Search results for "Guaiac"
showing 10 items of 40 documents
Dry vs soaked wood: Modulating the volatile extractible fraction of oak wood by heat treatments
2012
The aim of this study was to analyze the impact of the water content of wood on the concentrations of volatile compounds which can be extracted after heat treatments. Head Space-Solid Phase Micro Extraction Gas Chromatography coupled to Mass Spectrometry (HS-SPME GC-MS) has been used to compare the concentrations of six aroma compounds (vanillin, furfural, eugenol, guaiacol and cis- and trans-whisky lactones) in hydroalcoholic extracts of heated oak wood samples either previously soaked in hot water or not. Except for eugenol, concentrations of extracted aromas appeared to be lower in soaked woods than in dry woods for temperatures up to 200 °C. If a delaying effect of water could explain s…
Thermal inactivation at high temperatures and regeneration of green asparagus peroxidase
2019
A spectrophotometric method was developed for determining the peroxidase activity of green asparagus in small samples. The optimum conditions for the analysis in the cuvette were 45 mM of H2O2 36 mM of guaiacol, and pH 7. The method can be used to determine enzyme activity at up to two decimal reductions. A study was performed of the regeneration and inactivation kinetics of the enzyme when heated between 90 and 125°C. Regenerated asparagus peroxidase reached its maximum activity after being stored 6 days at 25°C. The regenerated enzyme followed first-order inactivation kinetics, showing an Ea = 13.62 kcal/mol and k100°C = 2.07 min-1.
Interaction Mechanisms between guaiacols and lignin: the conjugated double bond makes the difference.
2011
Lignin is considered to be responsible for a selective sorption of phenolic compounds on wood. In order to investigate the mechanisms involved, two similar guaiacol compounds--only differing by the nature of the para side chain--were adsorbed on oak wood extracted lignin. Vapor sorption-desorption isotherms indicated that about 3.5 wt % of 4-vinylguaiacol is adsorbed near saturation whereas it is only 0.8% for 4-ethylguaiacol. For both compounds, the isotherms displayed a hysteresis though significantly greater for 4-vinylguaiacol. Analyses of the hydroxyl stretching region of FTIR spectra of the lignin/4-ethylguaiacol and lignin/4-vinylguaiacol complexes indicated that physisorption via hy…
Gas chromatographic study of acetyl derivates of chlorinated guaiacols
1982
The gas chromatography of acetyl derivatives of guaiacol and all chlorinated guaiacols has been studied on SE-30, OV-351 and Carbowax 20M capillary columns. The retention order and relative retention times under isotermal and temperature-programmed conditions are discussed. Different retention times for all mono- and dichloro compounds have been observed on the SE-30 column. However, all trichloroguaiacol isomers were separated only on polar columns. The best overall temperature-programmed separations have been achieved on an SE-30 capillary column.
Comprehensive valorisation of technically relevant organosolv lignins via anodic oxidation
2021
Lignin represents the largest renewable feedstock of aromatic moieties in nature. However, its valorisation towards organic chemicals poses a challenging task. We herein report the selective electrochemical depolymerisation of several technically relevant organosolv lignins to aromatic fine chemicals with a simple two-electrode arrangement using caustic soda as electrolyte. Vanillin, syringaldehyde, the corresponding ketones and guaiacol were obtained with a combined maximum of 7.8 wt% isolated yield. Deeper insight in the process was provided by FT-IR, HSQC NMR and 31P NMR analyses of the lignins.
Chemical Composition of the Essential Oil of Teucrium flavum ssp. flavum from Zakynthos, Greece
2012
Essential oil extracted from dried aerial parts of Teucrium flavum ssp. flavum harvested in Zakynthos, Greece, was analysed by gas phase chomatography (GC) and gas chomatography mass spectrometry (GC-MS). The main constituents were caryophyllene (13.5%), caryophyllene oxide (8.5%), 4-vinyl guaiacol (6.0%) and α- humulene (5.0%).
Seducin, male sex pheromone of the cockroachNauphoeta cinerea: Isolation, identification, and bioassay.
1990
The male sex pheromone of the cockroachNauphoeta cinerea was isolated from adult sternal glands and identified by gas chromatography-mass spectrometry. This pheromone, which attracts females from a distance, is a multicomponent blend. It is composed principally of three compounds: 3-hydroxy-2-butanone (acetoin), 2-methylthiazolidine, and 4-ethyl-2-meth-oxyphenol. A mixture of synthetic compounds in a ratio of 4∶4∶1 (2700 ng) elicits maximal response and short latency of response by receptive females, similar to that induced by male sternal gland extracts. Tested separately, each compound induces a positive response, but the moving times spent by females are generally longer than with the mi…
Cost-effectiveness of screening for colorectal cancer in France using a guaiac test versus an immunochemical test
2010
Objectives: The aim of this study was to compare the cost and the effectiveness of two biennial fecal occult blood screening tests for colorectal cancer: a guaiac nonrehydrated test (G-FOBT) and an immunochemical test (I-FOBT) with the absence of screening.Methods: A Markov model was developed to compare these strategies in a general population of subjects aged 50 to 74 over a 20-year period.Results: Compared with the absence of screening, G-FOBT and I-FOBT were associated with a decrease in colorectal cancer mortality of 17.4 percent and 25.2 percent, respectively. With regard to cost-effectiveness, expressed as cost per life-year gained, I-FOBT was the most effective and most costly alter…
Screening for colorectal cancer with immunochemical faecal occult blood tests.
2012
Population-based studies have shown that guaiac faecal occult blood testing followed by colonoscopy in case of positivity can reduce colorectal cancer mortality. However these tests have been criticised for their fairly low sensitivity. For this reason attention has been given to alternative tests. The aim of this paper is to review the evidence for screening for colorectal cancer using qualitative immunochemical faecal occult blood tests. For the complete range of tested cut-off values, immunochemical faecal occult blood tests lead to higher diagnostic yield, improved sensitivity and greater participation. The optimal number of samples and the optimal cut-off value has to suit local resour…
Chemical composition of the essential oil of Centaurea grinensis Reuter and Centaurea apiculata Ledeb: Growing wild in Croatia and Bulgaria, respecti…
2016
AbstractIn the present study, the chemical composition of the essential oils from aerial parts of Centaurea grinensis Reuter (K) collected at Žuta Lova, near Senj (Croatia), and aerial parts (L1) and flowers (L2) of C. apiculata Ledeb. collected near Rebro village, near Breznik town, Znepole Region (Bulgaria), both belonging to subgenus Lopholoma (Cass.) Dobrocz, was evaluated by GC and GC-MS. The main components of K were 4-vinyl guaiacol (21.5%), hexadecanoic acid (16.2%), acetophenone (12.5%). Caryophyllene oxide (15.8%) together with sphathulenol (14.5%) and humulene epoxide II (9.4%) were recognized as the main constituent of both the aerial part (L1) and flowers (L2) of C. apiculata. …