Utilization of dragon fruit (Hylocereus spp.) peel as a natural colourant in valorisation

Abstract

The present experiment entitled "Utilization of dragon fruit (Hylocereus spp.) peel as a natural colourant in valorisation" was conducted at Department of Postharvest Management, College of Agriculture, Vellayani during the period of 2021-2023, with the objective to extract the dragon fruit peel colour and to utilize it as a source of natural colourant in valorisation. The study was carried out as three different continuous experiments utilizing good quality ripe dragon fruit types of white flesh with pink skin (Hylocereus undatus) and purple flesh with red skin ( Hylocereus polyrhizus) of uniform maturity. In the first part of the study, colour extracts were prepared from peels of both white and purple dragon fruits by different maceration techniques viz., hydromaceration, maceration in ethyl alcohol, hydromaceration of freeze-dried peel, low temperature hydromaceration and low temperature ethyl alcohol maceration for 24 hours adopting 1:2 peel to solvent ratio. Hydromaceration of purple dragon fruit peel produced extracts with the highest betalain content (67.14 mg L-1) and had an antioxidant activity of 62.49%. Highest total antioxidant activity of 83.61% was found in extracts prepared by low temperature hydromaceration of purple dragon fruit peel with a betalain content of 53.8 mg L-1. Cost of production of 100 mL extract was least (Rs. 51.25) for hydromaceration of the peels of white dragon fruit. Extracts prepared by hydromaceration and low temperature hydromaceration were subjected to ambient and low temperature (4 to 7 ⁰C) storage for three months for analyzing storage stability in the second part of the experiment. In general, storage of colour extract for three months resulted in reduction in betalain content and antioxidant activity. The reduction was comparatively less in hydromacerated samples stored under low temperature 112 (4 to 7 ⁰C) condition. Hydromaceration of the purple dragon fruit peel was selected as the extraction procedure for betalain content for utilization in squash preparation. The peel colour extract prepared by hydromaceration of purple dragon fruit peel was incorporated into white and purple fleshed dragon fruit squash prepared with and without seed for analysis of chemical and sensory quality parameters in the last part of the experiment. Squash prepared from purple fruit had higher betalain content where as antioxidant activity was higher in white fruited squash. The squash prepared with seed had higher antioxidant activity and ascorbic acid, but had lower betalain content. Peel colour extract incorporated squash had higher betalain content and antioxidant activity compared to squash without addition of peel colour. Incorporation of seed and or peel had resulted in enhanced antioxidant activity in both the fruit types. Seedless purple fleshed dragon fruit squash incorporated with peel colour extract had highest betalain content (58.86 mg L-1) with maximum overall acceptability score (8.3); hence subjected to a storage period of three months. Betalain content and antioxidant activity of squash were considerably reduced by three months. Appearance, colour and flavor of the squash did not change during storage period whereas the overall acceptability score was improved. Hydromaceration of purple- fleshed dragon fruit peels for 24 hours using 1:2 peel solvent ratio and storage at low temperature of 4 to 7 ⁰C can be recommended as the best maceration method for betalain pigment extraction. Incorporation of this pigment into white or purple fleshed dragon fruit squash significantly increased the betalain content, proving the potential of purple dragon fruit peel as a natural food colour source.