Mycotoxin Research Vol. 23, No. 3 (2007), 122-126 Comparison of growth characteristics and roquefortin C production of Penicillium roqueforti from blue-veined cheese G. Pose, V. Ludemann, A. Gbmez, J. Segura Universidad Nacionalde Quilmes, Departamento de Ciencia y Tecnologia, Avda. Calchaqui 5800, 1888 FlorencioVarela, Provinciade BuenosAires, Argentina Abstract The properties of 21 isolates of Penicillium roqueforti from just as many commercial blue-veined cheeses, purchased from the Argentinean market (domestic and imported products) were comparatively examined. Isolates were investigated for their ability to grow at different temperatures, pH values and concentration of NaCI, as well as for their proteolytic and lipolytic activities, respectively. The potential of these strains to produce roquefortin C in vitro, and the actual levels of roquefortin C in 10 of these cheeses were analysed by TLC. All strains showed similar growth properties in aspects of salt concentration and pH-value of the medium, and all grew well at 10 ~ Only four strains showed proteolytic activity on casein agar, while all strains were lipolytic on trybutirin agar. After incubation at 25 ~ for 16 days, all strains produced roquefortin C in Yeast Extract Sucrose (25.6-426.7 gg/g) and in reconstituted (10%) sterile skim milk (26.9-488 gg/g). Roquefortin C at >0.1 gg/g was also found in 9 out of 10 analysed samples of blue-veined cheeses (8 from Argentine, 1 from Spain), with a maximum value 3.6 gg/g. During the ripening process of blue- veined cheese, production of roquefortin seems to be unavoidable. Care should be taken to select strains with low toxin production characteristics, to minimize potential health risks. Roquefortin C production by P. roqueforti in vitro was not correlated with roquefortin C levels found in cheese. Keywords: blue-veined cheese, Penicillium roqueforti, starter cultures, roquefortin Introduction Penicillium spp. play an important role for the production of mould-fermented food (1). Strains ofPenicillium cammemberti are used in white surface mould cheeses such as Camembert, Brie and Coulommiers, while strains of Penicillium roqueforti are used for blue-veioed cheeses such as Danablu, Gorgon- zola, Roquefort, Cabrales, Edelpilzk~ise and Bleu de Bresse. These fungal starters are responsible for the appearance, consistency and flavours of these types of cheese. The shelf life of these products may be prolonged due to inhibition of unwanted microorganisms by Penicillium spp. P. roqueforti is well adapted to the specific food environment, and due to its proteolytic and lipolytic activities, it contributes both to Correspondence: Vanesa Ludemann, Universidad Nacional de Quilmes, Departamento de Ciencia y Tecnologia, Avda. Calchaqui 5800, 1888 Florencio Varela, Provincia de Buenos Aires, Argentina (vludemann@unq.edu.ar) Financial support: Research grants from the National University of Quilmes, Argentina Received 29 Nov 2006; accepted 19 July 2007 consistence and flavour of blue-veined cheese (2). However, excessive proteolytic activity may lead to undesirable liquefaction of the curd. The genetic constitution of each strain provides different technological properties when used as starter or ripening culture. A fungal strain used in food production should meet certain requirements, the most important one is that it should not have adverse health effects, in particular with respect to mycotoxin production. However, it has been demonstrated that certain strains of P. roqueforti are able to produce various toxins, namely isofumiga- clavin A (roquefortin A), isofumigaclavin B (roquefortin B), roquefortin C, mycophenolic acid, penicillic acid, and patulin (3, 1, 4, 5). Roquefortin C is an indole compound which was associated with paralyzing neurotoxic effects (6). An intraperitoneal (IP) LDs0 of 15- 20 mg/kg has been determined for this toxin in rats (7). Roquefortin C has also been reported to cause convulsion crises when administered to mice in intraperitoneal doses of 50-100 mg/kg (8, 9). Most P. roqueforti strains from blue-veined cheese seem to produce various amounts of roquefortin C (10). 122