Physical features, phenolic compounds, betalains and total antioxidant capacity of coloured quinoa seeds (Chenopodium quinoa Willd.) from Peruvian Altiplano

•Peruvian Altiplano coloured quinoa (Chenopodium quinoa Willd.) varieties.•High content of phenolics and betalains.•High total antioxidant capacity (TAC) measured by direct procedure.•Betalains correlated with colour parameters and total phenolic content.•TAC correlated with colour, and betalains and total phenolic content. Physical features, bioactive compounds and total antioxidant capacity (TAC) of coloured quinoa varieties (Chenopodium quinoa Willd.) from Peruvian Altiplano were studied. Quinoa seeds did not show a pure red colour, but a mixture which corresponded to different fractal colour values (51.0–71.8), and they varied from small to large size. Regarding bioactive compounds, total phenolic (1.23–3.24mg gallic acid equivalents/g) and flavonol contents (0.47–2.55mg quercetin equivalents/g) were highly correlated (r=0.910). Betalains content (0.15–6.10mg/100g) was correlated with L colour parameter (r=−0.569), total phenolics (r=0.703) and flavonols content (r=0.718). Ratio of betaxanthins to betacyanins (0.0–1.41) was negatively correlated with L value (r=−0.744). Whereas, high TAC values (119.8–335.9mmol Trolox equivalents/kg) were negatively correlated with L value (r=−0.779), but positively with betalains (r=0.730), as well as with free (r=0.639), bound (r=0.558) and total phenolic compounds (r=0.676). Unexploited coloured quinoa seeds are proposed as a valuable natural source of phenolics and betalains with high antioxidant capacity.