The nut industry is interested in application of appropriate postharvest Salmonella-control strategies. A current lack of knowledge about the ecology of Salmonella in pistachio production and processing environments has impeded development of targeted science-based food safety programs. The objective of this work was to quantify levels of aerobic bacteria and coliforms in pistachios from receipt at the huller to storage in the silo with a goal of identifying points where microbial loads increased or where microbial contamination could be reduced or controlled. Pistachios are mechanically harvested, wet hulled, separated in a float tank, and partially dried by forced hot air prior to further drying and storage in silos. Pistachios at receipt, and after the pre-cleaner, huller, float tank, dryer, and silo were aseptically collected weekly from three pistachio processors for 3 weeks during the 2010 California harvest. Triplicate 25-g subsamples were plated onto tryptic soy agar (aerobic plate count; APC) and 3M ECC Petrifilm (coliforms) for colony enumeration. Variable microbial levels were observed among individual samples but trends were similar among the three processing facilities. At receipt, the APC and coliform levels for pistachios with hulls ranged from 3.2 to 7.9 log CFU/g and <0.56 to 7.0 log CFU/g with averages of 4.6 and 3.4 log CFU/g, respectively. Average APC and coliform counts increased by 0.3 to 0.7 log CFU/g at the pre-cleaner, decreased by 0.2 to 0.8 log CFU/g on inshell pistachios after the huller and increased by 0.5 to 0.3 log CFU/g after the float tank. Reductions of 2 to 3 log CFU/g in APC and coliform counts were observed on inshell pistachios after the dryer with little change in population levels after 1 week of silo storage. These results indicate that significant microbial reductions can be achieved as freshly harvested pistachios are dried, and optimization of the drying process should be evaluated for control of Salmonella.
|Advisor:||Harris, Linda J.|
|Commitee:||Marco, Maria L., Winter, Carl K.|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||MAI 50/03M, Masters Abstracts International|
|Subjects:||Food Science, Microbiology|
|Keywords:||Almond, Escherichia coli, Listeria monocytogenes, Pistachio, Postharvest, Salmonella|
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