Behavior of Escherichia coli bacteria in whey protein and corn meal during twin screw extrusion processing at different temperatures

Authors: Ukuku, Dike; Onwulata, Charles; Mukhopadhyay, Sudarsan

Submitted to: Journal of Food Processing and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2012
Publication Date: 3/26/2012
Citation: Ukuku, D.O., Onwulata, C.I., Mukhopadhyay, S. 2012. Behavior of Escherichia coli bacteria in whey protein and corn meal during twin screw extrusion processing at different temperatures. Journal of Food Processing and Technology. 3(4):1000150.

Interpretive Summary: Many studies on the development of new and/ or value added nutritional corn meal and whey protein isolates for US consumers have been reported. However, information on the effect of treatment parameters on microbial safety of foods extruded below 100 deg C is limited. In this study, we investigated the effect of extrusion treatments at 35 deg C, 55 deg C, 75 deg C, and 95 deg C on viability loss of E. coli cell populations inoculated on corn meal and whey protein isolates. Corn and whey protein products were conveyed separately into a extruder with the speed set at 600 rpm, and E. coli water solution (9 log CFU/ml) was added into the extruder at the rate of 1.0 L/h with an electromagnetic dosing pump to achieve an initial bacterial population of 8.8 log CFU/g on both products. Extrusion treatments at 35 and 55 deg C were more effective in reducing bacterial populations in corn meal than the whey protein product. The E. coli populations killed in corn extruded at 35 and 55 deg C averaged >6 log CFU/g and <4 log CFU/g for whey protein. Treatments at 75C and above led to populations below detection (<20 CFU/g) of E. coli cells in corn meal while treatment at 95 deg C achieved a similar below detection (<20 CFU/g) in whey protein isolates. The results of this study suggest that corn product prepared by extrusion at 75 deg C or above may be considered safe while higher extrusion temperature of 95 deg C or above is required to achieve a microbial safe whey product.

Technical Abstract: Many studies on the development of new and/ or value added nutritional meal corn and whey protein isolates for US consumers have been reported. However, information on the effect of treatment parameters on microbial safety of foods extruded below 100 deg C is limited. In this study, we investigated the effect of extrusion treatments at 35 deg C, 55 deg C, 75 deg C, and 95 deg C on viability loss of E. coli cell populations inoculated on corn meal and whey protein isolates. The inoculated corn and whey protein products were conveyed separately 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, and E. coli water solution (9 log CFU/ml) was added into the extruder at the rate of 1.0 L/h with an electromagnetic dosing pump (Milton Roy, Acton, MA) to achieve an initial bacterial population of 8.8 log CFU/g on both products. Extrusion treatment at 35 and 55C was more effective in reducing bacterial populations in corn meal than the whey protein product. The viability loss for E. coli populations in corn extruded at 35 and 55C averaged >6 log CFU/g and <4 log CFU/g for whey protein. Treatments at 75 deg C and above led to populations below detection (<20 CFU/g) of E. coli cells in corn meal while treatment at 95C achieved a similar detection (<20 CFU/g) of E. coli cells in whey protein isolates. The results of this study suggest that corn product prepared by extrusion at 75 deg C or above maybe considered safe where as a higher extrusion treatment temperature at 95 deg C or above may be required to achieve microbial safe extruded whey product.