Lactobacillus acidophilus, L. bulgaricus, L. casei, L. delbrueckii, L. lactis and L. plantarum contained a pyruvate oxidase for the oxidation of pyruvate to acetyl phosphate and acetate. The presence of an acetate kinase converted the acetyl phosphate to acetate. L. casei and L. plantarum produced lactate and acetoin, in addition to acetate, under the conditions used while L. casei also produced diacetyL L. casei and L. plantarum were the only species to utilize citrate. L. helveticus and L. helveticus subsp. jugurti did not utilize pyruvate under the conditions used.

A ND M. J . C OV E NT RY . 1997. The effect of bacteriocin, piscicolin 126, on the growth of Listeria monocytogenes and cheese starter bacteria was investigated in milk and in Camembert cheese manufactured from milk challenged with 10 2 cfu ml −1 L. monocytogenes. In milk incubated at 30°C, piscicolin 126 added in the range of 512-2048 AU ml , and the viable count and acid production of these starter cultures in milk were not affected by the addition of 2048 AU ml −1 piscicolin 126. Camembert cheeses made from milk challenged with L. monocytogenes and with added piscicolin 126 showed a viable count of L. monocytogenes 3-4 log units lower than those without piscicolin 126. Inactivation of piscicolin 126 by proteolytic enzymes from cheese starter bacteria and mould together with the emergence of piscicolin 126-resistant isolates was responsible for the recovery of L. monocytogenes in the cheeses during ripening.

Mozzarella cheese was manufactured from milk containing either a low (olein) or a high (stearin) melting point fraction of milk fat or anhydrous milk fat. The fat was dispersed into skim milk by homogenization at 2.6 MPa before being manufactured into cheese. The melting point of the milk fat did not affect the size or shape of the fat globules, nor was there any effect of homogenization on the polymorphic state of the milk fat. There were no changes in milk fat globule size and shape concomitant with the amount of free oil formed. The polymorphic state of the milk fat did affect the amount of free oil formed and the apparent viscosity of the cheese. The lower melting point fraction yielded a larger amount of free oil. The higher melting point fraction yielded a higher viscosity of melted cheese at 60 degrees C. Mozzarella cheese was also manufactured from homogenized milk, nonhomogenized milk, and a 1:1 ratio of the two, without altering the milk fat composition. Increasing the proportion of homogenized milk yielded a lower free oil content and higher viscosity of the cheese.

A novel peptide bacteriocin produced by the lactic acid bacterium Carnobacterium piscicola JG126 isolated from spoiled ham was purified and characterized. This bacteriocin, designated piscicolin 126, inhibited the growth of several gram-positive bacteria, especially the food-borne pathogen Listeria monocytogenes, but had no effect on the growth of a number of yeasts and gram-negative bacteria. Bactericidal activity was not destroyed by exposure to elevated temperatures at low pH values; however, bactericidal activity was lost at high pH values, especially when high pH values were combined with an elevated temperature. Piscicolin 126 activity was not affected by catalase, lipase, or lysozyme but was destroyed by exposure to a range of proteolytic enzymes. Piscicolin 126 was purified to homogeneity and was found to be a peptide having a molecular weight of 4,416.6 ؎ 1.9. A sequence analysis revealed that this compound is a cystibiotic (class IIa) bacteriocin containing 44 amino acid residues and one intrapeptide disulfide ring. Piscicolin 126 has regions of homology with some other bacteriocins obtained from lactic acid bacteria and is most closely related to sakacin P and pediocin PA-1 (levels of identity, 75 and 55%, respectively). Addition of piscicolin 126 to a devilled ham paste test food system inhibited the growth of L. monocytogenes for at least 14 days. Piscicolin 126 was more effective than two commercially available bacteriocin preparations tested in the same system. MATERIALS AND METHODS Materials. Chemicals and other products were obtained from the following suppliers. Growth media and agar were obtained from Oxoid, Basingstoke, United Kingdom. Catalase was obtained from Boehringer, Mannheim, Germany. ␣-Chymotrypsin, ␤-chymotrypsin, lipase, lysozyme, pepsin, trypsin, protease type I, protease type XIV, protease type XXIII, and ␣-cyano-4-hydroxycinnamic acid were obtained from Sigma Chemical Co., St. Louis, Mo. Nisin (as Nisaplin) was obtained from Aplin and Barrett, Trowbridge, United Kingdom. ALTA 2431 was obtained from Quest International, Sydney, New South Wales, Australia. Devilled ham paste was obtained from Master Foods, Sydney, New South Wales, Australia. Plasmid pGEM-T was obtained from Promega Corp., Madison, Wis. CM-Sepharose Fast Flow was obtained from Pharmacia Biotech, Uppsala, Sweden. 2-Mercaptoethanol was obtained from BDH,

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