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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Food Science

Year Degree Awarded

2018

Month Degree Awarded

May

First Advisor

Lili He

Subject Categories

Food Chemistry

Abstract

Understanding of the behavior and fate of pesticides in fresh produce is of great significance for effectively applying pesticides and minimizing pesticide residues in food. There is lack, however, of an effective method that can monitor and characterize pesticide behaviors including penetration, persistence and translocation. Herein, we developed a novel method for real-time and in situ monitoring of pesticide behaviors in fresh produce based on surface-enhanced Raman scattering (SERS) mapping method. Taking advantage of penetrative gold nanoparticles as probes to enhance the internalized pesticide signals, the internal signals from pesticides were successfully obtained in situ. We found that systemic pesticides (e.g. thiabendazole and acetamiprid) penetrated more rapidly and deeply into fresh produce (e.g. apple, grape and spinach) than non-systemic pesticides (e.g. ferbam and phosmet). Live fresh produce allowed more and faster pesticide penetration than harvested fresh produce due to a higher transpiration level in live tissues. The degradation of thiabendazole on live leaves was detected after 1 week, whereas the apparent degradation of ferbam was detected after 2 weeks. When we evaluated the effectiveness of commercial and homemade washing agents in removing pesticide residues on and in apples, we found 1 % NaHCO3 washing agent was more effective than tap water or Clorox bleach. The overall effectiveness of the three methods to remove pesticide residues diminished as pesticides penetrated deeper into the fresh produce. In addition, we monitored the translocation of systemic pesticide (thiabendazole) on live tomato plants in a hydroponic system after inoculating different concentrations of pesticides for growing plants. We found pesticide signals appeared firstly along the midrib in the lowest leaves and move along to the margin of the leaves. The higher concentration of pesticides applied in the system caused the less time pesticide to take to translocate to the leaves. These results demonstrated a successful application of our gold nanoparticle-based SERS imaging as an effective method for measuring pesticides behaviors in fresh produce in situ. The information obtained could provide useful guidance for effective and safe applications of pesticides on foods.

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