ABSTRACT
Ten agar media were evaluated for their suitability to support spore germination and colony development by six strains of Alicyclobacillus acidoterrestris, three strains of Alicyclobacillus acidocaldarius, and one strain of Alicyclobacillus cycloheptanicus. The influence of plating method (pour versus spread), incubation temperature (43 degrees C and 50 degrees C), and incubation time (up to 10 days) on colony development were determined. K agar, Alicyclobacillus medium (ALI agar), and Bacillus acidoterrestris thermophilic (BAT) agar recovered the highest numbers of spores. Orange serum agar and Hiraishi glucose yeast extract agar were the least suitable. Overall, surface plating was superior to pour plating and, with the exception of one strain of A. acidocaldarius which grew better at 50 degrees C, incubation of K agar, ALI agar, and BAT agar plates at 43 degrees C or 50 degrees C resulted in recovery of equivalent numbers of spores. Essentially all viable spores were detected on media incubated for 3 days at 43 degrees C. The ability of one strain of each Alicyclobacillus species to grow in ten non-carbonated commercially manufactured beverages at 30 degrees C and 43 degrees C was markedly affected by the composition of the beverages. Results show that surface plating samples on BAT agar, followed by incubating plates at 43 degrees C for 3 days provide the most suitable conditions to enumerate ten strains of three species of Alicyclobacillus most commonly responsible for spoilage of beverages.
Subject(s)
Agar/chemistry , Beverages/microbiology , Colony Count, Microbial/methods , Food Contamination/analysis , Food Preservation/methods , Gram-Positive Endospore-Forming Rods/growth & development , Culture Media/chemistry , Food Microbiology , Gram-Positive Endospore-Forming Rods/isolation & purification , Temperature , Time FactorsABSTRACT
Gaseous chlorine dioxide (ClO2) was evaluated for effectiveness in killing Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes on fresh-cut lettuce, cabbage, and carrot and Salmonella, yeasts, and molds on apples, peaches. tomatoes, and onions. Inoculum (100 microl, ca. 6.8 log CFU) containing five serotypes of Salmonella enterica, five strains of E. coli O157:H7, or five strains of L. monocytogenes was deposited on the skin and cut surfaces of fresh-cut vegetables, dried for 30 min at 22 degrees C, held for 20 h at 4 degrees C, and then incubated for 30 min at 22 degrees C before treatment. The skin surfaces of apples, peaches, tomatoes, and onions were inoculated with 100 microl of a cell suspension (ca. 8.0 log CFU) containing five serotypes of Salmonella, and inoculated produce was allowed to dry for 20 to 22 h at 22 degrees C before treatment. Treatment with ClO2 at 4.1 mg/liter significantly (alpha = 0.05) reduced the population of foodborne pathogens on all produce. Reductions resulting from this treatment were 3.13 to 4.42 log CFU/g for fresh-cut cabbage, 5.15 to 5.88 log CFU/g for fresh-cut carrots, 1.53 to 1.58 log CFU/g for fresh-cut lettuce, 4.21 log CFU per apple, 4.33 log CFU per tomato, 1.94 log CFU per onion, and 3.23 log CFU per peach. The highest reductions in yeast and mold populations resulting from the same treatment were 1.68 log CFU per apple and 2.65 log CFU per peach. Populations of yeasts and molds on tomatoes and onions were not significantly reduced by treatment with 4.1 mg/liter ClO2. Substantial reductions in populations of pathogens on apples, tomatoes, and onions but not peaches or fresh-cut cabbage, carrot, and lettuce were achieved by treatment with gaseous ClO2 without markedly adverse effects on sensory qualities.
