Pectin from dragon fruit (hylocereus polyrhizus) peel as potential halal gelling agent

Abstract

Dragon fruit (Hylocereus polyrhizus) belongs to the group of Cactae from the genus Hylocereus. This tropical fruit is known to have multi benefits in terms of its nutritional, medical and commercial values. Dragon fruit is either eaten directly or processed into juice and the peel will be discarded. A massive amount of the waste can be transformed into beneficial materials. For example, the peel has a good ratio of insoluble to soluble dietary fibre and can be considered as a good source of pectin. Pectin is a type of plant-based gelling agent and is one of the key ingredients in food products. Commercial gelling agents currently available on the market come from sources of bovine and porcine. Nevertheless, due to religious constraints and restrictions on safety, the use of this animal-based food quality enhancer has become less common. For these reasons, there is an increasing demand for the replacement of animal-based gelling agents with plant-based agents. This study was conducted to achieve multiple objectives. The first was to determine the best extraction conditions to yield the maximum amount of pectin from dragon fruit peels by using hot acid extraction. The second objective was to determine the antioxidant activity of the extracted pectin using DPPH radical scavenging activity. The final objective was to determine the physicochemical characteristics of dragon fruit peel pectin in terms of Degree of Esterification (DE), DSC, moisture and ash content, water and oil holding capacity, swelling capacity and textural attributes. Distilled water was used as a solvent and hydrochloric acid (HCl) was used to achieve the acidic medium. The experiment was conducted in a beaker that was placed on the hot stirring plate. It was found that the best extraction conditions yield the highest pectin amount (33%) were pH 3.5 and 75 minutes of extraction. Antioxidant activity assessment using DPPH assays shows a decreasing trend of 50% inhibition activity of dragon fruit peel pectin, indicating the presence of an antioxidant activity in the extracted pectin. Dragon fruit peel pectin is categorized under the high methoxyl group as the calculated DE is 52%. FTIR spectra had detected polysaccharides, the functional group of pectin. Analysis using DSC revealed that melting temperature (Tm) (122.010C) and melting enthalpy (∆Hm) (385.40 mJ) of dragon fruit peel pectin is better in comparison to commercial pectin. The moisture content of the extracted pectin (14.03 ± 1.925) was significantly different compared with the commercial pectin (p< 0.05). Ash content of the extracted pectin (8.73 ± 1.218) was significantly different from the commercial pectin (p<0.05). For holding capacity of water and oil and swelling capacity, tests have been obtained to verify that the extracted pectin has a high potential to be used as a gelling agent. The differences of textural attributes of the extracted pectin gel were found to be insignificant in terms of hardness, cohesiveness and gumminess as compared to the commercial pectin gel. Overall, the results obtained show that the pectin extracted from dragon fruit peel is comparable to any commercial gelling agent. Consequently, the extracted pectin may be used as another source of gelling agents in food industries.