Summary of Awards to Date

Control of Listeria monocytogenes in processing/packing plants using antimicrobial blue light (aBL)


Jan. 1, 2021 - Dec. 31, 2021

Amount Awarded



Francisco Diez-Gonzalez, Ph.D.
University of Georgia


Govindaraj Dev Kumar, Ph.D.


Despite all advances in food safety measures, outbreaks and recalls related to produce continue to occur. One of the major concerns in this regard is Listeria monocytogenes. This bacterium not only may be present in the field and on produce before harvest but can also survive establish persistence in the environment, such as processing/packaging facilities. Its widespread presence in these environments may lead to post-harvest cross contamination. This brings a pressing need for the development and application of effective antimicrobial interventions to enhance the effect of current methods in use.

A novel method previously tested for clinical applications is the visible (400-470 nm) antimicrobial blue light (aBL) which has shown antimicrobial effects and it is considered safe for humans. The antimicrobial efficacy of aBL for food industry application has barely been studied. This project is an initial effort to assess the antimicrobial efficacy of aBL against L. monocytogenes on surfaces representative of produce processing equipment and supplies. Simply, L. monocytogenes as dried cells or biofilms will be placed on a wide range of surfaces (stainless steel, plastic, etc.) and exposed to aBL to evaluate its antimicrobial efficacy. Furthermore, decontamination effectiveness will be assessed in pilot plant scale. 

Technical Abstract

Contamination of produce remains a complex issue and could occur at different stages from farm to fork. L. monocytogenes is widespread in the environment and can be transmitted to fresh produce by contact to contaminated surfaces. The presence of native plant microbiota and organic matter can protect L. monocytogenes by reducing the efficacy of sanitizers as well as promoting biofilm formation. Post operation washing and sanitizing of produce contact surfaces might not be adequate in eliminating the presence of pathogens and commensal bacteria.

The use of a dynamic light technology during down time and close of operation could serve as a useful tool in preventing Listeria establishment and persistence. In this project, our goal is to assess the efficacy of antimicrobial blue light (aBL) against L. monocytogenes in a variety of produce processing related surfaces including but not limited to stainless steel (SS), plastic, wall coating, floor covering, nylon, polyester, cotton canvas and conveyor belts. The aBL’s antibacterial effect against a wide range of microbes including Listeria has been demonstrated at wavelengths between 400 and 470 nm. However, to the best of our knowledge it has not been evaluated for the surface decontamination of packing and processing surfaces. This study is intended to assess the possibility of aBL as a viable complimentary intervention to enhance microbial safety. 

A series of experiments will be conducted, using five L. monocytogenes strains from fresh produce origin. A cocktail of these strains will be used to form surface dried cells and biofilms on SS coupons. Light emitting diode (LED) lamps emitting at 405 420 and 460 nm wavelengths will be used for the surface exposure at different doses ranging from 30 to 600 J/cm2. Low (3 Log CFU/cm2) and high (6 Log CFU/cm2) inoculum levels will be used. The durations of exposure will consist of 4, 8 and 12 h, to mimic breaks and when operations cease. Following exposure, microbiological and statistical analyses will be performed, and optimal doses will be defined. The incorporation to surfaces of a photosensitizer, gallic acid, will also be evaluated as an aBL enhancing adjuvant. The minimum dose at which the largest reduction is obtained will be applied to all other target surfaces as well as on SS coupons to validate their inactivation results consistency with those of pathogenic L. monocytogenes. Finally, aBL decontamination effectiveness will be evaluated in pilot plant scale. 

This project will deliver novel experimental data supporting the idea of aBL as an effective intervention for surface decontamination for produce environment. aBL causes microbial damage affecting multiple molecules in bacteria by production of reactive oxygen species (ROS). This phenomenon also prevents tolerance development in bacterial cells. More importantly, aBL is safe for humans, unlike ultraviolet (UV) irradiation. Hence, data obtained in this project will provide a foundational blueprint for the design of blue light LED arrays for potential scaling up and an ultimate outcome as identification of suitable intervention points for the application of aBL for anti-Listeria treatment in produce processing/packaging plants.