Value-added Phytochemical Cocktail from Inedible Dragon Fruit Peel
Jason Chen
St George's School
Floor Location : S 052 R

This project aimed to utilize phytochemicals in inedible dragon fruit peel for value-added application. Phytochemicals in dragon fruit peel were extracted by 50% ethanol. The anti-microbial activity of the phytochemical extract towards E. coli and Lactobacillus fermentum was investigated by the diffusion well method; the effect of phytochemical extract in enhancing antibiotic activity was also tested. In addition, metal chelating activity of the phytochemical extract was evaluated. A practical application test to eliminate enzymatic browning in shrimp was carried out. As Cu2+ plays an important role for the enzymatic activity of tyrosinase. If metal chelating activity of the phytochemical extract was effective to chelate Cu2+, the enzymatic activity of tyrosinase present in shrimp would be inhibited. Therefore, the enzymatic browning of shrimps should be significantly alleviated. Furthermore, interaction among the three major phytochemical groups in dragon fruit peel (betacyanins, polyphenols, and flavonoids) was studied for both metal chelating and antioxidant activities. Betanin, tannic acid, and hesperetin were selected as the representative for each group. The bioactivities of individual compounds, two compounds together, and three compounds together were measured to identify their interaction types - synergistic, additive, antagonistic, and suppressive. The last part of this project was to compare solid-state fermentation of dragon fruit peel by a commercial Aspergillus strain to fermentation by natural microorganisms present. It was designed to explore whether the non-extractable phytochemicals which were bound to macromolecules (such as protein and polysaccharides) can be released by Aspergillus and natural microorganisms and to evaluate their effectiveness. A three-day fermentation of dragon fruit peel by Aspergillus was carried out. The contents of betacyanins, polyphenols, and total flavonoids were monitored at each day during fermentation.
No inhibition ring was observed for the phytochemical extract from dragon fruit peel, which indicated that phytochemicals from dragon fruit peel did not possess anti-microbial activity towards E. coli and Lactobacillus fermentum. In addition, no enhancement effect was observed for the phytochemical extract when it was used in combination with ampicillin to inhibit growth of E. coli and Lactobacillus fermentum. However, the phytochemical extract was determined to have very high metal chelating activity. The application for shrimp preservation showed significant elimination of enzymatic browning, which indicated that phytochemicals in dragon fruit peel can potentially applied for the Food Industry to eliminate enzymatic browning. The interaction study showed that the three phytochemicals selected had synergistic effect among each other for metal chelating activity; however, an antagonistic interaction was identified for the antioxidant activity among them. The interaction network among these phytochemicals is valuable for recipe development in future testings of the phytochemical cocktail. The solid-state fermentation showed similar trends for contents of betacyanins, polyphenols, and total flavonoids. Both Aspergillus and natural microorganisms degraded betacyanins and released conjugated forms of polyphenols and flavonoids during three-day fermentation, resulting in colorless phytochemical cocktail for more application. Solid-state fermentation by natural microorganisms in dragon fruit peel do not require additional cost for strains. Therefore, it is recommended for production of colorless phytochemical cocktail with higher contents of polyphenols and flavonoids.