The Bacterial Oxidation of Corn Oil

Abstract

The ability of 32 widely distributed spp. of bacteria to oxidize a practically pure triglyceride without hydrolysis was detd. by the Warburg apparatus. Studies were also made of their oxidizing as compared to their reducing ability as measured by the Thunberg technic. An attempt was made to correlate the oxidation of corn oil with the following chemical tests: acid number, peroxide number, iodine absorption number, saponification number, refractive index, aldehyde number, Kreis test and the fatty acids in the residue. The results showed that the Warburg apparatus was a dependable, time-saving instrument and yielded information not made available by cultural or chemical tests. A greater number of bacteria could oxidize corn oil than could dehydrogenate it: of the 32 organisms studied, 25 showed an increased rate of utilization of oxygen while only 6 evinced the ability to dehydrogenate it. Previous to this work only one species, Aerobacter aerogenes, had been shown to be fat-oxidative and non-lipolytic. The data showed that not only A. aerogenes but also Alkaligenes faecalis, Sarcina lutes, Micrococcus aurantiacus, M. flavescens, M. cinna-bareus, Flavobacterium arborescens, Phytomonas tume-jaciens and Pseudomonas mephitica are fat-oxidative and non-lipolytic. On prolonged incubation, the oxidative changes of lipids brought about in flasks containing bacteria are indistinguishable from strictly non-biological changes, as shown by detns. of the various fat constants. A conc. of 0.85% NaCl brought about a noticeable inhibition in the rate of respiration for 3 spp. of Pseudomonas; a conc. of 2.5% inhibited the respiration of all spp. except Pseudomonas fluorescens in the presence of oil to a point below that of endogenous respiration in saline-buffer suspension. The respiratory rate is influenced by a decreased pH, but a comparatively low pH, biologically speaking, is required to bring about a noticeable inhibition. Two antioxidants, hydroquinone and Avenex, did not prevent bacterial respiration in the presence of oil in the concs. used. The latter compound was utilized by 4 of the 5 spp. studied.