Background. Increased consumption of fruits and vegetables signifi cantly reduces the risk of cardio-vascular disease. This benefi cial eff ect on the human organism is ascribed to the antioxidant compounds these foods contain. Unfortunately, many products, particularly vegetables, need to be subjected to thermal processing before consumption. The aim of this study was to determine the eff ect of such thermal treatment on the antioxidant capacity and pigment contents in separated fractions of violet pigments (betacyanins) and yellow pigments (betaxanthins and betacyanins). Material and methods. Fractions of violet and yellow pigments were obtained by separation of betalain pigments from fresh roots of 3 red beet cultivars using column chromatography and solid phase extraction (SPE). The betalain pigment content was determined in all samples before and after thermal treatment (90°C/30 min) by spectrophotometry, according to Nilsson's method [1970] and antioxidant capacity was assessed based on ABTS. Betalain pigments in the separated fractions were identifi ed using HPLC-MS. Results. After thermal treatment of betacyanin fractions a slight, but statistically signifi cant degradation of pigments was observed, while the antioxidant capacity of these fractions did not change markedly. Losses of betacyanin content amounted to 13-15% depending on the cultivar, while losses of antioxidant capacity were approx. 7%. HPLC/MS analyses showed that before heating, betanin was the dominant pigment in the betacyanin fraction, while after heating it was additionally 15-decarboxy-betanin. Isolated fractions of yellow pigments in red beets are three times less heat-resistant than betacyanin fractions. At losses of yellow pigment contents in the course of thermal treatment reaching 47%, antioxidant capacity did not change markedly (a decrease by approx. 5%). In the yellow pigment fractions neobetanin was the dominant peak in the HPLC chromatogram, while vulgaxanthin was found in a much smaller area, whereas after heating additionally 2-decarboxy-2,3-dehydro-neobetanin was detected. Conclusion. Both groups of betalain pigments (betacyanins and betaxanthins) exhibit antioxidant capacity before and after heating. Violet beatacyjanins are 3 times more stable when heated than yellow betaxanthins.
Red beets and their products are mainly consumed after processing. In this study, the effect of pH on changes in antioxidant capacity (AC) and the content of betalain pigments were analysed during the heating of a betalain preparation solution. With pH ranging from 4 to 9 during the heat--treatment, the content of red pigments decreased depending on the pH level of the sample. The losses of red pigments in the investigated betalain preparation solution increased along with rising pH levels of the heated solution. The greatest losses were recorded at pH of 9.0. An opposite correlation was observed for yellow pigments. The content of yellow pigments in the heated betalain preparation solution was increasing along with increasing pH. The most pronounced increase in the content of yellow pigments was found at pH of 6.5 and 7.0. At the same time, the heated betalain preparation solution was shown to exhibit a higher antioxidant capacity at pH of 6.0 (14.9 μmol Trolox/mL) than at pH of 4.0 (12.6 μmol Trolox/mL). It was observed that the increase in the antioxidant capacity in heated betalain preparation solutions with pH in the 6.0-6.5 range occurred as a result of increased concentrations of neobetanin, assessed by HPLC, within the pH range from 5.0 to 6.5.
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