Study of colour and oxidative stability of pitaya fruit peels extract in muffins / Shaidatul Shida Waludin

Pitaya or locally known as dragon fruit has gained wide recognition as a potential crop in Malaysia. It has been planted in Malaysia since year 2000. In this study red-purple pitaya {Hylocereus polyrhizus) was used. The fruit components analysed was the peel of pitaya. This study was conducted to determine the optimum condition for the colour stability of pitaya peel extract and to determine the oxidative stability of pitaya peel extract (betalains) in muffins. Water was used as a solvent for the extraction. The optimum condition for the colour stability of pitaya peel extract is at pH 4 with absorbance range from 535 nm to 550 nm and it can withstand until 85°C with an addition of 1% ascorbic acid. The peak of absorbance in UV-Visible spectrophotometer analysis for colour and total betalains in pitaya peel extract was obtained. The highest peak was in the order: unheated control > unheated extract with 1% ascorbic acid > unheated extract with 5% ascorbic acid > heated extract with 1% ascorbic acid > heated control > heated extract with 5% ascorbic acid. Analysis on oxidative stability of muffins was conducted by doing peroxide value (PV) and Thiobarbituric acid (TB A) test to measure the product of lipid oxidation process. The highest PV (mEq/kg) and TBA (mg malonaldehyde/L) were in the order: control formulation > formulation with 20 ml pitaya peel extract > formulation with 200 ppm BHA/BHT > formulation with 40 ml pitaya peel extract. Colour analysis was determined and interpreted as L*, a* and b* values. Control formulation showed highest L* value followed by formulation with 20 ml pitaya peel extract, formulation with 200 ppm BHA/BHT and formulation with 40 ml pitaya peel extract. The highest a* and b* value are formulation incorporated with 40 ml pitaya peel extract > formulation with 200 ppm BHA/BHT > control formulation > formulation with 20ml pitaya peel extract started from day 3 onwards. The results indicated the pitaya peel extract had an oxidative stability effect on muffins but only a mild effect as a food colourant.