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United States Department of Agriculture

Agricultural Research Service

Research Project: Improvement & Maintenance of Flavor & Shelf-Life, Functional Characteristics & Biochem/Bioactive Process, & Use of Genetic/Genomic Resource

Location: Market Quality and Handling Research

Title: Salmonella surrogate reduction using industrial peanut dry roasting parameters

Authors
item Poirier, Dan -
item Sanders, Timothy
item Davis, Jack

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 31, 2014
Publication Date: May 23, 2014
Repository URL: doi: http://dx.doi.org/10.3146/PS13-21.1
Citation: Poirier, D., Sanders, T.H., Davis, J.P. 2014. Salmonella surrogate reduction using industrial peanut dry roasting parameters. Peanut Science. 41:72-84.

Interpretive Summary: Salmonella contamination has been a problem in peanut products several times over the last few years. These studies were conducted to evaluate the effectiveness of industrial peanut dry roasting parameters in Salmonella reduction using a Salmonella surrogate, Enterococcus faecium, which is slightly 8more heat tolerant than Salmonella. Using an oven specifically designed to simulate industrial dry roasting conditions, the study indicated that temperature, airflow, airflow direction and bed depth were all related to acceptable reduction of Salmonella. Regardless of roast conditions, peanuts in the middle of the roasting bed received the least amount of heat and hence, represent the worst case scenario for microbial reduction. When all other conditions were held constant, increasing air flow and decreasing the depth of peanuts in the roaster increased reduction of E. faecium in the middle of the bed. This work provides valuable practical information for manufacturers of roasted peanuts when validating Salmonella reductions under a particular set of roasting conditions.

Technical Abstract: Studies were conducted to evaluate the effectiveness of industrial peanut dry roasting parameters in Salmonella reduction using a Salmonella surrogate, Enterococcus faecium, which is slightly more heat tolerant than Salmonella. Runner-type peanuts were inoculated with E. faecium and roasted in a laboratory scale roaster simulator in which temperature, airflow, airflow direction and bed depth were highly controlled, allowing for conditions that duplicate industrial dry roasting. Temperature data were collected at the top, middle and bottom of the roasting bed in addition to internal peanut temperature via thermocouples in the bed of peanuts and embedded in a peanut. Regardless of roast conditions, peanuts in the middle of the roasting bed received the least amount of heat and hence, represent the worst case scenario for microbial reduction. E. faecium reductions, reported as the logarithm of colony forming units/g (log CFU/g), followed a linear trend with increasing roasting time when peanuts were roasted at 149, 163, and 177 C, with > 5-log CFU/g reductions occurring at the middle of the peanut bed after 21, 15 and 11 min, respectively, at a bed depth of 75 mm and an air flow of 1.3 m/s. Increased air flow increased E. faecium reduction. At 16 min roast time and a 75 mm bed depth, reduction at the middle of the bed was = 3-log CFU/g at 1 m/s and > 5-log CFU/g at 1.3 m/s. When all other roast parameters were held constant, decreasing bed depth also increased reduction of E. faecium in the middle of the bed. Comparing various samples roasted at 149, 163 and 177 C over a range of times, roast color (Hunter L-value) was positively correlated (R2 = 0.73) with the log reduction of E. faecium. Most peanuts with an L-value darker than 53, a common threshold for light roast had = 5-log CFU/g reductions; however, further study is required, including roasting peanuts from different origins and maturity, to fully understand the implications of roast color development and microbial reduction. This work provides valuable practical information for manufacturers of roasted peanuts when validating Salmonella reductions under a particular set of roasting parameters.

Last Modified: 9/21/2014
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