Pseudomonas perolens ATCC 10757 in sterile fish muscle (Sebastes melanops) were identified by combined gas-liquid chromatography and mass spectrometry. Compounds positively identified included methyl mercaptan, dimethyl disulfide, dimethyl trisulfide, 3-methyl-1-butanol, butanone, and 2-methoxy-3-isopropylpyrazine. Compounds tentatively identified included 1-penten-3-ol and 2-methoxy-3-sec-butylpyrazine. The substituted pyrazine derivative 2-methoxy-3-isopropylpyrazine was primarily responsible for the musty, potato-like odor produced by P. perolens. Castell and Greenough (2, 3) and Castell et al. (4) described a musty, potato-like odor that commonly developed in chilled fish muscle during the early stages of spoilage. Although this distinctive odor was observed under commercial conditions on chilled fillets of cod, haddock, and flounder, it was not detected on fresh or spoiling round and eviscerated fish. The causative bacterial species was identified as Pseudomonas perolens, a psychrophilic organism which utilizes a variety of substrates for growth and odor production (4). This investigation was initiated to identify the volatile compounds produced in sterile fish muscle (Sebastes melanops) by P. perolens. Particular emphasis was placed on the identification of the compound or compounds responsible for the characteristic musty, potato-like odor. MATERIALS AND METHODS Sterile muscle tissue. Black rockfish (Sebastes melanops), line-caught off the coast of Newport, Ore., were immediately killed by a blow on the head, individually wrapped in clean towels to prevent puncture damage to the skin, and packed in ice. Sterile fish flesh was obtained essentially as described by Lobben and Lee (11). The whole fish was washed in water, thoroughly swabbed with ethyl alcohol (70%), and dried under the flow of sterile air in a sterility test cabinet (BioQuest). Portions of skin were aseptically removed, and sections of exposed flesh were excised in the sterile atmosphere of the 'Technical Paper No. 3457, Oregon Agricultural Experi

Volatile compounds produced by Pseudomonas putrefaciens, P. fluorescens, and an Achromobacter species in sterile fish muscle (Sebastes melanops) were identified by combined gas-liquid chromatography and mass spectrometry. Compounds produced by P. putrefaciens included methyl mercaptan, dimethyl disulfide, dimethyl trisulfide, 3-methyl-i-butanol, and trimethylamine. With the exception of dimethyl trisulfide, the same compounds were produced by an Achromobacter species. Methyl mercaptan and dimethyl disulfide were the major sulfur-containing compounds produced by P. fluorescens. 'Technical Paper no. 3505, Oregon Agricultural Experi