Minor Pigments Research Articles

Drone-borne sensing of major and accessory pigments in algae using deep learning modeling

ABSTRACT Intensive algal blooms increasingly degrade the inland water quality. Hence, this study aimed to analyze the algal phenomena quantitatively and qualitatively using synoptic monitoring, algal pigment analysis, and a deep learning model. Water surface reflectance was measured using field monitoring and drone hyperspectral image sensing. The algal experiment conducted on the water samples provided data on major pigments including chlorophyll-a and phycocyanin, accessory pigments including lutein, fucoxanthin, and zeaxanthin, and absorption coefficients. Based on the reflectance and absorption coefficient spectral inputs, a one-dimensional convolutional neural network (1D-CNN) was developed to estimate the concentrations of the major and minor pigments. The 1D-CNN could model periodic trends of chlorophyll-a, phycocyanin, lutein, fucoxanthin, and zeaxanthin compared to the observed ones, with R2 values of 0.87, 0.71, 0.76, 0.78, and 0.74, respectively. In addition, major and secondary pigment maps developed by applying the trained 1D-CNN model to the processed drone hyperspectral image inputs successfully provided spatial information regarding the spots of interest. The model provided explicit algal biomass information using the estimated major pigments and implicit taxonomical information using accessory pigments such as green algae, diatoms, and cyanobacteria. Therefore, we provide strong evidence of the extendibility of deep learning models for analyzing various algal pigments to gain a better understanding of algal blooms.

Exploring Liu Kang’s Paris Practice (1929–1932): Insight into Painting Materials and Technique

This paper presents the results of an extensive study of 14 paintings by the pioneering Singapore artist Liu Kang (1911–2004). The paintings are from the National Gallery Singapore and Liu family collections. The aim of the study is to elucidate the painting technique and materials from the artist’s early oeuvre, Paris, spanning the period from 1929 to 1932. The artworks were studied with a wide array of non- and micro-invasive analytical techniques, supplemented with the historical information derived from the Liu family archives and contemporary colourmen catalogues. The results showed that the artist was able to create compositions with a limited colour palette and had a preferential use of commercially available ultramarine, viridian, chrome yellow, iron oxides, organic reds, lead white, and bone black bound in oil that was highlighted. This study identified other minor pigments that appeared as hue modifications or were used sporadically, such as cobalt blue, Prussian blue, emerald green, cadmium yellow, cobalt yellow, and zinc white. With regard to the painting technique, the artist explored different styles and demonstrated a continuous development of his brushwork and was undoubtedly influenced by Modernists’ artworks. This comprehensive technical study of Liu Kang’s paintings from the Paris phase may assist art historians and conservators in the evaluation of the artist’s early career and aid conservation diagnostics and treatment of his artworks. Furthermore, the identified painting materials can be compared with those used by other artists active in Paris during the same period.

Enhanced pigment content estimation using the Gauss-peak spectra method with thin-layer chromatography for a novel source of natural colorants.

Alternative pigment sources that are harmless to human health and can be produced in an eco-responsible way are of great research interest. The experiments undertaken in this study were conducted using autumn leaves of Aesculus hippocastanum as potential novel colorant sources. This study focused on improving the Gauss-peak spectra method (a less expensive alternative to high-pressure liquid chromatography) in combination with thin-layer chromatography, leading to the development of a new methodology. The collected leaves were stored at two different temperatures: 20°C and −20°C. The data obtained by spectrophotometric scanning of the samples were analyzed using the Gauss-peak spectra method in the R program with three wavelength ranges: 350–750 nm, 390–710 nm, and 400–700 nm. The results were then assessed for statistically significant differences in the estimated concentrations for the different wavelength ranges regarding (1) total pigment, carotenoid, and chlorophyll concentration (two-sample t-test) and (2) concentration of each indicated pigment (two-way analysis of variance). The results were also tested for differences between the estimated concentrations of samples stored under the different conditions. The Gauss-peak spectra results with and without thin-layer chromatography were statistically compared using a paired t-test. The results showed that thin-layer chromatography greatly enhanced the efficiency of the Gauss-peak spectra method for estimating the major and minor pigment composition without generating high additional costs. A wavelength range of 400–700 nm was optimal for all Gauss-peak spectra methods. In conclusion, the proposed method is a more successful, inexpensive alternative to high-pressure liquid chromatography.

Polyacylated Anthocyanins in Bluish-Purple Petals of Chinese Bellflower, Platycodon grandiflorum.

The bluish-purple petals of Chinese bellflower, Platycodon grandiflorum (kikyo in Japanese), contain platyconin (1) as the major anthocyanin. Platyconin (1) is a polyacylated anthocyanin with two caffeoyl residues at the 7-position, and its color is stable in a diluted, weakly acidic aqueous solutions. HPLC analysis of the fresh petal extract showed the presence of several minor pigments. Photo-diode array detection of minor pigments suggested that some of these were polyacylated anthocyanins. To establish the relationship between structure and stability of the acylated anthocyanins and to obtain information on their biosynthetic pathways, minor pigments were isolated from the petals, and their structures were determined by MS and NMR analyses. Four known (2–5) and three new anthocyanins (6–8) were identified, which contained a delphinidin chromophore, and four of these (5–8) were diacylated anthocyanins, in which the acyl-glucosyl-acyl-glucosyl chain was attached at the 7-O-position of the delphinidin chromophore. These diacylated anthocyanins exhibited a bluish-purple color at pH 6, which was stable for more than a week.

Eumelanin levels in rufous feathers explain plasma testosterone levels and survival in swallows.

Pigment‐based plumage coloration and its physiological properties have attracted many researchers to explain the evolution of such ornamental traits. These studies, however, assume the functional importance of the predominant pigment while ignoring that of other minor pigments, and few studies have focused on the composition of these pigments. Using the pheomelanin‐based plumage in two swallow species, we studied the allocation of two pigments (the predominant pigment, pheomelanin, and the minor pigment, eumelanin) in relation to physiological properties and viability in populations under a natural and sexual selection. This is indispensable for studying the evolution of pheomelanin‐based plumage coloration. Pheomelanin and eumelanin share the same pathway only during their initial stages of development, which can be a key to unravel the functional importance of pigment allocation and thus of plumage coloration. Using the barn swallow, Hirundo rustica, a migratory species, we found that plasma testosterone levels increased with increasing the proportion of eumelanin pigments compared with pheomelanin pigments, but not with the amount of pheomelanin pigments, during the mating period. In the Pacific swallow Hirundo tahitica, a nonmigratory congener, we found that, during severe winter weathers, survivors had a proportionally smaller amount of eumelanin pigments compared with pheomelanin pigments than that in nonsurvivors, but no detectable difference was found in the pheomelanin pigmentation itself. These results indicated that a minor pigment, eumelanin, matters at least in some physiological measures and viability. Because the major pigment, pheomelanin, has its own physiological properties, a combination of major and minor pigments provides multiple information to the signal receivers, potentially enhancing the signaling function of pheomelanic coloration and its diversification across habitats.

Spiroketalcarminic Acid, a Novel Minor Anthraquinone Pigment in Cochineal Extract Used in Food Additives.

Cochineal extract prepared from the scale insect Dactylopus coccus (American cochineal) has been used as a natural red dye for food, cosmetics, and pharmaceuticals. The major pigment in cochineal extract is carminic acid (CA), an anthraquinone glucoside, and several minor pigments have been previously reported. Our investigation aimed at establishing the safety of cochineal dye products using ultra performance liquid chromatography-photo diode array-electrospray ionization-time of flight (UPLC-PDA-ESI-TOF)/MS found an unknown minor pigment, spiroketalcarminic acid (1), in three commercial cochineal extract samples; cochineal extract used in food additives, carmine that is an aluminum salt of cochineal extract used as natural dye, and a research reagent of CA. The purification of 1 from cochineal extract involved sequential chromatographic techniques, including preparative reversed-phase HPLC. Two dimensional (2D)-NMR and mass analyses established the structure of 1 to be a novel anthraquinone with an unusual 6,5-spiroketal system instead of the C-glucosyl moiety of CA. The absolute stereochemistry of the spiroketal moiety in 1 was determined by nuclear Overhauser effect spectroscopy (NOESY) correlations and optical rotation. No data corresponding to 1 had previously been reported for extracts of dried cochineal insects and traditional art products dyed with cochineal extract, indicating that 1 is likely produced during the preparation of commercial cochineal extract.

A simple method to increase sensitivity for RP‐HPLC phytoplankton pigment analysis

HPLC analysis of phytoplankton pigments from natural samples usually requires the filtration of relatively large volumes of water (1–12 L) through filters of 25–47 mm diameter. Pigment extraction from filters of this size is performed with minimum volumes of 2‐5 mL extraction solvent, routinely 90% acetone. The difference in polarity between the solvent for extraction and the initial eluent for HPLC analysis of phytoplankton pigments limits the load to c.a. 150 µL sample into the chromatographic system. This implies that less than 10% of the sample is analyzed, with the consequent decrease of pigment detectability. Here, a procedure allowing injections of up to 1440 µL of 90% acetone without pigment loss is presented. The method can be easily implemented in current HPLC systems. The response of the peak area measured against volume injected was linear (r2 > 0.998 for any pigment). The precision for injections between 120 and 1440 µL varied between 0.08 and 4.9% (coefficient of variation, n = 4). This system increases the signal response one order of magnitude, reducing the amount of volume filtered and/or enhancing the detectability and identification of minor pigments.

Hemisynthesis and Structural and Chromatic Characterization of Delphinidin 3-O-Glucoside–Vescalagin Hybrid Pigments

During red wine maturation in the presence of oak wood, reactions involving anthocyanins and ellagitannins might affect wine organoleptic properties such as color and astringency. In this work, the condensation reaction between myrtillin (delphinidin 3-O-glucoside) and vescalagin has been performed to determine the behavior of this anthocyanin in this kind of reaction and to assess the possible impact of such a reaction in wine color modulation. Two different hybrid pigments have been hemisynthetized and characterized by HPLC-DAD-MS and NMR spectroscopy. These pigments have been identified as 1-deoxyvescalagin-(1β→8)-myrtillin (major) and 1-deoxyvescalagin-(1β→6)-myrtillin (minor). The minor pigment could be formed both by the condensation reaction and by a regioisomerization process from the major pigment. Moreover, the chromatic properties of these pigments have been studied and compared to those of myrtillin. The hybrid pigments showed an important bathochromic shift (ca. 20 nm) in the maximum absorbance wavelength and lower molar absorption coefficients.

Isolation of Anthocyanins by High-Speed Countercurrent Chromatography and Application of the Color Activity Concept to Different Varieties of Red Grape Pomace from Macedonia

Anthocyanins of Macedonian grape pomace from three varieties “Pinot noir”, “Merlot” and “Vranec” were isolated by high speed countercurrent chromatography. After purification of the fractions by means of preparative high performance liquid chromatography the structures of isolated pigments were elucidated by electrospray ionization multiple mass spectrometry (ESI-MSn) and nuclear magnetic resonance (NMR) spectroscopy. The major anthocyanin malvidin-3-glucoside and the minor pigments delphinidin-3-glucoside, cyaniding-3-glucoside, petunidin-3-glucoside, and malvidin-3-p-coumarоyl-glucoside were isolated. The “Color activity concept” was applied and visual detection thresholds of isolated anthocyanins were determined. The results of the “color activity value” of the isolated pigments and their detection thresholds were in good agreement with the color shade of the different varieties of red grape pomace.

CHARACTERIZATION OF DIFFERENT 'TROPEA RED ONION' (ALLIUM CEPA L.) ECOTYPES BY AROMA PRECURSORS, AROMA PROFILES AND POLYPHENOLIC COMPOSITION

Many epidemiological studies have shown that the consumption of fruits and vegetables is associated with a reduced risk for the development of chronic diseases, such as cardiovascular disease and cancer. Phytochemicals, including polyphenols and flavonoids, are suggested to be the major bioactive compounds of fruits and vegetables contributing to the health benefits. Onion bulbs (Allium cepa L.) are among the richest sources of dietary flavonoids and contribute to a large extent to the overall daily intake of flavonoids. A particular sweet red onion, ‘Tropea Red Onion’, characterized by a large red envelope and internal white tunics, grown in Calabria region (south of Italy), for the excellent organoleptic characteristics (tenderness, crispness, sweetness), is considered the pride of Calabrian’s horticultural products. Because of the few available scientific studies on this particular red onion, a large-scale study to characterize different ‘Tropea red onion’ ecotypes was started. Onions contain bioactive components belonging to two main chemical groups: the flavonoids and the alk(en)yl cysteine sulphoxides (ACSOs). Flavonoid and in particular the anthocyanins and flavanols such as quercetin were found in onion while the ACSOs are the flavour precursors, which, when cleaved by the enzyme alliinase, generate the characteristic odour and taste of onion (thiosulphinates, thiosulphonates, mono-, di- and tri-sulphides). Because of the few available scientific studies on this particular red onion, a large-scale study was started to characterize different ‘Tropea red onion’ ecotypes and to identify markers of authentication to protect it on the national and international market. Moreover, ‘Tropea red onion’ ecotypes are evaluated for their characteristic tastes, aroma profile and for their flavonoids composition in comparison with other red onions. The alk(en)yl-L-cysteine sulphoxides ACSOs are the main precursors of onion flavour due to the presence of thiosulphinates, thiosulphonates, mono-, di- and tri-sulphides that arise in the ground tissues after reaction with the enzyme alliinase. The components of aroma profile are correlated with the pattern of aroma precursors (cysteine sulfoxides). Altogether at least 25 different flavonols have been character¬ized; quercetin derivatives are the most important flavonoids in Calabrian onion ecotypes. Analogous derivatives of kaempferol and isorhamnetin have been identified as minor pigments. HPLC, GC/MS, SPME/GC/MS, and e-nose had been used to classify different ‘Tropea red onion’ ecotypes.

Free Radical Scavenging Activities of Naturally Occurring and Synthetic Analogues of Sea Urchin Naphthazarin Pigments

Antioxidant activities of minor pigments of sea urchins (1-5) and synthetic naphthazarins (7-13) were evaluated and compared with echinochrome A (6) using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) scavenging assays. Structure-activity relationships showed that the antioxidant activities of the tested compounds depended on the number and positions of hydroxyl groups. Compounds bearing 3 or 2 hydroxyl groups on a naphthazarin core (5,8-dihydroxy-1,4-naphthoquinone) were the most active in both assays. Echinochrome A (6) (IC50 7.0 microM) and its monomethyl ethers 7 (IC50 15.0 microM) and 8 (IC50 15.0 microM) displayed stronger activities than Trolox (IC50 16.0 microM) in the DPPH and ABTS assays (TE = 3.41, 2.35, and 2.35 mM, respectively). Compounds with either one or without hydroxyl groups on a naphthazarin core displayed activities significantly lower than Trolox in both assays. These results suggest that hydroxylated naphthazarin pigments of sea urchins have a potential use as natural antioxidants.

Application of LC–MS and tristimulus colorimetry to assess the ageing aptitude of Syrah wine in the Condado de Huelva D.O. (Spain), a typical warm climate region

The study of the evolutions of different wine pigment families, copigmentation/polymerisation processes and colour characteristics during the first year of ageing in oak barrel has allowed the assessment of the ageing aptitude of Syrah wines from “Condado de Huelva D.O.”, a warm climate region. A total of 32 anthocyanic pigments were identified, including 14 major compounds from grape and 18 minor derivatives formed during the vinification. The anthocyanin profile changed towards more chemical complexity, being vitisin-like pyranoanthocyanins the predominant minor pigments during the first month of ageing. As wine became older, a progressive increase on the content of 4-vinylcatechin, 4-vinylphenol and 4-vinylcatechol compounds took place. Results showed that copigmentation occurred during the whole process of ageing inducing visual perceptible colour effects. Simultaneously to the copigmentation decrease, the degree of polymerisation increased during ageing, being maximum at 9 months old wines (77%). The colour of wines evolved progressively in a positive way from 3 to 9 months of ageing, becoming darker and with more vivid colour. However, from 9 to 12 months of ageing, the chemical structure of wines was negatively affected resulting in lighter, with more red-orange hues and less vivid colours. The inclusion of the chemical and colorimetric information on the PCA model allows us to reach very good discriminations among the Syrah wines with different wood contact period.

Purification of l‐α‐Glycerylphosphorylcholine from the Enzyme Reaction Solutions by Resin Column Chromatography

AbstractColorless l‐α‐glycerylphosphorylcholine (l‐α‐GPC) was obtained at 98.8% purity, and with a specific rotation of −2.5° via a four‐step procedure. l‐α‐GPC was first produced by phospholipase A1 hydrolysis of phosphatidylcholine in an aqueous medium. Almost all the impurities were then removed using two successive D001 cation and D301‐111 anion exchange resin column chromatography procedures, followed by decoloration with active carbon to remove minor pigments and remaining impurities. D001 resin and D301‐111 resin showed remarkable ability for l‐α‐GPC isolation after being used eight times. Thus, this study presents a simple and cost‐effective method for preparing l‐α‐GPC with high purity, low costs, and environmental friendliness, and encourages future investigation into its adaptation for industrial applications.

Determination of detection limits for SEM-EDS and m-FTIR analysis of artwork

Scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) and micro-Fourier transform infrared (m-FTIR) spectroscopy are two of the primary analytical techniques used for the characterisation of artwork (Casadio and Toniolo, J. Cult. Herit. 2:71-78, 2001; Bruni et al., Vibr. Spectrosc. 20:15-25, 1999; Bouchard et al., e-Preserv. Sci. 6:27-37, 2009). Despite wide application of these techniques, no studies have been performed to evaluate their detection limits for this type of analysis. The characterisation of minor components used in a piece of art is important because these components may provide key information about the process of creation and answer questions regarding conservation and restoration (Casadio and Toniolo, J. Cult. Herit. 2:71-78, 2001; Bicchieri et al., Spectrochim. Acta B At. Spectrosc. 56:915-922, 2001). This study focused on easel paintings. Several mock-ups were prepared, and the painting layers were created with binary mixtures of three different blues (Prussian blue, phthalocyanine blue and ultramarine blue). Blue pigments have been used extensively in many art pieces and several studies have described problems related to their determination in low concentrations (Bouchard et al., e-Preserv. Sci. 6:27-37, 2009; Bicchieri et al., Spectrochim. Acta B At. Spectrosc. 56:915-922, 2001; Osticiolia et al., Spectrochim. Acta A Mol. Biomol. Spectrosc. 73:525-531, 2009; Giaccai, Mater. Res. Soc. Symp. Proc. 1047:233-242, 2008; Lutzenberger and Stege, e-Preserv. Sci. 6:89-100, 2009). This study indicated that the minimum concentrations at which the presence of the minor pigment is detected in at least half of the determinations performed are between 0.9% and 1.5% for phthalocyanine blue, between 0.8% and 1.3% for Prussian blue and between 0.3% and 1% for ultramarine blue with SEM-EDS; with m-FTIR spectroscopy, the minimum concentrations are between 0.9% and 1.5% for phthalocyanine blue, 2.4% or more for Prussian blue and 19% or more for ultramarine blue. The concentrations measured for some pigments were high and may result in errors in the description of the composition of a piece of art. The use of complementary techniques may address this limitation. On the basis of these results, the application of analytical procedures that include replicate determinations and analyses of areas of 100 × 100 μm(2) or greater and exclude single determinations are recommended to more accurately describe the material composition of a work of art.

Tigloylshikonin, a New Minor Shikonin Derivative, from the Roots and the Commercial Root Extract of Lithospermum erythrorhizon

Tigloylshikonin, a new shikonin derivative esterified with tiglic acid ((E)-2-methylbut-2-enoic acid), was isolated as a minor pigment from a food colorant "Shikon color," a commercial root extract from Lithospermum erythrorhizon SIEBOLD et ZUCCARINI. The structure of tigloylshikonin was elucidated using (1)H, (13)C, the difference nuclear Overhauser effect (NOE), and 2D NMR techniques. Its stereochemistry was determined by chiral-phase HPLC analysis. Tigloylshikonin was also found in the roots of L. erythrorhizon, which indicated that this new shikonin derivative is a typical component of naphthoquinone pigments in the roots of L. erythrorhizon.

Guanine Deaminase Functions as Dihydropterin Deaminase in the Biosynthesis of Aurodrosopterin, a Minor Red Eye Pigment of Drosophila

Dihydropterin deaminase, which catalyzes the conversion of 7,8-dihydropterin to 7,8-dihydrolumazine, was purified 5850-fold to apparent homogeneity from Drosophila melanogaster. Its molecular mass was estimated to be 48 kDa by gel filtration and SDS-PAGE, indicating that it is a monomer under native conditions. The pI value, temperature, and optimal pH of the enzyme were 5.5, 40 degrees C, and 7.5, respectively. Interestingly the enzyme had much higher activity for guanine than for 7,8-dihydropterin. The specificity constant (k(cat)/K(m)) for guanine (8.6 x 10(6) m(-1).s(-1)) was 860-fold higher than that for 7,8-dihydropterin (1.0 x 10(4) m(-1).s(-1)). The structural gene of the enzyme was identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis as CG18143, located at region 82A1 on chromosome 3R. The cloned and expressed CG18143 exhibited both 7,8-dihydropterin and guanine deaminase activities. Flies with mutations in CG18143, SUPor-P/Df(3R)A321R1 transheterozygotes, had severely decreased activities in both deaminases compared with the wild type. Among several red eye pigments, the level of aurodrosopterin was specifically decreased in the mutant, and the amount of xanthine and uric acid also decreased considerably to 76 and 59% of the amounts in the wild type, respectively. In conclusion, dihydropterin deaminase encoded by CG18143 plays a role in the biosynthesis of aurodrosopterin by providing one of its precursors, 7,8-dihydrolumazine, from 7,8-dihydropterin. Dihydropterin deaminase also functions as guanine deaminase, an important enzyme for purine metabolism.

Unique photosystems in Acaryochloris marina

A short overview is given on the discovery of the chlorophyll d-dominated cyanobacterium Acaryochloris marina and the minor pigments that function as key components therein. In photosystem I, chlorophyll d', chlorophyll a, and phylloquinone function as the primary electron donor, the primary electron acceptor and the secondary electron acceptor, respectively. In photosystem II, pheophytin a serves as the primary electron acceptor. The oxidation potential of chlorophyll d was higher than that of chlorophyll a in vitro, while the oxidation potential of P740 was almost the same as that of P700. These results help us to broaden our view on the questions about the unique photosystems in Acaryochloris marina.

Biosynthesis of food constituents: Natural pigments. Part 2 - a review

This review article is a part of the survey of the generally accepted biosynthetic pathways that lead to the most important natural pigments in organisms closely related to foods and feeds. The biosynthetic pathways leading to xanthones, flavonoids, carotenoids, and some minor pigments are described including the enzymes involved and reaction schemes with detailed mechanisms.

Onions: A Source of Unique Dietary Flavonoids

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.

Triacylated cyanidin 3-(3 X-glucosylsambubioside)-5-glucosides from the flowers of Malcolmia maritima

Three acylated cyanidin 3-(3 X-glucosylsambubioside)-5-glucosides ( 1– 3) and one non-acylated cyanidin 3-(3 X-glucosylsambubioside)-5-glucoside ( 4) were isolated from the purple-violet or violet flowers and purple stems of Malcolmia maritima (L.) R. Br (the Cruciferae), and their structures were determined by chemical and spectroscopic methods. In the flowers of this plant, pigment 1 was determined to be cyanidin 3- O-[2- O-(2- O-( trans-sinapoyl)-3- O-(β- d-glucopyranosyl)-β- d-xylopyranosyl)-6- O-( trans- p-coumaroyl)-β- d-glucopyranoside]-5- O-[6- O-(malonyl)-(β- d-glucopyranoside) as a major pigment, and a minor pigment 2 was determined to be the cis- p-coumaroyl isomer of pigment 1. In the stems, pigment 3 was determined to be cyanidin 3- O-[2- O-(2- O-( trans-sinapoyl)-3- O-(β- d-glucopyranosyl)-β- d-xylopyranosyl)-6- O-( trans- p-coumaroyl)-β- d-glucopyranoside]-5- O-(β- d-glucopyranoside) as a major anthocyanin, and also a non-acylated anthocyanin, cyanidin 3- O-[2- O-(3- O-(β- d-glucopyranosyl)-β- d-xylopyranosyl)-β- d-glucopyranoside]-5- O-(β- d-glucopyranoside) was determined to be a minor pigment (pigment 4). In this study, it was established that the acylation-enzymes of malonic acid has important roles for the acylation of 5-glucose residues of these anthocyanins in the flower-tissues of M. maritima; however, the similar enzymatic reactions seemed to be inhibited or lacking in the stem-tissues.