Novel value-added uses for sweet potato juice and flour in polyphenol- and protein-enriched functional food ingredients

Authors: GRACE, MARY - North Carolina State University; TRUONG, AN - North Carolina State University; Truong, Van Den; RASKIN, ILYA - Rutgers University; LILA, MARY ANN - North Carolina State University

Submitted to: Food Science and Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2015
Publication Date: 9/1/2015
Publication URL: https://handle.nal.usda.gov/10113/61780
Citation: Grace, M.H., Truong, A.N., Truong, V., Raskin, I., Lila, M. 2015. Novel value-added uses for sweet potato juice and flour in polyphenol- and protein-enriched functional food ingredients. Food Science and Nutrition. 3(5)415-424. doi: 10.1002/fsn3.234.

Interpretive Summary: Colored-fleshed sweetpotatoes (SP) have been processed into flours and juices with various levels of phytonutrients and proteins. This research aimed to develop novel functional food ingredients through fortification of yellow and orange SP flours with phenolics and anthocyanins from fruit juices, or, alternatively capturing bioactive polyphenols present in purple-fleshed SP juice into other protein-rich matrices. Results indicated that SP flours efficiently sorbed, concentrated and stabilized the antioxidant polyphenols in fruit juices like blackcurrant, blueberry and muscardine grape. Using the same strategy, purple sweetpotato polyphenols were loaded on protein-rich matrices like defatted soy flour, light roast peanut and rice protein concentrate to create food ingredient rich in both protein and stable SP polyphenols. All tested matrices were able to preserve anthocyanins and phenolics for a storage period up to 25 weeks, and the products retained their vibrant color, even when stored at 37 ºC. Nutritional analysis and sensory spectrum evaluation of the products suggested the potential use for highly functional food products.

Technical Abstract: Blackcurrant, blueberry, and muscadine grape juices were efficiently sorbed, concentrated, and stabilized into dry granular ingredient matrices which combined anti-inflammatory and antioxidant fruit polyphenols with sweet potato functional constituents (carotenoids, vitamins, polyphenols, fibers). Total phenolics were highest in blackcurrant-orange sweet potato ingredient matrices (34.03 mg/g), and lowest in muscadine grape-yellow sweet potato matrices (10.56 mg/g). Similarly, anthocyanins were most concentrated in blackcurrant fortified orange and yellow sweet potato matrices (5.40 and 6.54 mg/g, respectively). Alternatively, other protein-rich edible matrices (defatted soy flour, light roasted peanut flour, and rice protein concentrate) efficiently captured polyphenols (6.09–9.46 mg/g) and anthocyanins (0.77–1.27 mg/g) from purple-fleshed sweet potato juice, with comparable efficiency. Antioxidant activity correlated well with total phenolic content. All formulated ingredient matrices stabilized and preserved polyphenols for up to 24 weeks, even when stored at 37°C. Complexation with juice-derived polyphenols did not significantly alter protein or carbohydrate profiles of the matrices. Sensory evaluation of the ingredient matrices suggested potential uses for a wide range of functional food products.