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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Publications at this Location » Publication #349635
Research Project: Characterization and Mitigation of Bacterial Pathogens in the Fresh Produce Production and Processing Continuum

Location: Environmental Microbial & Food Safety Laboratory

Title: Impact of wastewater and roof-harvest water irrigation on microbial quality of spinach

Author
item YIN, HSIN-BAI - University Of Maryland
item GU, GANYU - Virginia Tech
item Nou, Xiangwu
item Patel, Jitu

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2018
Publication Date: 7/8/2018
Citation: Yin, H., Gu, G., Nou, X., Patel, J.R. 2018. Impact of wastewater and roof-harvest water irrigation on microbial quality of spinach. International Association for Food Protection. p.162.

Interpretive Summary:

Technical Abstract: Introduction: Secondary-treated wastewater (STWW) and roof-harvest rainwater (RHW) have been considered as alternative irrigation waters to overcome water scarcity. The impact of these waters on microbial safety of fresh produce requires further investigation. Purpose: The objective of this study was to investigate the effect of STWW and RHW irrigation on microbiological quality of spinach in the field. Methods: Two field trials of spinach in the summer and winter season were conducted in this study. Six-week old spinach grown in the field was spray irrigated by STWW, RHW, or ground water (GW, control) once a week for two weeks. Four replicate spinach and soil samples from each group (n=160) were collected weekly before irrigation and on 0, 1, 2, and 4 days-post-irrigation (dpi). Water, spinach, and soil samples were analyzed for the indicator bacterial populations and the presence of bacterial pathogens (Salmonella, Escherichia coli O157:H7 and L. monocytogenes). Results: For both trials, there was no significant increase in total coliforms and E. coli populations on STWW or RHW-irrigated spinach as compared to control irrigated-spinach. Fecal coliforms were significantly (P < 0.05) increased from 1.8 log to 3.2 log CFU/g on summer-grown control spinach (average temp. 70ºF) at 0 dpi due to the higher bacterial populations in GW. Bacterial die-off rate was higher on winter-grown spinach (average temp. 50ºF), and E. coli in all irrigation waters used during winter (0.6-1.8 log CFU/100 ml) were below the Food Safety and Modernization Act regulation (2.1 log CFU/100 ml). Bacterial pathogens were not detected in water or spinach samples. Significance: STWW and RHW containing low indicator bacterial populations may be used as irrigation waters without affecting the microbiological safety of spinach. Growing season influences the irrigation water quality and bacterial persistence on spinach. Microbiological quality of alternative waters must be determined prior to their use for irrigation.