The word "melanin" refers to a group of high molecular weight, black, and brown pigments formed through the oxidation and polymerization of phenolic compounds This pigment is present in all kingdoms of living organisms, but it remains the most enigmatic pigment in plants The poor solubility of melanin in particular solvents and its complex polymeric nature significantly constrain its study Plant melanin synthesis is mostly associated with the enzymatic browning reaction that occurs in wounded plant tissues This reaction occurs when, due to the disruption of cellular compartmentation, the chloroplast-located polyphenol oxidases (PPOs) release from the chloroplast and interact with their vacuolar substrates to produce o-quinones, which in turn polymerize to melanin Furthermore, the presence of melanin in intact seed tissues has been demonstrated by diagnostic physicochemical tests Unlike the well-studied enzymatic browning reaction, little is known about how melanin is formed in seeds Recent data have shown that it is a tightly controlled genetic process that involves many genes, among which the genes encoding PPOs might be key The present article aims to provide an overview of the current knowledge on melanin in plants and to discuss future perspectives on its study in light of recent findings

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Melanin Pigment in Plants: Current Knowledge and Future Perspectives.

Enterosorbents are widely-used materials for human body detoxification, which function by immobilizing and eliminating endogenous and exogenous toxins. Here, activated carbons, obtained from the lignocellulosic raw vegetal materials of indigenous provenance, have been studied. Walnut shell and wood from local species of nuts and apple-trees were carbonized, and further activated at high temperatures with water vapors in a rotary kiln. A second activation was carried out, in a fluidized bed reactor, but for shorter times. The textural properties of the samples were determined from the adsorption isotherms of nitrogen at 77 K, allowing the obtaining of highly mesoporous materials, while the adsorption capacity permitted an essential rise of six to seven times in the maximal adsorption values of the metabolites, which was determined by the reactivation process. A kinetic study of vitamin B12 and creatinine immobilization was performed, the optimal immobilization time for the apple-tree wood reactivated carbons being 2 times longer than for those originating from walnut shells. An additional investigation was also performed in specific conditions that simulate the real environment of immobilization: the temperature of a febrile human body (at the temperature T = 38 °C) and the characteristic acidity of the urinary tract and stomach (at the pH of 5.68 and 2.53, respectively). The activated carbonic adsorbents studied here, together with the results of the immobilization studies, show that these procedures can conduct a good incorporation of some endogenous metabolic products, such as vitamin B12 and creatinine, therefore presenting a good opportunity for their use as forthcoming commercial enterosorbents.

https://www.mdpi.com/1420-3049/25/13/3095/pdf

Adsorption Capacity of Vitamin B12 and Creatinine on Highly-Mesoporous Activated Carbons Obtained from Lignocellulosic Raw Materials

Anthocyanins and melanins are phenolic pigments of plants and accumulate in seed envelopes of the barley grain, thereby giving them a blue, purple, or black color. To explore the effects of combined accumulation of anthocyanins and melanins in the grain, a barley near-isogenic line (NIL), characterized by simultaneous accumulation in both pigments, was developed using a marker-assisted approach. The presence of both pigments in the grain pericarp was evaluated by light microscopy. Emergence of anthocyanin pigmentation proved to be temporally separated from that of melanin, and the formation of anthocyanin pigments began at an earlier stage of spike maturation. During spike maturation, a significantly higher total anthocyanin content was noted in the created NIL than in the parental anthocyanin-accumulating NIL, indicating a positive influence of the Blp1 gene on the anthocyanin content at some developmental stages. In a comparative analysis of yield components, it was found that the observed differences between the barley NILs are possibly caused by environmental factors, and the presence of pigments does not decrease plant productivity. Our results should facilitate investigation into genetic mechanisms underlying overlaps in the biosynthesis of pigments and into breeding strategies aimed at the enrichment of barley varieties with polyphenols.

/pdf/effects-of-combining-the-genes-controlling-anthocyanin-and-30imxr3a.pdf

Effects of Combining the Genes Controlling Anthocyanin and Melanin Synthesis in the Barley Grain on Pigment Accumulation and Plant Development

Using of buckwheat by-products (hull fine powder and melanin obtained from the hull) in formulations of desserts (by the examples of chocolate cream and honeysuckle mousse) can improve their sensory and physico-chemical characteristics, including antioxidant activity (AOA). The chemical composition of buckwheat hull fine powder was studied, and sensory evaluation of the powder and melanin was carried out. The values of AOA allowed one to determine the amounts of the powder and melanin in desserts as 1.5 and 0.037 g per serving accordingly. Sensory evaluation of dessert samples showed high-point values. There were also determined physico-chemical characteristics of dessert samples. Besides increasing of AOA, the buckwheat hull fine powder increases dietary fibers content in desserts. All dessert samples with addition of melanin satisfy more than 15% of the daily need in antioxidants, so the developed desserts can be considered as functional products.

Influence of buckwheat by-products on the antioxidant activity of functional desserts

The capillary and porous structure of the protein-cellulose complexes of Arctic brown algae Laminaria digitata and Saccharina latissima

The sorption properties of sunflower husk melanins were studied according to pharmacopoeial monograph GPM123002115 using marker compounds methylene blue, methyl orange, gelatin, and iodine The sorption capacities of the studied samples were found to be 1909 ± 42 mg/g for methylene blue; 3021 ± 18, methyl orange; 1147 ± 28, gelatin; and 384 ± 24%, I2  The sorption capacities of the samples were greater than those of the sorbents Polifepan and Polysorb and comparable with that of activated charcoal for medium-molecular-mass toxicants The melanins showed high affinity for anionic substances The protein-binding capacities of the melanins were inferior only to that of Polysorb and significantly greater than those of Polifepan and activated charcoal The sorption capacity for I2 matched that of Polifepan and was >15 times less than that of activated charcoal The results showed that enterosorbents based on melanins could be developed

N. V. Gracheva

Papers

Sorption Properties of Sunflower Husk Melanins