Jiali Yang

Structure identification of a polysaccharide purified from Lycium barbarium fruit

The water-soluble bioactive polysaccharides can contribute to the health benefits of Lycium barbarium fruit. However, the structure characteristics of these polysaccharides remain unclear yet. An important polysaccharide (LBPA) was isolated and purified from L. barbarium in this work. It was identified by chemical and spectroscopic methods as arabinogalactan with β-d-(1→6)-galactan as backbone, which was different to any reported polysaccharides from this species before. This arabinogalactan was comprised of Araf, Galp, GlcpA and Rhap with a molar ratio of 9.2:6.6:1.0:0.9. The side chains, including α-l-Araf-(1→, α-l-Araf-(1→5)-α-l-Araf-(1→, β-l-Araf-(1→5)-α-l-Araf-(1→ and α-l-Rhap-(1→4)-β-d-GlcpA-(1→6)-β-d-Galp-(1→, were linked to β-d-(1→6)-galactan at O-3. The putative structure was drawn as below. The molecular weight was determined to be 470,000g/mol by gel permeation chromatography.

Metabolomic analyses of banana during postharvest senescence by (1)H-high resolution-NMR.

Banana is a tropical fruit widely accepted by people over the world. Its chemical composition is critical for its organoleptic properties and nutritional value. In this work, the metabolite changes during postharvest senescence were investigated using NMR spectroscopy. The 1D and 2D NMR spectroscopic information revealed the primary and secondary metabolites in banana fruit, including organic acids, amino acids, carbohydrates and phenolics. Bananas at five senescence stages showed similar chemical profiles, but the levels of the individual compounds varied to a large extent. The principal metabolites responsible for postharvest senescence of banana were valine, alanine, aspartic acid, choline, acetate, glucose, malic acid, gallic acid and dopamine. At stage V, ethanol was present due to the conversion of glucose. Salsolinol was generated due to the conversion of dopamine. This was a characteristic marker for the postharvest senescence of banana fruit.

Structure, bioactivity, and synthesis of methylated flavonoids

Methylated flavonoids are an important type of natural flavonoid derivative with potentially multiple health benefits; among other things, they have improved bioavailability compared with flavonoid precursors. Flavonoids have been documented to have broad bioactivities, such as anticancer, immunomodulation, and antioxidant activities, that can be elevated, to a certain extent, by methylation. Understanding the structure, bioactivity, and bioavailability of methylated flavonoids, therefore, is an interesting topic with broad potential applications. Though methylated flavonoids are widely present in plants, their levels are usually low. Because developing efficient techniques to produce these chemicals would likely be beneficial, we provide an overview of their chemical and biological synthesis.

Identification of a flavonoid C-glycoside as potent antioxidant

Abstract Flavonoids have been documented to have good antioxidant activities in vitro. However, reports on the cellular antioxidant activities of flavonoid C‐glycosides are very limited. In this work, an apigenin C‐glycoside was purified from Artocarpus heterophyllus by column chromatography and was identified to be 2″‐O‐&bgr;‐D‐xylosylvitexin by nuclear magnetic resonance spectroscopy. The cellular antioxidant activity and anticancer activity of 2″‐O‐&bgr;‐D‐xylosylvitexin were evaluated for the first time. The quantitative structure‐activity relationship was analysed by molecular modeling. Apigenin presented an unexpected cellular antioxidation behaviour. It had an antioxidant activity at low concentration and a prooxidant activity at high concentration, whereas 2″‐O‐&bgr;‐D‐xylosylvitexin showed a dose‐dependent cellular antioxidant activity. It indicated that C‐glycosidation improved the cellular antioxidation performance of apigenin and eliminated the prooxidant effect. The ortho‐dihydroxyl at C‐3′/C‐4′ and C‐3 hydroxyl in the flavonoid skeleton play important roles in the antioxidation behaviour. The cell proliferation assay revealed a low cytotoxicity of 2″‐O‐&bgr;‐D‐xylosylvitexin. Graphical abstract Figure. No caption available. HighlightsThe bioactivity of 2″‐O‐&bgr;‐D‐xylosylvitexin was investigated.Its quantitative structure‐activity relationship was analysed.It had a good cellular antioxidant activity.C‐glycosidation improved the antioxidation performance.C‐glycosidation eliminated the prooxidant effect.

Regiospecific synthesis of prenylated flavonoids by a prenyltransferase cloned from Fusarium oxysporum

Due to their impressive pharmaceutical activities and safety, prenylated flavonoids have a high potent to be applied as medicines and nutraceuticals. Biocatalysis is an effective technique to synthesize prenylated flavonoids. The major concern of this technique is that the microbe-derived prenyltransferases usually have poor regiospecificity and generate multiple prenylated products. In this work, a highly regiospecific prenyltransferase (FoPT1) was found from Fusarium oxysporum. It could recognize apigenin, naringenin, genistein, dihydrogenistein, kampferol, luteolin and hesperetin as substrates, and only 6-C-prenylated flavonoids were detected as the products. The catalytic efficiency of FoPT1 on flavonoids was in a decreasing order with hesperetin >naringenin >apigenin >genistein >luteolin >dihydrogenistein >kaempferol. Chalcones, flavanols and stilbenes were not active when acting as the substrates. 5,7-Dihydroxy and 4-carbonyl groups of flavonid were required for the catalysis. 2,3-Alkenyl was beneficial to the catalysis whereas 3-hydroxy impaired the prenylation reaction. Docking studies simulated the prenyl transfer reaction of FoPT1. E186 was involved in the formation of prenyl carbonium ion. E98, F89, F182, Y197 and E246 positioned apigenin for catalysis.

The Plant Resources, Structure Characteristics, Biological Activities and Synthesis of Pyranoflavonoids.

Pyranoflavonoids are mainly distributed in Leguminosae, Moraceae. As a potent drug candidate, pyranoflavonoids have attracted much attention in late years due to their impressive pharmaceutical activities. The structure characteristics, plant resources and pharmaceutical activities of pyranoflavonoids are reviewed in this paper. The fragmentation in mass spectrometry is also discussed for quick identification of these chemicals. Due to the low abundance of this flavonoid sub-class in plants, it is required to find an efficient way to synthesize them. Therefore, an overview of chemical synthesis and biological synthesis is presented in this paper. The information given in this paper will be helpful to know pyranoflavonoids and to be utilized in medicines and nutraceuticals.

The structure changes of water-soluble polysaccharides in papaya during ripening

Papaya is a fruit mainly grown in tropical and subtropical regions. The structural changes of polysaccharides are highly involved in the organoleptic property change of papaya. However, it remains unclear how the structure characteristics of water-soluble polysaccharides are changed during postharvest ripening. It is interesting to work on this topic. In this work, the dominant water-soluble polysaccharide in papaya was purified. It was identified to be α-(1→4)-D-galacturonan by NMR. It remained stable during postharvest ripening. β-(1→4)-D-galactan was only detected in fully green papaya. Once the postharvest ripening initiated, this polysaccharide was rapidly degraded. There were no significant differences in the structure changes of water-soluble polysaccharides for the naturally ripening papaya and ethylene-treated papaya. These results extended the understanding about the relationship between polysaccharide structure and papaya ripening during postharvest storage.

Identification of an immunostimulatory polysaccharide in banana

Banana is a fruit widely accepted by people over the world. Besides having delicious taste, it shows multiple health benefits. In this work, the major polysaccharide was isolated from banana and purified. It was identified to be α-(1 → 6)-d-glucan. The in vivo immunomodulatory activity assay indicated that α-(1 → 6)-d-glucan could improve the immune status by elevating T cell proliferation, phagocytic function of macrophage, CD3+ T cell level, CD4+/CD8+ ratio, IL-6, IgG, IgM, TNF-α and hemolysin antibody levels. The immunostimulatory activities of α-(1 → 6)-d-glucan were similar to β-(1 → 3)-d-glucan, a clinical immunostimulatory drug. This work revealed that α-(1 → 6)-d-glucan was an important bioactive chemical for the immunostimulatory activity of banana. It could be used as a nutraceuticals candidate.

Morin as a Preservative for Delaying Senescence of Banana

Banana is a climacteric fruit with desirable palatability and high nutritional value. It ripens rapidly accompanied with metabolite changes during postharvest storage. In this work, morin was applied to treat banana to delay senescence. Nuclear magnetic resonance (NMR) spectroscopy was used to monitor the changes of metabolite composition and levels in banana. The results showed that morin significantly delayed the changes of color and firmness. 1D and 2D NMR spectra reflected that the levels and composition of metabolites were changed with the senescence initiation. The principal component analysis revealed that the first principal components responsible for banana senescence were carbohydrates, amino acids, lipids and phenolics. Morin treatment delayed the transformation of starch to glucose, fructose and sucrose, accelerated the accumulations of alanine and γ-Amino-butyrate (GABA), postponed the generations of valine and l-aspartic acid, suppressed the degradation of saponin a. It indicated that morin was effective in delaying banana senescence.