Identification of anthocyanins of pinta boca (Solanum stenotomum) tubers

The coloured tubers of Solanum stenotomum, a native and very common crop in the Bolivian and Peruvian Altiplano, were analysed to determine their anthocyanin composition. Tubers were boiled, ground and freeze-dried, in a pre-treatment step, in order to inhibit enzymatic reactions and to obtain a stable dried powder or “concentrate”. After dissolving the tuber concentrate and the subsequent purification, the anthocyanin composition was characterised by HPLC-DAD-MS. Eleven different compounds were found, all of them acylated with hydroxycinnamic acids and most of them having the same substitution pattern, anthocyanidin 3-acylrutinoside-5-glucoside. The principal anthocyanin was petunidin 3-O-p-coumaroylrutinoside-5-O-glucoside. Other anthocyanins found were 3-O-p-coumaroylrutinoside-5-O-glucoside of peonidin, malvidin and delphinidin, 3-O-feruloylrutinoside-5-O-glucoside of petunidin, peonidin and malvidin, 3-O-caffeoylrutinoside-5-O-glucoside of petunidin and peonidin and 3-O-p-coumaroylrutinoside of petunidin. The presence of acylation in all the anthocyanins found in the sample would improve their stability against some degrading factors and makes the pinta boca tubers a potential source of more stable anthocyanins.