Two widely applied spectrophotometric assays based on aluminium complex formation used for determination of total flavonoid content in food or medicinal plant samples were examined for several compounds from different classes of flavonoid family. The method which involves the measurement at 410–430 nm after addition of AlCl3 solution is selective only for flavonols and flavones luteolin. The procedure in the presence of NaNO2 in alkaline medium seems to be specific for rutin, luteolin and catechins, but also phenolic acids exhibit considerable absorbance at 510 nm. Application of both procedures to natural samples gave different order in terms of their flavonoid content. Thus, the expression “total flavonoid” content is not adequate as the results of both methods are dependent on the structure of the individual flavonoids present.

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Evaluation of Aluminium Complexation Reaction for Flavonoid Content Assay

Background Quercetin, one of the most well-known flavonoids, has been included in human diet for a long history. The use of quercetin has been widely associated with a great number of health benefits, including antioxidant, anti-inflammatory, antiviral and anticancer as well as the function to ease some cardiovascular diseases (i.e., heart disease, hypertension, and high blood cholesterol). However, poor water solubility, chemical instability and low bioavailability of quercetin greatly limit its applications. Utilization of delivery systems can improve its stability, efficacy and bioavailability. Scope and approach In this review, biological activities, chemical stability, metabolism and toxicity of quercetin and different delivery systems for quercetin were discussed. Key findings and conclusions Quercetin digested in human body (e.g., mouth, small intestine, liver, kidneys) undergoes glucuronidation, sulfation or methylation. During the food processing and storage, many factors such as heat, pH, metal ions, could affect the chemical stability (including oxidation and degradation) of quercetin. Utilization of delivery systems including lipid-based carriers, nanoparticles, inclusion complexes, micelles and conjugates-based encapsulation has the potential to improve both the stability and bioavailability and thus health benefits of quercetin. Each delivery system has its unique advantages and shortcomings, and the specific selection should be based on the application domains. Moreover, the exploration of natural food-grade ingredients as main compositions of delivery systems for quercetin might be required in the future.

The biological activities, chemical stability, metabolism and delivery systems of quercetin: A review

In the present study, a facile one-step hydrothermal treatment of coriander leaves for preparing carbon dots (CDs) has been reported. Optical and structural properties of the CDs have been extensively studied by UV-visible and fluorescence spectroscopic, microscopic (transmission electron microscopy, scanning electron microscopy) and X-ray diffraction techniques. Surface functionality and composition of the CDs have been illustrated by elemental analysis and Fourier transform infrared spectroscopy (FTIR). Quenching of the fluorescence of the CDs in the presence of metal ions is of prime significance, hence CDs have been used as a fluorescence probe for sensitive and selective detection of Fe3+ ions. Eventually, biocompatibility and bioimaging aspects of CDs have been evaluated on lung normal (L-132) and cancer (A549) cell lines. Qualitative analysis of cellular uptake of CDs has been pursued through fluorescence microscopy, while quantitative analysis using a flow cytometer provided an insight into the concentration and cell-type dependent uptake of CDs. The article further investigates the antioxidant activity of CDs. Therefore, we have validated the practicality of CDs obtained from a herbal carbon source for versatile applications.

Green synthesis of multifunctional carbon dots from coriander leaves and their potential application as antioxidants, sensors and bioimaging agents.

Neurodegenerative diseases pose a substantial socioeconomic burden on society. Unfortunately, the aging world population and lack of effective cures foreshadow a negative outlook. Although a large amount of research has been dedicated to elucidating the pathologies of neurodegenerative diseases, their principal causes remain elusive. Metal ion dyshomeostasis, proteopathy, oxidative stress, and neurotransmitter deficiencies are pathological features shared across multiple neurodegenerative disorders. In addition, these factors are proposed to be interrelated upon disease progression. Thus, the development of multifunctional compounds capable of simultaneously interacting with several pathological components has been suggested as a solution to undertake the complex pathologies of neurodegenerative diseases. In this review, we outline and discuss possible therapeutic targets in Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis and molecules, previously designed or discovered as pote...

Development of Multifunctional Molecules as Potential Therapeutic Candidates for Alzheimer’s Disease, Parkinson’s Disease, and Amyotrophic Lateral Sclerosis in the Last Decade

Heavy metals are naturally occurring in the earth‘s crust but anthropogenic and industrial activities have led to drastic environmental pollutions in distinct areas. Plants are able to colonize such sites due to several mechanisms of heavy metal tolerance. Understanding of these pathways enables different fruitful approaches like phytoremediation and biofortification. Therefore, this review addresses mechanisms of heavy metal tolerance and toxicity in plants possessing a sophisticated network for maintenance of metal homeostasis. Key elements of this are chelation and sequestration which result either in removal of toxic metal from sensitive sites or conduct essential metal to their specific cellular destination. This implies shared pathways which can result in toxic symptoms especially in an excess of metal. These overlaps go on with signal transduction pathways induced by heavy metals which include common elements of other signal cascades. Nevertheless, there are specific reactions some of them will be discussed with special focus on the cellular level.

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How plants cope with heavy metals

The 2,2-diphenylpicrylhydrazyl (DPPH) assay is widely used in plant biochemistry to evaluate the properties of plant constituents for scavenging free radicals. The method is based on the spectrophotometric measurement of the DPPH concentration change resulting from the reaction with an antioxidant. Several protocols have been followed for this assay using different conditions such as different reaction times, solvents, pH and different compounds used as antioxidant standards. This review shows to what extent the mentioned parameters have the influence on the presented results.

Application of free radical diphenylpicrylhydrazyl (DPPH) to estimate the antioxidant capacity of food samples

Quercetin, one of the most common dietary flavonols, was investigated in the presence of Cu(II) ions in methanolic solution in order to obtain some explanation on the mechanism interaction and its action against free radical-mediated damage. The spectroscopic studies (UV–VIS, IR, ESI–MS) were used to assess the extent to which it undergo complex formation through chelation or modification through oxidation. The reaction of quercetin with Cu(II) resulted in the formation of 1:1 metal–ligand complex (λmax = 436 nm) through the carbonyl oxygen and 3-OH group in C ring. Then quercetin is oxidized to the benzoquinone type products. The addition of EDTA destroyed the complex but did not regenerate the whole original spectrum of quercetin. From the other hand, the presence of EDTA inhibits formation of copper–quercetin complex and quercetin oxidation. The antioxidant activity of the Q + Cu solutions was evaluated by using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH∙) radical scavenging method and from an electrochemical point of view. The complex is much more effective as free radical scaveninger than the free flavonoid.

Interaction of quercetin with copper ions: complexation, oxidation and reactivity towards radicals

The 2,2'-diphenyl-1-picrylhydrazyl (DPPH) assay is commonly applied for the estimation of antioxidant activity of plant extracts. This article discusses the effect of a sample pH and the presence of metal ions on the results obtained using DPPH method for several tea infusions. Higher radical quenching was observed in less acidic media. The impact of metal ions depends of the types of metal ion and its concentration. Quercetin and epigallocatechin gallate were less efficient in the reaction with DPPH in the presence of Al(III). Desalting process using cation-exchange resin Dowex 50Wx8 decreased the content of metal ions in all studied tea infusions. The DPPH scavenging activity of the effluents after this process were higher than those of the primary extracts and this may be related to the actual antioxidant capacity of these samples.

Effect of pH and metal ions on DPPH radical scavenging activity of tea.

Objective
Antioxidant properties of the water extracts of the commercial bagged fruit and flavoured black teas were evaluated and compared with typical black teas of C. sinensis.

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Anna Pękal

Papers

Evaluation of Aluminium Complexation Reaction for Flavonoid Content Assay

Application of free radical diphenylpicrylhydrazyl (DPPH) to estimate the antioxidant capacity of food samples

Interaction of quercetin with copper ions: complexation, oxidation and reactivity towards radicals

Effect of pH and metal ions on DPPH radical scavenging activity of tea.

Evaluation of the antioxidant properties of fruit and flavoured black teas