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INTRODUCTIONStrains belonging to the species Lactobacillus casei can be isolated from very different environments, and some of them are now used as probiotics in commercial products. This species is currently involved in a serious controversy and is the subject of numerous taxonomic studies, because many strains previously characterized as L. casei show genotypic, phenotypic and phylogenetic differences when compared to the standing type strain of the species, L. casei subsp. casei ATCC 393 T (Mills & Lessel, 1973;Dellaglio et al., 1975Dellaglio et al., , 1991Dicks et al., 1996;Collins et al., 1989;Ferrero et al., 1996;Mori et al., 1997;Zhong et al., 1998;Chen et al., 2000;Felis et al., 2001).L. casei has been used in a number of pioneering studies on the physiology and genetics of the genus Lactobacillus. The type strain L. casei subsp. casei (L. casei) ATCC 393 T especially has been used in studies on the fermentation of glucose, lactose, citrate and pyruvate (Hegazi & Abo-Elanga, 1987;Palles et al., 1998), comparative studies on and molecular characterization of the enzyme L-lactate dehydrogenase (Gordon & Doelle, 1976;Hensel et al., 1977;Kim et al., 1991), characterization of an intracellular bglucosidase (Coullon et al., 1998), proteolytic activity (Hegazi & Abo-Elanga, 1987) and studies on the composition of the cell wall, antibiotic resistance and adherence factors (Billot-Klein et al., 1997;Pelletier et al., 1997). Also, the isolation and characterization of extrachromosomal genetic elements in the genus Lactobacillus was reported for the first time in strains of L. casei, such as ATCC 393 T , 61BG, 64H, ATCC 334, ATCC 4646 and ATCC 15820 T (Chassy et al., 1976;Chassy & Giuffrida, 1980;Lee-Wickner & Chassy, 1984, 1985. Flickinger et al. (1986) obtained a number of plasmid-cured derivatives from L. casei strains; among these, an ATCC 393 T variant cured of plasmid pLZ15 [ATCC 393 (pLZ15 2 )], which encodes a lactose permease and b-galactosidase, was found (Chassy & Alpert, 1989). Besides the added value of being a derivative of the standing type strain, this plasmid-cured strain showed a great potential for studies on lactose metabolism, as it still carried a second lactose-specific transport and hydrolysis system, the lactose phosphoenolpyruvate : phosphotransferase system (PTS) and a 6-phospho-b-galactosidase. It was soon shown by the same research laboratory that this strain was amenable to genetic transformation by electroporation (Chassy & Flickinger, 1987). From this point in time, L. casei ATCC 393 (pLZ15 2 ) became widely used in genetic and physiological studies on L. casei and it has been used for the characterization of lactose, glucose, xylose and sorbose transport and metabolism (Hemme et al., 1994; Veyrat et al.,Abbreviations: ARDRA, amplified rDNA restriction analysis; ITS, intergenic spacer sequence; L. casei, L. casei subsp. casei; RAPD analysis, random amplified polymorphic DNA.

The objective of this study was to evaluate the efficacy of propolis extract (PE) to reduce lipid oxidation and microbial growth on beef patties during refrigerated storage. Beef patties were manufactured by incorporating PE in 4 different treatments: (1) Control (no PE addition); (2) commercial propolis 1 (2% w/w; CP1); (3) commercial propolis 2 (2% w/w; CP2); and (4) noncommercial propolis (2% w/w; NCP). Raw patties were wrapped with polyvinyl chloride and stored at 2 °C for 8 d. Total phenolic content (TPC), free-radical scavenging activity (FRS), and polyphenolic content of the PE were evaluated using high-performance liquid chromatography (HPLC). Lipid oxidation (thiobarbituric acid-reactive substances (TBARS), conjugated dienes (CnDs), metmyoglobin (MetMb%), pH variation, and color (L*, a*, b*, C*, and h*), and microbial growth (mesophilic and psychrotrophic bacteria) of patty samples were measured. NCP treatment demonstrated the highest FRS (64.8% at 100 μg/mL), which correlated with TPC and the presence of polyphenolic compounds. Lipid oxidation (78.54%, TBARS; 45.53%, CnD; 58.57%, MetMb) and microbial mesophilic and psychrotrophic growth (19.75 and 27.03%, respectively) values were reduced by NCP treatment in refrigerated samples after 8 d. These results indicate that PE has great potential as a natural antioxidant and antimicrobial additive to extend the shelf life of beef patties.

Lactobacillus spp. from Mexican Cocido cheese were shown to produce bacteriocin-like substances (BLS) active against Staphylococcus aureus,Listeria innocua,Escherichia coli, andSalmonella typhimurium by using the disk diffusion method. Crude extracts of Lactobacillus fermentum showed strong inhibitory activity against Staph. aureus, L. innocua, E. coli, and Salmonella cholerae. Complete inactivation of antimicrobial activity was observed after treatment of crude extracts with proteinase K, pronase, papain, trypsin, and lysozyme, confirming their proteinaceous nature. However, antimicrobial activity was partly lost for some of the crude extracts when treated with α-amylase, indicating that carbohydrate moieties were involved. The antimicrobial activity of the crude extracts was stable at 65°C for 30min over a wide pH range (2-8), and addition of potassium chloride, sodium citrate, ethanol, and butanol did not affect antibacterial activity. However, antimicrobial activity was lost after heating at 121°C for 15min, addition of methanol or Tween 80. Fourteen out of 18 Lactobacillus spp. showed antimicrobial activity against different test microorganisms, and 12 presented bacteriocin-like substances. Generation time and growth rate parameters indicated that the antimicrobial activity of crude extracts from 3 different strains was effective against the 4 indicator microorganisms. One of the crude extracts showed inhibition not only against gram-positive but also against gram-negative bacteria. Bacteriocin-like substances produced by this specific Lactobacillus strain showed potential for application as a food biopreservative.