No abstract

The impact of heating at 75, 85, and 95 • C during 60 min on overall color and betalain retention of yellow-orange cactus pear (Opuntia ficus-indica [L.] Mill. cv. 'Gialla') juice after a 24-h color regeneration period was investigated. The addition of 0.1% isoascorbic acid prior to heating minimized color alteration as well as betalain degradation to a significant level. A correlation between the total betaxanthin retention and the indicaxanthin/isoindicaxanthin ratio was detected in heated juice samples, thus proving the indicaxanthin/isoindicaxanthin ratio as a valuable indicator of thermally treated cactus pear juices. Notably, the same ratio was instrumental for retrospectively calculating the initial betaxanthin content. Additionally, storage experiments over a period of 6 mo were conducted. Samples kept in the dark exhibited notably better color and pigment retentions as compared to illuminated samples. A significantly stabilizing effect was also observed in samples with isoascorbic acid fortification. While indicaxanthin and betanin were predominantly degraded through hydrolytic cleavage upon both heat exposure and storage, isomerization was only marginal for betanin. In contrast, 2-decarboxy-betanin formation was exclusively found for nonfortified heated samples while decarboxylated indicaxanthin could not be detected. Thermal treatment and pigment regenerationAliquots of 20 mL cactus pear juice (pH 4) with and without addition of 0.1% isoascorbic acid were heated in a water bath at 75, 85, and 95 • C under continuous stirring in a 100-mL round-neck glass sealed with a rubber stopper for 5, 10, 15, 30, 45, and 60 min, respectively. Immediately after heating, samples were cooled in an ice bath for 90 s to stop further degradation. Following a period