Effects of processing and storage on juice colour and betacyanin stability of purple pitaya (<Emphasis Type="Italic">Hylocereus polyrhizus</Emphasis>) juice

Purple pitaya (Hylocereus polyrhizus) fruits have been recently proposed as a promising source of betalains. In the present study, purple pitaya juice processing at pilot-plant scale is reported for the first time. Each processing step was examined in terms of juice colour and betacyanin retention. Lightness (L ^*) and hue angle (h°) values were strongly influenced by juice filtration, while chroma (C ^*) and betacyanin retention were most strongly altered by pasteurisation. Three systems of juice pasteurisation were evaluated. Betacyanin loss and colour alteration were minimal upon pasteurisation in an HTST system and a standard tubular heat exchanger, respectively. Additionally, storage experiments using mucilage-free purple pitaya juice were conducted. Whereas light exposure of unsupplemented samples resulted in significant pigment degradation, detrimental effects of light exposition were completely prevented by the addition of 1% ascorbic acid prior to storage. After 6 months, about 70% of the initial betacyanin content was retained in the presence of ascorbic acid, irrespective of illumination.     

Betalain Stability and Degradation—Structural and Chromatic Aspects

ABSTRACT:  In recent years, food coloring with artificial colorants has been increasingly disapproved by consumers. In return, application of coloring foodstuffs, among them betalain-containing fruits and vegetables, has gained importance for the food industry. As commonly true for natural pigments, betalains are afflicted with inferior stability compared to synthetic dyes. Especially temperature, oxygen, and light are known to exhibit detrimental effects on betalain integrity, while certain antioxidants and chelating agents may act as stabilizers. Only recently, several studies expanded the knowledge on betalain degradation pathways, especially focusing on betacyanin decomposition. Additionally, new findings on stability and stabilization of betalains in cactus fruit juices extended the application range of betalainic foodstuffs. Focusing on betacyanins, the present review discusses betalain degradation mechanisms and provides a survey of compounds and conditions governing betalain stability in a beneficial or an unfavorable way. Finally, strategies for maintaining the chromatic properties and tinctorial strength of betalain-based juices and pigment preparations as well as tools for color modulation by targeted betacyanin degradation are discussed.     

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

ABSTRACT: 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 yellow-orange 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.     

Thermal degradation of betacyanins in juices from purple pitaya [<Emphasis Type="Italic">Hylocereus polyrhizus</Emphasis> (Weber) Britton &; Rose] monitored by high-performance liquid chromatography–tandem mass spectometric analyses

Changes in betacyanin content and colour shade of juices from purple pitaya [Hylocereus polyrhizus (Weber) Britton & Rose] as affected by thermal processing and consecutive cold storage to allow pigment reconstitution were investigated. Pigments from purple pitaya displayed higher stability than earlier investigations on betalains suggested. A novel high-performance liquid chromatography method was established, allowing simultaneous detection of genuine pigments of purple pitaya juice together with their degradation products. In addition to previously described betanin cleavage products (betalamic acid, cyclo-dopa 5-O--glucoside) further degradation products generated after decarboxylation and/or dehydration of phyllocactin and hylocerenin, respectively, were found. Moreover, neobetanin was identified as a thermal degradation product of betanin for the first time. With this newly developed high-performance liquid chromatography method, heating of purple pitaya juice and a commercial pitaya juice concentrate was proven by the detection of thermal betacyanin degradation products that had not been described, so far.