Mild disintegration of the green microalgae Chlorella vulgaris using bead milling.

In this work, the mild disintegration of the microalgae Chlorella vulgaris for the release of intracellular products has been studied. By means of bead milling the microalgae suspensions were successfully disintegrated at different biomass concentrations (25-145 gDW kg(-1)) over a range of agitator speeds (6-12 m s(-1)). In all cases over 97% of cell disintegration was achieved resulting in a release of water soluble proteins. A clear optimum rate of disintegration and protein release was observed at an agitator speed of 9-10 m s(-1) regardless of the biomass concentration. Selective extraction of water soluble proteins was observed as proteins released sooner than cell disintegration took place. Proteins could be released at 85% lower energy input than for cell disintegration resulting in specific energy consumptions well below 2.5 kWh kgDW(-1).

Enrichment of antioxidant compounds from lemon balm (Melissa officinalis) by pressurized liquid extraction and enzyme-assisted extraction.

In this work enzyme-assisted extraction (EAE) and pressurized liquid extraction (PLE) are applied for extraction of natural compounds from lemon balm (Melissa officinalis). Cellulase, endo-ß-1,4 xylanase and pectinase were studied in order to degrade cell wall of lemon balm leaves and to release phenolic compounds. On the other hand, in order to compare the performance obtained with EAE, PLE using water and ethanol was employed maintaining 150°C as extraction temperature. The obtained extracts were characterized in terms of antioxidant capacity by using DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging and trolox equivalent antioxidant capacity (TEAC) in vitro assays, whereas the Folin-Ciocalteu procedure was employed to estimate the total phenols content. On the other hand, extracts were chemically characterized by liquid chromatography tandem mass spectrometry (LC-MS/MS). The results showed that EAE enhanced the total phenolic content and the antioxidant capacity compared to a non-enzymatic control. PLE extracts presented higher amount of phenols and antioxidant capacity than enzyme-assisted extracts, reaching the highest values on water extracts (193.18mggallicacid/gextract and EC50=6.81µg/mL). Among the bioactive phenolic compounds identified in lemon balm, rosmarinic acid was the main component, although other important compounds were also identified, such as caffeic acid derivatives (salvianolic acids, lithospermic acid) and rosmarinic acid derivatives (rosmarinic acid hexoside, sagerinic acid, sulfated rosmarinic acid). The present study confirms that EAE and PLE can be considered alternative methods for the extraction of natural compounds with biological activity from natural sources.

Chemical composition of bioactive pressurized extracts of Romanian aromatic plants.

In this contribution, pressurized liquid extraction (PLE) has been employed to isolate bioactive compounds from three native Romanian plants, oregano (Origanum vulgare), tarragon (Artemisia dracunculus) and wild thyme (Thymus serpyllum). Different PLE conditions have been tested including extraction with water, ethanol and their mixtures in a wide range of extraction temperatures (50-200°C), and the antioxidant capacity of the extracts was measured using different assays (DPPH radical scavenging, TEAC assay and Folin-Ciocalteau assay to measure total phenols). Moreover, a complete chemical characterization by using LC-MS/MS was carried out to be able to correlate the bioactivity with the particular chemical composition of each extract and plant. The use of PLE with water as a solvent at the highest temperature tested (200°C) always provided the highest extraction yields for the three studied plants, being maximum for oregano (>60%). Besides, oregano's pressurized water extracts at lower temperatures (50°C) presented the highest content on total phenols (184.9 mg gallic acid/g extract) and the best antioxidant activities (EC(50) 6.98 µg/ml). In general, oregano extracts were the most active, followed by wild thyme extracts. The antioxidant capacity measured by DPPH assay was highly correlated with the amount of total phenols. Moreover, the use of a LC-MS/MS method allowed the identification of 30 different phenolic compounds in the different extracts, including phenolic acids, flavones, flavanones and flavonols, which have an important influence on the total antioxidant capacity of the different extracts.