Onion bulbs (Allium cepa L.) are among the richest sources of dietary flavonoids and contribute to a large extent to the overall intake of flavonoids. This review includes a compilation of the existing qualitative and quantitative information about flavonoids reported to occur in onion bulbs, including NMR spectroscopic evidence used for structural characterization. In addition, a summary is given to index onion cultivars according to their content of flavonoids measured as quercetin. Only compounds belonging to the flavonols, the anthocyanins, and the dihydroflavonols have been reported to occur in onion bulbs. Yellow onions contain 270-1187 mg of flavonols per kilogram of fresh weight (FW), whereas red onions contain 415-1917 mg of flavonols per kilogram of FW. Flavonols are the predominant pigments of onions. At least 25 different flavonols have been characterized, and quercetin derivatives are the most important ones in all onion cultivars. Their glycosyl moieties are almost exclusively glucose, which is mainly attached to the 4', 3, and/or 7-positions of the aglycones. Quercetin 4'-glucoside and quercetin 3,4'-diglucoside are in most cases reported as the main flavonols in recent literature. Analogous derivatives of kaempferol and isorhamnetin have been identified as minor pigments. Recent reports indicate that the outer dry layers of onion bulbs contain oligomeric structures of quercetin in addition to condensation products of quercetin and protocatechuic acid. The anthocyanins of red onions are mainly cyanidin glucosides acylated with malonic acid or nonacylated. Some of these pigments facilitate unique structural features like 4'-glycosylation and unusual substitution patterns of sugar moieties. Altogether at least 25 different anthocyanins have been reported from red onions, including two novel 5-carboxypyranocyanidin-derivatives. The quantitative content of anthocyanins in some red onion cultivars has been reported to be approximately 10% of the total flavonoid content or 39-240 mg kg (-1) FW. The dihydroflavonol taxifolin and its 3-, 7-, and 4'-glucosides have been identified in onions. Although the structural diversity of dihydroflavonols characterized from onions is restricted compared with the wide structural assortment of flavonols and anthocyanins identified, they may occur at high concentrations in some cultivars. From bulbs of the cultivar "Tropea", 5.9 mg of taxifolin 7-glucoside and 98.1 mg of taxifolin have been isolated per kilogram of FW.

No abstract

This study on anthocyanin colour variation (intensity, l max , 4) over the pH range 1±9 during 60 days of storage, was conducted on petunidin 3- C. Compared to cy3glc, petanin aorded higher colour intensity and higher or similar stability throughout the whole pH range. At pH 4.0, 84% of petanin was intact after 60 days storage at 10 C, while the corresponding solution of cy3glc was totally degraded. At pH 8.1 the colour intensity of petanin was even higher than at the lowest pH values. The visible l max absorption of petanin after 5 days at pH 8.1 at 10 C was similar or higher than the corresponding absorptions of the fresh solutions of cy3glc at any pH. The use of anthocyanins like petanin as food colorants in slightly alkaline products (bakery, milk, egg, etc.) should therefore be consideredÐat least in products with limited storage time kept in a refrigerator. #

Tomatoes ( Lycopersicon esculentum Mill.) have been recognized as an important source of dietary flavonoids because of a high consumption worldwide. The qualitative and quantitative flavonoid compositions of assorted tomato cultivars including individual quantitative contributions of the five most significant flavonoids have been determined in this work. The dihydrochalcone phloretin 3',5'-di-C-beta-glucopyranoside and the flavonol quercetin 3-O-(2''-O-beta-apiofuranosyl-6''-O-alpha-rhamnopyranosyl-beta-glucopyranoside) were identified for the first time in Solanaceae spp. and found to be among the main flavonoids in all cultivars. Phloretin 3',5'-di-C-glc is the first C-glycoside identified in tomatoes and also the first dihydrochalcone from this species. In addition, chalconaringenin, kaempferol 3-rutinoside, and quercetin 3-rutinoside (rutin), though previously reported to occur in tomato, were fully characterized by extensive use of 2D NMR techniques and high-resolution LCMS. The total flavonoid content of different tomato types varied from 4 to 26 mg 100 (-1) g FW with chalconaringenin as the predominant compound comprising 35 to 71% of the total flavonoid content. The individual quantities of quercetin 3-O-(2''- O-beta-apiofuranosyl-6''- O-alpha-rhamnopyranosyl-beta-glucopyranoside) and phloretin 3',5'-di-C-beta-glucopyranoside was similar to that of rutin in several cultivars.

Twelve flavonoids, including seven flavones, four flavonols and one flavanone, were isolated from methanolic extract of the herbal drug 'Crataegi folium cum flore' (hawthorn leaves and flowers) by a combination of CC (over Amberlite XAD-7 and Sephadex LH-20) and preparative HPLC. Their structures, including that of the novel flavonol 8-methoxykaempferol 3-O-(6"-malonyl-beta-glucopyranoside), were elucidated by homo- and heteronuclear NMR and electrospray/MS. The 1H- and 13C-NMR of all compounds, including rotameric pairs of five flavone C-glycosides, were assigned. The presence and relative proportion of each rotamer was shown by various NMR experiments, including two-dimensional nuclear Overhauser and exchange spectroscopy, to depend on solvent, linkage position and structure of the C-glycosyl substituent.

No abstract

Recently, a novel 87-amino acid influenza A virus protein with proapoptotic properties, PB1-F2, has been reported that originates from an alternative reading frame in the PB1 polymerase gene and is encoded in most known human influenza A virus isolates. Here we characterize the molecular structure of a biologically active synthetic version of the protein (sPB1-F2). Western blot analysis, chemical cross-linking, and NMR spectroscopy afforded direct evidence of the inherent tendency of sPB1-F2 to undergo oligomerization mediated by two distinct domains located in the N and C termini, respectively. CD and 1 H NMR spectroscopic analyses indicate that the stability of structured regions in the molecule clearly depends upon the hydrophobicity of the solvent. In aqueous solutions, the behavior of sPB1-F2 is typical of a largely random coil peptide that, however, adopts ␣-helical structure upon the addition of membrane mimetics.1 H NMR analysis of three overlapping peptides afforded, for the first time, direct experimental evidence of the presence of a C-terminal region with strong ␣-helical propensity comprising amino acid residues Ile 55 -Lys 85 connected via an essentially random coil structure to a much weaker helix-like region, located in the N terminus between residues Trp 9 and Lys 20 . The C-terminal helix is not a true amphipathic helix and is more compact than previously predicted. It corresponds to a positively charged region previously shown to include the mitochondrial targeting sequence of PB1-F2. The consequences of the strong oligomerization and helical propensities of the molecule are discussed and used to formulate a hypothetical model of its interaction with the mitochondrial membrane.Influenza A virus (IAV) 3 is one of the most common pathogens threatening humans and animals, with the potential to cause disastrous pandemics. In the last century, it was the origin of at least three pandemics, the most serious outbreak being the "Spanish flu" (1918 -1919) that claimed 20 -50 million casualties worldwide (for a review, see Ref. 1). Apart from various mammals, IAV also infects avian hosts, and particularly aquatic birds have been shown to be the primary reservoir. Sporadically, some of these avian strains acquire the capability to infect other mammals or humans either as a whole or more likely upon genetic reassortment with prevailing human IAV strains. This process termed antigenic (viral) shift appears to occur via the pig as an intermediate host and "mixing vessel" and can lead to new IAV subtypes of mixed surface antigens (2, 3).The genome of IAV, a representative of the orthomyxoviruses, consists of eight separate linear segments of negative sense RNA and was thought to encode 10 gene products. Only very recently, while screening for major histocompatibility complex class I epitopes derived from out-of-frame viral polypeptides, an 11th IAV gene product, named PB1-F2, was incidentally discovered (4). Like the two proteins M1 (matrix protein) and M2 (ion channel) encoded on the M gene segment and t...

Three red onion (Allium cepa) cultivars, top onion (A. cepa var. viviparum), A. altaicum and chive (A. schoenoprasum) contained several or all of the following anthocyanins: 3-(6"-malonyl-3"-glucosylglucoside), 3-(3",6"-dimalonylglucoside), 3-(6"-malonylglucoside), 3-(3"-malonylglucoside), 3-(3"-glucosylglucoside) and 3-glucoside of cyanidin. Trace amounts of two pelargonidin derivatives and the 3,5-diglucosides of cyanidin and peonidin were for the first time reported in red onion. Carbon NMR data showed that the sugars of the 3-(6"-malonyl-3"-glucosylglucoside), 3-(6"-malonylglucoside) and 3-glucoside of cyanidin were pyranoses. Substitution either by sugar or acid in the sugar 3-position of an anthocyanin has never been reported outside the genus Allium.