绿茶、乌龙茶、红茶中的主要组分和酚类化合物抑制脂肪氧合酶活性和抗油脂自动氧化特性的研究

绿茶、乌龙茶和红茶中含有多种抑制脂肪氧合酶及抗油脂自动氧化的有效成分。实验结果表明,其中以表没食子儿茶素没食子酸酯(EGCG)的抗氧化活性最强,延缓猪油自动氧化诱导期为55.5小时,比无添加抗氧化成分的延长11倍,抑制脂肪氧合酶活性的IC_(50)值为10.0μmol/L。茶黄素单酯-2B(TFM-2B)和茶黄素双酯(TFD)比EGCG抑制脂肪氧合酶活性的效果更强,其IC_(60)值分别为0.57和0.23μmol/L。在三种茶叶的四种溶剂萃取物中,以乙酸乙酯萃取物的抗氧化活性最强。本文还研究了茶叶中主要生物活性物质的分离与纯化方法,以及抗氧化活性与结构的关系。     

Time-course tracer studies on the metabolism of cinnamic acid in Cestrum poeppigii

Time-course tracer studies were performed on the metabolism of trans-cinnamic acid-[3-¹⁴C] and trans-p-coumaric acid-[2-¹⁴C] in the     

Polyphenols of mature plant,seedling and tissue cultures of Theobroma cacao

The major flavone in mature cocoa leaves is isovitexin, with smaller amounts of vitexin and 7-O-glucosides of apigenin, luteolin and chrysoeriol. F     

Natural polyphenols-iron interaction

The iron-binding capacity of different fractions of natural polyphenols extracts was determined by chromatographic and electrophoretic methods. Their effects on iron-induced calcium homeostasis changes in liver tissue suspension showed that mate tea and green tea extracts provoke a very significant inhibition of the iron effects, whereas it is much less significant with red wine extract. The biological importance of this phenomenon is discussed.     

Enzymatic formation of a resorcylic acid by creating a structure‐guided single‐point mutation in stilbene synthase

A novel C17 resorcylic acid was synthesized by a structure‐guided Vitis vinifera stilbene synthase (STS) mutant, in which threonine 197 was replaced with glycine (T197G). Altering the architecture of the coumaroyl binding and cyclization pocket of the enzyme led to the attachment of an extra acetyl unit, derived from malonyl‐CoA, to p‐coumaroyl‐CoA. The resulting novel pentaketide can be produced strictly by STS‐like enzymes and not by Chalcone synthase‐like type III polyketide synthases; due to the unique thioesterase like activity of STS‐like enzymes. We utilized a liquid chromatography mass spectrometry‐based data analysis approach to directly compare the reaction products of the mutant and wild type STS. The findings suggest an easy to employ platform for precursor‐directed biosynthesis and identification of unnatural polyketides by structure‐guided mutation of STS‐like enzymes.     

Above‐ and belowground linkages in Sphagnum peatland: climate warming affects plant‐microbial interactions

Peatlands contain approximately one third of all soil organic carbon (SOC). Warming can alter above‐ and belowground linkages that regulate soil organic carbon dynamics and C‐balance in peatlands. Here we examine the multiyear impact of in situ experimental warming on the microbial food web, vegetation, and their feedbacks with soil chemistry. We provide evidence of both positive and negative impacts of warming on specific microbial functional groups, leading to destabilization of the microbial food web. We observed a strong reduction (70%) in the biomass of top‐predators (testate amoebae) in warmed plots. Such a loss caused a shortening of microbial food chains, which in turn stimulated microbial activity, leading to slight increases in levels of nutrients and labile C in water. We further show that warming altered the regulatory role of Sphagnum‐polyphenols on microbial community structure with a potential inhibition of top predators. In addition, warming caused a decrease in Sphagnum cover and an increase in vascular plant cover. Using structural equation modelling, we show that changes in the microbial food web affected the relationships between plants, soil water chemistry, and microbial communities. These results suggest that warming will destabilize C and nutrient recycling of peatlands via changes in above‐ and belowground linkages, and therefore, the microbial food web associated with mosses will feedback positively to global warming by destabilizing the carbon cycle. This study confirms that microbial food webs thus constitute a key element in the functioning of peatland ecosystems. Their study can help understand how mosses, as ecosystem engineers, tightly regulate biogeochemical cycling and climate feedback in peatlands     

Natural and synthetic antioxidants: An updated overview

Abstract

The current understanding of the complex role of ROS in the organism and pathological sequelae of oxidative stress points to the necessity of comprehensive studies of antioxidant reactivities and interactions with cellular constituents. Studies of antioxidants performed within the COST B-35 action has concerned the search for new natural antioxidants, synthesis of new antioxidant compounds and evaluation and elucidation of mechanisms of action of both natural and synthetic antioxidants. Representative studies presented in the review concern antioxidant properties of various kinds of tea, the search for new antioxidants of herbal origin, modification of tocopherols and their use in combination with selenium and properties of two promising groups of synthetic antioxidants: derivatives of stobadine and derivatives of 1,4-dihydropyridine.     

Optimization of the extraction of polyphenols and antioxidant activity from Malva parviflora L. leaves using Box–Behnken design

Abstract

Box–Behnken Design (BBD) was used to optimize the extraction conditions of polyphenols from Malva (Malva parviflora L.) leaves. The effect of ethanol concentration (20–80%), solvent/leaf powder ratio (10:1 to 30:1, v/w) and extraction time (5–45?min) on the polyphenols yield and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of the obtained extracts were investigated. Quadratic models fit well. The optimal conditions (53.40% ethanol, solvent/leaf powder ratio 20:1 (v/w), and 15?min) resulted in an extract with a maximum yield of polyphenols (1098.4?mg GAE/100?g leaf powder) and high inhibition percentage of DPPH radical (33.31%) with desirability 0.742. High Performance Liquid Chromatography (HPLC) analysis indicated that the major identified polyphenol compounds extracted at the optimal conditions were naringenin, ρ-coumaric acid, apigenin-7-glucoside, luteolin, and cinnamic acid. These findings indicate that M. parviflora leaf extracts possess DPPH radical scavenging activity and could be used as a natural source for bioactive products.     

Experimental climate effect on seasonal variability of polyphenol/phenoloxidase interplay along a narrow fen–bog ecological gradient in Sphagnum fallax

Extracellular phenoloxidase enzymes play an important role in the stability of soil carbon storage by contributing to the cycling of complex recalcitrant phenolic compounds. Climate warming could affect peatland functioning through an alteration of polyphenol/phenoloxidase interplay, which could lead them to becoming weaker sinks of carbon. Here, we assessed the seasonal variability of total phenolics and phenoloxidases subjected to 2–3 °C increase in air temperature using open‐top chambers. The measurements were performed along a narrow fen–bog ecological gradient over one growing season. Climate warming had a weak effect on phenoloxidases, but reduced phenolics in both fen and bog areas. Multivariate analyses revealed a split between the areas and also showed that climate warming exacerbated the seasonal variability of polyphenols, culminating in a destabilization of the carbon cycle. A negative relationship between polyphenols and phenoloxidases was recorded in controls and climate treatments suggesting an inhibitory effect of phenolics on phenoloxidases. Any significant decrease of phenolics through repeatedly elevated temperature would greatly impact the ecosystem functioning and carbon cycle through an alteration of the interaction of polyphenols with microbial communities and the production of extracellular enzymes. Our climate treatments did not have the same impact along the fen–bog gradient and suggested that not all the peatland habitats would respond similarly to climate forcing.