Inactivation of Desiccation-Resistant Salmonella on Apple Slices Following Treatment with ε-Polylysine, Sodium Bisulfate, or Peracetic Acid and Subsequent Dehydration.

Salmonella is capable of surviving dehydration within various foods, such as dried fruit. Dried fruit, including apple slices, have been the subject of product recalls due to contamination with Salmonella. A study was conducted to determine the fate of Salmonella on apple slices, following immersion in three antimicrobial solutions (viz., ε-polylysine [epsilon-polylysine or EP], sodium bisulfate [SBS], or peracetic acid [PAA]), and subsequent hot air dehydration. Gala apples were aseptically cored and sliced into 0.4 cm thick rings, bisected, and inoculated with a five-strain composite of desiccation-resistant Salmonella, to a population of 8.28 log CFU/slice. Slices were then immersed for 2 min in various concentrations of antimicrobial solutions, including EP (0.005, 0.02, 0.05, and 0.1%), SBS (0.05, 0.1, 0.2, and 0.3%), PAA (18 or 42 ppm), or varying concentrations of PAA + EP, and then dehydrated at 60°C for 5 h. Salmonella populations in positive control samples (inoculated apple slices washed in sterile water) declined by 2.64 log after drying. In the present study, the inactivation of Salmonella, following EP and SBS treatments, increased with increasing concentrations, with maximum reductions of 3.87 and 6.20 log (with 0.1 and 0.3% of the two compounds, respectively). Based on preliminary studies, EP concentrations greater than 0.1% did not result in lower populations of Salmonella. Pretreatment washes with either 18 or 42 ppm of PAA inactivated Salmonella populations by 4.62 and 5.63 log, respectively, following desiccation. Combining PAA with up to 0.1% EP induced no greater population reductions of Salmonella than washing with PAA alone. The addition of EP to PAA solutions appeared to destabilize PAA concentrations, reducing its biocidal efficacy. These results may provide antimicrobial predrying treatment alternatives to promote the reduction of Salmonella during commercial or consumer hot air drying of apple slices.

Minimum Concentrations of Slow Pyrolysis Paper and Walnut Hull Cyclone Biochars Needed to Inactivate Escherichia coli O157:H7 in Soil.

Antimicrobial properties of biochar have been attributed to its ability to inactivate foodborne pathogens in soil, to varying degrees. High concentrations of biochar have reduced E. coli O157:H7 in soil and dairy manure compost, based on alkaline pH. Preliminary studies evaluating 31 different biochars determined that two slow pyrolysis biochars (paper biochar and walnut hull cyclone biochar) were the most effective at inactivating E. coli in soil. A study was conducted to determine the lowest percentages of paper and walnut hull cyclone biochars needed to reduce E. coli O157:H7 in soil. A model soil was adjusted to 17.75% moisture, and the two types of biochar were added at concentrations of 1.0, 1.5, 2.0, 2.5, 3.5, 4.5, 5.5, and 6.5%. Nontoxigenic E. coli O157:H7 were inoculated into soil at 6.84 log CFU/g and stored for up to 6 weeks at 21°C. Mean E. coli O157:H7 counts were 6.01-6.86 log CFU/g at all weeks between 1 and 6 in soil-only positive control samples. Populations in all soil amended with 1.0 and 1.5% of either type of biochar (as well as 2.0% of the walnut hull biochar) resulted in ≤0.68 log reductions at week 6, when compared with positive controls. All other concentrations (i.e., ≥2.0% paper and ≥2.5% walnut hull) inactivated ≥2.7 log at all weeks between 1 and 6 (p < 0.05). At the end of 6 weeks, E. coli O157:H7 declined by 2.84 log in 2.0% paper biochar samples, while concentrations of between 2.5 and 6.5% paper biochar completely inactivated E. coli O157:H7, as determined by spiral plating, at weeks 5 and 6. In contrast, 2.0% walnut hull biochar lowered populations by only 0.38 log at week 6, although 2.5-6.5% concentrations of walnut hull biochar resulted in complete inactivation at all weeks between 3 and 6, as assessed by spiral plating. In summary, ≥2.5% paper or walnut hull biochar reduced ≥5.0 log of E. coli O157:H7 during the 6-week storage period, which we attribute to high soil alkalinity. Amended at a 2.5% concentration, the pH of soil with paper or walnut hull biochar was 10.67 and 10.06, respectively. Results from this study may assist growers in the use of alkaline biochar for inactivating E. coli O157:H7 in soil.

A Review of Essential Oils as Antimicrobials in Foods with Special Emphasis on Fresh Produce.

ABSTRACT: Consumer safety concerns over established fresh produce washing methods and the demand for organic and clean-label food has led to the exploration of novel methods of produce sanitization. Essential oils (EOs), which are extracted from plants, have potential as clean-label sanitizers because they are naturally derived and act as antimicrobials and antioxidants. In this review, the antimicrobial effects of EOs are explored individually and in combination, as emulsions, combined with existing chemical and physical preservation methods, incorporated into films and coatings, and in vapor phase. We examined combinations of EOs with one another, with EO components, with surfactants, and with other preservatives or preservation methods to increase sanitizing efficacy. Components of major EOs were identified, and the chemical mechanisms, potential for antibacterial resistance, and effects on organoleptic properties were examined. Studies have revealed that EOs can be equivalent or better sanitizing agents than chlorine; nevertheless, concentrations must be kept low to avoid adverse sensory effects. For this reason, future studies should address the maximum permissible EO concentrations that do not negatively affect organoleptic properties. This review should be beneficial to food scientists or industry personnel interested in the use of EOs for sanitization and preservation of foods, including fresh produce.