Effect of bed-depth on Inactivation of Enterococcus faecium NRRL B-2354 During Hot-Air Drying of Fresh Cut Apple Cubes
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EmailPrevious research evaluated the effect of hot-air drying of apple cubes on the lethality of two microorganisms at two temperatures. However, the effect of the drying bed depth on the lethality of the drying process is still unknown.
Introduction: Previous research evaluated the effect of hot-air drying of apple cubes on the lethality of two microorganisms at two temperatures. However, the effect of the drying bed depth on the lethality of the drying process is still unknown.
Purpose: To study the thermal inactivation of E. faecium on apple cubes during air drying as affected by bed depth and temperature.
Methods: E. faecium was grown on TSAYE. Culture was harvested in buffered peptone water. Cored, peeled Gala apple cubes (~6.35mm) were inoculated at 8.32±0.19 log CFU/sample. Apple cubes were dried at 104°C for up to 70 min or 135°C for up to 40 min in ~0.75 kg batches using a hot-air dryer with a vertically directed heat source and a fixed bed height. Three subsamples consisting of 4 inoculated cubes, at each time point (n≥5) from top of the bed (4.5 cm), were enumerated on modified TSAYE. Water activity (aw) measurements were taken at corresponding time intervals.
Results: Drying at 104°C led to a 0.63±0.42 and 3.99±2-log CFU/sample E. faecium reduction after 30 and 70 min, respectively. During 135°C drying, there was a 1.06±0.42 and 4.7±2.0-log CFU/sample E. faecium reduction after 20 and 37 min, respectively.. Inoculated apple cubes’ aw dropped from 0.98±0.01 to 0.31±0.10 (104°C, 70 min) and 0.53±0.16 (135°C, 37 min). Comparing to our previous study where a 9 cm bed depth was used, a lower bed depth lead to less total E. faecium inactivation (p<0.05) at the end of drying at 104 °C , similar total E. faecium inactivation (p>0.05) was observed at the end of 135 °C drying with different bed depth.
Significance: Under the conditions tested, less than 5-log CFU/sample reduction was achieved at the end of drying. A lower bed depth when drying apple could lead to similar or less E. faecium inactivation at the end of drying than using a higher bed depth.
