Assessment of interplay between UV wavelengths, material surfaces and food residues in open surface hygiene validation.

The use of UV-visible radiation for detecting invisible residue on different surfaces as a means of validating cleanliness was investigated. Wavelengths at 365, 395, 435, 445, 470 and 490 nm from a monochromator were used to detect residues of beef, chicken, apple, mango and skim milk. These were on three surfaces: aluminium, fibre re-enforced plastic (FRP; Q-Liner®) and stainless steel, pre- and post a cleaning step using commercial detergent. The area covered by residues as detected by specific wavelengths was compared statistically. The sensitivity of the wavelengths for detection differed significantly (p < 0.05) for various residues depending on the material surfaces. Generally, wavelengths 365-445 nm were consistently able to illuminate all residue before cleaning, though sensitivity varied, while 490 nm showed more of the surface structural features instead of residue. The 365-395 nm wavelengths were significantly more sensitive (p < 0.05) for detecting beef and chicken residues on aluminium and stainless steel both before and after cleaning. The 435-445 nm wavelengths were significantly more sensitive for detecting apple and mango residues on the FRP both before and after cleaning. It is important when UV-systems are used as real-time tools for assessing cleanliness of surfaces that the surface materials being illuminated are taken into account in the choice of lamp wavelength, in addition to expected residue. This will ensure higher confidence in results during the use of UV-light for real-time hygiene validation of surfaces.