Ruengvisesh, Songsirin (2016-04). Inhibition of Bacterial Foodborne Pathogens on the Surfaces of Fresh Produce Using Plant-Derived Antimicrobial Essential Oils in Surfactant Micelles. Doctoral Dissertation.
Thesis
This research was undertaken to: i) quantify numbers of native microbiota on leafy greens, jalapeno peppers, tomatoes, and cantaloupes; ii) study internalization in fresh produce with and without aid of temperature and pressure differential; iii) formulate essential oil component (EOC)-containing nano-micelles and analyze rheological and loading characteristics of particles; iv) identify the minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) of antimicrobial essential oil-containing micelles against Escherichia coli O157:H7 and Salmonella enterica serotype Saintpaul; and v) determine inactivation efficacy of EOC-containing micelles and other antimicrobial agents against E. coli O157:H7, S. Saintpaul, and epiphytic microbiota on surfaces of fresh produce. Numbers of native microbiota on leafy greens obtained from South Texas in spring harvest seasons ranged from 0.7+-0.0 to 6.2+-0.1 log10 CFU/g. Higher counts of certain microbial groupings were observed with leafy green samples collected at higher ambient temperature. Native microbiota on surfaces of jalapeno pepper, tomato, and cantaloupe obtained from spring and fall harvest seasons were in the range of 0.2+-0.0 to 3.9+-0.7 log10 CFU/cm^2 , 0.2+-0.0 to 3.8+-0.9 log10 CFU/cm^2 , and 1.1+-1.3 to 6.0+-0.8 log10 CFU/cm^2 , respectively. In general, stem scars of tomato and cantaloupe bore greater counts of native microbiota versus skins/rinds. Dye penetration in intact and non-intact tomatoes with aid of temperature and pressure differential was 1.71+-1.36 cm and 0.10+-0.06 cm, respectively. The study of microbial internalization without aid of temperature and pressure differential showed that internalization of E. coli K12 occurred through stem scar channels; however, E. coli K12 was unable to travel deeply in the stem. The study of maximum additive concentration (MAC) of EOCs in surfactant micelles showed that sodium dodecyl sulfate (SDS) possessed the highest encapsulation efficiency among all tested surfactants. Carvacrol and eugenol encapsulated in SDS and CytoGuard LA20 (CG) micelles were most effective for pathogen inhibition in microbroth assay. In produce commodities, overall, encapsulated eugenol, free eugenol, chlorine, and empty micelles were similarly effective in reducing pathogens and native microbiota on tomato surfaces at 5 ?C during 10 days of storage. At 15 ?C, empty micelles were less effective than other antimicrobial treatments in reducing pathogens on tomato surfaces. Compared to encapsulated eugenol, free eugenol and empty micelles, decreased antifungal effect of chlorine was also observed at 15 ?C in tomatoes. For spinach, encapsulated eugenol, free eugenol, and chlorine seemed to be similarly effective in reducing pathogen levels and were more effective than empty micelles and water at 5 and 15 ?C. Overall, encapsulated eugenol and free eugenol were more effective than other treatments in reducing levels of aerobic bacteria and Enterobacteriaceae during storage at 5 and 15 ?C. Excepting water, antifungal effects of all treatments did not differ during the entire storage period. The study suggests EOCloaded micelles could be used as an alternative to conventional intervention methods for decontamination of fresh produce as well as increasing shelf life of fresh produce.
