Extraction of flavonoids and carotenoids from Thai silk waste and antioxidant activity of extracts

Extraction of carotenoids and flavonoids from yellow Thai silk waste was investigated. The total recovery of 0.7 mg carotenoids and 5.1 mg flavonoids/g dry weight was obtained by ethanol extraction. Different methods for extractions of these pigments were carried out using two benign solvents: ethanol and subcritical water (SW) to determine the extraction efficiency of the solvents in various extraction conditions. For extraction of carotenoids, ethanol was suitable as extraction solvent and the amount of carotenoids increased with increasing temperature and extraction time. For flavonoids, SW extraction was suitable but the amount of flavonoids decreased with increasing SW temperature and extraction time due to decomposition at such conditions. In addition, the silk extracts were found to have low IC₅₀ values (15.6–23.3 μg/ml), the concentrations of the silk extracts that exhibit 50% reduction in 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), (ABTS) free radicals, thus indicating high antioxidant activities.     

钨酸钠-分光光度法测定银杏黄酮含量

提出了钨酸钠—分光光度法测定药物制剂中银杏黄酮含量的新方法。该法是基于银杏黄酮能与钨酸钠反应生成黄色钨酸酯，该物质在304nm处有最大吸收。该方法的线性范围为4—120μg/ml,r^2＝0．9997，回收率为100．0％—100．6％。     

Identification and quantification of polyphenolic compounds from okra seeds and skins

The aims of the present work were to identify and quantify the polyphenolic profile of okra (Abelmoschus esculentus), a vegetable almost worldwide consumed. Since the knowledge about the okra polyphenolic compounds is limited, the seeds and the skins of okra were separately analyzed. The seeds, which represent the 17% of the vegetable and are richer in phenolic compounds, were mainly composed by oligomeric catechins (2.5 mg/g of seeds) and flavonol derivatives (3.4 mg/g of seeds). The skins polyphenolic profile was composed principally by hydroxycinnamic and quercetin derivatives (0.2 and 0.3 mg/g of skins). These findings in associations with the high content of okra in carbohydrates and proteins enhance the importance of this foodstuff in the human diet.     

Floral nectar phenolics as biochemical markers for the botanical origin of heather honey

In order to find out biochemical markers for the botanical origin of heather (Erica) honey, the phenolic metabolites present in heather floral nectar, collected from the honey-stomach of bees gathering nectar from these flowers, were analysed. The flavonoid fraction of nectar contained four main flavonoids. Two of them were quercetin and kaempferol 3-rhamnosides, and the other two were tentatively identified as myricetin 3-methyl ether and isorhamnetin 3-rhamnosides. Since the natural glycosides are hydrolysed by bee enzymes to render the corresponding aglycones, which are the metabolites detected in honey, acid hydrolysis of the nectar glycosides was achieved. The aglycones quercetin, myricetin 3-methyl ether, kaempferol and isorhamnetin were identified, as well as the gallic acid derivative ellagic acid. The analysis of Portuguese heather honey samples showed that ellagic acid was present in all the samples in significant amounts ranging between 100 g and 600 g per 100 g honey. The other nectar-derived flavonoids were also present, although some of them in very variable amounts. Ellagic acid and myricetin 3-methyl ether, which have not been detected in any of the monofloral honey samples investigated so far, with the only exception being a French honey sample of the botanically relatedCalluna (Ericaceae) which also contained ellagic acid, seem to be the most useful potential markers for the floral origin of heather honey. However, more detailed and extensive investigations are needed to prove the utility of these markers.     

Germination as a process to increase the polyphenol content and antioxidant activity of lupin seeds (Lupinus angustifolius L.)

In this work, the effect of germination of lupin seeds (Lupinus angustifolius L., c.v. Zapatón) on bioactive phenolic compounds as well as on the antioxidant activity was studied. Phenolic compounds were analysed by HPLC-PAD-ESI/MS. The antioxidant activity was determined by spectrophotometry, evaluating the free radical scavenging activity of the samples. Germination produced significant changes in flavonoids and non-flavonoid phenolic compounds. In the analysed samples, isoflavones, flavones and dihydroflavonols in free and conjugated forms were identified. The results obtained indicate that germination modifies the quantitative and qualitative polyphenolic composition of lupin (Lupinus angustifolius L.) seeds during the different days of the process, with a significant increase of flavonoids. An increase in the antioxidant activity was also observed as a consequence of the process. Germination was shown to be a good process to increase the phenolic content of lupin seeds as well as their antioxidant activity.     

Study of flavonoids in aqueous spinach extract using positive electrospray ionisation tandem quadrupole mass spectrometry

The presence of three flavonols (quercetin, kaempferol, myricetin) and two flavones (apigenin, luteolin) were investigated in the extract of fresh spinach leaves. Aqueous spinach extracts were prepared with a leaf/water ratio of 1:2 at 80 °C for 30 min stirring. Ferric ammonium sulphate method was used for measuring total polyphenols in the extracts and expressed as catechins and tannic acid equivalents. The flavonoids glycosides in the extract were hydrolysed to their aglycons with 1.2 M HCl in boiling 50% water methanol solution. The resulting aglycons were identified and quantified by a C18 reverse phase high-performance liquid chromatography (RP-HPLC). Furthermore, the results were confirmed by HPLC coupled to an electrospray ionisation tandem triple-quadrupole mass spectrometer ESI-MS performing low-energy collision induced dissociation (CID-MS/MS) in the collision cell (HPLC-ESI-MS/MS). Analyses were made in the multiple reaction monitory (MRM) mode. Results showed that total polyphenols contents in fresh spinach leaves were 270 mg kg⁻¹ and 390 mg kg⁻¹ as tannic acid and catechin equivalents, respectively, in which, major flavonoids aglycons were apigenin (170 mg kg⁻¹), quercetin (50 mg kg⁻¹) and kaempferol (30 mg kg⁻¹).     

Antioxidants in spring leaves of Oxalis acetosella L.

Oxalis acetosella L. is a common, edible wild plant native to the northern hemisphere. The contents of selected antioxidants, and the antioxidant capacity of young and old spring leaves of O. acetosella, were evaluated. The present study reports foliar contents of ascorbic acid, tocopherols, carotenoids, chlorophyll, flavonoids, phenolic acids and total phenolics, and compares the nutritional value of O. acetosella with other cultivated and wild plants. The composition of foliar antioxidants was found to depend on leaf age. On the other hand, the antioxidant capacity of old leaves were in the same range as young leaves. A comparison between O. acetosela with lettuce analysed in our study, and with numerous cultivated and wild edible plants from other studies, showed that O. acetosella is very rich in β-carotene, ascorbic acid, tocopherols and xanthophylls, and that it is one of the best sources of flavonoids (flavonol glycosides and flavan-3-ols), especially rutin. Therefore, O. acetosella is a potentially important dietary source of antioxidants.     

Antioxidant activities of extract and fractions from Tuber indicum Cooke & Massee

The antioxidant activities of ethanolic crude extract (ECE) and its four different solvent sub-fractions (namely, petroleum ether fraction (PEF), ethyl acetate fraction (EAF), n-butyl alcohol fraction (BAF) and the rest fraction (RF)) from Tuber indicum were investigated using several in vitro antioxidant assays. ECE and four sub-fractions possessed different antioxidant and radical-scavenging activities in different assays. BAF showed the most potent radical-scavenging activity on DPPH radicals, superoxide anion radicals and reducing power, with EC₅₀ values of 1.38, 0.96, 16.0 mg/ml, respectively. EAF exhibited the highest hydroxyl radical-scavenging and ferrous ion chelating activities with EC₅₀ values of 3.31 and 0.70 mg/ml, respectively. The total phenolics (TP) and total flavonoids (TF) were also determined. BAF had the highest TP and TF contents, and the next was EAF. These results showed that the amounts of phenolics and flavonoids were in accordance with higher effectiveness in scavenging radicals and chelating ferrous ions.     

Comparison of positive and negative ion detection of tea catechins using tandem mass spectrometry and ultra high performance liquid chromatography

Tea catechins are an important group of natural compounds associated with health promoting effects and desired commodities for the growing market of dietary supplements and functional foods. Consequently these compounds attract more interest of research groups worldwide. A reliable quantitative analysis of tea catechins is essential for human intervention studies, manufacturers of dietary supplements and quality control by authorities. UHPLC–ESI-MS/MS analytical method was chosen due to rapid runtime, high sensitivity and selectivity. The chromatographic separation of eight tea catechins was achieved within 2.5 min on C₁₈ BEH analytical column (100 mm × 2.1 mm i.d.; 1.7 μm), whilst the gradient elution mode was employed using water:methanol mobile phase with addition of volatile organic acid. The concentration of organic acids in the mobile phase was optimised within the range of 0.01–0.1% (v/v). High sensitivities were achieved in positive (10.2-16.8 fmol/inj.) and negative ion detection mode (102.1-168.1 fmol/inj.), through accurate and complex tuning of MS parameters. The UHPLC-ESI-MS/MS method was validated in terms of linearity (>0.9997; >0.9990), range (0.02–2.40 mg L⁻¹; 0.15-24.00 mg L⁻¹), LOD (3.0–4.8 μg L⁻¹; 30.1–48.0 μg L⁻¹), LOQ (9.9–15.8 μg L⁻¹; 150.5-240.0 μg L⁻¹), intra-day precision (4.4-7.1% RSD; 3.3-5.1% RSD), accuracy (94.06-113.7%; 89.5-108.4%), retention time repeatability (0.0-0.5% RSD; 0.0-0.6% RSD), and peak area repeatability (1.2-4.0% RSD; 2.4-3.5% RSD) for positive and negative ion detection modes, respectively. The statistical comparison of the quantitative results obtained in positive and negative ion detection mode was performed.     

微波萃取——分光光度法测定萹蓄中的总黄酮

采用微波辅助萃取法萃取萹蓄中的总黄酮,以芦丁为对照品,用分光光度法测定总黄酮的含量。利用正交实验考察了萃取温度、料液比、乙醇体积分数和回流时间对总黄酮含量的影响。实验结果表明:最佳条件为萃取温度80℃、料液比1∶40、乙醇体积分数为85%、回流时间7min。在最优条件下测得总黄酮的平均质量分数为2.099mg/g,总黄酮的平均萃取率为3.481%,相对标准偏差为0.304%(n=6),回收率为94.17%～99.50%。