The influence of pH and moderate heating (50°C) on the color and individual betacyanin content of pigment extracts from cactus pear fruits (Opuntia stricta) is studied in the course of this paper. The study is carried out by using a high-performance liquid chromatograph equipped with a photodiode array detector and coupled to a mass spectrometer. The results point to a pH-dependent degradation mechanism, which is reflected in the chromatographic patterns obtained at different exposure times (0-28 h). At pH 3, 15-descarboxy-betanin is the most resistant betacyanin derivative. At pH 5, seven peaks are detected after 8 h, the most prominent being betanin, cyclo-dopa-5-O-β-glucoside, and betalamic. In the assay conducted at pH 7, rapid color loss affects all the pigments, except for betanin.