to be synthesized from phenylalanine by phenylalanine ammonia-lyase activity followed by a decarboxylation catalysed by a cinnamic acid decarboxylase.

Eight strains of Geotrichum candidum isolated from cheese were compared for aroma production. Twenty-four components, including alcohols, methyl ketones, fatty acids and esters, were identified by gas–liquid chromatography and gas chromatography–mass spectrometry of the volatile compounds produced by G. candidum cultures. Strains could be differentiated by their ability to produce dimethyldisulphide, phenol, phenylethanol and methyl ketones.