3.3. Bacterial stacking structure analysisFig. 4 shows topographical images of inoculated bacterial suspensions (10μl) observed at the same magnification on various food contact surfaces for qualitative analysis by using NanoMap software. Among the surfaces, glass showed the lowest height of bacterial stacking structure from the basis line and silicon had the greatest height. As hydrophobicity increased, which produced a greater droplet height of inoculated bacterial suspension, higher bacterial structures were observed. Also, thetotal maximum heights ofthesurfaces above the meanline (Rp) are presented in Table 3. As hydrophobicity increased, Rp values increased in ascending order of hydrophobicity. The Rp value of silicon was approximately 47μm, which was the highest observed, and 6μm was measured for that of the glass surface, which was shown to be the lowest. Rp values of silicon, Teflon, and SUS No.4 were not significantly different (P > 0.05) when all the five surfaces were analyzed by the Statistical Analysis System (SAS). However, when Rp values were analyzed for two surfaces at a time using SAS, significant differences were observed among silicon, Teflon, and SUS No.4.3.4. Bactericidal effect of mild heat and UVC LED combination treatmentFig. 5 shows the bactericidal effect of UVC LED and mild heat combination treatments on the five material surfaces at the designated dosages; 1mJ/cm2 for E. coli O157:H7 and 2mJ/cm2 for S. Typhimurium and L. monocytogenes. Mild heat treatment alone resulted in approximately less than 0.5 log reductions of foodborne pathogens on all coupon surfaces, and UVC LED treatments achieved 1 to 1.5 log reductions. The synergistic bactericidal effect was observed when mild heat and UVC LED combination treatments were applied to L. monocytogenes on abiotic material surfaces, so that further 0.5 to 1.5 log reductions were achieved. Approximately 2 log reductions of L. monocytogenes were achieved on all surfaces, except for silicon, when treated with mild heat and UVC LEDs, while 1 log reductions of the same pathogen were observed when treated only with UVC LEDs. However, for E. coli O157:H7 and S. Typhimurium, only the additive effect of