The antioxidant activity of flours from coloured-fleshed potatoes and the pellet snacks produced with the coloured flour serving as one of the dried components varied depending on the potato variety. Blanching in a solution of SO2 during potato flour production was the most important factor affecting the antioxidant and antiradical activity of coloured flour and increased the antioxidant activity from 2 to 15 times, dependant on the potato variety and method of determination. However, this increase was not found in the flours obtained from the Blue Congo and Valfi varieties of purple-fleshed potatoes. Flour with the highest antioxidant activity was prepared from Salad Blue and Herbie 26 potato varieties, and Valfi potatoes had the lowest activity. Blue Congo potatoes had much greater total polyphenols and anthocyanins compared to purple-fleshed Salad Blue and red-fleshed Herbie 26 potatoes. In purple-coloured flour, petunidin-2-p-coumarylrutinoside-5-glucoside dominated; and in red-coloured flour, pelargonidin-3-p-coumaorylrutinoside-5-glucoside dominated. Thermal process applied in experimental flour production caused a 38–68% decrease in polyphenols and a 58–72% decrease in anthocyanins and was particularly high in products prepared from tubers of the purple-fleshed Blue Congo and Valfi varieties. The compounds in the dry matter of purple-fleshed Salad Blue and, to a lower degree, present in red-fleshed Herbie 26 affected the higher stability of the anthocyanins present in tubers during the blanching process. The least stabile anthocyanins were found in the purple-fleshed potatoes, malwidin-3-p-coumarylrutinoside-5-glucoside and petunidin-2-p-coumarylrutinoside-5-glucoside, and the most stable were petunidin-3-rutinoside-5-glucoside. In Herbie 26 flour, pelargonidin-3-rutinoside-5-glucoside, pelargonidin-3-caffeoylrutinoside-5-glucoside and pelargonidin-3-rutinoside anthocyanins were present in lower quantities but were better stabilised during thermal processes than the same anthocyanins in the other potatoes varieties examined.
Snacks produced with coloured potato flour had 2–3 times higher antioxidant activity, particularly when measured by DPPH, compared to control samples with commercial potato grits as the flour component and contained on average 40% more of polyphenols. The processes of low shear extrusion and frying utilised for snack production affected a decrease in the antioxidant activity of products with flour from the Blue Congo and Valfi varieties but an increase in activity in snacks with flour from the Salad Blue and Herbie 26 varieties. The anthocyanin content in snacks depends on the variety of potato used for coloured flour production. The highest content of these compounds and the lowest losses during snack processing were in snacks with flour from the purple-fleshed Blue Congo and the red-fleshed Herbie 26 potatoes. The utilisation of experimental, coloured potato flours favourably affected the colour and expansion index of the obtained snacks and did not changed their texture. In particular, the red-coloured flour from Herbie 26 potatoes resulted in an attractive snack colour.