title: Enhanced Antimicrobial Activity Based on a Synergistic Combination of Sublethal Levels of Stresses Induced by UV-A Light and Organic Acids.
abstract: The reduction of microbial load in food and water systems is critical for their safety and shelf life. Conventionally, physical processes such as heat or light are used for the rapid inactivation of microbes, while natural compounds such as lactic acid may be used as preservatives after the initial physical process. This study demonstrates the enhanced and rapid inactivation of bacteria based on a synergistic combination of sublethal levels of stresses induced by UV-A light and two food-grade organic acids. A reduction of 4.7 ± 0.5 log CFU/ml inEscherichia coliO157:H7 was observed using a synergistic combination of UV-A light, gallic acid (GA), and lactic acid (LA), while the individual treatments and the combination of individual organic acids with UV-A light resulted in a reduction of less than 1 log CFU/ml. Enhanced inactivation of bacteria on the surfaces of lettuce and spinach leaves was also observed based on the synergistic combination. Mechanistic investigations suggested that the treatment with a synergistic combination of GA plus LA plus UV-A (GA+LA+UV-A) resulted in significant increases in membrane permeability and intracellular thiol oxidation and affected the metabolic machinery ofE. coliIn addition, the antimicrobial activity of the synergistic combination of GA+LA+UV-A was effective only against metabolically activeE. coliO157:H7. In summary, this study illustrates the potential of simultaneously using a combination of sublethal concentrations of natural antimicrobials and a low level of physical stress in the form of UV-A light to inactivate bacteria in water and food systems.IMPORTANCEThere is a critical unmet need to improve the microbial safety of the food supply, while retaining optimal nutritional and sensory properties of food. Furthermore, there is a need to develop novel technologies that can reduce the impact of food processing operations on energy and water resources. Conventionally, physical processes such as heat and light are used for inactivating microbes in food products, but these processes often significantly reduce the sensory and nutritional properties of food and are highly energy intensive. This study demonstrates that the combination of two natural food-grade antimicrobial agents with a sublethal level of physical stress in the form of UV-A light can greatly increase microbial load inactivation. In addition, this report elucidates the potential mechanisms for this synergistic interaction among physical and chemical stresses. Overall, these results provide a novel approach to develop antimicrobial solutions for food and water systems.
authors.affiliation: Department of Food Science and Technology, University of California, Davis, Davis, California, USA.|CAPES Foundation, Ministry of Education of Brazil, Brasilia, Brazil.
authors.forename: Erick F
authors.identifier: http://orcid.org/0000-0002-5444-1202
authors.initials: EF
authors.lastname: de Oliveira
authors.affiliation: Department of Food Science and Technology, University of California, Davis, Davis, California, USA.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cossu
authors.affiliation: Department of Nutrition and Food Science, University of Maryland, College Park, Maryland, USA.
authors.forename: Rohan V
authors.initials: RV
authors.lastname: Tikekar
authors.affiliation: Department of Food Science and Technology, University of California, Davis, Davis, California, USA nnitin@ucdavis.edu.|Department of Biological and Agricultural Engineering, University of California, Davis, Davis, California, USA.
authors.forename: Nitin
authors.initials: N
authors.lastname: Nitin
mesh_terms: D019453:Escherichia coli O157 / Q000187:drug effects* / Q000254:growth & development / Q000528:radiation effects*; D005506:Food Contamination / Q000032:analysis / Q000517:prevention & control; D005519:Food Preservation / Q000295:instrumentation / Q000379:methods*; D005707:Gallic Acid / Q000494:pharmacology*; D019344:Lactic Acid / Q000494:pharmacology*; D018545:Lactuca / Q000382:microbiology; D018724:Spinacia oleracea / Q000382:microbiology; D014466:Ultraviolet Rays
chemical_list: D019344:Lactic Acid; D005707:Gallic Acid
keywords: UV-A light; food-grade antimicrobial; gallic acid; lactic acid; microbial inactivation; sublethal stress; synergism