1a. Objectives (from AD-416):
To determine sensory, nutritional and/or product quality impacts of efficacious food processing interventions and combinations of interventions. To develop antimicrobial packaging-based treatments for controlling pathogens. To identify compounds of potential concern formed by novel non-thermal food processing interventions. To develop/optimize treatment processes and combinations to control pathogens and to minimize loss of product quality and value.
1b. Approach (from AD-416):
An integrated approach to enhance microbial safety while maintaining product quality will be adopted by combining efficacious treatments and processes with antimicrobial packaging. Current antimicrobial treatments, processes, and intervention technologies that have been demonstrated to be effective in inactivating human pathogens will be modified and evaluated to confirm their effectiveness in obtaining a minimum 3 log CFU/g reduction of E. coli O157:H7 and Salmonella spp. on fresh and fresh-cut produce (mainly leafy green vegetables and tomatoes). Novel intervention technologies with higher efficacy of pathogen reduction will be developed and optimized. The impact of efficacious chemical and physical intervention technologies on sensory properties, nutrients, and shelf-life will be determined using the intensity (time, concentration, dose, etc.) that achieves a 3-log CFU/g reduction of the pathogens. In addition, new antibrowning/antimicrobial formulas will be developed to minimize risk of L. monocytogenes contamination during processing of cut fruit while inhibiting tissue browning. Furthermore, accumulation of chemical by-products as a result of chemical sanitizers and physical interventions will be investigated. Antimicrobial packaging as the final defense against human pathogens will be developed for a variety of food products (fresh-cut produce, meats, etc.) to reduce or control the re-growth of surviving pathogens during storage. Finally, combinations of efficacious intervention technologies with antimicrobial packaging will be evaluated for additive or synergistic inhibition of pathogens and preservation of product quality. Strategies and treatments will be developed to minimize adverse effects of intervention technologies and antimicrobial packaging on product quality. By combining efficacious intervention technologies and treatments with antimicrobial packaging, a 5-log reduction of common pathogens may be achieved. Intervention technologies either alone or in combination with antimicrobial packaging will be transferred to industry to enhance microbial safety of commercial food products.
3. Progress Report:
Within this FY, research has been conducted to evaluate product quality changes as a result of antimicrobial treatments and to explore a new way of formulating antimicrobial coating and film to accomplish objectives 1 and 2 of the project. In addition, antimicrobials have been applied alone, in combinations and as electrostatic spraying to address objective 4 of the project. Detailed progress to achieve the overall objectives is listed below. Quality of fruits and vegetables as a result of intervention technologies/treatments has to be investigated before the intervention being considered for commercial application. Cherry tomatoes were treated with combinations of different types of acids and with the combination of acids and essential oil. Sensory properties (color, texture, smell and appearance) of treated fruit were evaluated during 21 days of storage at 10 C. Results suggested that the treatments with mustard oil resulted in a residue odor on tomato fruit. However, other formulations did not significantly affect sensory quality of cherry tomatoes while enhancing microbial safety. Development of new edible coating solutions and films using natural biopolymers and nanotechnology is in progress. Coating solutions with natural polymers and emulsifiers were treated by high pressure homogenization (HPH, 138 MPa, 3 cycles). HPH treatment significantly reduced polymer particle sizes in the emulsion to about one micrometer. Resultant films from the coating solution were softer, less rigid and more stretchable than those without HPH treatments. The coating films form micro channels and pores that would facilitate the release of antimicrobials/antioxidants, and modify barrier properties to CO2, O2, moisture, and UV light. The HPH treated films showed higher antimicrobial efficiency than non-HPH treated films. Contamination of fresh or minimally processed produce with human pathogens still remains a high concern. Minimally processed spinach and tomato contaminated with pathogens have been associated with multiple outbreaks of foodborne illnesses. Studies were conducted to investigate the ability of hydrogen peroxide (H2O2) to inactivate human bacterial pathogens and spoilage microflora on leafy green and tomatoes. In a preliminary experiment, 3% H2O2 was proven to be more effective than 5% H2O2. A 3% solution of H2O2 was capable of reducing population of a five-strain cocktail of E. coli O157:H7 on baby spinach and three serotypes mixture of Salmonella enterica on tomato by more than 99% in a 3 minute wash under mild agitation. Non-thermal treatments utilizing ultraviolet light (0.60 kJ/m2) and 3% H2O2 provided a strong synergy inactivating greater than 99.99% of both E. coli O157:H7 and Salmonella enterica on spinach and tomato. Ultraviolet light is FDA approved surface decontamination technique and H2O2 is classified as a generally recognized as safe substance. Hence this combination technology may ensure safe and effective inactivation of foodborne pathogens on produce and would greatly benefit the food industry. It is suspected that the use of communal dump tanks could serve as a source of contamination in fresh and fresh-cut produce processing. Electrostatic spraying offers a non-recirculating technique for applying sanitizers on fresh and fresh-cut produce. An electrostatical spraying system was acquired and a treatment chamber specific for the spraying system was built to test treatment efficiency. The uniformity of spraying coverage on tomato fruit was evaluated in terms of the spraying time and charge (positively vs negatively) of antimicrobials. The effect of electrostatic spray of a peroxyacetic acid-based sanitizer, organic acids and plant extracts on E. coli and Salmonella Typhimurium was conducted on tomato fruit. Initial results suggested the treatments reduced population of the bacteria by 90-99%. The system needs to be optimized to achieve better results. Mesquite pod flour has been involved in recent recalls due to contamination with Bacillus cereus. Non-thermal processing technology is needed to reduce the population of microorganisms in the flour because heating deteriorates its desired characteristic flavor. A study was conducted to investigate the efficacy of ionizing irradiation in decontaminating two types of mesquite pod flour naturally contaminated with B. cereus and to evaluate the effect of irradiation on formation of furan, a possible human carcinogen. The information generated from the study would be helpful to food industry to enhance the microbial safety of the product. Following initial screening a variety of antimicrobials, validation tests were conducted at USDA-ARS against E. coli O157:H7 and Salmonella spp. on ground meat trims to confirm and validate the efficacy of the best antimicrobials. Selected antimicrobials from the validation test result were experimented on a large scale CO2 plus platform at our collaborator’s site (Air Liquide). An abstract entitled "The Use of Liquid CO2 as a Conveying and Dispersing Agent to Simultaneously Chill Meat Products and Broadcast Various Anti-Microbial Processing Aids during a Meat Mixing Process" was approved by cooperators (USDA & Air Liquide), which will be presented at the 2014 International Association for Food Protection Annual Meeting at Indianapolis, Indiana.
1. Chlorine by-product formation in wash water and fresh-cut produce. Chlorine (sodium hypochlorite) is a commonly used sanitizer by the food industry while citric acid is often used to adjust its pH in order to achieve higher efficacy of the chlorine treatment. However, formation of chlorine by-products is a concern due to their potential adverse health effect. ARS researchers at Wyndmoor, Pennsylvania studied the formation of trichloromethane (a chlorine by-product) in water, and fresh-cut produce and as affected by the presence of citric acid. Results showed that trichloromethane was formed in chlorated water, but not in chlorine dioxide solution. Higher amount of trichloromethane (up to 280 ng/mL) was produced in the chlorine solution used for washing cut-lettuce than for diced onions while levels of trichloromethane in the final products (cut vegetables) were much lower (14-22 ng/g) than that in the water. Citric acid reacted with chlorine producing more than 1,000 ng/mL of trichloromethane in chlorine solution. Therefore, citric acid should be replaced with other pH adjustors to reduce the formation of trichloromethane in wash water. The information can be used by the produce industry to minimize the formation of chlorine by-products in water and fresh produce.
2. Double-layer antimicrobial packaging films for ready-to-eat (RTE) meat. The contamination of foodborne pathogens in RTE meat products has been a concern for the meat industry. ARS researchers at Wyndmoor, Pennsylvania developed edible chitosan-acid solutions incorporating antimicrobials on polylactic acid (PLA) packaging films to produce double-layer antimicrobial packaging films. The films reduced 99.9 percent of Listeria and 99 percent of Salmonella on RTE meat and inhibited their growth over 5 weeks at 10 C. This study provides the packaging industry and RTE meat processors a new way to provide safer products to consumers.
3. Antimicrobial coatings for fresh strawberry. Strawberries are esteemed as healthful and rich in vitamins and antioxidants. However, a 2011 outbreak of hemorrhagic colitis, which resulted in the death of two individuals, was associated with contaminated strawberries. ARS researchers at Wyndmoor, Pennsylvania developed antimicrobial coating formulas to kill pathogens and spoilage microorganism on fresh strawberry. The coating treatments were capable of reducing Salmonella and E. coli O157:H7 by more than 99.9% on strawberry. No mold growth and appearance change were observed for the treated samples stored at 4 C for 19 days. Results from this study will provide processors with viable options for designing antimicrobial coatings to improve the microbiological safety and quality of strawberry.
4. UV-C treatment for safer tomato. UV-C treatment is a simple and inexpensive processing technology which leaves no chemical residues behind. The impact of UV-C on E. coli O157:H7 and Salmonella population on tomato fruit was conducted by ARS researchers at Wyndmoor, Pennsylvania. Results showed that surface characteristics, i.e., rough stem scar vs. smooth surface played an important role in bacterial attachment and inactivation as pathogen reductions were lower when pathogens were located at the stem scar site compared to smooth surface. A UV-C dose of kilojoules per square meter 6 kJ/m2 was capable of reducing the viable population of E. coli O157:H7 and Salmonella enterica by more than 99.9%. Yeast and mold population was reduced by about 99% by the same treatment. The firmness and color of the tomatoes were not affected by the UV-C doses during post-treatment storage. Hence UV-C treatment may prove worthy to use in post-harvest situations to improve safety and maintain quality of tomatoes.
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Guo, M., Jin, Z.T., Geveke, D.J., Fan, X., Sites, J.E., Wang, L. 0203. Evaluation of microbial stability, bioactive compounds, physicochemical properties, and consumer acceptance of pomegranate juice processed in a commercial scale pulsed electric field system. Food and Bioprocess Technology. DOI:10.1007/s11947-013-1185-6.
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Ukuku, D.O., Mukhopadhyay, S., Olanya, O.M. 2013. Effect of organic acid treatments on microbial safety and overall acceptability of fresh-cut melon cubes. International Journal of Food, Agriculture, and the Environment. 11(3&4):340-345.