Jan. 1, 2009 - Dec. 31, 2009Award Number
Center for Produce Safety & UC ANRAmount Awarded
Xiuping Jiang, Ph.D.
J. Kim, F. LuoSummary
Raw or inadequately composted animal manure has been considered as a potential source of pre-harvest contamination of fresh produce. Composting, as a practical way for waste management on farm, can inactivate human pathogens, but the outcome can be affected by many environmental factors. Therefore, there is a need for developing composting guidelines and standards to apply to a wide range of conditions. In this proposed study, we hypothesize that the extended mesophilic composting phase may induce heat-shock response in human pathogens, which become resistant to subsequent lethal temperatures during thermophilic phase of composting. Other sub-optimal conditions, such as slow heat-up of compost, low moisture contents and carbon to nitrogen ratio (C:N) in compost, may also enhance the survival of stress-adapted human pathogens during composting. Therefore, our first approach will determine the thermal resistance of heat-adapted cultures in compost at elevated composting temperatures by simulating early stage of on-farm composting. Due to nonlinear reduction of pathogens by composting, a mathematical model will be developed to describe thermal inactivation of stress-induced pathogens in compost under non-isothermal conditions. Second approach will apply indigenous microorganisms as a secondary treatment to prevent pathogen regrowth in cured compost. Finally, we will improve the sensitivity of pathogen detection from compost by using bacteriophages to suppress indigenous microflora, and Pathatrix® system to concentrate the target pathogens from enrichment cultures. We expect the results from this proposed study will provide scientifically validated composting guidelines to compost industry, and thereby to reduce contamination of fresh produce by pathogens in compost.