Elimination of salmonella typhimurium and escherichia coli on leafy vegetables by using ozone microbubbles

Name: Asama Phaephiphat

LCSH: Kasetsart University -- Theses. M.S. (Food Science) 2017

Classification :.DDC: TP443

LCSH: Kasetsart University. Department of Food Science and Technology -- Theses

LCSH: Microbubbles -- Utilization

LCSH: Food contamination

LCSH: Salmonella typhimurium

LCSH: Escherichia coli

Abstract: The effectiveness of microbubbles technology in washing process to decontaminate microorganisms in vegetables was investigated. Morning glory, lettuce and ginger were used as the representative for the smooth, wrinkle and root vegetable, respectively. The effect of microbubbles combined with sodium hypochlorite (NaOCl) on reducing microorganisms was conducted. The highest microbial reduction in washing process among these three vegetables was with 80 mg/L NaOCl. Total microbial counts on surface of morning glory, lettuce and ginger were reduced by 1.7 (97.5%), 2.4 (99.6%) and 1.5 (97.0%) log CFU/ml, respectively. Meanwhile, using microbubbles alone performed less microbial reduction by 0.5-0.6 log CFU/ml or 70%. Optimization of the washing condition was examined by using sweet basil as a vegetable sample due to the incidence of pathogen contamination in exported vegetables from Thailand in years 2012 to 2017. Inoculated S. Typhimurium on sweet basil were washed with various treatments, 30 and 10°C of wash water (tap water, microbubbles water (MB) and ozone microbubbles water (OMB) (0.5, 1.0 and 2.0 mg/L)), for 2, 5 and 7 min by shaking at 60 rpm. The highest on reduction of S. Typhimurium was obtained when washing for 7 min, which were 2.58 and 2.20 log CFU/g for 1.0 mg/L OMB at 30°C and 2.0 mg/L OMB at 10°C, respectively. Washing with microbubbles alone showed similar result on bacterial reduction compared with tap water at both temperatures. However, the greater results on bacterial reduction were observed when washing with microbubbles combined with ozone. Bacterial reduction varied from 1.68-2.58 log CFU/g (97.9-99.7%). Washing inoculated sweet basil with low initial load (4 log CFU/g) of S. Typhimurium and E. coli were conducted by using MB, OMB, NaOCl (50 and 100 mg/L). The populations of S. Typhimurium and E. coli reduced 1.94-4.17 and 1.01-2.05 log CFU/g, respectively. Using OMB as an alternative sanitizer, instead of chemical agents such as NaOCl, could be implemented in the washing step to enhance the safety of fresh vegetable production. Moreover, to understand the inactivation mechanism of sanitizers on bacterial cells, attachment and microstructure of bacterial cells on sweet basil and in suspension after exposed to sanitizers were observed by using Scanning Electron Microscope (SEM). Micrographs revealed that microbubbles has no bactericidal effect. However, microbubbles could help to remove contaminants on leaf surface. Bacterial cells lysis was achieved when using OMB and NaOCl. Lastly, this study demonstrates that using tap water to generate microbubbles cannot achieve the general requirement for microbiological safety. Thus, sanitizing agents should be applied in the washing process to improve microbiological quality of these vegetables.

Kasetsart University. Office of the University Library

Address: Bangkok

Email: tdckulib@ku.ac.th

Name: Warapa Mahakarnchanakul

Role: Thesis Advisor

Name: Kullanart Tongkhao

Role: Thesis Co-Advisor

Name: Kriskamol Na Jom

Role: Thesis Co-Advisor

Created: 2017

Modified: 2023-06-15

Issued: 2023-06-15

วิทยานิพนธ์/Thesis

application/pdf

URL: https://kasetsart.idm.oclc.org/login?url=https://www.lib.ku.ac.th/KUthesis/2560/asama-pha-all.pdf

CallNumber: TP443.A83

eng

DegreeName: Master of Science

Level: Master's Degree

Descipline: Food Science

Grantor: Kasetsart University

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