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Research Project: Improved Processes for the Preservation and Utilization of Vegetables, Including Cucumber, Sweetpotato, Cabbage, and Peppers to Produce Safe, High Quality Products with Reduced Energy Use and Waste

Location: Food Science Research

Title: Acid inhibition on polyphenol oxidase and peroxidase in processing of anthocyanin-rich juice and co-product recovery from purple-fleshed sweetpotatoes

Author
item TRUONG, AN - North Carolina State University
item THOR, YIWEN - North Carolina State University
item HARRIS, KEITH - North Carolina State University
item SIMUNOVIC, JOSIP - North Carolina State University
item Truong, Van Den

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2019
Publication Date: 7/1/2019
Citation: Truong, A.N., Thor, Y., Harris, K., Simunovic, J., Truong, V. 2019. Acid inhibition on polyphenol oxidase and peroxidase in processing of anthocyanin-rich juice and co-product recovery from purple-fleshed sweetpotatoes. Journal of Food Science. 84(7):1730:1736. https://doi.org/10.1111/1750-3841.14664.
DOI: https://doi.org/10.1111/1750-3841.14664

Interpretive Summary: Sweetpotatoes (SP) are rich in phytonutrients and antioxidant activities. For juice extraction, SP are usually subjected to a heat treatment to inactivate the pigment-degrading enzymes. However, heating gelatinizes starch and produces cooked flavor, which are drawbacks in SP juice extraction. An alternative process using acidified water to inactivate the enzymes was developed to overcome the stated problems and recover the co-products, namely starch and high fiber residue. With the developed process, 167 g dried starch and 140 g dried high-fiber residue were obtained for each kg raw PFSP, as well as the highly pigmented-juice. The results demonstrate an efficient process to produce pasteurized SP juice with high bioactive compounds and provide an alternative for the sweetpotato industry in producing natural colorants and functional beverages from SP with varying flesh colors.

Technical Abstract: With high phytochemical and starch contents, purple-fleshed sweetpotatoes (PFSP) have been processed into various functional ingredients and food products including juices and natural colorants. For juice processing, PFSP are usually subjected to heat treatment for inactivation of pigment-degrading enzymes. However, heating of sweetpotatoes gelatinizes starch and produces thick slurry with cooked flavor, which are the drawbacks. Development of alternative processes to overcome the stated problems will be beneficial to sweetpotato processors. This study demonstrated that acidified water (greater than or equal to 3% w/v citric acid) was effective in inhibiting polyphenol oxidase and peroxidase in raw PFSP resulting in an attractive reddish juice. About 93% total phenolics (TP) and 83% total monomeric anthocyanins (TMA) in PFSP were extracted by two repeated extractions. The combined PFSP juice (3.2 L/kg PFSP) had high levels of TP (1,850 mg/L) and TMA (475 mg/L). With the developed process, 167 g dried starch, and 140 g dried high-fiber pomace were obtained for each kg raw PFSP, besides the highly pigmented juice. Pasteurization of the PFSP juice samples (pH 3.2) at 80 °C for 12 s resulted in 15% loss in TMA and had no effect on TP. The results indicated an efficient process to produce sweetpotato juice with high bioactive compounds and recovery of starch and high dietary fiber pomace as co-products.