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ARS Home » Northeast Area » Wyndmoor, Pennsylvania » Eastern Regional Research Center » Food Safety and Intervention Technologies Research » Research » Publications at this Location » Publication #320458
Title: Inhibition of enteric pathogens and surrogates using integrated, high intensity 405nm led light on the surface of almonds

Author
item Lacombe, Alison
item Niemira, Brendan
item Sites, Joseph
item Boyd, Glenn
item Gurtler, Joshua
item Tyrell, Breanna
item Fleck, Melissa

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary: Nuts are at risk for contamination by Escherichia coli O157:H7, Salmonella, and other foodborne pathogens. High-intensity light is an emerging technology for disinfecting this type of food. An LED (light-emitting diode) which emits only a single wavelength of high-intensity blue light was tested for its ability to inactivate the pathogens E. coli O157:H7 and Salmonella. It was also tested on E. coli K12 and a strain of Salmonella which has been attenuated (rendered harmless), both of which are non-pathogenic “surrogates”, often used in pilot-scale research where using live pathogens are impractical. Almonds were inoculated with high and low levels (8 or 5 colony forming units per g) of the various types of bacteria and treated with the blue light for 0, 60, 120, 240, 360, 480, or 600 seconds. Almonds were 7 cm from the LED lamp. While the almonds were being treated, cooling air was directed onto them at a rate of 4 cubic feet per minute, sourced through a container of dry ice. An infrared camera was used to monitor the temperature readings after each run. For the non-pathogenic surrogate E. coli K12, maximum reductions (compared to the untreated control) were 98.5% or 97.7% for “High” and “Low” inoculum levels, respectively. Maximum reductions for the pathogen E. coli O157:H7 were 99.6% and 96.3% for “High” and “Low” inoculum levels, respectively. Salmonella isolates were generally less sensitive overall. Attenuated Salmonella was reduced by up to 71.1% and 89.2%, while pathogenic Salmonella was reduced by up to 80.0% and 71.8% (“High” and “Low”, respectively for each). The minimum effective treatment time for all the bacteria tested ranged from 60 to 240 s. Temperatures remained below ambient throughout treatment. High-intensity blue light treatment doesn’t rely on heat as a mode of action, and is therefore a nonthermal process. These results indicated that the high-intensity blue light tested in this study may be an effective antimicrobial treatment for low-moisture foods contaminated with E. coli O157:H7, while applications for Salmonella contamination may be more limited.

Technical Abstract: The disinfecting properties of 405 nm light were investigated against Escherichia coli O157:H7, Salmonella, and their non-pathogenic surrogate bacteria on the surface of almonds. High intensity monochromatic blue light (MBL) was generated from an array of narrow-band 405 nm light-emitting diodes (LED). Almonds were inoculated with high and low level (8 or 5 CFU/g) E. coli O157:H7 and pathogenic Salmonella, as well as the non-pathogenic surrogates E. coli K-12 and an avirulent strain of Salmonella Typhimurium. Inoculated almonds were treated with 405 nm light for 0, 60, 120, 240, 360, 480, and 600 sec at a working distance of 7 cm. Simultaneous to treatment, cooling air was directed onto the almonds at a rate of 4 CFM, sourced through a container of dry ice. An infrared camera was used to monitor the temperature readings after each run. For E. coli K12, maximum reductions from untreated control were 1.85 or 1.63 log cfu/g for “High” and “Low” inoculum levels, respectively. Maximum reductions for E. coli O157:H7 were 2.44 and 1.44 log cfu/g for “High” and “Low” inoculum levels, respectively. Salmonella was generally less sensitive overall. Attenuated Salmonella was reduced by up to 0.54 and 0.97 log cfu/g, while pathogenic Salmonella was reduced by up to 0.70 and 0.55 log cfu/g (“High” and “Low”, respectively for each). Minimum effective treatment time ranged from 60 to 240 s. Temperatures remained below ambient throughout treatment, indicating MBL as a nonthermal process. These results indicated that MBL may be an effective antimicrobial treatment for low-moisture foods contaminated with E. coli O157:H7, while applications for Salmonella contamination may be more limited.