Red-fleshed dragon fruit (Hylocereus polyrhizus) is renowned not only for its vibrant color and unique flavor but also for its significant nutritional and health benefits, derived from its flesh, seeds, and outer peel. Currently, the most commonly processed dragon fruit products available on the market include wine, syrup, bread, jelly, gummies, dried powder, and instant noodles [5]. However, these products primarily utilize the fruit pulp, leaving the red-fleshed dragon fruit peels largely underutilized. This not only raises environmental concerns if the peel is not properly managed but also represents a missed opportunity to transform these by-products into higher-value economic goods.
Figure 1. Processing of Frozen Red-Fleshed Dragon Fruit
A Treasure Trove of Bioactive Compounds
Recent studies have shed light on the rich potential of dragon fruit peel as a source of two key bioactive compounds, such as betalains—a natural pigment with health-boosting properties like antioxidant, anti-cancer, and antibacterial properties (Vulić et al., 2013; Gandía-Herrero et al., 2016; Khan 2016a, b; Belhadj et al., 2017; Miguel 2018; Yong et al., 2018)—and pectin, a multifunctional polysaccharide widely used as a gelling, stabilizing, binding, and emulsifying agent, widely applied in food processing and edible film production [5].
Figure 2. Betalains and Pectin Extracted from Red-Fleshed Dragon Fruit Peel [5]
The European Union and the European Food Safety Authority have approved the use of betalains as a natural coloring agent E162 due to their vibrant hues and well-preserved biological benefits. Betalains are structurally classified into betacyanins (red-purple) and betaxanthins (yellow). These pigments are found in various plant tissues, predominantly stored in cell vacuoles within the epidermal and subepidermal layers. In some cases, they also accumulate in stems, as observed in in beetroot, red beets, and red-fleshed dragon fruit [2].
As with many natural pigments, betalain stability is a critical challenge. Their stability is enhanced under conditions such as high betalain content, high levels of glycosylation and acylation, low water activity (aw), pH between 3 and 7, the presence of antioxidants, chelating agents, low temperatures, and protection from light and oxygen exposure [1]. Conversely, instability arises from degrading enzymes (peroxidase, polyphenol oxidase, glucosidase), low glycosylation/acylation, high aw, metal cations, pH <3 or >7, high temperatures, light exposure, O₂, and H₂O₂ [2,5]. Due to their inherent instability, betalains have limited applications in the food industry unless suitable stabilization strategies are employed.
Pectin is an essential polysaccharide found in plant cell walls, playing a crucial role in cell wall expansion and structural integrity. Commercially, apple pomace and citrus peels serve as the primary sources of pectin. However, recent studies have investigated alternative raw materials such as sugar beet pulp, okara (soybean residue), passion fruit peel, and prickly pear. Dragon fruit has also been identified as a promising source for high-methoxyl pectin extraction. Given its stabilizing and gelling as well as its potential health impacts, pectin holds promise for applications in food technology and biomedical research. In Europe, pectin is classified as a safe food additive, with an “unspecified” acceptable daily intake (ADI) level set by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), the Scientific Committee for Food (SCF), and the Generally Recognized as Safe (GRAS) classification, under the international code E440 [1].
Merging Betalains and Pectin: A New Frontier in Food Innovation
The combined use of betalains and pectin in food technology is of growing interest for developing products with natural, vibrant colors and desirable textural properties. Recent studies have applied betalains for coloring yogurt, jelly, gummies, jam, etc. However, the potential of red-fleshed dragon fruit peel as a dual source of betalains and pectin remains underexplored. Moreover, the factors affecting betalain content during processing and storage require further optimization. Research suggests that pasteurization at 80°C for under 30 minutes helps preserve jelly color, while storage in dark glass jars and over a short duration is recommended due to sensitivity to water activity.
Figure 3. (A) Gummy Candy [5]; (B) Red-Fleshed Dragon Fruit Jelly [2]
Towards a Sustainable Future: Industrial Potential and Challenges
With growing global interest in sustainable food production and waste valorization, red-fleshed dragon fruit peel presents an eco-friendly alternative to synthetic colorants and commercial pectin sources. Researchers at the department are now exploring advanced microencapsulation and freeze-drying techniques to enhance betalain stability, expanding its potential applications beyond food into biocosmetics and pharmaceuticals.
However, current formulations still face challenges in color retention, indicating the need for further research before achieving a fully stable pigment for industrial-scale. Additionally, pectin extracted from dragon fruit peel has demonstrated high brightness and significant content, making it a viable candidate for replacing commercial pectin. Scaling up this extraction process would not only reduce agricultural waste from red-fleshed dragon fruit but also contribute to producing higher-value products in a rapidly advancing circular economy.
Conclusion
The red-fleshed dragon fruit peel, once regarded as mere agricultural waste, is now emerging as a valuable source of natural pigments and functional polysaccharides. With increasing efforts of the researchers and lecturers of our department to optimize betalain stability and enhance pectin extraction, this underutilized by-product could soon play a pivotal role in food, biocosmetics, and pharmaceutical applications. As our research progresses, harnessing the full potential of dragon fruit peel will not only support sustainable resource utilization but also contribute to the rapidly expanding circular economy.
References:
1. Juan Pablo Carreón-Hidalgo et al., Betalain plant sources, biosynthesis, extraction, stability enhancement methods, bioactivity, and applications, Food Research International, 151, 2022, 110821.
2. Nguyễn Đức Toàn, Effect of Pasteurization on Betacyanin Stability in Red Dragon Fruit Jelly (Hylocereus polyrhizus), Industry and Trade Journal – Scientific Research and Technology Application Results, Issue 12, May 2023.
3. Nguyễn Hải Đăng et al., Pectin Extraction from Dragon Fruit Peel for Gummy Candy Lotion Gel, 2021.
4. S.J. Calva-Estrada et al., Betalains and their applications in food: Processing, stability, and future opportunities, Food Chemistry: Molecular Sciences, 4, 2022, 100089.
5. Uyen D. H. Huynh et al., Processing red dragon fruit peels into valuable compounds towards the development of circular economy, Industry and Trade Magazine, 18 (2), 157–167.