title: Enhancing the antibacterial effect of 461 and 521 nm light emitting diodes on selected foodborne pathogens in trypticase soy broth by acidic and alkaline pH conditions.
abstract: Light emitting diodes (LEDs) with their antibacterial effect present a novel method for food preservation. This effect may be influenced by environmental conditions such as the pH of the food contaminated by the pathogen. Thus, it is necessary to investigate the influence of pH on the antibacterial effect of LEDs before their application to real food matrices. Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in trypticase soy broth were illuminated using 10-W 461 (22.1 mW/cm(2)) and 521 nm (16 mW/cm(2)) LEDs at pH values of 4.5, 6.0, 7.3, 8.0 and 9.5 for 7.5 h at 15 °C. Using the 461 nm LEDs, the populations of E. coli O157:H7 decreased by 2.1 ± 0.02, 1.2 ± 0.08 and 4.1 ± 0.42 log CFU/ml at pH 4.5, 7.3 and 9.5 respectively, after a dosage of 596.7 J/cm(2). For L. monocytogenes, approximately a 5.8 ± 0.03 log reduction was observed after 238.7 J/cm(2) at pH 4.5 using the 461 nm LEDs, while the bacterial concentration was reduced by 1.8 ± 0.01 log at pH 9.5 after 596.7 J/cm(2). Bacterial inactivation using the 521 nm LEDs showed similar trends to the 461 nm LEDs at both acidic and alkaline pH conditions but with lower (1-2 log CFU/ml) reductions after 432 J/cm(2). Lower D-values were observed for L. monocytogenes when exposed to LEDs at acidic pH values, while the sensitivity of E. coli O157:H7 and S. Typhimurium to LED was markedly increased at an alkaline pH. Regardless of the pH at which the cultures were illuminated, the percentage of sublethal injury increased with the treatment time. These results highlight the enhanced antibacterial effect of the 461 nm LED under acidic and alkaline pH conditions, proving its potential to preserve foods as well as to have synergistic effect with acidic and alkaline antimicrobials.
authors: Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, 117543, Singapore.
authors: Vinayak
authors: V
authors: Ghate
authors: Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, 117543, Singapore.
authors: Ai Ling
authors: AL
authors: Leong
authors: Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, 117543, Singapore.
authors: Amit
authors: A
authors: Kumar
authors: Department of Food and Nutrition, Yeungnam University, 214-1 Dae-dong, Gyeongsan-si, Gyeongsangbuk-do, 712-749, South Korea.
authors: Woo Suk
authors: WS
authors: Bang
authors: Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, 117543, Singapore; National University of Singapore (Suzhou) Research Institute, No. 377 Linquan Street, Suzhou Industrial Park, Suzhou, Jiangsu, 215123, China.
authors: Weibiao
authors: W
authors: Zhou
authors: Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, 117543, Singapore; National University of Singapore (Suzhou) Research Institute, No. 377 Linquan Street, Suzhou Industrial Park, Suzhou, Jiangsu, 215123, China. Electronic address: chmyukhg@nus.edu.sg.
authors: Hyun-Gyun
authors: HG
authors: Yuk
mesh_terms: D002364:Caseins / Q000737:chemistry*; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000254:growth & development / Q000528:radiation effects*; D005514:Food Irradiation / Q000379:methods*; D005516:Food Microbiology; D008027:Light; D008089:Listeria monocytogenes / Q000254:growth & development / Q000528:radiation effects*; D011492:Protein Hydrolysates / Q000737:chemistry*; D012486:Salmonella typhimurium / Q000254:growth & development / Q000528:radiation effects*
chemical_list: D002364:Caseins; D011492:Protein Hydrolysates; C026375:trypticase-soy broth
keywords: Antibacterial effect; Foodborne pathogens; Light emitting diode; pH