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.
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