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United States Department of Agriculture

Agricultural Research Service

Research Project: Development of a Solar Thermal Drum Dryer for Specialty Crop Purees and Pomaces

Location: Healthy Processed Foods Research

Title: Process and formulation effects on solar thermal drum dried prune pomace

item Milczarek, Rebecca
item Ferry, Jonathan
item Alleyne, Fatima
item Olsen, Carl
item Olson, Donald
item Winston, Roland

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: 3/18/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The processing of dried plums into prune juice and concentrate yields prune pomace as a coproduct; the pomace could potentially be utilized as a food ingredient but requires stabilization for long-term storage. Drum drying is one method that could be used to dry and stabilize prune pomace, and a drum dryer run by solar thermal energy has been developed for this purpose. However, the effects of processing conditions and formulations on the quality of the dried product must be determined. In this work, a pilot-scale double drum dryer heated with oil from a 20 kW solar thermal array was used to dry industrially-produced prune pomace of initial moisture content of 65.5% (wet basis). Based on a split-plot experiment design, various feed blends of pomace, maltodextrin (carrier), and water were drum-dried at varying surface temperatures (92°C to 132°C) for varying lengths of time (2 min to 4 min) while gap width was held contant at 125 µm. Regression equations were generated for the water activity, moisture content, L*, a*, and b* color values of the dried material, as well as for the overall color change ('E), hue, and chroma. The R2 values for the fits of these quality metrics were 75.6%, 59.6%, 75.7%, 85.9%, 84.0%, 74.4%, 71.0%, and 84.5%, respectively. The significance of the various formulation and process variable terms, as well as that of their square and interaction terms, was determined. All dried prune pomace samples were well below the water activity limit of 0.6 for stability. The water activity and 'E were significantly (p < 0.05) affected by the added water and maltodextrin contents but not by the drying time or temperature. The other quality metrics showed more complex dependencies on the process and formulation variables. To minimize both water activity and 'E, no maltodextrin carrier should be added, 3 parts water should be added for every 10 parts pomace, dwell time should be 2.7 min, and the drum surface temperature should be 92°C. The results of this work will inform the operation of a solar thermal-powered drum dryer that can produce high-quality dried purees and pomaces.

Last Modified: 08/21/2017
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