The Neutral Carbonyl Compounds in Blue-Mold Type Cheese

Departq~e~,t of Animal D~d~stries, Storrs Agric~dt~ral Experi~tet~t Statio~b Sto~'rs, Conncctic,tt The importance of methyI ketones as flavor constituents of cheese in which Penicilli~m roq~leforti is the ripening agent was indicated by Starkle (9) and Hammer and Bryant (2) and more recently has been conclusively established by Patton (6).The latter isolated pentanone-2, heptanone-2, and nonanone-2 by fractional distillation of the steam volatiles obtained from a rather large quantity of a domestic Blue cheese of good quality.Further investigation by this author indicates that heptanone-2 has a flavor and aroma typical of Blue cheese and that Blue cheese flavor could be simulated in salad oil by addition of this ketone and butyric acid (7).In light of the above reports the development of a simple and rapid test for qualitative and semi-quantitative evaluation of the ketonic flavor constituents of blue-mold cheese would seem desirable.Experience with a chromatographic procedure for the separation and identification of 2,4-dinitrophenylhydrazones of aldehydes and ketones (5) has led to the development of such a test.EXPERI~CIEiNTAL PROCEDURE Ten ~-tb.samples of blue-mold type cheese representative of the cheese sold at nearby retail outlets were obtained.No information concerning these samples other than the variety, brand, and source was available.The samples were examined for flavor, aroma, and mold growth. Distillation of c]~eese samples.Fifty grams of cheese from which all traces of rind and outer portions had been removed was mixed in a Waring blendor with 50 ml. of water until homogeneous.The cheese suspension was poured into a 250-ml.Erlenmeyer flask containing several glass beads and one drop of Dow Corning Silicone Antifoam A. Thirty ml. of 0.2% 2,4-dinitrophenylhydrazine in 2 N HC1 was added to a 125-ml.Erlenmeyer flask.The two flasks were connected to a Y-shaped distillation tube similar to that described by Van Slykc et al. (11) by means of tight-fitting rubber stoppers.The third arm of the distillation tube was fitted with a short piece of heavy-walled rubber tubing and a screw-clamp.The assembled apparatus was connected to a mechanical vacuum pump protected by a calcium sulfate moisture trap.The distilling apparatus was swirled rapidly and evacuated until a head of foam developed on the cheese mixture.The vacuum was interrupted by closing the screw-clamp, and the cheese mixture was agitated until the foam dissipated.This procedure was repeated until the cheese mixture boiled gently without appreciable foam formation when the screw-clamp was opened momentarily.The flask containing the 2,4-dinitrophenylhydrazine solution was then immersed in an ice-water bath,