Stability of yellow-orange cactus pear (Opuntia ficus-indica [L.] Mill. cv. 'Gialla') betalains as affected by the juice matrix and selected food additives

The impact of added ascorbic, isoascorbic, and citric acid on heat stability of cactus pear betalains was investigated at pH 4 and 6, respectively. To assess the influence of cactus pear juice matrix compounds such as sugars, organic acids, amino acids, and pectic substances on pigment stability, juice and purified pigment preparations derived there from were assayed separately. Immediately after heating at 85 degrees C for 1 h and a 24 h cool storage period, betalain retention, betanin and proline-betaxanthin isomerisation as well as overall colour changes were determined. Pigment stability and colour characteristics depended on type and concentration of the respective additive as well as on pH conditions. Interestingly, the stabilising effects of the additives under investigation were less pronounced in matrix-free pigment preparations compared to juice samples. Maximum pigment retention amounting to 79% was obtained when 0.1% citric acid was added to the juice at pH 6. For the first time, formation of 2-decarboxybetanin upon thermal treatment of yellow-orange cactus pear juice being more distinct at pH 4 as compared to pH 6 is reported.