Geotrichum candidum and Penicillium camembertii were cultivated in pure and mixed cultures on Camembert juice. This juice extracted from curd at the demoulding contains the whole substrates available for growth of surface flora in situ. A synergistic effect of G. candidum on P camembertii growth was clearly shown in mixed culture; the enzymatic activities of G. candidum (low molecular weight peptides hydrolysis) allowed an easier assimilation of peptides and amino acids as carbon sources by P. camembertii, no other carbon sources were needed, or used only at the end of culture for cell maintenance, as was the case for citrate. A lower number of amino acids were convenient carbon sources for P. camembertii compared to G. candidum, resulting in its assimilation of lactose, lactate and citrate during pure culture, while G. candidum assimilated lactate and citrate only at the end of culture for the energy supply for cell maintenance. Peptides and amino acids metabolic behaviour was shown to be the main factor accounting for medium alkalinization, since their assimilation as carbon sources (in addition to nitrogen sources) resulted in ammonium production, which was found to be closely related to proton transfer. (c) 2005 Elsevier Inc. All rights reserved.