Quercetin is a flavonoid largely employed as a phytochemical remedy and a food or dietary supplement. We present here a novel biocatalytic methodology for the preparation of quercetin from plant-derived rutin, with both substrate and product being in mostly an undissolved state during biotransformation. This "solid-state" enzymatic conversion uses a crude enzyme preparation of recombinant rutinosidase from Aspergillus niger yielding quercetin, which precipitates from virtually insoluble rutin. The process is easily scalable and exhibits an extremely high space-time yield. The procedure has been shown to be robust and was successfully tested with rutin concentrations of up to 300 g/L (ca 0.5 M) at various scales. Using this procedure, pure quercetin is easily obtained by mere filtration of the reaction mixture, followed by washing and drying of the filter cake. Neither co-solvents nor toxic chemicals are used, thus the process can be considered environmentally friendly and the product of "bio-quality." Moreover, rare disaccharide rutinose is obtained from the filtrate at a preparatory scale as a valuable side product. These results demonstrate for the first time the efficiency of the "Solid-State-Catalysis" concept, which is applicable virtually for any biotransformation involving substrates and products of low water solubility.

• Keywords
• Aspergillus niger, quercetin, rutin, rutinose, rutinosidase, “solid-state biocatalysis”,
• MeSH
• Aspergillus niger enzymology   genetics   MeSH
• Biocatalysis * MeSH
• Disaccharides chemistry   metabolism   MeSH
• Fungal Proteins genetics   metabolism   MeSH
• Glycoside Hydrolases genetics   metabolism   MeSH
• Pichia genetics   metabolism   MeSH
• Industrial Microbiology methods   MeSH
• Quercetin chemistry   metabolism   MeSH
• Rutin chemistry   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• beta-rutinosidase MeSH Browser
• Disaccharides MeSH
• Fungal Proteins MeSH
• Glycoside Hydrolases MeSH
• Quercetin MeSH
• Rutin MeSH
• rutinose MeSH Browser

Natural flavonoids, especially in their glycosylated forms, are the most abundant phenolic compounds found in plants, fruit, and vegetables. They exhibit a large variety of beneficial physiological effects, which makes them generally interesting in a broad spectrum of scientific areas. In this review, we focus on recent advances in the modifications of the glycosidic parts of various flavonoids employing glycosidases, covering both selective trimming of the sugar moieties and glycosylation of flavonoid aglycones by natural and mutant glycosidases. Glycosylation of flavonoids strongly enhances their water solubility and thus increases their bioavailability. Antioxidant and most biological activities are usually less pronounced in glycosides, but some specific bioactivities are enhanced. The presence of l-rhamnose (6-deoxy-α-l-mannopyranose) in rhamnosides, rutinosides (rutin, hesperidin) and neohesperidosides (naringin) plays an important role in properties of flavonoid glycosides, which can be considered as "pro-drugs". The natural hydrolytic activity of glycosidases is widely employed in biotechnological deglycosylation processes producing respective aglycones or partially deglycosylated flavonoids. Moreover, deglycosylation is quite commonly used in the food industry aiming at the improvement of sensoric properties of beverages such as debittering of citrus juices or enhancement of wine aromas. Therefore, natural and mutant glycosidases are excellent tools for modifications of flavonoid glycosides.

• Keywords
• catechin, enzymatic hydrolysis, hesperetin, icariin, naringenin, puerarin, quercetin, rhamnosidase, rutinosidase, transglycosylation,
• MeSH
• Flavonoids metabolism   MeSH
• Glycoside Hydrolases metabolism   MeSH
• Isoflavones metabolism   MeSH
• Catechin metabolism   MeSH
• Humans MeSH
• Quercetin metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Flavonoids MeSH
• Glycoside Hydrolases MeSH
• Isoflavones MeSH
• Catechin MeSH
• puerarin MeSH Browser
• Quercetin MeSH

Interaction of flavonoids with transition metals can be partially responsible for their impact on humans. Stoichiometry of the iron/copper complex with a flavonoid glycoside isoquercitrin, a frequent component of food supplements, was assessed using competitive and non-competitive methods in four (patho)physiologically-relevant pH values (4.5. 5.5, 6.8, and 7.5). Isoquercitrin chelated all tested ions (Fe2+, Fe3+, Cu2+, and Cu⁺) but its affinity for Cu⁺ ions proved to be very low. In general, the chelation potency dropped with pH lowering. Metal complexes of 1:1 stoichiometry were mostly formed, however, they were not stable and the stoichiometry changed depending on conditions. Isoquercitrin was able to reduce both Cu2+ and Fe3+ ions at low ratios, but its reducing potential was diminished at higher ratios (isoquercitrin to metal) due to the metal chelation. In conclusion, this study emphasizes the need of using multiple different methods for the assessment of chelation potential in moderately-active metal chelators, like flavonoids.

• Keywords
• Job’s method, chelator, copper, iron, quercetin-3-O-β-glucopyranoside, reduction, stoichiometry,
• MeSH
• Chelating Agents chemistry   MeSH
• Flavonoids chemistry   MeSH
• Hydrogen-Ion Concentration MeSH
• Copper chemistry   MeSH
• Quercetin analogs & derivatives   chemistry   MeSH
• Iron chemistry   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chelating Agents MeSH
• Flavonoids MeSH
• isoquercitrin MeSH Browser
• Copper MeSH
• Quercetin MeSH
• Iron MeSH