Effect of Drying and in vitro Gastrointestinal Digestion on Antioxidant Activities of Orange and Purple Fleshed Sweet Potatoes
Keywords:Sweet potatoes, Hot air drying, Antioxidant activities, In vitro gastrointestinal digestion
Colored sweet potato flesh is especially rich in bioactive compounds that exert antioxidant properties. Drying was applied to reduce moisture content of sweet potatoes for a safe storage. However, little is known how their antioxidant activity changes after drying and gastrointestinal digestion. In this research, orange (OFSP) and purple (PFSP) fleshed sweet potato were peeled, sliced and subsequently dried at three different conditions including 55 °C for 16 h, 70 °C for 10 h and 85 °C for 8 h to reduce moisture content below 8% (wb). Bioactive compounds in terms of total phenolic content (TPC), total carotenoid content (TCC), total anthocyanin content (TAC) and their associated antioxidant activities by Ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays were analyzed. In addition, the digesta obtained in each phase (oral, gastric and intestinal) of gastrointestinal digestion were used to determine all antioxidant activities, accordingly. Results showed drying at 70 and 85 °C tended to give negative effects since TPC and TCC of OFSP and TPC and TAC of PFSP decreased to a significant extent (p < 0.05) compared to those of freeze dried samples. The exception was for PFSP dried at 55 °C that showed the increased TPC and TAC corresponding to the highest antioxidant activities either by FRAP and DPPH. Based on in vitro gastrointestinal digestion, a slight increase or decrease in TPC, FRAP and DPPH of both sweet potato varieties was observed during gastric and intestinal phases. Results suggested that low drying temperature at 55 °C was recommended for both OFSP and PFSP since it provided high antioxidant properties which were stable through gastrointestinal digestion.
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