Previous physicochemical stress exposures influence subsequent resistance of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes to ultraviolet-C in coconut liquid endosperm beverage.
This study investigated the influences of prior exposures to common physicochemical stresses encountered by microorganisms in food and food processing ecologies such as acidity, desiccation, and their combinations, on their subsequent susceptibility towards UV-C treatment in coconut liquid endosperm beverage. Cocktails of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes were separately subjected to gradually acidifying environment (final pH 4.46), exposed to abrupt desiccation by suspension in saturated NaCl solution (aw=0.85) for 4, 8, and 24h, and sequential acidic and desiccated stresses before suspending in the coconut beverage for UV-C challenge. The exposure times (D) and UV-C energy dose values (DUV-C) necessary to reduce 90% of the population of the different test organisms varied with previous exposures to different sublethal stresses, indicating possible influence of implicit microbial factors towards resistance to UV-C. All tested individual and combined stresses resulted in increased resistance, albeit some were not statistically significant. Non-stressed cells had D values of 3.2-3.5s, and corresponding DUV-C values of 8.4-9.1 mJ/cm(2). Cells exposed to previous acid stress had D values of 4.1-4.8s and corresponding DUV-C values of 10.7-12.5 mJ/cm(2). Prior exposure to desiccation resulted in D values of 5.6-7.9s and DUV-C values of 14.7-20.6 mJ/cm(2), while exposure to combined acid and desiccation stresses resulted in D values of 6.1-8.1s and DUV-C values of 15.9-21.0 mJ/cm(2). The D and DUV-C values of S. enterica after previous exposure to sequential acid (24 h) and desiccation (24 h) stresses were found significantly greatest, making the organism and physiological state an appropriate reference organism for the establishment of UV-C pasteurization process for the beverage.
Department of Food Science and Nutrition, College of Home Economics, Alonso Hall, A. Ma. Regidor Street, University of the Philippines Diliman, 1101 Quezon City, Philippines. Electronic address: alonzo.gabriel@gmail.com.
Alonzo A
AA
Gabriel
D000222:Adaptation, Physiological / Q000528:radiation effects; D001628:Beverages / Q000382:microbiology*; D003059:Cocos / Q000382:microbiology; D056625:Endosperm / Q000378:metabolism / Q000382:microbiology; D019453:Escherichia coli O157 / Q000502:physiology / Q000528:radiation effects*; D005511:Food Handling; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000502:physiology / Q000528:radiation effects*; D050296:Microbial Viability; D019779:Salmonella enterica / Q000502:physiology / Q000528:radiation effects*; D013312:Stress, Physiological; D014466:Ultraviolet Rays
Coconut beverage; Non-thermal food processing; Pasteurization; Stress adaptation; Ultraviolet radiation