Biological and Agricultural Engineering

June 1 – Exit Seminar: Development of a combined thermal process with surface disinfectants for reducing the microbial load of nut products

Monday, June 1, 2015
2:00 PM

2045 Bainer Hall


Speaker: Fredy Salazar, PhD Candidate (Exit Seminar)      


Title: Development of a combined thermal process with surface disinfectants for reducing the microbial load of nut products


Abstract: Due to Salmonella spp. outbreak in almonds, regulatory standards have been established requiring that almonds achieve a minimum of 4 log10 CFU/g reductions of Salmonella spp. Today, and with existing technologies, this requirement has not been achieved efficiently, reliably, and without quality deterioration. However, this work identified and studied a potential solution based upon the use of an additive combination of radiofrequency (RF) heating (a thermal process) with the rapid and transient application of alternative surface disinfectants (SD). Factors and levels to achieve high log10 reduction (>4 CFU/g) were studied using experimental designs. Commercial-quality samples of nuts (mostly almonds) were infected using wet inoculation at levels of 107-109 CFU/g of either Enterococcus faecium NRRL-B-2354 (a surrogate organism for Salmonella spp) or live Salmonella enteritis ATCC 1045. The radiofrequency experiments in the heat-double-spray process achieved high log10 reductions of 6.7, 4.7, 3.8, and 3.5 log10 CFU/g of Enterococcus faecium for almonds, pecans, pistachios, and walnuts, respectively. Furthermore, the use of radiofrequency heating and ethanol 70% in the heat-single-spray process achieved 5.8 log10 CFU/g reductions. In this experimental mode independent heat and spraying achieved 2.9 and 3.0 log10 CFU/g reduction, which corresponds to a contribution of 50% each to the combined heat-spray process using radiofrequency heating. These results corroborate previous findings using conventional heating (as a simulation of radiofrequency) and Salmonella spp: the single heat-spray process has additive model (p<0.05), while the heat-double-spray process has shown interaction (p<0.05) in addition to additive characteristics. Therefore the use of spray process after radiofrequency heating further enhances the log10 reduction of a heat phase alone. The implications of these findings are that both the heat-single-spray and heat-double spray process may become alternatives to current almond disinfection process to achieve high log10 reduction with similar postharvest characteristics.


2045 Bainer Hall University of California Davis

Loading Map....