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Thesis Wenbo Yang FABE.pdf (5.33 MB)

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Effect of Chlorine Dioxide Gas Treatment on Bacterial Inactivation Inoculated on Spinach Leaves and on Pigment Content

Yang, Wenbo, Ms.
http://rave.ohiolink.edu/etdc/view?acc_num=osu1429609779

Abstract Details

2015, Master of Science, Ohio State University, Food, Agricultural and Biological Engineering.
Leafy green vegetables are gaining popularity due to the health benefit. However, the safety of fresh produce has been a major issue in recent years. So the elimination of microorganisms during the post-harvesting processing is significant. As a strong oxidizing agent, chlorine dioxide (ClO2) gas is an effective sanitizer for reducing bacteria on fresh produce. However, gaseous chlorine dioxide usually causes both the inactivation of bacteria and color damage of leafy greens. Consumers desire safe and high quality fresh produce with long shelf-life. Therefore, optimizing the conditions including ClO2 concentration and exposure time is critical. The effect of gaseous ClO2 at concentrations 2.05, 3.10, 4.73, and 5.86 mg/L on inactivating E. coli K-12 inoculated on spinach leaves were determined in this study. The inactivation of E. coli O157:H7 by ClO2 treatments with concentration 2.05 mg/L and exposure time 12 and 20 min was also studied. A kinetic model describing the inactivation of E. coli K-12 as a function of time and ClO2 concentration was developed. The morphological changes of inoculated bacteria caused by ClO2 treatment were obtained using scanning electron microscopy (SEM). The fresh spinach was dip-inoculated with E. coli K-12 resistant to nalidixic acid. After ClO2 treatments, the populations of survived bacteria were determined by plate counting and the survival ratios of bacteria, N(t)/N0, were calculated as a function of time. Two models were fitted to N(t)/N0 data. A semi-logarithmic survival model, log[N(t)/N0] =-k(C)t, with sanitizer concentration dependence k= k0 eP C was compared to the Weibull model, log [N(t)/N0] =-b(C) tn(C), with concentration dependence b(C) = a + g C. The optimal value of parameters in two models were obtained by using Matlab. Log reduction as high as 2.79 log CFU/g was achieved by the treatment with ClO2 concentration of 4.73 mg/L and exposure time of 14min. Weibull model was showed to describe the bacterial inactivation kinetics by gaseous ClO2 more accurately (R2=0.950) compared with semi-logarithmic survival (R2=0.188). The Weibull model parameter, n, was less than 1 for the inactivation of E. coli K-12 inoculated on spinach leaves, indicating an upward concavity of survival curve. This result suggested an increased resistance of remaining E. coli K-12 cells. The Weibull model parameter, b, which is relevant to the rate of inactivating bacteria, was shown to depend on the concentration of gaseous ClO2 linearly, which indicated that the inactivation rate increased with the increasing of ClO2 concentration. According to SEM photomicrographs, E. coli K-12 cells tend to attach natural crevices and junctions between leaf cells. SEM images also showed that the bacterial cells exhibited deformation and possible lysis after ClO2 treatment. Chlorophylls and carotenoids are important for leafy greens attributed to the contribution to the appearance and nutritional benefit. The fully extraction of these photosynthetic pigments and suitable quantitative analysis method are significant for determining the pigment content of leafy greens. This study determined that compared to 80% acetone, 100% acetone is more effective for extracting chlorophylls and carotenoids from spinach leaves, especially for the less polar pigment chlorophyll a. The ratio of (sample mass/acetone volume) for the extracting pigments from normal fresh spinach leaves using 100% acetone can be as high as 30mg/ml. According to the results of stability test of the pigment extract, applying liquid nitrogen may increase the stability of the extract. Transferring the clear supernatant to clean centrifuge tubes may result in more accurate quantitative results of pigment content if the extract has to be stored. The study of the effectiveness of gaseous ClO2 on pigment content indicated that the ratio of (chlorophyll content/carotenoid content) did not show obvious change with the increasing of exposure time, though apparent color damage was observed after ClO2 treatment. The kinetic study of the pigment degradation showed that the degradation of chlorophylls and carotenoids in spinach during ClO2 treatment with concentration 4.73 mg/L follows first-order kinetic model. The kinetic plots based on the quantitative results of UV-VIS analysis indicated that the rate constants for chlorophyll and carotenoid degradation were similar during the treatment, and the plots of normalized peak area of every pigment detected by HPLC showed that carotenoids degraded faster than chlorophylls. This results may explain that the ratio of (chlorophyll content/carotenoid content) kept consistent.
Kaletunc Gonul, Dr. (Advisor)
211 p.
Agricultural Engineering
gaseous chlorine dioxide, Weibull model, semi-log survival model, chlorophylls, carotenoids

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Citations

  • Yang, W. (2015). Effect of Chlorine Dioxide Gas Treatment on Bacterial Inactivation Inoculated on Spinach Leaves and on Pigment Content [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429609779

    APA Style (7th edition)

  • Yang, Wenbo. Effect of Chlorine Dioxide Gas Treatment on Bacterial Inactivation Inoculated on Spinach Leaves and on Pigment Content. 2015. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1429609779.

    MLA Style (8th edition)

  • Yang, Wenbo. "Effect of Chlorine Dioxide Gas Treatment on Bacterial Inactivation Inoculated on Spinach Leaves and on Pigment Content." Master's thesis, Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429609779

    Chicago Manual of Style (17th edition)

osu1429609779
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© 2015, some rights reserved.Creative Commons License Effect of Chlorine Dioxide Gas Treatment on Bacterial Inactivation Inoculated on Spinach Leaves and on Pigment Content by Wenbo Yang Ms. is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by The Ohio State University and OhioLINK.
Release 3.2.12