Abstract
Sweet potato proteins have been shown to possess antioxidant and antidiabetic properties in vivo. The ability of a protein to exhibit systemic effects is somewhat unusual as proteins are typically susceptible to digestive enzymes. This study was undertaken to better understand how digestive enzymes affect sweet potato proteins. Two fractions of industrially processed sweet potato peel, containing 6.8% and 8.5% protein and 80.5% and 83.3% carbohydrate, were used as a source of protein. Sweet potato proteins were incubated with pepsin, trypsin, and chymotrypsin and protein breakdown was visualized with SDS-PAGE. After pepsin digestion, samples were assayed for amylase inhibitory activity. Sporamin, the major storage protein in sweet potatoes, which functions as a trypsin inhibitor as well, exhibited resistance to pepsin, trypsin, and chymotrypsin. Sporamin from blanched peel of orange sweet potatoes was less resistant to pepsin digestion than sporamin from outer peel and from extract of the white-skinned Caiapo sweet potato. Trypsin inhibitory activity remained after simulated gastric digestion, with the Caiapo potato protein and peel samples exhibiting higher inhibitory activity compared to the blanched peel sample. Amylase and chymotrypsin inhibitory activity was not present in any of the samples after digestion.
Highlights
Sweet potato proteins possess numerous nutraceutical properties
Multiple proteins isolated from sweet potatoes have been shown to possess trypsin inhibitory activity (Sugiura et al 1973; Obidairo and Akpochafo 1984; Hou and Lin 1997; Jaw et al 2007); the protein found in the greatest quantity that possesses trypsin inhibitory activity a 2014 The Authors
The objectives of this study were to determine if proteins were present in sweet potato extracts that were resistant to digestive enzymes and if activities were retained after in vitro digestion, in order to better understand how sweet potato proteins could exhibit systemic effects in the body
Summary
Sweet potato proteins possess numerous nutraceutical properties. Sweet potato trypsin inhibitor proteins have been shown to possess antioxidant properties with scavenging abilities against 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl radical (Hou et al 2001, 2005), and reactive nitrogen species (Huang et al 2007a). They have been shown to increase serum superoxide dismutase, catalase, and glutathione peroxidase activity in mice (Huang et al 2008).
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