Impact of Thermal Treatment on Color and Pigment Pattern of Red Beet (Beta vulgaris L.)Preparations

The impact of heating at 85 °C during 8 h on overall color and betalain pattern of red beet (Beta vulgaris L. ssp. vulgaris)juice was investigated. Although the hue angle of 358° in fresh juice was indicative of the typical red-purple appearance, heating for 8 h induced an unexpected shift to 62° resulting in a yelloworange solution. To monitor the underlying structural alterations of betalains, a new high-performance liquid chromatography separation compatible with mass spectrometry was developed. Applying this method, 2 novel yellow neobetanin structures and 2 orange-red betanin degradation products were preliminarily identified, and neobetanin formation resulting from heat exposure was proven for the 1st time. These 5 compounds were held responsible for the orange shift of red beet juice during thermal treatment. The relevance of these findings for industrial beet processing was demonstrated by comparison of pigment patterns of heated red beet juice samples and a commercial concentrate. On the basis of these results, a scheme for the thermal degradation of betanin is proposed.