Challenges in the microbiological food safety of fresh produce: Limitations of post-harvest washing and the need for alternative interventions

Increased consumption, larger scale production and more efficient distribution of fresh produce over the past two decades have contributed to an increase in the number of illness outbreaks caused by this commodity. Pathogen contamination of fresh produce may originate before or after harvest, but once contaminated produce is difficult to sanitize. The prospect that some pathogens invade the vascular system of plants and establish "sub-clinical" infection needs to be better understood to enable estimation of its influence upon risk of human illness. Conventional surface sanitation methods can reduce the microbial load, but cannot eliminate pathogens if present. Chlorine dioxide, electrolyzed water, UV light, cold atmospheric plasma, hydrogen peroxide, organic acids and acidified sodium chlorite show promise, but irradiation at 1 kGy in high oxygen atmospheres may prove to be the most effective means to assure elimination of both surface and internal contamination of produce by pathogens. Pathogens of greatest current concern are Salmonella (tomatoes, seed sprouts and spices) and Escherichia coli O157:H7 on leafy greens (spinach and lettuce). This review considers new information on illness outbreaks caused by produce, identifies factors which influence their frequency and size and examines intervention effectiveness. Research needed to increase our understanding of the factors influencing microbial safety of fresh produce is addressed. Copyright © 2012 Elsevier Ltd. All rights reserved.

This review provides the fundamental and essential knowledge of UV-LEDs to better apply LED technology in environmental application. The UV-light emitting diode (LED) has been attracting significant attention as a new UV source that can replace conventional mercury gas-filled lamps in water disinfection applications. However, the UV-LED remains a relatively new addition to the water treatment toolbox. The current lack of fundamental understanding risks underutilizing uniquely advantageous features of the UV-LED due to unguided design and non-optimized disinfection practices. Our review presents the necessary fundamental knowledge required for the successful implementation of UV-LEDs, including the mechanism of light generation, LED chip fabrication, package design, and essential properties of UV-LEDs. We introduce distinct advantages, such as wavelength tuning, control of radiation patterns, and array design, while emphasizing the significant differences between LED and mercury lamp technologies required to achieve successful technology transfer. Previous studies investigated the design of UV-LED disinfection systems; however, little consensus has yet emerged regarding the integration of LEDs into flow-through reactors. While UV-LED disinfection systems will undisputedly mature in the near future, environmental engineers face a number of urgent research needs in this area including heat sink design, radiation pattern and array design optimization for uniform UV dose delivery, targeted pathogen-wavelength considerations, improved light extraction, and component monitoring systems.