Thermal inactivation of Salmonella spp. in commercial tree nut and peanut butters in finished packaging

Abstract

Peanut and tree nut butters have been implicated in Salmonella outbreaks in recent years. Previous studies investigated efficacy of thermal treatments to reduce Salmonella in multiple peanut butter formulations; however, evidence is lacking to support thermal treatment of tree nut butters. This study evaluated thermal treatments to reduce Salmonella in commercial nut butter formulations in final package. Formulations (n 5 6) were inoculated with a Salmonella cocktail and packaged in glass jars before thermal treatment (boiling waterbath, holding times: 0-90 min, >90 8C). Salmonella survivors were enumerated using standard dilution and plating on Hektoen Enteric Agar (37 8C, 24-48 hr). Low levels of survivors (<1 CFU/g) were quantified using a one-tube most probable number technique. Thermal treatments at >90 8C with a 30-min hold time effectively reduced >5 log CFU/g of Salmonella in tree nut formulations; however, holding times >60 min were required to achieve similar reductions in peanut butter. Practical applicationsThis study was designed to provide evidence to support a reconditioning proposal for the processing of tree nut butters that were linked to an outbreak of Salmonella Paratyphi L(1)tartrate(1).There were no previous reports in the scientific literature to demonstrate the efficacy of thermal treatment to inactivate Salmonella spp. in tree nut butters, including nut butters with more complex formulations. Ideally, reconditioning of contaminated product would not require repackaging of the products; therefore, this study was designed to determine treatment parameters that could be easily achieved with the product remaining in its original packaging. This report supports thermal treatment as an option for reconditioning contaminated tree nut butter products using a thermal process that is less intense than what would be necessary to reduce Salmonella spp. in peanut butter products. spreads, and pastes using conventional thermal inactivation study approaches (He et al., 2013;He, Guo, Yang, Tortorello, & Zhang, 2011;Keller et al., 2012;Li, Huang, & Chen, 2014;Shachar & Yaron, 2006). Time and temperature were consistently verified as critical parameters; however, heat resistance of Salmonella spp. was significantly influenced by product formulation (He et al., 2011;Kataoka et al., 2014;Li et al., 2014;Ma et al., 2009;Shachar & Yaron, 2006). Reduced fat formulations with increased carbohydrate content required significantly longer treatment times (15-45 min) at 90 8C to achieve a 5-log reduction of Salmonella spp. compared to standard formulations (10-25 min) (He et al., 2011;Li et al., 2014). Given the variability in thermal resistance of Salmonella spp. in different peanut butter product formulations and the diversity of commercial nut butter products in the marketplace, there is a lack of evidence to critically evaluate processing or reconditioning proposals for products other than basic peanut butter formulations. | I NTR OD U CTI ONIndustrial application of thermal processing is further compli...

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