Bacteriophages are potentially useful in controlling foodborne pathogens on minimally processed products since phage application is a non-destructive treatment. The purpose of this study was to evaluate the efficacy of a newly isolated environmental bacteriophage against enterohemorrhagic Escherichia coli on fresh produce, and optimize the treatment with consideration for potential application. Seven anti E. coli O157:H7 EDL933 bacteriophages were isolated from various sources; the most promising was isolated from municipal wastewater. This isolate (designated as E. coli phage OSY-SP) was propagated with the host, in a growth medium, to a titer of 10(8) PFU/ml. Before inoculation into fresh produce, E. coli phage OSY-SP was incubated with the host bacterium, spent medium was filter-sterilized, and the resulting crude lysate was used as a source of phage inocula for preliminary experiments. For optimized testing, phage in the crude lysate was purified by ultra-centrifugation and resuspension in phosphate-buffered saline. Efficacy of phage treatments was determined as a function of fresh produce type (cut green pepper or spinach leaves), treatment time (2 or 5min rinsing), and temperature of holding treated produce (4°C, 25°, or a combination of both temperatures). Cut green pepper was treated with UV light, to eliminate background microbiota, then spot-inoculated with E. coli O157:H7 EDL933 on cut edges, and the inoculum was allowed to dry. Because of its susceptibility to damage, baby spinach leaves were not subjected to a decontamination treatment. These leaves were inoculated with the green fluorescent protein-labeled E. coli O157:H7 B6-914 to facilitate inoculum enumeration in the presence of background microbiota. Phage suspension was applied to the inoculated fresh produce that was subsequently held for three days under variable storage conditions. The optimized phage treatment decreased the populations of pathogenic E. coli by 2.4-3.0logCFU/g on cut green pepper (5-min rinse) and 3.4-3.5logCFU/g on spinach leaves (2-min rinse), during 72h storage. The majority of this decline was caused by the antimicrobial action of the phage. These findings suggest the utility of bacteriophage to selectively control pathogens on fresh produce.

The physical quality and functionality of shell eggs, pasteurized with heat or a combination of heat and ozone, were assessed during eight weeks of storage at 4 or 25 °C. Shell eggs were treated as follows: (1) immersion heating that mimics commercial pasteurization processes (egg internal temperature of 56 ± 0.1 °C for 32 min), or (2) a newly developed combination process comprised of heating (56 ± 0.1 °C, internal, for 10 min) followed by gaseous ozone treatment. Eggs were tested for yolk index, Haugh units, albumen pH, albumen turbidity, and percent overrun. Additionally, albumen samples were assayed for lysozyme activity and free sulfhydryl group content, and were analyzed using differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy. Both processed and unprocessed eggs maintained superior quality when stored at 4 °C, as opposed to 25 °C. Pasteurization, regardless of method, led to superior maintenance of Haugh units during storage but also increased albumen opacity and decreased albumen overrun. Detrimental effects on quality markers were more severe in heat-pasteurized eggs than those treated with the ozone-based process. Pasteurization of shell eggs by either process did not affect lysozyme activity or sulfhydryl group content. Changes in protein secondary structure, as indicated by FTIR analysis, suggest that the ozone-based process is less damaging to albumen proteins than is the heat-alone process. In conclusion, heat-ozone pasteurization, by virtue of its less severe heat treatment, yields a safe final product that more closely resembles untreated shell eggs.

Popular foods such as fresh produce and dry nuts are increasingly implicated in outbreaks of food-transmitted diseases. These products are not amenable to conventional processing technologies; therefore, many alternative decontamination methods are actively investigated. Ozone is a versatile sanitizer with promising applications in some high-risk foods. This antimicrobial agent is active against a broad spectrum of microorganisms, and it can be used effectively in its gaseous or aqueous state. The flexibility afforded by ozone use makes it a viable option for application on easy-to-damage products like fresh produce. If process parameters are adequately controlled, ozone treatment can enhance safety and increase shelf life without adversely affecting product quality. Despite these advantages, ozone may not be suitable for some applications, including treatment of liquid foods and products rich in unsaturated fats and soluble proteins. Ozone, as a powerful oxidizer, must be carefully controlled at all times, and equipment must be rigorously maintained to ensure safety of workers.

The purpose of this study was to investigate the effect of osmotic shock and adaptation at low water activity (aw) and the type of humectant used to lower the aw, on heat resistance of three Salmonella enterica serovars (Saintpaul 02-109, Tennessee 2053H, and Elmsbuettel 1236H). The serovars were grown (adapted) or transferred (osmotic shocked) in low-aw broths and subjected to heat treatment at 55°C for up to 45 min; samples were removed at 5-min intervals and immediately placed in an ice-water bath until plating. The aw of tryptic soy broth (TSB) was lowered by the addition of 20% (wt/wt) glycerol (aw 0.94), 4% (wt/wt) sodium chloride (NaCl; aw 0.97), or 35% sucrose (wt/wt) (aw 0.95). The type of humectant and cell adaptation significantly affected the D55°C-value. Cells merely suspended in 20% glycerol broth (i.e., nonadapted) prior to heat treatment showed a larger D55°C-value (3.0 to 3.9 min), when compared with that of cells adapted in the same medium (D55°C-values of 0.86 to 0.98 min). Interestingly, cells adapted to TSB plus glycerol were not more resistant to heat than were the controls. NaCl and sucrose showed a net protective effect for all serovars under both the adapted and nonadapted conditions, with sucrose providing the most protection. Highest D55°C-values were obtained for cultures adapted to TSB plus sucrose. Based on these results, the effect of reduced aw on thermal resistance of Salmonella serovars varies greatly, depending on medium constituents and adaptation of the pathogen in these media.