Evaluation of sanitizing treatments for sizer carriers in stone fruit packinghouses

Ensuring the safety of fresh fruit is a top priority of fresh produce packinghouses. The aim of this one-year research project is to evaluate and improve sanitizing treatments for sizer carriers in stone fruit packinghouses. The project will not only describe the potential for sizer carriers to harbor pathogens and allow for their growth under different environmental conditions, but will also define a set of sanitizers and application methods that represent the greatest promise for evaluation at the commercial level. Environmental sampling will be performed in active commercial packinghouses to determine natural microbial loads on fruit contact surfaces of sizer carriers. Subsequently, laboratory inoculation studies will be performed to determine the growth potential of foodborne pathogens on fruit sizer carriers under varied humidity and temperature. Furthermore, the potential of clean-in-place (CIP) sanitization will be evaluated by applying no-rinse sanitizers (steam and aerosol antimicrobial chemicals) to the sizer carriers. Results from this study potentially will be applicable to diverse fresh fruit packinghouses for preventing pathogen cross-contamination in produce packing operations. Findings and recommendations will be reported and/or disseminated through industry meetings and technical publications.

This proposal aims to evaluate and improve sanitizing treatments for sizer carriers in stone fruit packinghouses. The primary objectives of this one-year project are 1) To evaluate natural microbial loads on fruit contact surfaces of sizer carriers; 2) To evaluate the growth potentials of foodborne pathogens on fruit sizer carriers; and 3) To evaluate potential clean-in-place (CIP) sanitizing treatments for fruit sizer carriers. Environmental sampling will be performed in active commercial packinghouses to determine natural microbial loads on fruit contact surfaces of sizer carriers based on total microbial, psychotropic (cold tolerating and thriving microbes), yeast and mold, and total coliform counts. Subsequently, laboratory inoculation studies will be performed to determine the growth potentials of Salmonella and Listeria on fruit sizer carriers under varied environmental conditions. Furthermore, the potential of CIP sanitization by treating the sizer carriers with no-rinse sanitizers (including dry steam and antimicrobial aerosols) will be investigated. We anticipate that data from this study will help to identify effective approaches and/or justify for further process development and validation studies on practical and cost-effective sanitizing treatments for sizer carriers. The results of this study potentially will be applicable to diverse fresh fruit packinghouses for preventing pathogen cross-contamination in fresh produce packing operations.

1. Evaluating natural microbial loads on fruit contact surfaces of sizer carriers. 

2. Evaluating the growth potentials of foodborne pathogens on fruit sizer carriers. 

3. Evaluating potential CIP sanitizing treatments for fruit sizer carriers.

Packinghouse sanitation considers the environment of the facility, equipment design, packing practices, and personnel hygiene (Yaptenco and Esguerra, 2012). Many factors, including fruit condition, equipment cleanliness, washing system, wax and fungicide application may influence or contribute to the microbial loads of sizer carriers. The results of this study show that fruit carrier surfaces of sizers in stone fruit packinghouses are susceptible to general microbial attachment. The presence of microbes on the fruit-contact surfaces of sizer carriers is not surprising since field fruit has the ability to bring natural microflora into packing and processing facilities (Pao and Davis, 2001). For example, Pao and Brown (1998) reported average aerobic plate counts of ~4.0 log CFU/cm2 and yeast and mold counts of 3.3 log CFU/cm2 on citrus fruit surfaces before packinghouse fruit washing. Johnston et al. (2005) reported microbial increases in cantaloupes from field through packing, with ranges of 6.4 to 7.0 log CFU/g for aerobic plate count and 2.1 to 4.3 log CFU/g for coliforms. The presence of natural microflora on fresh produce and their direct contact surfaces is unavoidable and does not normally present a food safety issue. Results of this study (e.g., Figure 1) also show that, in general, the cleaning step for sizer carriers in Central California stone fruit packinghouses is capable of significantly reducing potential bacterial contamination introduced from stone fruit and/or handling operations. This bacterial reduction ability, if further validated and/or improved per individual packinghouse standard operation procedures, could be considered as a preventive control in practical operations for low levels of sporadic or accidental contamination of foodborne pathogens in packinghouses. In risk assessment, all produce contact surfaces in packinghouse should be under review. For practical risk analysis it may be useful for packinghouse operators to characterize their environment, particularly near fruit handling areas, and see where they fall within the spectrum of conditions discussed in this study. Data from this study (Tables 1 and 2) revealed that the plastic and rubber surfaces of sizer carriers, with or without wax deposits from commercial packing operations, may not support the growth of S. enterica and L. monocytogenes in ambient conditions. Prior studies also demonstrated that foodborne pathogens such as Salmonella declined on the surfaces of plastic chopping boards (Gough and Dodd, 1998), rubber picker fingers for poultry processing (Arnold and Yates, 2009) and various tomato packing line materials (Allen et al., 2005). Similarly, Chaitiemwong et al. (2010) reported the decline of inoculated L. monocytogenes on a conveyor belt material. Although no growth was found, Salmonella exhibited greater persistence on sizer carriers under 95% humidity. This finding corroborates previous observations related to greater survival and/or growth of surface attached foodborne pathogens under highly humid conditions (Iturriaga et al., 2007; Pao et al., 2012). The finding highlights the importance of good air ventilation and careful water usage to avoid excessive moisture accumulation in fruit packing areas. Furthermore, this study demonstrated that moderate environmental conditions (such as 34 or 40°C in combination with 75 or 85% humidity) have the potential to minimize microbial contamination of packing lines. For example, the exposure of inoculated carriers to the combination of 75% humidity and 40°C resulted in >5-log reductions of both Salmonella and Listeria within 4 hours. This pathogen elimination phenomenon by natural conditions (without chemical intervention) merits further exploration for its practicality as a produce safety control in packinghouse operations. Currently, firms in the U.S. are required to inspect, maintain, and clean and sanitize, when necessary and appropriate, all food-contact surfaces of equipment and tools used in covered activities as frequently as reasonably necessary to protect against contamination of covered produce (FDA, 2013). Since this study shows rapid decline instead of growth for Salmonella and Listeria on sizer carriers under various experimental conditions, it would be interesting to either evaluate the necessity of having a sanitizing treatment after carrier cleaning or consider incorporating the temperature/humidity control as an appropriate sanitizing step. In conclusion, this study confirms that cleaning is a beneficial step for reducing microbial contamination on sizer carriers in stone fruit packinghouse operations. Plastic or rubber surfaces of the carriers are unlikely to support the growth of S. enterica or L. monocytogenes under ambient conditions. Further evaluation on the influences of the ability of pathogens to adapt to environments and the presence of fruit debris on pathogen contamination of carriers would be interesting. We recommend additional research to explore the potential of applying moderate, yet lethal, temperature and humidity conditions to combat microbial contamination on produce- and food-contact surfaces.