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>The effects of superheated steam processing conditions on the functionality and microflora of oat flour intended for use in infant food formulations.
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The effects of superheated steam processing conditions on the functionality and microflora of oat flour intended for use in infant food formulations.
Superheated steam (SS) processing was evaluated as an alternative method for the heat treatment of oat groats (Avena saliva) particularly with respect to its ability to inactivate bacterial spores. The objectives of this research were to access the efficiency of a commercial kiln drying process to reduce the bioload of oat groats; to evaluate temperature (115°C, 121°C, 130°C, 145°C 160°C and 175°C), moisture (12 and 17%), inoculum level (104 and 107 cfu/g) and steam velocity (0.52 and 1.10m/s) with respect to SS performance and reduction of thermophilic spores in oat groats, and to examine the functional and chemical properties of oat flour after SS treatment. Of the 30 oat groat samples analyzed following kiln treatment, 26 (87%) contained thermophilic and flat sour spores. In contrast, only 11(37%) of the 30 samples taken before kiln treatment contained spores. Overall, samples taken from the interior of the kiln at the cooling sections appeared to contain the highest numbers of thermophilic and flat sour spores.;Survivor curves for Geobacillus stearothermophilus ATCC 10149 spores in groats were plotted and D values were calculated. Increasing the temperature of SS from 115°C to 175°C resulted in a progressive increase in spore lethality. Temperatures of 160 and 175°C effectively reduced spore levels by approximately 5 log10 cfu/g, however, the groats were deemed unfit for further use based on color. At 130 and 145°C, maximum decreases in spore populations (usually less than 2 log) were observed at 5-10 min of treatment; thereafter all survivor curves exhibited distinct tailing. Raising the superheated steam velocity from 0.52 to 1.10m/s had a minimal effect on spore lethality. Also, tempering groats from 12 to 17% moisture content did not appear to improve the sporicidal effect.;The color change of oat groats following SS was most noticeable in samples treated at 160°C and 175°C; in this respect the groats appeared dark and exhibited a burnt appearance and odor. In all cases, neither an increase in the treatment times nor the flow rate had any noticeable effect on the pasting profile. Superheated steam processing successfully stabilized degradative enzymes, producing peroxidase negative samples at temperatures above 115°C. Under the processing conditions examined in this study, superheated steam processing (compared to conventional thermal treatment) was of limited value for the reduction of Geobacillus stearothermophilus spore viability. Further investigations of other steam velocities and temperature profiles may increase spore lethality and also produce oat groats with improved sensory and functional properties.
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