Electrostatic Spraying of Food-Grade Organic and Inorganic Acids and Plant Extracts to Decontaminate Escherichia coli O157:H7 on Spinach and Iceberg Lettuce

Dept of Food Science, Univ of Arkansas, Fayetteville, AR 72704, USA.
Journal of Food Science (Impact Factor: 1.7). 07/2012; 77(7):M391-6. DOI: 10.1111/j.1750-3841.2012.02719.x
Source: PubMed


The prevalence of foodborne illnesses is continually on rise. In the U.S.A., Escherichia coli O157:H7 (E. coli) has been associated with several outbreaks in minimally processed foods. Spinach and lettuce pose higher food safety risks and recurring food recalls suggest the insufficiency of current disinfection strategies. We aimed at offering a natural antimicrobial alternative using organic acids (malic, tartaric, and lactic acids [MA, TA, and LA, respectively]) and grape seed extract (GSE) and a novel application method using electrostatic spraying to evenly distribute the antimicrobials onto produce. Spinach and lettuce samples were washed, sanitized with sodium hypochlorite solution (6.25 mL/L), dip inoculated in water containing E. coli (7.0 log CFU/mL) for 24 h, and rewashed with sterile water to remove nonadhered pathogens. The samples were sprayed electrostatically with MA, LA, and GSE alone and in combinations and for comparison, with phosphoric acid (PA) and pH controls with deionized water adjusted to 1.5/2.3/3.6 and stored at 4 °C. When combined with LA (3%), MA (3%) showed 2.1 to 4.0 log CFU/g reduction of E. coli between the days 1 and 14 on spinach and 1.1 to 2.5 log CFU/g reduction on lettuce. Treatment with PA (1.5%) and PA (1.5%)-GSE (2%) exhibited 1.1 to 2.1 log CFU/g inhibition of E. coli on spinach during the 14-d storage. Our findings demonstrated the efficacy of electrostatic spraying of MA, LA, and GSE on fresh produce to improve the safety and lower the public health burden linked to produce contamination.

Practical application:
Electrostatic spraying is an emerging technique that can be adopted to improve the distribution and application of antimicrobials during fresh produce sanitation. Relatively simple and quick, the process can access most/all parts of produce surface and offer protection from food pathogens. The use of malic and lactic acids with or without grape seed extract can serve as effective antimicrobials when sprayed electrostatically, lowering the risk from postcontamination issues with spinach and iceberg lettuce. This application technology can be extended to improve the commercial food safety of other produce, fruits, poultry, and meat.

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    • "Organic acids are Generally Recognized As Safe (GRAS) and their bactericidal efficacy against E. coli O157:H7, Listeria monocytogenes and Salmonella on fresh produce was previously investigated (Akbas and Olmez, 2007; Ganesh et al., 2012; Huang and Chen, 2011; Sagong et al., 2011; Samara and Koutsoumanis, 2009). Lactic acid exhibits increased effectiveness against E. coli O157:H7 compared to other organic acids (malic, citric, tartaric or acetic acid) when applied on fresh spinach or lettuce leaves at ambient temperature (20–25 °C). "
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    ABSTRACT: Aqueous extract of Origanum vulgare (oregano), sodium hypochlorite (60 and 300ppm of free chlorine), Citrox® (containing citric acid and phenolic compounds [bioflavonoids] as active ingredients), vinegar, lactic acid, and double combinations of Citrox, lactic acid and oregano were evaluated against Escherichia coli O157:H7 and total mesophilic microbiota on fresh-cut spinach and lettuce and for their impact on color of treated vegetables. Spinach and lettuce leaves were inoculated with E. coli O157:H7 to a level of 5-6logCFU/g and immersed in washing solutions for 2 or 5min at 20°C, followed by rinsing with ice water (30s). Bacterial populations on vegetables were enumerated immediately after washing and after storage of the samples at 5°C for 7days under 20% CO2: 80% N2. No significant post-washing microbial reductions were achieved by chlorinated water, whereas after storage total microbiota was increased by 2.4logCFU/g on lettuce. Vinegar wash was the most effective treatment causing E. coli O157:H7 reductions of 1.8-4.3logCFU/g. During storage, pathogen was further decreased to below the detection limit level (<2logCFU/g) and total microbiota exhibited the highest reductions compared to other treatments. Lactic acid reduced pathogen by 1.6-3.7logCFU/g after washing; however levels of total microbiota increased by up to 2logCFU/g on packaged lettuce during storage. Washing lettuce samples with oregano for 2min resulted in 2.1logCFU/g reduction of E. coli O157:H7. When Citrox was combined with oregano, 3.7-4.0logCFU/g reduction was achieved on spinach and lettuce samples, with no significant effect on color parameters. Additionally, rinsing with ice water after decontamination treatments contributed to maintenance of color of the treated vegetables. In conclusion, the results indicated that vinegar, lactic acid or oregano aqueous extract alone or in combination, as alternative washing solutions to chlorine, may be effectively used to control E. coli O157:H7 and sustain acceptable appearance of fresh cut spinach and lettuce.
    No preview · Article · Dec 2015 · International journal of food microbiology
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    ABSTRACT: The objective of the study was to determine the effects of organic acids and plant extract alone and in combination when applied by electrostatic spraying on Escherichia coli O157:H7-inoculated cantaloupe cubes. Inoculated cubes were sprayed with malic (M) and lactic (L) acids and grape seed extract at different concentrations (alone and various combinations) then stored at 4C. Under optimized concentrations, ML 2% was able to reduce E. coli O157:H7 by 1.9 logs after 12 days of storage and was significantly different from the controls (P < 0.05). Increasing the concentration of M (4%) alone and in combination with L (2%) caused an increase in log reduction (4.6 logs). These treatments can be used as alternatives to commercial sanitizers in order to improve the safety of fresh-cut cantaloupe cubes. Multiple hurdle technology of electrostatic sprayer combined with natural antimicrobials can be effective in improving the safety of food. Electrostatic sprayer is a technology that can be used to enhance the effectiveness of antimicrobials. Organic acids and plant extracts can be used as antimicrobials to efficiently reduce contaminated cantaloupe cubes when combined with electrostatic sprayer. This multiple hurdle technology can be used in different food industry settings.
    No preview · Article · Feb 2013 · Journal of Food Safety
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    ABSTRACT: Purpose of the review: Fresh cut produce continues to be implicated in foodborne illness outbreaks with the principle pathogens being norovirus, Escherichia coli O157:H7, Salmonella, Listeria monocytogenes and enteric protozoan. There has been a strong reliance on post-harvest washing to remove field acquired contamination and has been the subject of intensive research over the last 15 years. This review focuses on recent advances in the efficacy of different approaches to inactivate, remove or minimize cross-contamination of human pathogens associated with post-harvest fresh produce. Findings: Post-harvest washing only achieves a negligible reduction in human pathogen levels but can significantly increase the potential of cross-contamination between batches. Consequently recent advances in produce washing have focused on reducing crosscontamination events through stabilizing sanitizers (ie, chlorine) in the presence of high organic loading to retain residual antimicrobial activity (organic acids). Alternative interventions such as electrochemical oxidation are directed at decontaminating wash water as opposed to inactivating pathogens directly on produce. More successful produce decontamination technologies are not based on washing but rather on sanitizers applied in the gas phase or physical techniques such as gas plasma, UV and E-beams. Directions for future research: With the limitations of aqueous-based washing it can be envisaged that a post-wash intervention step will be implemented for controlling human pathogens associated with fresh produce. Transferring technologies from the laboratory to commercial processing will be challenging and the focus of future research.
    No preview · Article · Mar 2013 · Stewart Postharvest Review
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