Dietary bioactive compounds and possible health benefits of dragon fruit and star fruit
Novel plant-based products with a high content of phenolic compounds have been studied to assess their effect on health. This thesis has explored three different species of dragon fruit, Hylocereus polyrhizus (red flesh), Hylocereus undatus (white flesh), and Hylocereus megalanthus (yellow peel) as well as one species of star fruit (Averrhoa carambola) that may exert beneficial effects on health due to their bioactive potential. A literature review was conducted followed by three experiments: 1) an in vitro study to analyse the total polyphenol content (TPC) and their antioxidant capacity in fresh, dehydrated, and frozen forms for all species, as well as their in vitro digestion. 2) A sensory evaluation and an in vitro digestion of red flesh dragon fruit and star fruit based beverages. 3) An in vivo trial in healthy individuals and those at risk of type two diabetes (T2D) to determine the effect of a beverage based on frozen red flesh dragon fruit on blood pressure, glycaemic and insulin response. The results highlighted the bioactive potential of red flesh dragon fruit and star fruit. Frozen for one-week red flesh dragon fruit (FRDF) showed higher TPC than other dragon fruit forms; star fruit showed the highest TPC for all fruits assessed. A correlation was found between TPC and antioxidant capacity. The highest release of polyphenols from all fruits and forms evaluated occurred during intestinal phase and there was a correlation between TPC and antioxidant capacity. Red flesh dragon fruit and star fruit were selected to prepare beverages based on fresh, frozen for one-week, and dehydrated forms; the FRDF based beverage was the more accepted and showed a high TPC during the intestinal phase of the in vitro digestion. The consumption of the FRDF based beverage during a 4-week period shown to reduce blood pressure and the insulin response-incremental area under the curve (IR-iAUC) in individuals at risk of T2D. To our knowledge, this is the first study to look at the bioaccessibility of dragon fruit and star fruit and the first to assess the bioactive potential of FRDF to be considered as a functional food.
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