Lactobacillics plantarum was for some time considered to be the principal species responsible for the acid fermentation of cucumbers. Etchells and Joiies (7) isolated and studied 49 cultures from commercial fermentations brined a t 20, 30 and 40" salometer (5.3, 7.8 and 10.6% NaC1). All 49 cultures were found to be L. plantarum. Of 20 cultures isolated from commercial fermentations by Costillow and Fabian ( 4 ) ) 16 were found to be L. plantarzcna.Recent studies (12, j 3 ) of a large number of cultures isolated from fermentations brined in glass jars under laboratory conditions have indicated that there may be up to 5 species of lactic acid bacteria active in cucumber brines. The species found were Leuconostoc meselzteroides, Xtreptococczcs f aecalis, Pediococcus cerevisiae, Lactobacillus brevis and L. plawtaritrn in the order of increasing prevalence. These workers reported that the flora may be influenced by both salt-concentration and temperature of fermentation. Rorg et al. ( 1 ) identified 92 cultures of acid-forming bacteria from commercial cucumber fermentation; " 51 were similar to Pediococcus cerevisiae, 28 resembled L. plantarum and 13 belonged to another species of Lactobacillus."This study was initiated to determine the types of acid-forming bacteria active in cucumber fermentations in Michigan. Also, we wished to investigate what effects, if any, that sorbic acid might have on the prevailing types present. METHODS Fermentations Studied and Methods of SamplingEight hundred and f orty-eight cultures of acid-forming bacteria mere isolated from 84 cucumber fermentations during the brining seasons of 1953 and 1954. The source of the cultures isolated as to salting stations, fermentations, brining treatments and samples are given in Table 1. The 12 fermentations studied in 1953 were all brined in 45-gal. barrels at one salting station. I n 1954, 53 lots were brined in barrels located at 5 salting stations and the other 19 fermentations sampled were commercial lots located at the same 5 stations.I n 1954, one-third of the barrels of each brining treatment a t each station were treated with 0.1% sorbic acid, one-third with 0.05% sorbic acid and the other one-third

The addition to steaks of cell suspensions of a number of aerobic bacteria and of Saccharomyces cerevisiae greatly increased the rate of discoloration. Low inocula resulted in the more rapid appearance of the brown color of metmyoglobin, whereas high cell populations quickly produced the purple color of myoglobin. Sonically treated suspensions of Pseudomonas geniculata produced similar changes in surface color but less rapidly. No such effect was observed with Lactobacillus plantarum . The visible changes in color were found to be associated with the oxygen demand of the surface tissue including, of course, the demand of any contaminating microorganisms. Inhibitors of respiratory activity inhibited the rate of discoloration under normal atmospheric conditions. However, when the oxygen level in the atmosphere was reduced, the inhibitors had no significant effect. In an oxygen-free atmosphere, the steak surfaces were the purple color of myoglobin; at 10 mm oxygen pressure, the pigment was oxidized to metmyoglobin and the surface was brown in color. No bacterial activity was necessary for pigment oxidation under low oxygen pressures. Addition of dilute solutions of glucose oxidase resulted in rapid oxidation of the meat pigment to metmyoglobin both in extracts and on steak surfaces. More concentrated solutions resulted in further oxidation as evidenced by the appearance of a green color. Horseradish extract with a high peroxidase activity added with H 2 O 2 resulted in rapid oxidation of the pigment but neither were very effective alone, although H 2 O 2 did result in a browning reaction in aged steaks. It is concluded that the primary role of the bacteria in meat discoloration is in the reduction of the oxygen tension in the surface tissue. The implications of the data are discussed and a possible mechanism of myoglobin oxidation is proposed.