Table 3.

The antimicrobial efficacy of LED in liquid system

Tested food product	LED used	Tested microorganisms	Quality and mode of action	Major findings	References
Suspension in suitable buffers	UV-A LED (365 nm); working distance, 20 mm	E. coli DH5α, Enteropathogenic E. coli, Vibrio parahaemolyticus, Staphylococcus aureus, and Salmonella enterica serovar Enteritidis		3.9 log reduction in E. coli DH5α with 54 J/cm2 dose; the inactivation was higher at the illumination temperature of 20 °C and pH 8 and varied for different bacterial species	Mori et al. [85]
Suspension in PBS	UV-A LED (365 nm); maximum current of one diode was 0.5 A, the voltage was 4.5 V; intensity was 70 mW/cm2, working distance, 2 cm	E. coli DH5α, Enteropathogenic E. coli, Vibrio parahaemolyticus, Staphylococcus aureus and Salmonella enterica serovar Enteritidis	Oxidative DNA damage observed (2.6 folds higher 8-OHdG formation); involvement of ROS like OH− and H2O2 observed in the LED inactivation effect	E. coli DH5α, Enteropathogenic E. coli, Vibrio parahaemolyticus, Staphylococcus aureus were reduced by > 5 log CFU/ml by 75 min treatment with 315 J/cm2 dose; Salmonella was reduced by > 4 log CFU/ml with 672 J/cm2 dose for 160 min with UV-A LED	Hamamoto et al. [39]
Ultrapure water, nutrient water and nutrient water with humic acids	UV LEDs (269 and 276 nm); sample volume 25 ml with stirring	E. coli K12		3 to 4 log CFU/cm3 reduction observed; presence of humic acids and turbidity affected the UV irradiation and inactivation caused; 269 nm LED was more effective	Vilhunen, Särkkä and Sillanpää [126]
Bacterial suspension in PBS	265 nm LEDs; placed over a 6.5 mm wide aluminum channel 1 mm above the water surface; water depth, 7 mm; treatment dose, 0 to 20 mJ/cm2	E. coli K12		> 3 log CFU/ml reduction with 20 mJ/cm2 dose of UV LED treatment	Chatterley and Linden [17]
Bacterial suspension in appropriate buffers	255, 280, 365, and 405 nm LEDs; pH tested, 6 and 8; treatment times, 60, 120 and 180 s	3 strains of E. coli and 2 strains of E. faecalis	pH did not show any significant effect	280/365 and 280/405 nm combination of LED treatment were most effective for bactericidal effect; 20 h after the UV irradiation all the tested samples showed 7 log reduction in all treated strains	Chevremont et al. [21]
Bacterial suspension in deionized water	269 and 282 nm LEDs	Bacillus subtilis		269 nm LED produced better germicidal effect than 282 nm LED treatment	Rtele et al. [129]
Water samples from tertiary effluent from the City of Regina wastewater treatment plant (WWTP) and bacterial suspension in suitable broth	260 nm UV LEDs	E. coli ATCC 25922		High turbidity of WWTP resulted in inconsistent effect; 1–2.5 log reduction obtained with 20 and 50 min treatment in a time dependent manner	Nelson et al. [91]
Bacterial suspension in PBS	UV LEDs emitting wavelengths 265, 280 and 310 nm; 0.7, 1.3 and 1.1 mW output power, respectively; used for treatment individually and in combinations	E. coli K12		310 nm LED showed least antibacterial effect in batch system; 265 and 280 nm LEDs produced ~ 4 log reduction in both batch and flow-through system with dose of 10.8 and 13.8, and 16.4 and 25.5 mJ/cm2, respectively	Oguma et al. [92]
Bacterial suspension in 0.9% saline solution	UV-C LED (281.8 nm); Glass tube (quartz) and soda lime glass; 9 ml of bacterial suspension; treatment times, 10, 40, and 90 s; doses, 8.64, 34.59, and 77.82 mJ/cm2	Escherichia coli DSM 498 and Bacillus subtilis DSM 402		Quartz glass had better transmittance of light; B. subtilis was reduced by 1.04 (soda lime glass) and 1.79 log CFU/ml (quartz glass) and, E. coli was reduced by 1.85 (soda lime glass) and 2.8 log CFU/ml (quartz glass) with 90s treatment; mixing of the samples improved the inactivation	Gross et al. [37]
Bacterial suspension in appropriate buffer	260 nm (UV) LEDs and low pressure UV lamp	Escherichia coli B, a non-enveloped virus (MS-2), and a bacterial spore Bacillus atrophaeus		Comparable inactivation efficacy for E. coli B and MS-2; LED produced better inactivation for Bacillus atrophaeus; dose required for 4 log reductions for UV LEDs were as follows: E. coli B, 6.2 mJ/cm2; MS-2, 58 mJ/cm2, and B. atrophaeus, 18.7 mJ/cm2	Sholtes et al. [114]
Bacterial suspension in 0.05 M NaCl	Semi-commercial LED arrays (270–740 nm); treatment time, 6 h	Escherichia coli K12 ATCC W3110 and Enterococcus faecalis ATCC 19433		270, 365, 385, and 405 nm arrays produced > 5 log10 reduction; 430 and 455 nm LED arrays resulted in ≈ 4.2 and 2.3-log10 reduction in E. coli and E. faecalis cell counts; 310 nm produced insufficient disinfection doe commercial application; 525, 590, 623, 660, and 740 nm arrays produced insignificant disinfection	Lui et al. [76]
	Four UV-LED units emitting wavelengths 265, 280 nm, the combination of 265/280 (50%), and 265/280 (75%)	E. coli	Photoreactivation and dark repair decreased in case of 280 nm LED treatment	265 nm LED resulted in the maximum inactivation	Li et al. [70]
Microbes in appropriate buffers	UV-C LED emitting 260 and 280 nm LED and 260/280 nm combination used for treatment	Escherichia coli, MS2 coliphage, human adenovirus type 2 (HAdV2), and Bacillus pumilus spores	DNA and RNA damage observed for individual LED treatments	Over 3 log reduction observed in E. coli with all UV LEDs; 260 nm LED was most effective in the inactivation of MS2 coliphage; A dose of 122, 89, and 105 mJ/cm2 of 260, 280, and 260/280 nm LEDs required for 4-log reduction; 260 and 260/280 nm LED more effective for B. pumilis inactivation	Beck et al. [9]
Real wastewater samples and suspension in laboratory water	UV LED (265 nm); sample volume, 50 ml; frequency tested, 0.1, 1, 10, 100, 1 kHz; duty rate-10, 25, 50, 75, 90%	E. coli ATCC 11229, coliphage MS2 ATCC 15597-B1		No significant difference in the microbial inactivation observed between continuous and pulsed LED treatments	Song, Taghipour and Mohseni [119]
Dechlorinated tap water	UV LED (285 nm)	Heterotrophic plate count (HPC)		UV LED treatment showed decreased HPC for 5 days storage; Methylobacterium species was UV resistant	Oguma et al. [94]
Bacterial suspension in sterile distilled water	UV-A (365 nm) and UV-C (265 nm) LEDs; treatment times, 20 or 30 min (UV-A) and 5–16 min (UV-C); sample volume, 15 ml	E. coli (ATCC 25922, ATCC 700891, ATCC 15597, and ATCC 700891)	UVA pre-radiation showed: Insignificant effect in photo repair of bacteria; suppressed dark repair; no role of hydroxyl radical in the inactivation; improved CPD formation only in E. coli ATCC 15597	Synergistic effect of UV-A and UV-C was effective for E. coli (ATCC 11229, ATCC 15597, and ATCC 700891)	Xiao et al. [131]
Microbes in appropriate buffers	UV LEDs (265, 280, and 300 nm)	Pseudomonas aeruginosa and Legionella pneumophila, E. coli, Bacillus subtilis spores, and bacteriophage Qb		Energy consumption was least for 280 nm LED for 3 log reduction; linear curve observed for L. pneumophila and bacteriophage Qb; sigmoidal curve observed for E. coli, P. aeruginosa, and B. subtilis spores	Rattanakul and Oguma [107]
UHT skim milk (< 0.5% fat)	405 (NUV-Vis), 433 and 460 nm (blue) LEDs; illumination temperature, 5–15 °C; treatment time, 0–90 min	E. coli ATCC 25922	No significant effect on physicochemical properties of the LED treated milk	Highest inactivation at higher temperature and lower wavelengths; 406 nm LED treatment at 13.8 °C for 37.83 min can yield 5 log reduction with minimal color change	Srimagal, Ramesh and Sahu [120]
Clear and cloudy apple juice	Four UV LEDs emitting wavelengths 254, 280, 365 and 405 nm; working distance, 1 cm; sample volume, 3 ml	E. coli K12 (ATCC 25253)	Highest inactivation of PPO enzyme obtained by 280/365 and 280/405 nm LED treatment; lowest color difference observed with 280/365 nm LED combination	UV LEDs most effective in clear apple juice; highest inactivation in cloudy apple was ~ 2 log CFU/ml by 280 nm and 280/365 nm LEDs; 280 nm LED produced 4.4 log reduction in clear apple juice	Akgün and Ünlütürk [2]
Colored beverages and two different commercially available orange juices (A and B)	UV-A LED (365 nm); intensity, 70 mW/cm2; coloring pigment concentrations, 0.001, 0.01, 0.1, and 1.0%; treatment time, 30 min; dose, 126 J/cm2	E. coli DH5α	Increasing the concentration of coloring agents decreased the antibacterial effect	Maximum log reduction was 1.75 log CFU/ml in the beverage containing 0.001% β carotene; orange juices (A and B) showed 0.35 and 1.58 log reduction, respectively	Lian et al. [74]
Orange juice	Blue (460 nm) LED; irradiances used, 92, 147.7, and 254.7 mW/cm2; illumination temperatures, 4, 12, and 20 °C	Cocktail of Salmonella enterica serovars Gaminara, Montevideo, Newport, Typhimurium, and Saintpaul	Significant color changes observed	2–5 log reduction observed in Salmonella cocktail; best treatment conditions obtained was an irradiance of 92 mW/cm2 for 13.58 h corresponding to dose of 4500 J/cm2 at 12 °C	Ghate et al. [35]