Title: Effect of storage temperatures on injured escherichia coli cell populations in whey and corn meal snacks treated with a twin screw extruder Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 7, 2011
Publication Date: June 11, 2011
Citation: Ukuku, D.O., Mukhopadhyay, S., Onwulata, C.I. 2011. Effect of storage temperatures on injured escherichia coli cell populations in whey and corn meal snacks treated with a twin screw extruder. IFT Annual Meeting and Food Expo, June 11-14, 2011, New Orleans, LA., Volume 1, P.1. Technical Abstract: The effect of extrusion treatment parameters on injured populations of corn meal and whey protein isolate inoculated with surrogate E. coli populations has been reported. However, information on the effect of treatment parameters on injured bacterial populations of treated corn and whey protein products during storage is limited. In this study, we investigated the effect of different storage temperatures on extrusion injured E. coli cell populations in corn product (CP) and whey product (WP). The extrusion treatment temperatures were set at 35C, 55C, 75C, and 95C and the feed materials corn and whey protein isolate were conveyed into the extruder with a series 6300 digital feeder, type T-35 twin screw volumetric feeder (K-Tron Corp., Pitman, NJ) at a set speed of 600 rpm. E. coli water solution (log 10 CFU/ml) was added into the extruder at the rate of 1.0 L/h with an electromagnetic dosing pump (Milton Roy, Acton, MA). Percent injured populations in the initial E. coli cells before treatments averaged 4% in both CP and WP. The injured populations among the surviving E. coli cells in both CP and WP treated at 35C averaged approximately 18%. The injured populations in CP and WP treated at 55C and above disappeared, suggesting the lethality of the treatment at 55C and above. However, the highest populations of injured cells were determined in whey protein meal treated at 55C but when treatment temperature was set at 75C, the population of injured cells decreased to <8 % and disappeared at 95C. The injured populations of E. coli cells in CP treated at 35C and stored at 5C for 20 days recovered and increased the total populations by 3.8 log. Similar recovery trend was observed in whey samples treated at 35 and 55C, respectively. Unlike the CP, the injured E. coli populations in WP samples recovered during storage at 23C for 10 days. The results of this study suggest immediate storage of extruded corn or whey isolates at 5C for at least 24 h to enhance the microbial safety of products extruded below 100C.