Abstract
Red pitaya fruits have become a source of natural dye, because they are rich in betacyanin, a pigment that imparts a red-violet colour. However, natural dyes can be highly unstable and prone to rapid degradation. In this study, an experiment was initially carried out to determine the best extraction solution with an extraction time of 20 min for each solution at room temperature (50% methanol, water, 95% ethanol and 80% acetone), in different pH ranges (4.0 to 9.0) and wavelength (485, 535 and 700 nm), for the red pitaya bark. The stability of the pigments extracted from pitaya peel meal was analysed taking into account the best extraction solutions by spectrophotometric measurements at 15-day intervals, during a 60-day storage period, in the absence and presence of light and under different storage conditions. Pigments stored in the absence of light at freezing temperatures for less than 15 days showed least degradation. The FTIR spectrum in shows two distinct peaks at 3263.870 and 1636.807, these absorption bands are characteristic of betalain functional groups. The spectrum indicates the presence of hydroxy and amine groups as strong, broad, stretching-mode bands, appearing between 3200 cm-1 and 3600 cm-1.
Highlights
Pitaya (Hylocereus costaricensis) is a tropical fruit from the rainforest regions of Mexico and Central and South America
Pitaya peel is rich in antioxidant compounds and a good source of natural pigments, pigment stability after extraction may be affected by extrinsic factors such as light, oxygen, metal ions, pH levels, and high temperatures
The various extraction conditions for red pitaya peel flour pigments described in the methodology were evaluated by analysis of variance (ANOVA)
Summary
Pitaya (Hylocereus costaricensis) is a tropical fruit from the rainforest regions of Mexico and Central and South America. The seeds are rich in essential fatty acids and phytosterols, and the peel contains high amounts of pectin, fibres, and antioxidant compounds, especially betalains, which are responsible for the strong and attractive colour of the fruit, making it a promising source of natural colorant. This is attractive to the food industry, because the search for natural pigments to replace synthetic ones has intensified (Gengatharan et al, 2016). Glycolysis, and hydrolysis may occur during the extraction process, causing rapid degradation of extracted pigments (Kushwaha et al, 2018; Stintzing & Carle, 2007)
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