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Within the angiosperm order Caryophyllales, an unusual class of pigments known as betalains can replace the otherwise ubiquitous anthocyanins. In contrast to the phenylalanine-derived anthocyanins, betalains are tyrosine-derived pigments which contain the chromophore betalamic acid. The origin of betalain pigments within Caryophyllales and their mutual exclusion with anthocyanin pigments have been the subject of considerable research. In recent years, numerous discoveries, accelerated by -omic scale data, phylogenetics and synthetic biology, have shed light on the evolution of the betalain biosynthetic pathway in Caryophyllales. These advances include the elucidation of the biosynthetic steps in the betalain pathway, identification of transcriptional regulators of betalain synthesis, resolution of the phylogenetic history of key genes, and insight into a role for modulation of primary metabolism in betalain synthesis. Here we review how molecular genetics have advanced our understanding of the betalain biosynthetic pathway, and discuss the impact of phylogenetics in revealing its evolutionary history. In light of these insights, weexplore our new understanding of the origin of betalains, the mutual exclusion of betalains and anthocyanins, and the homoplastic distribution of betalain pigmentation within Caryophyllales. We conclude with a speculative conceptual model for the stepwise emergence of betalain pigmentation.

Purpose To evaluate the plasma bioavailability of betanin and nitric oxide (NOx) after consuming beetroot juice (BTJ) and whole beetroot (BF). BTJ and BF were also analysed for antioxidant capacity, polyphenol content (TPC) and betalain content. Methods Ten healthy males consumed either 250 ml of BTJ, 300 g of BF or a placebo drink, in a randomised, crossover design. Venous plasma samples were collected pre (baseline), 1, 2, 3, 5 and 8 h post-ingestion. Betanin content in BTJ, BF and plasma was analysed with reverse-phase high-performance liquid chromatography (HPLC) and mass spectrometry detection (LCMS). Antioxidant capacity was estimated using the Trolox equivalent antioxidant capacity (TEAC) and polyphenol content using Folin–Ciocalteu colorimetric methods [gallic acid equivalents (GAE)] and betalain content spectrophotometrically. Results TEAC was 11.4 ± 0.2 mmol/L for BTJ and 3.4 ± 0.4 μmol/g for BF. Both BTJ and BF contained a number of polyphenols (1606.9 ± 151 mg/GAE/L and 1.67 ± 0.1 mg/GAE/g, respectively), betacyanins (68.2 ± 0.4 mg/betanin equivalents/L and 19.6 ± 0.6 mg/betanin equivalents/100 g, respectively) and betaxanthins (41.7 ± 0.7 mg/indicaxanthin equivalents/L and 7.5 ± 0.2 mg/indicaxanthin equivalents/100 g, respectively). Despite high betanin contents in both BTJ (~194 mg) and BF (~66 mg), betanin could not be detected in the plasma at any time point post-ingestion. Plasma NOx was elevated above baseline for 8 h after consuming BTJ and 5 h after BF (P < 0.05). Conclusions These data reveal that BTJ and BF are rich in phytonutrients and may provide a useful means of increasing plasma NOx bioavailability. However, betanin, the major betalain in beetroot, showed poor bioavailability in plasma

Deep eutectic solvents (DES) using magnesium chloride hexahydrate [MgCl2·6H2O] and urea [U] proportions (1:1) and (2:1), were prepared for their use as extracting and stabilizer agents for red and violet betalains from beetroot (Beta vulgaris) waste. The synthetized DES [MgCl2·6H2O] [U] showed similar properties to eutectic mixtures, such as, liquid phase, low melting points and conductivity, thermal stability, and variable viscosity. In turn, betalain DES extracts (2:1) exhibited compatibility in the extraction and recovery of betalains from beetroot wastes, showing a betalain content comparable to that of betalain extracts. Betalain stability was determined by degradation tests; the exposure conditions were visible light (12 h), molecular oxygen from atmospheric air and environmental temperature (20–27 °C) for 40 days. The kinetic curves of the betalain degradation of water samples depicted a first-order model, indicating the alteration of a violet colouration of betalains from beetroot waste for 5–7 days. However, betalains from DES extracts were kept under visible light for 150 days, and for 340 days in storage (amber vessels), achieving a stability of 75% in comparison with initial beet extracts.

Betalains are water-soluble pigments present in vacuoles of plants of the order Caryophyllales and in mushrooms of the genera Amanita, Hygrocybe and Hygrophorus. Betalamic acid is a constituent of all betalains. The type of betalamic acid substituent determines the class of betalains. The betacyanins (reddish to violet) contain a cyclo-3,4-dihydroxyphenylalanine (cyclo-DOPA) residue while the betaxanthins (yellow to orange) contain different amino acid or amine residues. The most common betacyanin is betanin (Beetroot Red), present in red beets Beta vulgaris, which is a glucoside of betanidin. The structure of this comprehensive review is as follows: Occurrence of Betalains; Structure of Betalains; Spectroscopic and Fluorescent Properties; Stability; Antioxidant Activity; Bioavailability, Health Benefits; Betalains as Food Colorants; Food Safety of Betalains; Other Applications of Betalains; and Environmental Role and Fate of Betalains.

Betalain pigments are unique to the Caryophyllales and structurally and biosynthetically distinct from anthocyanins. Two key enzymes within the betalain synthesis pathway have been identified: 4,5-dioxygenase (DODA) that catalyzes the formation of betalamic acid and CYP76AD1, a cytochrome P450 gene that catalyzes the formation of cyclo-DOPA. We performed phylogenetic analyses to reveal the evolutionary history of the DODA and CYP76AD1 lineages and in the context of an ancestral reconstruction of pigment states we explored the evolution of these genes in relation to the complex evolution of pigments in Caryophylalles. Duplications within the CYP76AD1 and DODA lineages arose just before the origin of betalain pigmentation in the core Caryophyllales. The duplications gave rise to DODA-α and CYP76AD1-α isoforms that appear specific to betalain synthesis. Both betalain-specific isoforms were then lost or downregulated in the anthocyanicMolluginaceae and Caryophyllaceae. Our findings suggest a single origin of the betalain synthesis pathway, with neofunctionalization following gene duplications in the CYP76AD1 and DODA lineages. Loss of DODA-α and CYP76AD1-α in anthocyanic taxa suggests that betalain pigmentation has been lost twice in Caryophyllales, and exclusion of betalain pigments from anthocyanic taxa is mediated through gene loss or downregulation. [Correction added after online publication 13 May 2015: in the last two paragraphs of the Summary the gene name CYP761A was changed to CYP76AD1.]

Transient expression and induction of RNA silencing by agroinfiltration is a fundamental method in plant RNA biology. Here, we introduce a new reporter assay using RUBY, which encodes three key enzymes of the betalain biosynthesis pathway, as a polycistronic mRNA. The red pigmentation conferred by betalains allows visual confirmation of gene expression or silencing levels without tissue disruption, and the silencing levels can be quantitatively measured by absorbance in as little as a few minutes. Infiltration of RUBY in combination with p19, a well-known RNA silencing suppressor, induced a fivefold higher accumulation of betalains at 7 days post infiltration compared to infiltration of RUBY alone. We demonstrated that co-infiltration of RUBY with two RNA silencing inducers, targeting either CYP76AD1 or glycosyltransferase within the RUBY construct, effectively reduces RUBY mRNA and betalain levels, indicating successful RNA silencing. Therefore, compared to conventional reporter assays for RNA silencing, the RUBY-based assay provides a simple and rapid method for quantitative analysis without the need for specialized equipment, making it useful for a wide range of RNA silencing studies.

The possibility of obtaining a carmine or pink color on ordinary cooked ham by applying natural dyes from three plant species, namely red radish (Raphanus sativus L.), hibiscus (Roselle sabdariffa L.) and red beetroot (Beta vulgaris L.), was investigated. The extracts were evaluated for the stability at physical-chemical parameters and subjected to cytotoxicity assays in the gastric cell line AGS Encapsulation of the extracts in soybean lecithin liposomes and maltodextrin microcapsules was performed. Lyophilized extracts before and after encapsulation in maltodextrin were applied in the formulation of ordinary cooked ham and used in a pilot scale of production. The color of cooked ham samples from different assays was evaluated visually and by colorimetry. The results suggest that the coloration of ordinary cooked ham obtained with extracts of red beetroot is very promising for future applications in this type of meat product.

Betalains are tyrosine‐derived red‐violet and yellow pigments, found in plants only of the Caryophyllales order. Although much progress has been made in recent years in the understanding of the betalain biosynthetic process, many questions remain open with regards to several of the proposed steps in the pathway. Most conspicuous by its absence is the characterization of the first committed step in the pathway, namely the 3‐hydroxylation of tyrosine to form l‐3,4‐dihydroxyphenylalanine (l‐DOPA). We used transcriptome analysis of the betalain‐producing plants red beet (Beta vulgaris) and four o'clocks (Mirabilis jalapa) to identify a novel, betalain‐related cytochrome P450‐type gene, CYP76AD6, and carried out gene silencing and recombinant expression assays in Nicotiana benthamiana and yeast cells to examine its functionality. l‐DOPA formation in red beet was found to be redundantly catalyzed by CYP76AD6 together with a known betalain‐related enzyme, CYP76AD1, which was previously thought to only catalyze a succeeding step in the pathway. While CYP76AD1 catalyzes both l‐DOPA formation and its subsequent conversion to cyclo‐DOPA, CYP76AD6 uniquely exhibits only tyrosine hydroxylase activity. The new findings enabled us to metabolically engineer entirely red‐pigmented tobacco plants through heterologous expression of three genes taking part in the fully decoded betalain biosynthetic pathway.

The underutilized Amaranthus leafy vegetables are a unique basis of pigments such as β-cyanins, β-xanthins, and betalains with radical scavenging capacity (RSC). They have abundant phytonutrients and antioxidant components, such as pigments, vitamins, phenolics, and flavonoids. Eight selected genotypes (four genotypes from each species) of underutilized Amaranthus leafy vegetables were evaluated for phytonutrients, pigments, vitamins, phenolics, flavonoids, and antioxidants in a randomized complete block design under ambient field conditions with three replicates. The studied traits showed a wide range of variations across eight genotypes of two species of Amaranthus leafy vegetables. The highest fat, β-xanthins, K, dietary fiber, Mg, β-cyanins, Mn, chlorophyll ab, Zn, TP, TF, betalains, chlorophyll a content, and (RSC) (DPPH) and RSC (ABTS+) were obtained from A. tricolor accessions. Conversely, the highest protein, Cu, carbohydrates, Ca, and chlorophyll b content were obtained from A. lividus accessions. The highest dry matter, carotenoids, Fe, energy, and ash were obtained from A. tricolor and A. lividus. The accession AT2 confirmed the highest vit. C and RSC (DPPH) and RSC (ABTS+); AT5 had the highest TP content; and AT12 had the highest TF content. A. tricolor accessions had high phytochemicals across the two species, such as phytopigments, vitamins, phenolics, antioxidants, and flavonoids, with considerable nutrients and protein. Hence, A. tricolor accessions can be used as high-yielding cultivars comprising ample antioxidants. The correlation study revealed that vitamin C, pigments, flavonoids, β-carotene, and phenolics demonstrated a strong RSC, and showed a substantial contribution to the antioxidant potential (AP) of A. tricolor. The investigation exposed that the accessions displayed a plentiful origin of nutritional values, phytochemicals, and AP with good quenching ability of reactive oxygen species (ROS) that provide enormous prospects for nourishing the mineral-, antioxidant-, and vitamin-threatened community.

Betalains are applicable to many aspects of life, and their properties, characteristics, extraction and biosynthesis process have been thoroughly studied. Although betalains are functionally similar to anthocyanins and can substitute for them to provide pigments for plant color, it is rare to study the roles of betalains in plant responses to adverse environmental conditions. Owing to their antioxidant capability to remove excess reactive oxygen species (ROS) in plants and humans, betalains have attracted much attention due to their bioactivity. In addition, betalains can also act as osmotic substances to regulate osmotic pressure in plants and play important roles in plant responses to adverse environmental conditions. The study of the physiological evolution of betalains is almost complete but remains complicated because the evolutionary relationship between betalains and anthocyanins is still uncertain. In this review, to provide a reference for the in-depth study of betalains compared with anthocyanins, the biochemical properties, biosynthesis process and roles of betalains in response to environmental stress are reviewed, and the relationship between betalains and anthocyanins is discussed.