Action of Microorganisms on the Peroxides and Carbonyls of Fresh Lard

SUMMARY— The effect of 28 microorganisms on the accumulation of hydroperoxides and monocarbonyls in fresh fat has been determined. Pseudomonas ovalis, Micrococcus freudenreichii and two strains of Streptomyces increased the concentration of peroxides; M. freudenreichii also produced an increase in 2‐enals, 2, 4‐dienals, and alkanals. Pseudomonas fragi, Geotrichum candidum , and Candida lipolytica produced an increase in alkanals and methyl ketones. All other cultures either removed the small amount of peroxides and monocarbonyls in fresh fat and prevented any build‐up or had no effect. The ability of microorganisms to oxidatively attack fats was not related to their oxidase reactions or their ability to produce lipase. Differences in oxidative activity on fresh and rancid lard are discussed.