Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2008
Publication Date: 7/1/2008
Citation: Steed, L.E., Truong, V. 2008. Anthocyanin content, antioxidant activity and selected physical properties of flowable purple-fleshed sweetpotato purees. Journal of Food Science. 73(5):S215-S221. Interpretive Summary: Purple-fleshed sweetpotatoes (PFSP) have been utilized as a healthy food commodity and source of natural food colorants in Asia. Research indicated that the extracted anthocyanins from PFSP have high antioxidant capacity that helps to reduce the risk of chronic diseases. Recently, there are growing interests in the sweetpotato industry in the United States in exploring the market opportunities for PFSP as table stocks and processed products. In sweetpotato processing, the process usually begins by transforming the roots into puree. For the orange-flesh sweetpotatoes (OFSP) with dry matter content of 17 – 25%, the predominant cultivars in the local industry, the materials have successfully been processed into flowable purees that can be handled in various processing operations. However, PFSP have higher dry matter content (30 – 38%), and potentially different starch properties, which present challenges for the commercial puree production. For the PFSP puree to be used as an ingredient, it must flow so that it can be mixed and pumped through processing equipment. The objectives of this research were to examine the nutraceutical characteristics of PFSP that have recently been grown in limited commercial production in the United States, and to evaluate the rheological properties of the PFSP purees, in order to develop a process for producing flowable purees to be utilized as functional ingredients in the food industry. Results indicated that, the locally grown PFSP have nutraceutical components in competitive levels with other food commodities known to be good sources of antioxidants. Both raw and steamed PFSP had high phenolic and anthocyanin content. In order to make a flowable puree, water must be added to the steamed PFSP to reduce the dry matter content to 18-21%. The flowable PFSP puree exhibited shear thinning behavior similar to the commercial purees from OFSP, and its nutraceutical content was within the range of the high antioxidant purees from other fruits and vegetables. With its flowability, attractive purple color and high nutraceutical content, the PFSP puree has potential as a functional food ingredient in various food systems.
Technical Abstract: With high levels of polyphenolic compounds, purple-fleshed sweetpotatoes (PFSP) have been utilized as a healthy food commodity and source of natural food colorants in Asia. In the sweetpotato industry of the United States, there are growing interests in exploring these market opportunities for PFSP. A locally grown PFSP cultivar was analyzed for nutraceutical properties. Total phenolic content ranged from 313.6 to 1483.7 mg chlorogenic acid equivalent/100 g fresh weight (fw), and anthocyanin contents were between 51.5 and 174.7 mg anthocyanins/100 g fw, respectively. The DPPH radical scavenging activities were 47.0 to 87.4 µmol trolox equivalent/g fw, and the oxygen radical absorbance capacity (ORAC) values were between 26.4 and 78.2 µmol trolox equivalent/g fw. Unlike orange-fleshed sweetpotatoes (OFSP), the steamed roots of PFSP formed a thick paste which required a process modification to produce flowable purees. Rheological testing indicated that adjusting the dry matter of PFSP to 18% produced purees with flow properties similar to the OFSP purees. Nutraceutical values of the PFSP purees were within ranges reported for fruits and vegetables with high polyphenolic content and antioxidant capacity.