Selection of Sweetpotato Lines with High Protein Content and/or Low Trypsin Inhibitor Activity

Abstract

Low content of protein and the presence of an anti-nutritional factor, ‘trypsin inhibitor (TI)’ reduce the nutritional value of sweetpotato (Ipomoea batatas (L.) Lam.) when used as animal feed. Attempts have been made to develop sweetpotato varieties with a high protein content and/or low trypsin inhibitor activity (TIA). Using approx. 800 breeding lines of sweetpotato, the crude protein content and TIA were determined during 6 seasons from 1998 to 2003. Fifteen lines with a high protein content (27.8–44.6 mg/g DW) and 7 lines with a low TIA (11–137 U/mg DW) were selected, when compared to the standard variety ‘Shiroyutaka’ (crude protein content: 19.9 mg/g DW, TIA: 186 U/mg DW). Among the lines used, there was a strong positive correlation between TIA and the crude protein content (r = 0.871**). However, lines, ‘Q94128-1’ (crude protein content: 28.9 mg/g DW, TIA: 21 U/mg DW) and ‘KNF94225-13’ (crude protein content: 35.5 mg/g DW, TIA: 63 U/mg DW) showed a high protein content and a low TIA. Electrophoretic analysis and activity staining of TIs extracted from these two lines revealed a considerably lower amount of trypsin inhibitory bands compared to that in ‘Shiroyutaka’. Partially purified TIs from ‘Shiroyutaka’ were estimated to correspond to sporamins, sweetpotato major storage root proteins.