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Improvement of heating uniformity in packaged acidified vegetables pasteurized with a 915MHz continuous microwave system
- Continuous microwave processing to produce shelf-stable acidified vegetables with moderate to high salt contents poses challenges in pasteurization due to reduced microwave penetration depths and non-uniform heating. Cups of sweetpotato, red bell pepper, and broccoli acidified to pH 3.8 with citric acid solution containing 0-1% NaCl were placed on a conveyor belt and passed through a microwave tunnel operating at 915MHz and 4kW with a 4min residence time. The time-temperature profiles of vegetable pieces at 5 locations in the package were measured using fiber optic temperature sensors. Addition of 1% NaCl to the cover solution lowered microwave penetration into vegetable pieces and decreased the mean temperature in cups of acidified vegetables from 84 to 73°C. Soaking blanched vegetables for 24h in a solution with NaCl and citric acid prior to processing improved microwave heating. Heating was non-uniform in all packages with a cold spot of approximately 60°C at a point in the container farthest from the incident microwaves. More uniform heating was achieved by implementation of a two-stage rotation apparatus to rotate vegetable cups 180° during processing. Rotating the cups resulted in more uniform heating and a temperature of 77°C at the cold spot. This is above the industrial standard of 74°C for in-pack pasteurization of acidified vegetables. The effective treatment involved blanching, soaking for 24h in a NaCl and citric acid solution, and 180° rotation. This work has contributed to a better understanding of the influence of salt addition and distribution during dielectric heating of acidified vegetables using a 915MHz continuous microwave system.
Koskiniemi, Craig B. , Truong, Van-Den , Simunovic, Josip , McFeeters, Roger F.
sweet potatoes , broccoli , sweet peppers , acidification , food packaging , pasteurization , microwave treatment , heat , spatial variation , sodium chloride , citric acid , solutions
- Includes references
- Journal of food engineering 2011 July, v. 105, no. 1
- [New York, NY]: Elsevier Science Pub. Co.
Journal Articles, USDA Authors, Peer-Reviewed
- Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.