73C-2 |
Microbial reduction in refractance window drying of pumpkin purees |
H. FENG, Dept. of Food Science & Human Nutrition, Univ. of Illinois, Urbana-Champaign, Urbana, IL 61801, D. H. Kang, Food Science & Human Nutrition, Washington State Univ., Pullman, WA, G. Q. Shen, ShanXi Agricultural Univ., Taigu, China, and J. Tang, Biological Systems Engineering, Washington State Univ., Pullman, WA 99164-6120.
Drying of liquid and semiliquid food products is an important operation in the food industry. Traditional drying methods are either energy inefficient or with considerable quality degradation. Refractance Window (RW) drying is a novel film drying method that can produce dehydrated foods with good quality in a short drying time (2-5 min) at moderate temperatures (80-97 C). Microbial counts are important quality index of dehydrated products. No previous studies have been documented in the literature that focused on the microbial reduction in film drying of foodstuffs. It was the intention of this study to evaluate microbial reduction in Refractance Window dried purees. Our objective was to evaluate the reduction in the total aerobic microbial count (APC), Listeria innocua, coliforms, and Escherichia coli during RW drying of purees. Fresh purees were inoculated with Listeria innocua, coliforms, and E. coli cultures to reach ca. 6.0 log CFU/ml as initial inoculum level. In the case of APC, the natural microflora was used for determining total microbial reduction. The inoculated purees were then dried on a pilot-scale RW system. For microbial enumeration, Plate count agar, Listeria Selective agar, Violet Red Bile agar, and Eosin Methylene Blue agar media were used for enumeration of APC, L. innocua, coliforms, and E. coli, respectively. Our experiment results with pumpkin purees using a pilot scale Refractance Window drying system showed that the RW drying resulted in a 5.0 log reduction (from ca. 7.0 log CFU/ml to a. 2.0 log CFU/ml) when the water temperature was 95oC and the drying time was 7 min. Selecting appropriate temperature and time combinations in the RW drying systems can produce dried products that meet regulatory requirements related to food safety. The reported results will help provide guidance in the operation of RW drying system to produce microbial safe products.
Session 73C, Food Engineering: Transport Processes and Kinetics
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