Irina Volf

A critical review of methods for characterisation of polyphenolic compounds in fruits and vegetables

Phenolic compounds, ubiquitous in plants, are of considerable interest and have received more and more attention in recent years due to their bioactive functions. Polyphenols are amongst the most desirable phytochemicals due to their antioxidant activity. These components are known as secondary plant metabolites and possess also antimicrobial, antiviral and anti-inflammatory properties along with their high antioxidant capacity. Many efforts have been made to provide a highly sensitive and selective analytical method for the determination and characterisation of polyphenols. The aim of this paper is to provide information on the most recent developments in the chemical investigation of polyphenols emphasising the extraction, separation and analysis of these compounds by chromatographic and spectral techniques.

Thermal stability, antioxidant activity, and photo-oxidation of natural polyphenols

The thermal stability (60°C, 80°C, 100°C), antioxidant activity, and ultraviolet C light (UV-C) stability of standard polyphenols solutions (catechin, gallic acid, and vanillic acid) and of vegetal extracts from spruce bark and grape seeds were investigated. Exposure of the standard solutions and vegetal extracts to high temperatures revealed that phenolic compounds were also relatively stable (degradations ranged from 15 % to 30 % after 4 h of exposure). The highest antioxidant activity was obtained for ascorbic acid and gallic acid followed by catechin and caffeic acid and the grape seeds. The results show that, after 3 h of UV-C exposure, approximately 40 % of vanillic acid, 50 % of gallic acid, and 83 % of catechin were removed. Similar degradation rates were observed for vegetal extracts, with the exception of the degradation of catechin (40 %) from grape seeds. In addition, the photo-oxidation of polyphenols in the presence of food constituents such as citric acid, ascorbic acid, sodium chloride, and sodium nitrate was assessed.

Optimization of ultrasound-assisted extraction of polyphenols from spruce wood bark.

Here we describe the ultrasound-assisted extraction of the phenolic compounds from spruce wood bark and present a straight-forward experimental planning method, allowing the optimisation of the process. The effect of ethanol concentration, temperature and extraction time were evaluated through a 3(2)·2 experimental planning. The efficiency of the extraction process was appreciated based on factorial ANOVA results. The maximum extraction yield of total polyphenols (13.232mg gallic acid equivalents (GAE)/g of spruce bark tested) was obtained using a process time of 60min, an extraction temperature of 54°C and a concentration of ethanol of 70% respectively. These results indicate that an important quantity of bioactive compounds can be extracted from spruce wood bark by ultrasound assisted extraction technology.

A Comparative Analysis of the ‘Green’ Techniques Applied for Polyphenols Extraction from Bioresources

From all the valuable biomass extractives, polyphenols are a widespread group of secondary metabolites found in all plants, representing the most desirable phytochemicals due to their potential to be used as additives in food industry, cosmetics, medicine, and others fields. At present, there is an increased interest to recover them from plant of spontaneous flora, cultivated plant, and wastes resulted in agricultural and food industry. That is why many efforts have been made to provide a highly sensitive, efficiently, and eco‐friendly methods, for the extraction of polyphenols, according to the green chemistry and sustainable development concepts. Many extraction procedures are known with advantages and disadvantages. From these reasons, the aim of this article is to provide a comparative analysis regarding technical and economical aspects related to the most innovative extraction techniques studied in the last time: microwave‐assisted extraction (MAE), supercritical fluid extraction (SFE), and ultrasound‐assisted extraction (UAE).

Kinetic modeling of the ultrasound-assisted extraction of polyphenols from Picea abies bark.

In this paper, the kinetics of polyphenols extraction from spruce bark (Picea abies) under ultrasounds action was investigated. Studies were performed in order to express the effect of some specific parameters (as: ultrasounds, surface contact between solvent and solid, extraction time and temperature) on the total phenolic content (TPC). Experiments were performed in the presence and absence of ultrasounds, using different contact surfaces between solvent and solid, for times from 5 to 75min and temperatures of 318, 323 and 333K. All these factors have a positive influence on the process, enhancing the extraction rate by recovering higher amounts of polyphenols. The process takes place in two stages: a fast one in the first 20-30min (first stage), followed by a slow one approaching to an equilibrium concentration after 40min (second stage). In these conditions, the second-order kinetic model was successfully developed for describing the mechanism of ultrasound-assisted extraction of polyphenols from P. abies bark. Based on this model, values of second-order extraction rate constant (k), initial extraction rate (h), saturation concentration (Cs) and activation energy (Ea) could be predicted. Model validation was done by plotting experimental and predicted values of TPCs, revealing a very good correlation between the obtained data (R(2)>0.98).

Seasonal variations of the phenolic constituents in bilberry (Vaccinium myrtillus L.) leaves, stems and fruits, and their antioxidant activity.

The seasonal variations of the content and diversity of phenolic compounds, as well as the antioxidant activity of leaves, stems and fruits of bilberry collected in May, July and September, were evaluated for two consecutive years. UPLC/MS(n) analyses showed the predominance of anthocyanins in fruits, caffeic acid derivatives in leaves whereas flavanol oligomers represented more than half of the phenolic compounds in stems. Thioacidolysis revealed degrees of polymerization between 2 and 4 and (-)-epicatechin as the main flavanol unit. The sum of the phenolic compounds by UPLC was highly correlated with the total polyphenol content and the antioxidant activity in the DPPH test for all the extracts except for May leaves. The latter were relatively rich in p-coumaric acid derivatives. Seasonal effects were more marked for leaves, which exhibited higher antioxidant activities and phenolic contents in July and September when these parameters were at their highest in July for stems.

Valorization of Pistia stratiotes Biomass as Biosorbent for Lead(II) Ions Removal from Aqueous Media

In this study the valorization of Pistia stratiotes biomass as biosorbent for lead(II) removal from aqueous media was investigated in batch system. About 0.125 g of biomass was sufficient to remove 96% of lead(II) from 25 mL of solution in 60 min, at room temperature, and the maximum of biosorption has been reached in a large pH interval. The equilibrium biosorption data are well represented by the Langmuir model, while the pseudo-second order model was applicable to the kinetic data. The lead(II) could be easily eluted with 0.1 mol/L HCl, and the biomass may be reused in three biosorption/desorption cycles.

Lignins and Polyphenols in Bioremediation

Bioremediation by definition is concerned with the fate and, if necessary, removal of unwanted organic chemicals from soil and/or water. At present, bioremediation is considered as a less expensive alternative to physical and chemical means of degradation of organic pollutants. It deals with substances that are anthropogenic, distributed in nature and recalcitrant. At the same time, it is not lacked of interest to involve the bioremediation to improve some properties of the soils. The lignins are biosynthesized in plants to carry out different functions, such as storage of energy, bonding agent between plant cells, protection agent against microorganisms, antioxidant, and hydrophobic agent. Lignin is an important precursor for stabilized soil organic carbon. Terrestrial ecosystems that produce large amounts of lignin are thought to have high potential for sequestering carbon which can decrease global warming by reducing atmospheric CO2. After the death of the plants, their compounds are transformed at the soil level with humus formation. Based on biological transformation some utilization of lignins could be developed among other things such as crop cultivation and bioremediation (Abaecherli and Popa, 2005).

INFLUENCE OF EXTRACTION METHODS ON CARAWAY (Carum carvi L.) ESSENTIAL OIL YIELD AND CARVONE/LIMONENE RATIO

The caraway (Carum carvi L.) samples were collected from little meadows situated in Harghita Mountain (Madaras Ciuc, Harghita Bai, Jigodin, Tusnadu Nou), where a relatively small area was covered by a group of rich populations of wild cumin. The harvested plants are dried by: a) convective laboratory dryer in thick layer, b) static outdoors in sunshine, and (c) static in a warm indoor place in darkness. The hand-picked seeds were separated from debris by sieving and elutriation. The essential oil was obtained with electrically heated Clevenger-type laboratory steam distillation equipment both with and without microwave pretreatment. The variation of the obtained essential oil volume in time was measured and the final yield was determined. For comparison the composition, supercritical fluid extraction of the caraway essential oil with carbon dioxide in a laboratory scale batch supercritical extractor was made. Each sample was analyzed by gas chromatography, following the influence of drying and extraction method on the carvone/limonene ratio. The investigation shows that the essential oil yield is around 7 mL/100 g, less in the case of green plant (6 mL/100 g) and higher in case of the mature plant (10 mL/100 g). The results show that by batch supercritical fluid extraction with CO2 (at first purge) lowest carvone/limonene ratio was obtained.

Enhancing copper and lead bioaccumulation in rapeseed by adding hemp shives as soil natural amendments

AbstractThe current study reveals the results of a phytoremediation process applied to a multi metal contaminated soil, located in close proximity to an energy power plant. Phytoremediation process was studied using the rapeseed cultivation, both in the presence and absence of hemp shives, considered as potential natural soil amendments. The physiological responses of the rapeseed plants, such as variations in length and accumulation of biomass, as well as the content of assimilating pigments were investigated. The concentrations of Cu (II) and Pb (II) ions have also been determined in soil and plants aiming at locating the metal ions in different organs of the plants. By using hemp shives as amendments, bioaccumulation of copper and lead ions in plant increases. The plants cultivated in the presence of high amounts of heavy metal ions have been characterized by an inhibition of growth and development that consisted in decrease of root and stem lengths, as well in the amount of biomass accumulated in diff...