Abstract
New studies on the development of low-temperature extruded value-added nutritional foods containing corn meal and whey protein isolate have been reported. However, information on the effect of extrusion treatment parameters on microbial safety of foods below 100°C is limited. In this study, we investigated the effect of extrusion treatments at 35°C, 55°C, 75°C, and 95°C on reduction of E. coli cell populations inoculated onto corn meal (CM) and whey protein concentrate (WPC80) at 8.8 log 10 CFU/g. Inactivation of E. coli bacteria on CM and WPC80 extruded at 35 and 55°C averaged 4.8 log, 6.9 log and 1.8 log, 4.3 log, respectively. Extrusion treatment at 75°C and above reduced E. coli (ATCC-25922) cells on CM to below detection (<20 CFU/g); but treatment at 95°C was needed to achieve a similar below detection (<20 CFU/g) for WPC80. The results of this study suggest that corn meal products extruded at 75°C or above, and whey protein isolate extruded at 95°C, will enhance the microbiological safety of the extrudates.
Highlights
Physical and chemical treatments are used in food processing to eliminate or at least reduce the presence of pathogenic and spoilage microorganisms in foods [1,2,3]
The background populations of bacterial contamination determined from corn meal (CM) and WPC80 at each day of the study were below detection levels
After inoculation of CM and WPC80 with E. coli bacteria, the bacterial populations determined in CM and WPC80 was approximately 8.8 log10 CFU/g and this number is considered to be the initial bacterial population before treatment
Summary
Physical and chemical treatments are used in food processing to eliminate or at least reduce the presence of pathogenic and spoilage microorganisms in foods [1,2,3]. Food ingredients developed by this extrusion have improved texture with enhanced physical properties including ex-vivo or in-vivo functionality [5]. Texturization of proteins by extrusion processing occurs at temperatures ranging from 50 to 100°C at short residence times of approximately 2 min [6]. Information of this processing treatment on the survival and viability loss of microbial organisms present on treated food items is limited. The authors stated that destruction of spores in the extruder was a function of temperature and residence time at constant moisture levels (18%) for a corn-soybean (70%/30% [wt/wt]) mixture
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