Effects of processing and storage on juice colour and betacyanin stability of purple pitaya (Hylocereus polyrhizus) juice
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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.
KeywordsPurple pitaya Hylocereus polyrhizus Betacyanins Stability Juice processing Storage Colouring foodstuff
The authors are grateful to Mr. K. Mix for his excellent technical assistance in the production of purple pitaya juice. AB Enzymes (Darmstadt, Germany), Biocatalysts (Cardiff, UK), DSM Specialties (Seclin, France), Erbslöh Geisenheim Getränketechnologie (Geisenheim, Germany) and Novozymes Switzerland (Dittingen, Switzerland) are acknowledged for providing the enzyme preparations.
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