Lactobacillus reuteri strain 12002 was used for reuterin production in the two-step fermentation process. A batch culture fermentation was used to produce a maximum biomass of L. reuteri. Then cells were harvested, resuspended in a glycerol-water solution, and anaerobically incubated to produce reuterin. The lyophilized supernatants (approximately 4000 activity units (AU) of reuterin per ml) were diluted in distilled water for decontamination and preservation trials. The MIC values of reuterin for Escherichia coli O157:H7 and Listeria monocytogenes were 4 and 8 AU/ml, respectively. In meat decontamination experiments, the surface of cooked pork was inoculated with either L. monocytogenes or E. coli O157:H7 at a level of approximately log10 5 CFU/cm2, incubated for 30 min at 7 degrees C, and decontaminated by exposure to reuterin (500 AU/ml). The bactericidal effect of reuterin was analyzed 15 s and 24 h after exposure at 7 degrees C. After 15 s of exposure to reuterin, viable numbers decreased by 0.45 and 0.3 log10 CFU/cm2 for E. coli O157:H7 and L. monocytogenes, respectively. After 24 h the numbers decreased by 2.7 log10 CFU/cm2 for E. coli O157:H7 and by 0.63 log10 CFU/cm2 for L. monocytogenes. In the same experiment, the combined effect of reuterin and lactic acid was also investigated. Adding lactic acid (5%, vol/vol) to reuterin significantly enhanced (P < or = 0.05) the efficacy of reuterin. No additional effect (P < or = 0.05) was found when ethanol (40%) was added to the mixture of reuterin and lactic acid. To evaluate the preservative effect of reuterin during meat storage, reuterin was added to raw ground pork contaminated with E. coli O157:H7 or L. monocytogenes. Reuterin at a concentration of 100 AU/g resulted in a 5.0-log10 reduction of the viability of E. coli O157:H7 after 1 day of storage at 7 degrees C. Reuterin at a concentration of 250 AU/g reduced the number of the viable cells of L. monocytogenes by log10 3.0 cycles after 1 week of storage at 7 degrees C.

A broad-spectrum reuterin produced during anaerobic fermentation of glycerol by Lactobacillus reuteri strain 12002 was found to be inhibitory and bactericidal for Listeria monocytogenes and Escherichia coli O157:H7. Lyophilized reuterin was prepared by a two-step fermentation process. A batch fermentation in a 15-liter fermentor was applied to produce a maximum biomass of L. reuteri using a modified MRS broth at pH 4.3. Further, harvested cells were used to ferment glycerol (250 mM) under anaerobic conditions. The sensitivity to reuterin of 10 strains of Listeria spp., including 6 strains of L. monocytogenes, and 6 strains of E. coli, including one enterotoxigenic E. coli strains and two enterohemorrhagic E. coli strains, was estimated. Strains of L. monocytogenes were more resistant to reuterin than E. coli strains. In cottage cheese, pH 5.4, L. monocytogenes increased by 0.4 log while E. coli O157:H7 decreased by 0.5 log in 21 days at 7 degrees C; addition of reuterin (50 to 250 units per g) to the cottage cheese reduced the viability of both organisms. The inactivation rate was more pronounced (P < or = 0.05) with E. coli O157:H7 than L. monocytogenes and it was dependent on reuterin concentration. The rate of E. coli O157:H7 population reduction reached to 2, 3, and 6 log cycles by day 7 for reuterin concentrations of 50, 100, and 150 units per g of creamed cottage cheese, respectively. While, 100, 150, and 250 units of reuterin per g caused reductions in L. monocytogenes counts by 2, 5, and greater than 5 log cycles, respectively. In UHT skim milk with 150 units of reuterin per ml, stored at 7 degrees C, the decline in the numbers of L. monocytogenes cells was higher than that in cottage cheese. Milk fat in the range of 0.5 to 3% did not affect the reuterin activity (P< or = 0.05). Addition of 3% salt enhanced the lethal effect of reuterin and diminished the initial population of L. monocytogenes by 4.5 log cycles in three days at 7 degrees C.

No abstract

No abstract

No abstract

No abstract

No abstract

The level of monomer styrene migrated from polystyrene containers (PS) was measured in different dairy products at various fat contents, storage periods and temperatures. The dairy products were packed in PS containers and divided into groups according to storage period and temperature. The samples were included whole milk (3.6% fat) kept at 100 °C for two hours (group 1), yogurt (3% fat), sour cream (6% fat), cream (30% fat) and drinking yogurt (3% fat) stored in polystyrene packages at 4°C for 14 days (group 2), mozzarella cheese (14.0% fat), cheddar cheese (34.4% fat) and butter (81.7% fat) stored at 4°C for 60 days (group 3) and ice-cream (16% fat) stored at -10°C for 60 days (group 4). Extending storage time and increasing temperature were found to be significantly elevated (p ≤ 0.05) the migration rate of styrene. Styrene migration was found to be strongly (p ≤ 0.05) dependent upon the fat content. Maximum migration limit has occurred with the highest fat content; butter (81.7%) at a concentration of 0.102 mg/kg.The calculated consumed quantity of styrene from each dairy food items in adults ranged from 0.018 to 0.170 μg/kg wt/day which corresponding to 1.1 -10.2 μg/ day/person while, total daily consumption of all the tested products is amounted to 50.6 μg/day. The study showed that the styrene intake from each tested dairy product item is less than the international allowable level. The results postulate that consumption of foods rich in fat content especially, at high storage temperatures in PS packages could represent health hazard while they are highly stimulating migration of monostyrene.