Date of Graduation

12-2013

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Navam S. Hettiarachchy

Committee Member

Luke Howard

Second Committee Member

Casey Owens

Third Committee Member

Kristen Gibson

Keywords

Biological sciences, Escherichia coil, Salmonella Typhimurium

Abstract

The safety of fresh produce is often challenged by the sporadic incidences of outbreaks owing to Salmonella Typhimurium (S.T.) and Escherichia coli O157:H7 (E.c.). Washing and current disinfection strategies do not completely decontaminate leafy greens such as spinach and iceberg lettuce. Therefore, more effective treatments are essential to ensure the microbial safety of the produce at the selling point. Here, a multiple hurdle approach was applied: (1) Natural antimicrobials - organic acids (malic, lactic and tartaric acids; MA, LA, TA, respectively) and plant extract (grape seed extract, GSE) and (2) Application method - Electrostatic spraying, was examined as a possible solution to the problem of production and post-harvest contamination of leafy greens. Comparisons of electrostatic versus conventional spraying and organic versus inorganic acid (phosphoric acid, PA) treatments were conducted. The concentrations of antimicrobials sprayed electrostatically were optimized using response surface methodology and determined as 3% each of MA, LA and GSE. Malic acid (3%)-LA (3%) and MA (2%)-GSE (3%) combinations were demonstrated to reduce S.T. on spinach by 4.3 log CFU/g and 3.3 log CFU/g, respectively, when sprayed electrostatically. When combined with LA (3%), MA (3%) showed 2.1-4.0 logs CFU/g reduction of E.c. between the days 1 and 14 on spinach and 1.1-2.5 logs CFU/g reduction on lettuce. The electrostatic spraying of MA-LA-GSE (3% each) showed reduction of 2.6 log CFU/g of S.T. and 2.3 log CFU/g of E.c. on the day 14 of incubation of iceberg lettuce. Conventional spraying of these antimicrobials did not reduce the pathogens efficiently. Though PA (1.5%) and PA (1.5%)-GSE (2%) exhibited 1.1-2.1 logs CFU/g reduction of E.c. and PA (2%) and PA (2%)-GSE (2%) reduced ~2.0-2.7 log CFU/g of S.T. on spinach during the 14-day storage, the color of spinach was significantly affected. The combination of malic and lactic acids (3% each) applied by electrostatic spraying is recommended for use in commercial applications. The combination of these antimicrobials applied by electrostatic spraying can serve as effective multiple hurdle technologies at post-harvest level intervention for decontaminating leafy greens and enhancing food safety.

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