Doctor of Philosophy (PhD)


School of Nutrition and Food Sciences

Document Type



Pre- and post-harvest practices can pose microbial risk on fresh produce thus, appropriate intervention strategies to inactivate foodborne pathogens without compromising quality is important. The first part of this study investigated the effect of steam conditioning on inactivating Enterococcus faecium, a surrogate for Salmonella enterica, on in-shell pecans; and second part determined the in vitro and in vivo antimicrobial efficacy of pullulan coating incorporated with pecan shell extract on produce. The treatments’ effect on quality of pecans and produce during storage were also evaluated. In-shell pecans inoculated with Enterococcus faecium (7.28±0.17logCFU/g) were treated with steam at 70°C, 80°C or 90°C for 0-300s. A 5-log reduction of the organism could be achieved within 385s, 130s, or 25s at 70, 80, or 90°C, respectively. The 90°C treated pecans’ peroxide value were lower (P<0.05) than control by end of storage indicating delayed rancidity. Steam had no significant effect on the quality and consumer acceptability of pecans, instead higher purchase intention was observed after knowing steam treatment’s benefit on safety. For antimicrobial coating study, PSE-P (5% w/v aqueous pecan shell extract+5% w/v pullulan), P (5% w/v pullulan) and control coating solutions were spray coated on blueberries or strawberries inoculated (5 log CFU/g) with Listeria monocytogenes, Salmonella enterica or Staphylococcus aureus; and stored at 4°C, 50±10% RH. Extracts showed greater antimicrobial effect on tested gram-positive organisms than gram-negative and showed no antifungal effect when evaluated in vitro against tested organisms. Extract significantly reduced Listeria monocytogenes by 1.32-2 log CFU/g and native aerobic microflora by 0.7 log CFU/g for produce, which slightly reduced (P>0.05) during storage with survival similar to control or pullulan; no significant effect (P>0.05) on the survival of Salmonella enterica, Staphylococcus aureus, and native fungal population were observed. PSE-P maintained the firmness of fruit until end of 10 and 15 days of storage with no significant effect on its color, TSS and pH. Spoilage rate was significantly reduced (P<0.05) by extract and weight loss was minimized (P<0.05) throughout storage. The findings show that the tested thermal and chemical intervention strategies have potential for maintaining safety and improving quality of pecans and produce, respectively.



Committee Chair

Adhikari, Achyut



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