Structural and chromatic stability of purple pitaya (Hylocereus polyrhizus [Weber] Britton & Rose) betacyanins as affected by the juice matrix and selected additives

Ascorbic, isoascorbic, and citric acids were applied for stabilisation of betacyanins during thermal treatment of purple pitaya juice at pH 4 and 6, respectively. In addition, to exclude matrix effects of juice constituents, selected food ingredients were added to a pigment preparation comprising the entire betacyanin pattern of purple pitaya, but being devoid of sugars, acids and pectic substances. After thermal treatment at pH 4, pigment retention, overall colour changes, betanin isomerisation, and phyllocactin deacylation were determined. As supported by statistical analyses, pigment stability and colour depended on type and concentration of the respective additive as well as on the pH conditions. Unexpectedly, the stabilising effects of the additives under investigation were more pronounced in purple pitaya juice than in the pigment preparation. After heating at 85 °C for 1 h, optimal pigment retention amounting to 91% was obtained in the juice supplemented with 1% ascorbic acid and adjusted to pH 4. For the first time, formation of indicaxanthin and isoindicaxanthin upon thermal treatment of purple pitaya juice is reported.