Red Dragon Fruit and Gut Microbiota: from beta-cyanins to Akkermansia, shaping the microbiota towards intestinal and systemic health

Back to Spain, the country where I currently live with my family, from a recent trip to Portugal, I bring with me many memories and emotions. Every trip always leaves its mark, and in this, unexpectedly, where I assumed to remain speechless in front of the waves of Nazarè, the difference was made by the Bolh?o Porto Market where I could taste a lot of delicacies. Maybe because there were no waves at all, and we always had beautiful sun and spring temperatures despite being in January, anyway, I was enthralled like a child in front of the fruit counter. I was able to taste for the first time a mysterious fruit (at least for me), called the Red Dragon fruit which I learned to be the red Pitaya indeed.

What am I talking about?

Pitaya fruit is classified according to the colour of the pulp and the peel: white-pulp with pink peel pitaya (Hylocereus undatus), red-pulp with pink peel pitaya (Hylocereus polyrhizus), that is the one I tried ??, also known as dragon fruit, and white-pulp with yellow skin (Hylocereus megulanthus)(1). It is a member of the Cactaceae family and is widely cultivated in tropical and subtropical areas. During the time the fruit has gained attention worldwide because of its economic value and potential health benefits. The body of the fruit is tasty and rich in polysaccharides with a lot of tiny and grainy black seeds. These seeds contain oil, very similarly to other fruit seeds such as seeds of grape, kiwi, linseeds blackberry, blueberry, and red raspberry seeds(2). ?Seed oil from pitaya fruit can be easily extracted and are well appreciated in food, health and cosmetic applications… Both pitaya seeds and peels have higher concentrations of total polyphenols, beta-cyanins and amino acid than pulp, while anthocyanins are abundant only in the pulp extracts. In this fruit, the protagonists are the red-violet beta-cyanins and the yellow betaxanthin, (a type of betalains) mostly concentrated in the red and yellow pitaya fruit which exhibit antidiabetic effects and modulate glycaemic response(3), apart being strong antioxidant, free-radical scavenger, antimicrobial and antitumoral secondary metabolites(4). The phenolics and flavonoids were found to rise gradually with the maturation and pigmentation processes of the fruit and concentrate earlier in the pulp than peel, as observed in a similar way in Opuntia species. With less than 50 Cal/100g of pulp, the pitaya fruit is a good source of vitamins (vitamin C), dietary fibre (most of which are prebiotic polysaccharides), beta-cyanin, organic acids, inositol, amino acids, polyunsaturated fatty acids (linoleic and linolenic acids) and sugars as glucose, fructose, sorbitol, and sucrose(4).

Health Benefits and Applications of Bioactives in Pitaya: a focus on Gut Microbiota

The phytochemicals and natural pigment from pitaya can be easily extracted and purified and applied as healthy, natural, and low-cost compounds in food industry, including meat, wine, bakery, dairy, and confectionery products. Least but not last several applications can be found in the green, sustainable, natural cosmetics. Yellow pitaya has the highest levels of gallic acid and quercetin, while having the lowest amounts of rutoside, beta-cyanins and total polyphenols. Caffeic acid was the primary phenolic acid detected in white pitaya. Comparatively, red pitaya fruits exhibits the highest concentration of protocatechuic acid, total polyphenols, antioxidant activity and cytotoxic properties compared to that in both white and yellow pitaya fruits. The bioactive components in pitaya also exert a certain influence on the human gut microbiota, apart from participating in the glycaemic control, lipid metabolism, inflammation, competitive microbial growth, and mutagenicity, even if more exhaustive research will be necessary in the future to unravel the complexity of these processes(5).

In the previous decade, different species of colonic microbiota involved in polyphenols metabolism and hydrolysis have been identified, such as Eubaterium ramulus, Eubacterium cellulosolvens, ?Enterococcus casseliflavus, Bacteroides uniformis, Bacteroides distasonis, and Bacteroides ovatus8. The ingested flavonoids are quite often difficult to absorb in the small intestine and most of them easily reach the colon. Not only this, but flavonoid conjugates formed by the human host are excreted back into the intestine via the enterohepatic circulation. Once there, they may affect the composition and metabolic activities of the gut microbiota, by promoting beneficial bacteria and inhibiting potentially pathogenic species, acting as potential therapeutic agents and selecting specific bacteria able to improve their absorption. Once metabolized by the resident microbiota, the resulting, secondary products may have higher bioactivity, making them different from their parent compounds. So, the bacterial conversion plays a pivotal, unquestionable role on the potential health effects of plat-derived secondary metabolites on human host.

As Luo and colleagues well reported in their comprehensive review on the impact of fruits and vegetables on gut microbiota(6), dragon fruit oligosaccharides and polyphenols, as reported from tests on rat gut models, are able to increase fecal Bifidobacteria and Lactobacilli and impair the growth of Bacteroides and Clostridia. Additionally, dragon fruit is a good source of prebiotics (fibres who nourish gut microbiota) since it provides a large proportion of oligosaccharides very are similar to inulin/fructooligosaccharide (FOS), one of the best choices for our bacteria to ferment! For example, a study by Van den Abbeele et al., (2018)(9), using in vitro human gut model, showed how a blend of xylooligosaccharides and polyphenol could selectively promote the growth of Lactobacillus and Bifidobacterium in ascending colon, and exert immune-modulating properties on human cells through the secretion of SCFA (short chain fatty acids). SCFAs, butyrate, acetate and propionate also promote other health benefits and positively influence gut-associated diseased condition. For instance, butyrate serves not only as an antioxidant in colonocyte metabolism but also as a promoter for brain health and contribute to prevent the leaky-gut syndrome; propionate can enter the hepatic gluconeogenesis, thus glucose neo synthesis, and counteract cholesterol neosynthesis in hepatic tissue participating to the cholesterol-lowering effect of dietary fiber. Finally, acetate aids in the synthesis of long chain fatty acids, beta-hydroxybutyrate, glutamate and glutamine. As a by-product of mucin chewing,?Akkermansia muciniphila produces short-chain fatty acids?(SCFAs) feeding both gut bacterium and intestinal cells. This bacterium, which normally lives in our intestine, is one of the most important in the production of butyrate, together with Faecalibacterium prausnitzii. Butyrate is a super influential SCFA that supports gut health, modulates the immune system, and impair systemic inflammation strengthening the tight junctions. Interestingly, a study conducted on mice by Song and colleagues(10) showed that beta-cyanin supplemented diet significantly reduced mice body weight gain (despite being raised with a high-fat diet model) and modulated gut microbiota composition. They repported a decrease in the content of Firmicutes, Bacteroidetes and Proteobacteria and an increase in the proportion of Akkermansia, Anaerotruncus, Mucispirillum which contribute to maintain a healthy human gastrointestinal tract and barrier, particularly Akkermansia(7). ?In which way? I will leave for the next time the myriad of health-related properties of Akkermansia muciniphila…

Who knows what I will take away from the next trip… I don't know, but I will certainly not stop wondering about the microbiota and how our lifestyle and food choices can impact it... I firmly believe in the one health principle, which sees us as part of a large ecosystem, and not at its centre, but at the same level of the other elements. Our health strictly depends on the environment we are part of, including the bacterial contamination that we receive or do not receive from the outside (soil, air, food, water, animal contact and the overall community), which enriches and populates our microbiota. Being part of this planet is a gift and we should focus on how to integrate biologically with our surroundings rather than selfishly exploiting every resource. In the end what is sustainability if not this? Can we further extend the concept to the microbial sustainability? In the hope you might appreciated it, I will leave for you my final reflections and scientific evidence, trip by trip!

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Bibliografy

1.???????Raj G.B et al., 2020??https://pubmed.ncbi.nlm.nih.gov/32502959/

2.???????Zulkifli S.A. et al., 2020 https://pubmed.ncbi.nlm.nih.gov/32059460/

3.???????Adeshirlarijaney A. et al.,?2020 ?https://pubmed.ncbi.nlm.nih.gov/32005089/

4.???????Hua Q. et al., 2018 ??https://pubmed.ncbi.nlm.nih.gov/29522973/

5.???????Huang Y. et al., ??2021?https://doi.org/10.3390/ foods10112862

6.???????Luo J. et al., ?2020 ???https://doi.org/10.1111/ijfs.14927

7.???????Derrien M. et al., ?2016 ??https://dx.doi.org/10.1016/j.micpath.2016.02.005

8.???????Braune A. et al., 2016 https://doi.org/10.1080/19490976.2016.1158395

9.???????Van den Abbeele P. et al., 2018??https://doi.org/10.1016/j.jff.2018.05.053

10.????Song H. et al., 2016 ??https://pubmed.ncbi.nlm.nih.gov/26699443/