Semester of Graduation

Summer 2026

Degree

Master of Science (MS)

Department

School of Nutrition and Food Sciences

Document Type

Thesis

Abstract

Pecans are low-moisture foods capable of supporting long-term survival of foodborne pathogens despite low water activity. The objectives of this study were to evaluate saturated steam treatment as kill-step for in-shell pecans and assess efficacy of peroxyacetic acid (PAA) during float tank operation of pecan halves. In-shell pecans inoculated with nalidixic acid-resistant strains (7.61 ± 0.48 log CFU/g) were steam-treated at 70, 80, or 90 ± 1 °C for up to 210 s (20 s come-up time). Survivor curves were fitted using log-linear and Weibull models, and D- and Z-values were determined using log-linear model. A 5-log reduction of L. monocytogenes was achieved within 150, 60, and 15 s at 70, 80, and 90 °C, respectively, whereas S. enterica reductions of 3.57 ± 0.38 log CFU/g were achieved after 210 s at 70 °C, while 5-log reductions were achieved within 90 and 25 s at 80 and 90 °C, respectively. E. faecium exhibited the greatest thermal resistance, with D-values of 63.89 ± 11.07, 20.33 ± 1.01, and 8.13 ± 0.49 s at 70, 80, and 90 °C, respectively, and Z-value of 28.63 ± 2.81 °C. Although Weibull models provided slightly better fit statistics, log-linear models remained appropriate for thermal process validation. Steam treatment did not significantly affect kernel quality and improved shelling efficiency. In the float tank study, commercial pecan wash water exhibited high microbial and organic loads, with APC 5.52 to 5.64 log CFU/mL and turbidity up to 376 ± 12.29 NTU, highlighting substantial contamination risk. Treatment with 80 ppm PAA significantly reduced generic E. coli populations on pecan halves compared to water treatment alone (1.96 ± 0.05 log CFU/g at 300 s). Cross-contamination of E. coli to uninoculated pecan halves was observed during float tank treatment, despite no detectable bacterial populations in wash water. These findings suggest that residual PAA may suppress bacterial populations in wash water phase while bacterial transfer to pecan surfaces can still occur during float tank processing operations. Overall, saturated steam treatment demonstrated strong potential as an effective kill-step intervention for in-shell pecans, while PAA showed promising antimicrobial intervention during pecan float tank operations.

Date

7-10-2026

Committee Chair

Karuna Kharel

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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