Pulsed UV laser light on Escherichia coli and Saccharomyces cerevisiae suspended in non-alcoholic beer

BACKGROUND The aim of this study was to investigate the effect of pulsed ultra-violet (UV) irradiation on inactivation of beer spoilage microorganisms. UV irradiation is nowadays cost effective enough to compete with traditional biological, physical, and chemical treatment technologies and has become an alternative to such methods. MATERIAL AND METHODS Photoinactivation effects of pulsed UV laser with the wavelengths of 355 and 266 nm, which inactivate typical prokaryotic (Escherichia coli) and eukaryotic (Saccharomyces cerevisiae) microorganisms, were examined with different doses and exposure times. RESULTS A dose of 100 J/cm(2) of the 355 nm pulsed UV laser was able to reduce about 1 to 2 log (88.75%) of E.coli with the population of 1.6×10(8) colony-forming units (CFU/ml), and 97% of 3.2×10(7), 3×10(6), 5.5×10(5), and 9×10(4) CFU/ml. In the case of 266 nm, more than 99% reduction in E. coli serial dilutions was inactivated, using 10 J/cm(2) with exception of 7×10(4) CFU/ml which was not detected any bacterial growth using 5 J/cm2. In addition, 50, 40, and 20 J/cm(2) energy were used successfully to inactivate S. cerevisiae at the populations of 5.4×10(6), 7×10(5), 5×10(4) and 4×10(3) CFU/ml, respectively. As a result, pulsed UV Laser with 266 nm was strong enough to inactivate a high titer of bacterial and yeast indicator standards suspended in non-alcoholic beer in comparison with 355nm doses. CONCLUSION Results indicate that pulsed UV technology, in principle, is an attractive alternative to conventional methods for the inactivation of indicator microorganisms and has potential in irradiation of unpasteurized beer.