BETANINE STABILITY IN BUFFERED SOLUTIONS CONTAINING ORGANIC ACIDS, METAL CATIONS, ANTIOXIDANTS, OR SEQUESTRANTS

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Abstract
The rate of betanine degradation as affected by monocarboxylic acids (lactic acid, acetic acid), metal cations (Fe+++, Cu++), antioxidants (ascorbic acid, α‐tocopherol) and sequestrants (citric acid, Na2 EDTA) was studied. Betanine was extracted from beets using water, and purified by molecular exclusion and adsorption chromatography. Column packings used were Sephadex G‐25, polyacrylamide, and polyvinylpolypyrrolidone. The effect of food additives on the rate of oxidation of betanine in buffered systems was determined using a modification of the active oxygen method. A betanine solution was placed in a reaction chamber, held at 75° C, and oxygen was passed through the solution at a rate of 3 ml/min. The half‐life value of betanine at 75° C, pH 5.0 in a phosphate buffer was 48.0 ± 1.0 min (control). Addition of 100 ppm lactic acid had no effect on stability (41 ± 1.7 mm), while 5.9% acetic acid caused a decrease in stability (33.4 ± 1.9 min) possibly as a result of pH changes at elevated temperatures. Metal ions at a level of 100 ppm caused an increase in the degradation rate compared to that of the control with addition of iron resulting in a half‐life value of 33 ± 1.4 min. Copper had the greatest effect, reducing the half‐life value to 6.0 ± 0.2 mm. Neither 100 ppm ascorbic acid nor 100 ppm a‐tocopherol affected the half‐life value of betanine (45.3 ± 2.3 and 50.2 ± 3.4 min, respectively). Ascorbic acid at 1000 ppm decreased the halt‐life value (32.3 ± 3.3 min), whereas 10,000 ppm citric acid and 10,000 ppm EDTA caused an increase in the half‐life value of 1.5 times compared to that of the control (69.4 ± 3.1 and 70.7 ± 7.1 min). Both 100 and 1000 ppm citric acid had no effect on betanine stability.