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vol. 15, nr. 2 (2010)
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Colour changes of anthocyanin pigments from purple carrot juice in aqueous solutions at various pH values
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Marcin Kidoń, Janusz Czapski
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Department of Fruit and Vegetable Technology, Institute of Food Technology of Plant Origin Poznań University of Life Sciences ul. Wojska Polskiego 31, 60- 624 Poznań |
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vol. 15 (2010), nr. 2,
pp. 333-345
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abstract:
In this study changes of colour parameters CIE L*a*b*, absorption of light, and anthocyanin pigment contents in purple carrot juice solutions at pH values from 1.0 to 8.0 before and after heating at 80°C for 6 hours were investigated. The initial anthocyanin content of solution was 10.8 mg(100 cm3)-1, 25% of which were non-acylated pigments. It was found that in highly acidic conditions (pH 1.0 to 3.0) colour differences between the solutions were almost invisible. Significant colour differences were found between the solution with pH 1.0 and solutions with pH above 4.0. Increasing pH values from 1.0 to 6.0 resulted in a reduction of the quantity of absorbed light. Beyond pH 6.0 absorbance values increased, while batochromic shifts towards longer wavelength were observed. After 6 hours of heating in solution with pH 1.0, 65% of the initial anthocyanin pigment content remained, while at pH 4.5 and pH 6.0, 46% and only 30%, respectively. Anthocyanins degradation proceed the fastest at pH 6.0 (k = 0.256 h-1), and the slowest at pH 1.0 (k = 0.049 h-1). Heating for 6 hours at pH from 1.0 to 3.0 caused slight colour changes. At higher pH the changes were greater – red parameter (a*) and yellow parameter (b*) decreased, while lightness (L*) increased.
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keywords:
anthocyanin pigments, colour, heating, purple carrot
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original in:
Polish
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