Development of Pitaya Peel Milk for Fiber Fortification

Tan, Kim Mei (2018) Development of Pitaya Peel Milk for Fiber Fortification. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Pitaya peel is often discarded as agricultural by-product during processing. Crude fiber content and physicochemical properties of pitaya peel were determined to evaluate its potential use as functional food ingredient. The influence of hot-air oven drying temperature (60°C, 70°C and 80°C) on crude fiber content and colour attributes of red pitaya (Hylocereus polyrhizus) peel and white pitaya (Hylocereus undatus) peel was investigated. Crude fiber content of both red and white pitaya peel decreased with drying temperature, though insignificantly different. Crude fiber content of red pitaya peel at 60°C drying was 31.96 ± 0.218%, then decreased to 31.83 ± 0.221% at 70°C drying and 31.73 ± 0.104% at 80°C drying respectively. Whereas, the crude fiber content of white pitaya peel was 30.55 ± 0.187% at 60°C drying, then decreased to 30.45 ± 0.330% at 70°C drying and 30.22 ± 0.350% at 80°C drying respectively. Crude fiber content of both varieties of pitaya peel was found to be significantly different. Drying temperature at 60°C was selected since the crude fiber content was the highest and ΔE (colour change) was the least (18.47 ± 0.632 for red pitaya peel powder, 16.22 ± 0.413 for white pitaya peel powder). Pitaya peel powder was then added into cow’s milk for fiber fortification. Proximate analysis, physicochemical tests and sensory evaluation of pitaya peel milk and control fresh milk were then conducted. Proximate analysis showed that crude fiber content of pitaya peel milk (1.64 ± 0.113% for white pitaya peel milk; 1.68 ± 0.120% for red pitaya peel milk) was higher than 1.5 g fiber/100 mL, thus can be claimed as source of fiber. Crude fat of pitaya peel milk (3.15 ± 0.126% for white pitaya peel milk; 3.12 ± 0.084% for red pitaya peel milk) was significantly lower than control (3.43 ± 0.156%), while ash content of pitaya peel milk (1.12 ± 0.113% for white pitaya peel milk; 1.09 ± 0.038% for red pitaya peel milk) was significantly higher than control (0.49 ± 0.031%). Physicochemical tests showed that pitaya peel milk had significantly lower pH and significantly higher Brix than control. Red pitaya peel milk and white pitaya peel milk recorded a pH reading of 6.52 ± 0.010 and 6.51 ± 0.020 respectively as well as a Brix reading of 16.50 ± 0.200 and 16.03 ± 0.153 respectively. On the other hand, the pH and Brix reading of control were 6.67 ± 0.021 and 13.07 ± 0.252 respectively. The overall acceptability score of red pitaya peel milk (6.58) in hedonic ranking of 9-point scale was comparable and slightly higher than control (6.20), although with insignificant difference. Preference test showed that majority (50%) of panellists rated red pitaya peel milk as their most preferred sample. Sensory panellists were also quite neutral towards dragon fruit aroma and taste as well as graininess in pitaya peel milk. These three attributes which were absent in control obtained likeness score of around 6 (like slightly).