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Chemical constituents and antioxidant capacity of extracts from Elaeis guineensis leaves / Ang Chun Hui
Get PDFThe present study investigated compounds present in Elaeis guineensis leaves and their potentials to act as natural antioxidants. Fresh leaves from Elaeis guineensis fronds were subjected to solvent extraction and ultrasonic-assisted methanol extraction. The chemical constituents were identified by gas chromatography-mass spectrometry (GC-MS). The crude methanolic extract (MeOH) obtained from the ultrasonic-assisted methanol extraction was then fractionated by repeated extractions, sequentially with solvents of different polarity into n-hexane (HEX), ethyl acetate (EA), water (WATER) and insoluble residue (INSOL) fractions. Major compounds identified in the methanolic crude extract which was further partitioned by n-hexane (MeOH-HEX) extract were phytol (42.94%), α-tocopherol (24.97%), squalene (14.95%), β-sitosterol (9.39%) and stigmasterol (5.84%). The same crude methanolic extract treated with activated carbon (MeOH-Activated C) extract yielded 2,4-di-tert-butylphenol (30.88%), phytol (23.80%), methyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (13.49%), 16-heptadecenal (11.72%) and 3,7,11,15-tetramethyl-2-hexadecen-1-ol (7.80%). Maceration using n-hexane as extracting solvent (Maceration-HEX) yielded α-tocopherol (30.51%), squalene (24.23%), arundoin (21.73%), 3-hexen-1-ol (5.31%) and β-sitosterol (4.77%). Maceration using ethyl acetate as extracting solvent (Maceration-Et2O) yielded similar components in slightly different quantities with squalene (29.34%), α-tocopherol (24.35%), phytol (12.54%), arundoin (8.63%) and 3,7,11,15-tetramethyl-2-hexadecen-1-ol (7.42%). The antioxidant activities of the crude methanolic extract and its fractions were evaluated by in vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity, lipid peroxidation (LPO) inhibition and β-carotene bleaching assays. The total phenolic contents (TPC) in the fractions were determined using Folin-Ciocalteu reagent. The results indicated that the INSOL fraction showed the highest activity in DPPH radical-scavenging activity assay and β-carotene bleaching assay, while the EA fraction exhibited the highest activity through LPO inhibition. DPPH radical-scavenging activities of the fractions were negatively correlated (correlation coefficients = -0.896, -0.943 respectively, P < 0.050) with the TPC based on Pearson Product Moment Correlation and Spearman Rank Order Correlation. The findings of this present study suggests that Elaeis guineensis leaves have a high potential to be utilized as a natural source of antioxidants in palm oil producing countries such as Indonesia, Malaysia and Thailand, where Elaeis guineensis leaves are abundantly available
Antioxidant activities of Elaeis guineensis leaves
No full textFresh leaves from Elaeis guineensis fronds were subjected to ultrasonic-assisted methanol extraction. The
crude methanolic extract (MeOH) was then fractionated by repeated extractions, sequentially with solvents
of different polarity into n-hexane (HEX), ethyl acetate (EA), water (WATER) and insoluble residue
(INSOL) fractions. The antioxidant activity of the crude extract and its fractions was evaluated by in vitro
2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity, lipid peroxidation (LPO) inhibition
and beta-carotene bleaching assays. Total phenolic contents (TPC) in the fractions were determined with
Folin-Ciocalteu reagent. The results indicated that the INSOL fraction showed the highest activity in
DPPH radical-scavenging activity assay and beta-carotene bleaching assay, while EA fraction exhibited
highest activity through LPO inhibition. DPPH radical-scavenging activity of the fractions was negatively
correlated (correlation coefficients = -0.896, -0.943 respectively, P < 0.050) with the TPC based on Pearson
Product Moment Correlation and Spearman Rank Order Correlation. The findings of present study suggests
that oil palm leaves have high potential to be utilised as natural source of antioxidants in palm oil producing
countries such as Indonesia, Malaysia and Thailand, where oil palm leaves are abundantly available
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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