Changes in the carbonyl content and methyl ketone composition of blue cheese were studied at progressive stages of ripening. The 2,4-dinitrophenylhydrazones (DNP) obtained from «-hexane extracts of the cheese were separated into various classes of carbonyl compounds on activated celite-Sea Sorb 43 columns. The methyl ketone fraction was regenerated with concentrated sulfuric acid, and the relative concentrations of the individual methyl ketones were determined by gas chromatography.

Spore suspensions of P. roqueforti metabolized sodium palmitate into carbon dioxide and a variety of carbonyl compounds, including a homologous series of methyl ketones. Both D-glucose and L-proline suppressed the catabolism of palmitate to COS but stimulated the rate of formation of carbonyl compounds, including methyl ketones. Spore concentrations of 6.3 X lo8 spores/ml produced the optimum yield of (32.4%) carbonyl compounds from the incubation of 5 m M of palmitate in the presence of 20 m M of D-glucose under optimum conditions of pH and tempera-ture; i,e., pH 6.5 (0.1 M phosphate buffer) and 30". Analyses of carbonyl compounds formed from [U-14C]palmitate revealed that a homologous series of labeled methyl ketones, C3 to C15 inclusive, was produced. Pentadecanone contained the highest radioactivity, followed by tridecanone and undecanone, with the lower methyl ketones containing varying amounts of radioactivity. Appreciable amounts of carbonyl compounds other than methyl ketones (Le., labeled, saturated, and unsaturated aldehydes) were also produced from [14C]palmitic acid.

Cultures of Penicillium roqueforti spores oxidized [U-14C]lauric acid into carbonyl compounds including a series of n-methyl ketones. Spore concentrations of 6.3 x 108 spores/ml in the presence of 2 mM of D-glucose under optimum conditions of pH and temperature, i.e., pH 6.5 and 30°, oxidized 16-20% of [U-14C]lauric acid (5 mM) to carbonyl compounds. D-Glucose stimu-lated the formation of carbonyls and suppressed the complete oxidation of the lauric acid. A homologous series of methyl ketones C3 to Cll inclusive was formed. Some unidentified carbonyl compounds other than methyl ketones were also produced. Metabolic CO2 increased the conversion of [U-14C]lauric acid into labeled methyl ketones by the Penicillium spores.Many fungi including Penicillium roqueforti metabolize fatty acids of short and medium chain lengths into methyl ketones with one less carbon atom (Gehrig and Knight, 1963; Hammer and Bryant, 1937; Lawrence, 1966;Lawrence and Hawke, 1968;Starkle, 1924). Gehrig and Knight (1963) attributed this ability to the spores of P. roqueforti; however, Rolinson (1954), Vinze andGhosh (1962), andLawrence andHawke (1968) demonstrated the formation of methyl ketones from fatty acids by the mycelium of P. roqueforti.Fatty acids may be toxic to P. roqueforti, and the degree of toxicity is dependent upon chain length, concentration of acid, and pH of the incubation medium (Franke et ai, 1962; Lawrence and Hawke, 1968). It has been suggested that the oxidation of fatty acids into methyl ketones may be a detoxifying mechanism employed by the mold. This tendency of P. roqueforti to form methyl ketones from fatty acids is exploited in manufacture of specific cheeses, i.e., Roquefort, Blue, and Stilton (Anderson and Day, 1966; Niki et ai, 1966;Patton, 1950).Lawrence and Hawke (1968) reported that P. roqueforti oxidizes lauric and palmitic acid to only 2-undecanone and 2-pentadecanone, respectively. Dartey and Kinsella (1973) found that the spores of P. roqueforti generated the homologous series of radioactively labeled methyl ketones, C3 to C15 inclusive, from [U-14C]palmitate.To determine the relationships of various fatty acids to the formation of specific methyl ketones, the metabolism of individual fatty acids by spore suspensions of P. roque-