Graduate Thesis Or Dissertation


An evaluation of blackberry harvest sanitation and the ability of foodborne pathogens to survive in blackberry products Public Deposited

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  • Blackberries, genus Rubus, are an important Oregon agricultural commodity. In their fresh and processed forms, they offer many health benefits and may be able to help Americans better achieve fruit consumption recommendations because of convenience and pleasant sensory qualities. However, the susceptibility of blackberry products to contamination with bacterial pathogens of human health concern is unknown. Blackberries have never directly been implicated in a food safety incident; however, raspberries, also in the Rubus genus, have been the vehicle for hepatitis A, norovirus, and Cyclospora cayetanensis outbreaks. Furthermore, strawberries were recently the source of an Escherichia coli O157:H7 outbreak in Oregon. To better understand the potential for microbial pathogen contamination and the ability of these microorganisms to survive or grow in blackberry products, several studies were conducted. Fresh berries from the 'Obsidian' and 'Triple Crown' cultivars were evaluated at different harvest periods for the aerobic plate count, coliforms, yeasts, and molds to establish a baseline microbial population. Environmental samples were taken from a clean mechanical harvester and then from the same harvester that had been intentionally left soiled with berry harvest debris to determine the impact of harvester microbial quality. Samples from 'Marion' and 'Black Diamond' cultivars were hand harvested and evaluated for E. coli O157:H7 and Salmonella spp. by rapid detection methods via the NEOGEN® Reveal® 2.0 systems. Fresh, wild 'Himalaya' blackberries and frozen blackberries from the 'Triple Crown' cultivar were spot inoculated with Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus to determine the ability of these microorganisms to survive on the berry surface. 'Himalaya' samples were stored for 3 days at ambient temperatures and 'Triple Crown' for 6 months at -23.3°C. Lastly, juice and wine were made from 'Marion' and 'Black Diamond' purees. The juices and wines were used for pathogen survival studies using the aforementioned microorganisms to better understand what constituents of blackberries may contribute to bactericidal effects, as well as the survival patterns in these products. Aerobic plate counts for 'Obsidian' and 'Triple Crown' cultivars ranged from 3.52-4.62 log CFU/g of berry with later harvests tending to have higher values. 'Triple Crown' mid-late harvest samples were significantly higher than the early harvest samples (p = 0.005). Yeasts and molds ranged from 3.01-4.73 log CFU/g of berry with later harvests having significantly higher values for both cultivars (p = 0.048 'Obsidian'; p <0.001 'Triple Crown'). Coliforms were detected in 'Obsidian' mid-harvest and 'Triple Crown' early-harvest samples at 2.10 and 1.40 log CFU/g of berry, respectively. The aerobic plate counts measured from the clean and intentionally soiled mechanical harvester were not significantly different. Escherichia coli O157:H7 and Salmonella spp. were not detected using rapid detection methods in evaluated 'Marion' and 'Black Diamond' samples. Escherichia coli O157:H7 was not detectable in fresh or frozen inoculated samples. Salmonella Typhimurium was detected in 2 frozen samples with 2.95 and 3.21 log reductions. Listeria monocytogenes was only detected in frozen samples and experienced log reductions ≥ 2.42. Staphylococcus aureus was detectable on every fresh and frozen berry inoculated with log reductions ranging from 0.67 to 3.48. The greatest reductions occurred with fresh samples. Growth of microorganisms was not observed in any juice or wine samples. Maximum observed survival times in juices ranged from 12 h for L. monocytogenes to 108 h for Salmonella Typhimurium. Maximum survival times in wines were 40 m for both E. coli O157:H7 and Salmonella Typhimurium, and 80 m for both L. monocytogenes and S. aureus. Adding ethanol to juice samples to equal that of their counterpart wines decreased survival time for all microorganisms evaluated by several hours. Increasing the pH of wines by approximately one unit increased the survival time from minutes to hours, and in some cases, days. The overall results suggest that blackberries are not an ideal environment for E. coli O157:H7, Salmonella Typhimurium, L. monocytogenes, and S. aureus to grow. However, these microorganisms may be able to survive depending on the type of blackberry product and its subsequent storage. Many constituents of blackberries may provide bactericidal activity, with organic acids appearing to have the greatest effect.
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