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Title: Extraction of anthocyanins from industrial purple-fleshed sweetpotatoes and enzymatic hydrolysis of residues for fermentable sugars


Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2010
Publication Date: 11/11/2010
Citation: Bridgers, E., Chinn, M.S., Truong, V. 2010. Extraction of anthocyanins from industrial purple-fleshed sweetpotatoes and enzymatic hydrolysis of residues for fermentable sugars. Industrial Crops and Products. 32(3):613-620.

Interpretive Summary: Recent awareness in health and wellness as well as cost of fossil fuel provides opportunities for utilizing agricultural crops including purple-fleshed sweetpotatoes in the processing of functional foods, chemicals and biofuels. The purple-fleshed industrial sweetpotatoes (ISP) have been bred not only for high levels of antioxidants in the form of anthocyanins but also high starch content which can be hydrolyzed into sugars for use as feedstock in bioethanol and bio-based chemical production. The reported investigation aimed to develop a process for extracting anthocyanin pigments from ISP and utilizing the residues for the production of fermentable sugars. The effects of solvents (water, methanol and ethanol) and temperatures on anthocyanin extraction, and how they impact on the hydrolysis of the residues into fermentable sugars were evaluated. Acidified methanol at 80°C showed the highest anthocyanin content in the extracts. On the other hand, the solid residues derived from extraction with acidified ethanol at 50°C had highest recovery of glucose. Overall, fermentation of the residues from anthocyanin extraction with solvents resulted in 38% less ethanol as compared to the treatment that did not undergo extraction. The results provide benchmark information for further development of an integrated process to achieve a high recovery of anthocyanins and starch conversion to fermentable sugars for industrial applications.

Technical Abstract: Recent trends in health and wellness as well as fossil fuel dependent markets provide opportunities for agricultural crops as renewable resources in partial replacement of synthetic components in food, clothing and fuels. This investigation focused on purple-fleshed industrial sweetpotatoes (ISPs), a crop which is used for industrial purposes because it produces relatively high quantities of antioxidants in the form of anthocyanins as well as high starch content for potential hydrolysis into fermentable sugars. Laboratory extraction and enzymatic hydrolysis studies were conducted on purple-fleshed ISPs in order to evaluate the effects of solvent, extraction temperature and solid loading on recovery of anthocyanins and fermentable sugars. Total monomeric anthocyanin and phenolic concentrations of the extracts were measured. Residual solids from anthocyanin extraction were subsequently hydrolyzed for sugar production (maltotriose, maltose, glucose and fructose). Extraction temperature of 80 °C using acidified methanol at 3.3% (w/v) solid loading showed the highest anthocyanin recovery at 186.1 mg cyanidin-3-glucoside/100 g fw. Acidified solvents resulted in 10–45% and 16–46% more anthocyanins than non-acidified solvents of ethanol and methanol, respectively. On average, glucose production ranged from 268 to 395 mg/g dry ISP. Solid residues that went through extraction with acidified ethanol at 50 °C at 17% (w/v) solid loading had the highest average production of glucose at 395 mg/g dry ISP. Residues from methanol solvents had lower glucose production after hydrolysis compared to those of ethanol based extraction. Fermentation of produced sugars from ISP residues was limited, where 38% less ethanol was produced from extraction residues compared to treatments that did not undergo initial extraction. Overall, purple-fleshed ISPs are amenable to anthocyanin and phenolic extraction, making it a suitable substrate for development of industrial colorants and dyes. However, more research is needed to obtain a suitable extraction point when trying to achieve a high recovery of anthocyanins and effective starch conversion to fermentable glucose.