Development and Characterization of Spray Dried Sweetpotatoes
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Date
2005-12-18
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Abstract
Sweetpotatoes are a nutritious vegetable rich in calories, vitamins, minerals, and biologically active phytochemicals. However, the consumption of sweetpotatoes has been declining. Very few sweetpotato product choices exist for consumers beyond the raw root. Furthermore, special storage and handling requirements for sweetpotatoes have proven to be a challenge to incorporating this healthy vegetable into processed food products.
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. One 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.
Several methods of producing a functional powder in an efficient manner were investigated since spray drying has never been applied to sweetpotato puree. The high viscosity of sweetpotato puree was anticipated to be a challenge in pumping and atomization during the spray drying process. Moreover, the sticky behavior due to high sugar content in sweetpotato puree may affect spray drying efficiency. Many spray dried products make use of a drying aid such as maltodextrin in order to increase the glass transition temperature and reduce stickiness thus facilitating product recovery. These pre-drying treatments of viscosity reduction and maltodextrin addition, as well as drying temperature, were expected to have effects on the physicochemical characteristics of the final spray dried powder. Thus, model-fitting using response surface methodology was performed to examine the effects of the pre-drying treatments and spray drying conditions on the moisture content, color, water absorption, solubility, particle size, bulk density, and glass transition temperature of the spray dried powder.
Elevated temperature and the action of amylase proved to be effective in reducing puree viscosity. Furthermore, pre-treatment with alpha-amylase resulted in dried powders with a lower glass transition temperature and smaller particle size. The addition of maltodextrin significantly increased powder solubility, altered the hue value, and raised the glass transition temperature of the powder. Sound models were developed for some attributes while further study is needed to accurately develop prediction models for other powder characteristics. Difficulty existed in determining the optimal drying conditions for sweetpotatoes as the best finished product characteristics for dried sweetpotato powders are dependent on the finished product application. However, spray drying sweetpotatoes with a combination of amylase treatment and maltodextrin created a quality powder balancing all functional characteristics.
To better determine potential applications of powders produced with various levels of amylase and maltodextrin, nutrient composition and rheological properties of the powders in solution were examined and compared to sweetpotato puree. Many of the characteristic sweetpotato nutrients such as beta-carotene and ascorbic acid were severely reduced during the spray drying of sweetpotato puree. Further isomerization of beta-carotene also occurred during dehydration. In addition to thermal degradation of components, the addition of maltodextrin as a drying aid diluted the amount of nutrients in the resulting powder. Rheological characterization of the powders found the viscosity of the reconstituted solutions was much lower than that of the puree at the same solid concentration. However, the reconstituted sweetpotato slurries did behave similarly to pregelatinized starch solutions.
Spray dried sweetpotato powders have been developed to become a functional ingredient in foods by enhancing natural color, flavor, and functionality. Overall, results show that good quality sweetpotato powders can be produced using this drying method. Despite the need for further increased nutrient retention, these powders have the potential to be a good source of beta-carotene and minerals as well as used in food systems as a thickener. As product developers research ways to improve food products, sweetpotato powders could potentially be used in dry mixes, soups, beverages, and other food and nutraceutical products. Furthermore, additional research could optimize the physicochemical characteristics for a specific product application.
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Keywords
spray drying, glass transition, beta-carotene, maltodextrin, rheology, alpha-amylase, sweetpotatoes
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Degree
MS
Discipline
Food Science
