Salmonella Surrogate Reduction Using Industrial Peanut Dry Roasting Parameters

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.

Evaluating the Risk of Salmonellosis from Dry Roasted Sunflower Seeds

“…Unpublished Conagra Brands studies indicated there is a loss of 31% moisture when brined sunflower seeds are hot-air roasted at 1358C for 20 min. Although the water activity of peanuts before roasting in Poirier et al (36) is comparable to our brined sunflower seeds, the differences in moisture loss between both studies (4.4 versus 31%) could account for the observed differences in heat resistance of Salmonella. Our estimated product temperature corresponding to a minimum of a 4-and 5-log reduction in Salmonella was lower (77.8 and 85.88C, respectively) compared with that of Poirier et al (36).…”

“…E. faecium NRRL B-2354 has been commonly used as a surrogate organism for Salmonella Enteritidis phage type 30 for performing validation of thermal treatments for almonds (35). Although performing a study with a surrogate such as E. faecium is outside the scope of our research, it is worth discussing the findings of Poirier et al (36) because the initial water activity of peanuts before roasting was similar to that of sunflower seeds in our study. Poirier et al (36) noted the water activity of the peanuts reduced from 0.73 a w to 0.33 to 0.13 a w , whereas the moisture content of the peanuts decreased from 6.1 to 1.7%.…”

“…This disagreement can be attributed to both the drum roasting process we used and the increased water activity due to brining of sunflower seeds before roasting. Experimental design protocols in previously published studies with roasted peanuts and almonds (2,36,37) primarily mimic the conditions in continuous-bed roasters that are typically used to produce roasted peanuts or almonds. Because we used the typical drum roasting process for sunflower seeds, thermodynamics of heat and mass transfer during the drum roasting process may be significantly different compared with conventional dry roasting processes used for peanuts and almonds (2,36,37).…”

Characterization of peanuts after dry roasting, oil roasting, and blister frying

“…The peanuts had been cured, shelled, sized using standard screens, blanched and stored utilizing standard industry practices prior to delivery to the USDA ARS Market Quality & Handling Research Unit at North Carolina State University (Raleigh, NC, USA). A pilot plant scale roaster previously described (Poirier, Sanders, & Davis, 2014) built by the Bühler Aeroglide Corporation (Cary, NC, USA) with an adjustable air flow rate (up to 1.27 m/s), air flow direction, bed depth, and temperature control (up to 204 ºC) was used for the dry roasting. The air flow direction was changed from up-flow to down-flow at the half point of the roasting time.…”

Development and Experimental Results of a Thermal Oil Based Roasting System for Decentralized Processing of Groundnuts

“…These conventional methods of roasting are uncontrolled, inefficient, energy and time consuming and provide a very un-hygienic environment to the operators such as direct exposure to heat radiations and smoke. On an industrial scale, groundnuts are roasted either using gas-fired revolving oven or continuous or batch type roasters which offer more flexible options for precisely controlling the process conditions like temperature, time and product flow rate, ensuring a uniformly processed product [10]. However, these large scale units are economically out-of-reach for small to medium scale farming communities accompanied by the additional burden of escalating fossil fuel prices that upsurges the processing cost.…”