Monitoring by liquid chromatography coupled to mass spectrometry the impact of pH and temperature on the pigment pattern of cactus pear fruit extracts.

The influence of pH and moderate heating (50 degrees 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-beta-glucoside, and betalamic. In the assay conducted at pH 7, rapid color loss affects all the pigments, except for betanin.