Soft cheese ripening is mainly controlled by proteolytic activities of Geotrichum candidum and Penicillium camembertii. To investigate the proteolytic activities involved in the synergistic effect, pure and mixed cultures of both micro-organisms were performed on Camembert juice. Proteolysis monitored throughout culture using SDS-PAGE and RP-HPLC profiles, as well as free amino acids (FAAs) concentration time-courses showed that G. candidum degrades immediately large and medium peptides in FAAs, which were partly assimilated, while P camembertii assimilated large peptides but medium and small peptides were less consumed. The similar chromatograms of the mixed and G. candidum cultures tend to demonstrate that the proteolytic activities of G. candidum dominated in the mixed culture up to 112 h. Continuous proteolysis and assimilation of peptides occurred throughout the second part of P. camembertii culture, leading to the production of FAAs. These activities allow G. candidum to have medium and small peptides to hydrolyse during the mixed culture. Because of the rapid degradation of these peptides in FAAs, no more peptides were available for P camembertii growth, which should therefore assimilate FAAs, leading to a rapid decrease of their concentration. The synergistic effect between G. candidum and P. camembertii was therefore predominant during the second part of culture. (c) 2005 Elsevier Inc. All rights reserved.