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Title: Spray-drying of amylase hydrolyzed sweetpotato puree and physicochemical properties of powder

Author
item GRABOWSKI, JULIE - NC STATE UNIVERSITY
item Truong, Van Den
item DAUBERT, CHRISTOPHER - NC STATE UNIVERSITY

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2006
Publication Date: 5/1/2006
Citation: Grabowski, J.A., Truong, V., Daubert, C.R. 2006. Spray-drying of amylase hydrolyzed sweetpotato puree and physicochemical properties of powder. Journal of Food Science. 71:E209-E217.

Interpretive Summary: Sweetpotatoes are highly nutritious vegetables rich in calories and health beneficial phytochemicals. However, sweetpotato consumption has been on the decline in the United States. Limited choices of sweetpotato products for consumers beyond the raw roots, as well as difficulties in storage and handling of the produce for food processors, contribute to consumption decline. Therefore, a need exists to develop alternative processing methods to produce a functional and stable form of sweetpotatoes that is readily available for the food processing industry. A strategy is to convert sweetpotato puree into a dried powder to be used as a functional ingredient in different food systems. Spray drying, which has been used for commercial production of several fruit and vegetable powders, has not yet been applied to sweetpotato processing. Thus, this study was undertaken to determine the technical feasibility of processing sweetpotato puree into spray-dried powders. The high viscosity of sweetpotato puree was anticipated to be a challenge in pumping and atomization during the spray-drying process, and the sticky behavior due to high sugar content in sweetpotato puree may affect spray-drying efficiency. The results showed that a combination of elevated temperature and alpha-amylase treatment was effective in reducing the viscosity of sweetpotato puree for spray-drying. For the amylase-treated puree, maltodextrin should also be used as a drying aid to reduce stickiness and aid product recovery. The pre-drying treatments and drying temperature impacted the final characteristics such as color, moisture, water absorption index, particle size and bulk density of the spray-dried sweetpotato powders. Overall, good quality powders can be produced by spray-drying of sweetpotato puree. Adoption of spray drying technology in sweetpotato processing would, therefore, open up a new market opportunity for the sweetpotato industry.

Technical Abstract: An approach intended to increase the consumption of sweetpotatoes is to convert sweetpotato puree into a dried powder to be used as a functional ingredient in food systems. Spray-drying, which has been used for commercial production of several fruit and vegetable powders, has not yet been studied for sweetpotato processing. Thus, the objective was to determine the effects of alpha-amylase, maltodextrin concentration, and inlet air temperature on the physicochemical characteristics of spray-dried sweetpotato powder. Amylase and elevated temperature were employed to reduce puree viscosity before spray-drying in a pilot-scale dryer. A face center cube design was used to evaluate the effects of amylase level (0, 3.75, and 7.5 ml/kg puree), maltodextrin concentration (0, 10 and 20%), and inlet air temperature (150, 190 and 220C) on powder characteristics. Model-fitting using response surface methodology was performed to examine the effects of independent variables on the moisture content, color, water absorption, solubility, particle size, bulk density, and glass transition temperature. The data was fit to a full second order polynomial equation; however, only the linear and quadratic terms proved to be significant for most dried powder attributes. Maltodextrin significantly increased powder solubility, altered the hue value, and raised the glass transition temperature of the powder. Pre-treatment with alpha-amylase resulted in a lower glass transition temperature and a decrease in particle size. Overall, results show that good quality sweetpotato powders can be produced using this drying method, with potential applications in food and nutraceutical products.