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ARS Home » Northeast Area » Wyndmoor, Pennsylvania » Eastern Regional Research Center » Food Safety and Intervention Technologies Research » Research » Publications at this Location » Publication #282403
Title: Effect of storage temperature on survival and recovery of thermal and extrusion injured Escherichia coli populations in whey protein concentrate and corn meal

Author
item Ukuku, Dike
item Mukhopadhyay, Sudarsan
item Onwulata, Charles

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2012
Publication Date: 1/1/2013
Citation: Ukuku, D.O., Mukhopadhyay, S., Onwulata, C.I. 2013. Effect of storage temperature on survival and recovery of thermal and extrusion injured Escherichia coli populations in whey protein concentrate and corn meal. Foodborne Pathogens and Disease. Volume 10(1):62-68.

Interpretive Summary: Previously, we reported killing of Escherichia coli populations in corn (CP) and whey protein products (WPP) extruded at different temperatures. In that study, information on the effect of storage temperatures on injured E. coli populations was not addressed. In this study we investigated the behavior of the injured populations during storage at 5, 10 and 23 deg C for 5 days. Corn (CP) and whey protein products (WPP) were inoculated with E. coli bacteria at 8.8 log CFU/g and then extruded at 35, 55, 75, and 95 deg C. The effect of heat at 35, 55, 75, and 95 deg C alone on injury was also monitored using thermal death time disk (TDT). The extruded and TDT-disk treated samples were stored at 5, 10 and 23 deg C and the effect of storage temperatures on injured populations and recovery were investigated everyday for 5 days. TDT disks treatment at 35 and 55 deg C did not cause significance changes in the population of the surviving bacteria including injured populations. Extrusion treatment at 35 and 55 deg C caused a 99.99% and 99.9% reduction of E. coli populations in CP and WPP, respectively. The injured populations among the surviving E. coli cells in CP and WPP extruded at 35 deg C averaged approximately 18% but were reduced further during storage. Recovered populations of E. coli bacteria were higher in samples stored at 23 deg C than 10 and 5 deg C. The results of this study indicate that pressure and heat combination led to higher percentage of injured population in extruded samples than the TDT even at 35 deg C extruded samples. Therefore, storage at 5 deg C for at least 24 h for CP and WPP extruded at 75 deg C and above will enhance the microbial safety of the products.

Technical Abstract: In a previous study, we reported viability loss of Escherichia coli populations in corn (CP) and whey protein products (WPP) extruded at different temperatures. However, information on the effect of storage temperatures on injured bacterial populations was not addressed. The objective of this study was to investigate the effect of storage temperature on the survival and recovery of thermal death time (TDT) disks and extrusion injured E. coli populations in CP and WPP. Corn and WPP inoculated with E. coli bacteria at 8.8 log CFU/g were conveyed separately into the extruder with a series 6300 digital type T-35 twin screw volumetric feeder set at a speed of 600 rpm and extruded at 35, 55, 75, and 95 deg C. Also, the CP and WPP inoculated with bacteria was placed inside the TDT disk and the disks were submerged into water bath set at 35, 55, 75, and 95 deg C for 120 s. Populations of surviving bacteria including injured cells in all treated samples were determined immediately and every day for 5 days and, up to 10 days for untreated samples during storage at 5, 10 and 23 deg C. TDT disks treatment at 35 and 55 deg C did not cause significance changes in the population of the surviving bacteria including injured populations. Extrusion treatment at 35 and 55 deg C led to significant (p< 0.05) reduction of E. coli populations in CP as opposed to WPP. The injured populations among the surviving E. coli cells in CP and WPP treated at 35C averaged approximately 18%. WPP treated at 55 deg C showed higher populations of injured bacteria than the CP. At 75 deg C, these populations decreased to < 8 %, and disappeared at 95 deg C. The results of this study showed that further inactivation of the injured populations occurred during storage at 5, 10 and 23 deg C for 5 days suggesting the need for immediate storage of 75 deg C extruded CP and WPP at 5 deg C for at least 24 h to enhance their microbial safety.