17H-3 |
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P. CORONEL1, V.-D. Truong2, J. Simunovic1, K. P. Sandeep1, and G. Cartwright1. (1) Dept. of Food Science, North Carolina State Univ., 39 Schaub Hall, Box 7624, Raleigh, NC 27695-7624, (2) USDA-ARS-South Atlantic Area-Food Science Research Unit, North Carolina State Univ., Dept. of Food Science, Box 7624, Raleigh, NC 27695-7624 With high levels of nutrients and bio-active compounds, sweetpotato puree can be considered as a functional food ingredient for processed foods. However, due to low heat conductivity and high viscosity of the puree, conventional thermal processing usually results in poor product quality and high nutrient losses. Alternative technologies providing rapid and uniform heating such as microwave energy could help overcome these problems. This study evaluated the feasibility of aseptic processing sweetpotato puree using a continuous flow cylindrical microwave system operating at 915 MHz. Dielectric properties of the puree were measured using an open-ended coaxial probe and an automatic network analyzer. Ten liters of sweet potato puree were pumped at 0.5 l/min to achieve a single-pass heating from room temperature to 90, 100, and 121°C using a 5 kW microwave heating unit. Samples were rapidly cooled and analyzed for color and rheological properties. Dielectric constant values of sweetpotato puree (10 C to 95 C) ranged from 70 to 62 and loss tangent values from 0.25 to 0.47. Based on these values, the maximum diameter of the applicator tube was calculated to be 42 mm. The puree treated in the 5 kW microwave absorbed 88% and 90% of the microwave energy during heating to end point temperatures of 90°C and 121°C, respectively. Color and rheological results indicated that the treatment at 121°C produced good quality puree. Subsequently, sweetpotato puree (100 kg) was processed using a two-stage 60 kW continuous flow microwave heater to a center temperature of 121°C, holding for 20 s, cooling to 20°C, and packaging in an aseptic bag-in-box filler. The resulting product was stable under refrigeration conditions. Further studies are in progress to develop the technology for producing shelf-stable aseptic puree from sweetpotatoes as well as other highly viscous food products.
Session 17H, Food Engineering: Thermal processes
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