Inactivation of Salmonella spp. in wheat flour by 395 nm pulsed light emitting diode (LED) treatment and the related functional and structural changes of gluten

Salmonella spp. is one of the top foodborne pathogens associated with low-moisture foods and they exhibit significant resistance to conventional thermal treatments. UV light pulses emitted from light emitting diode (LED) has shown antimicrobial potential in high-moisture foods and water. However, limited information is available about the antimicrobial potential of UV light with different wavelengths, including 395 nm in low-moisture foods. The objectives of this study were to investigate the antimicrobial potential of 395 nm pulsed LED light in wheat flour and the resulting quality changes. This study demonstrated a maximum 2.91 log reduction of Salmonella cocktail in wheat flour treated with 395 nm pulsed LED for 60 min in a semi-closed system. Oxidation occurred in wheat flour after 30 and 60 min exposure to the 395 nm LED, which subsequently led to bleaching, and polymerization of gluten components through disulphide linkage. The water holding capacity of gluten was reduced by oxidation, and the contents of secondary structures were altered significantly after pulsed LED treatment, but the rheological properties were not deteriorated. The disulfide bond formation naturally happens during dough formation and the oxidation triggered by pulsed LED treatment may play a role on accelerating this process. The 395 nm pulsed LED treatment could be a promising decontamination technology for wheat flour with an additional benefit of bleaching of the flour without chemicals. Industrial relevance: A number of foodborne outbreaks and recalls have been related to low-moisture foods in these decades and recently several outbreaks were reported due to the occurrence of Salmonella in wheat flour. However, it is difficult to solve this problem through conventional thermal approaches because of the increased thermal resistance of Salmonella at low water activity environment. The emerging LED light source can produce light with monochromatic wavelengths without the use of mercury vapor lamps. It also has high durability, low heat generation, and is relatively easy to be adapted in an existing production line. Therefore, there is a great potential of using certain UV wavelengths emitted from LED to disinfect the low-moisture foods in food industries. To the best of our knowledge, no research was conducted on decontamination of wheat flour by using LEDs and only limited studies are available on the influence of pulsed LED treatment on food quality. The aim of this study was to explore the possibility of using 395 nm pulsed LED treatment as a novel tool for decontamination of Salmonella in a low-moisture food product (wheat flour) with industrial feasibility, and investigate the influence of the pulsed LED treatment on quality changes in the product.