Chemical and enzymatic oxidation of oleuropein: an EPR study
About: This article is published in Chemistry and Physics of Lipids.The article was published on 2004-01-01. It has received 5 citations till now. The article focuses on the topics: Oleuropein.
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TL;DR: Quantification of a large number of phenolic compounds in virgin olive oil can be accomplished by integration of the appropriate signals in the 31P NMR spectrum and the use of the phosphitylated cyclohexanol as internal standard.
Abstract: 31P NMR spectroscopy has been employed to detect and quantify phenolic compounds in the polar fraction of virgin olive oil. This novel analytical method is based on the derivatization of the hydroxyl and carboxyl groups of phenolic compounds with 2-chloro-4,4,5,5-tetramethyldioxaphospholane and the identification of the phosphitylated compounds on the basis of the 31P chemical shifts. Quantification of a large number of phenolic compounds in virgin olive oil can be accomplished by integration of the appropriate signals in the 31P NMR spectrum and the use of the phosphitylated cyclohexanol as internal standard. Finally, the validity of this technique for quantitative measurements was thoroughly examined. Keywords: Olive oil; phenolic compounds; 31P NMR spectroscopy
50 citations
TL;DR: Assessment of the agreement between analytical methodologies based on 1H and 31P NMR spectroscopy and conventional analytical methods for measuring certain minor and major constituents of olive oil showed strong correlations between NMR and conventional methods and good correlations for linoleic acid, free hydroxytyrosol, and free tyrosol.
Abstract: The present study was designed to assess the agreement between analytical methodologies based on 1H and 31P NMR spectroscopy and conventional analytical methods (titration, gas chromatography, and high performance liquid chromatography) for measuring certain minor and major constituents (free acidity, fatty acids, iodine value, and phenolic compounds) of olive oil. The standard deviations of the NMR method were comparable to those of the conventional methods, except perhaps those of the total hydroxytyrosol and total tyrosol. Linear regression analyses showed strong correlations between NMR and conventional methods for free acidity, total hydroxytyrosol, total tyrosol, total diacylglycerols, (+)-pinoresinol, (+)-1-acetoxypinoresinol, and apigenin; good correlations for linoleic acid, free hydroxytyrosol, and free tyrosol; and weak correlations for oleic acid, linolenic acid, saturated fatty acids, and luteolin. Furthermore, a method comparison study was conducted and the agreement between NMR and conventional methods was evaluated by using the Bland and Altman statistical analysis. The distribution of the data points in the bias plot showed that 96.4% and 100% of the measurements of free acidity and iodine value, respectively, were within the limits of agreement of the two methods. For the remaining constituents of olive oil, the percentage of measurements, located within the limits of agreement, ranged from 94% to 98.5%.
46 citations
TL;DR: In this article, the effects of debittering methods on physico-chemical and sensory characteristics of fermentation media were investigated, and the average salt concentrations of the brines were determined as 5.718, 5.769 and 4.825, for T I, T II and T III, respectively.
Abstract: Edincik-Su variety black olives, grown in Marmara region, were processed by three different debittering methods [fermentation with Lactobacillus plantarum (T I), fermentation with β-glucosidase enzyme + L. plantarum (T II), modified ripe-olive fermentation (T III)], and the effects of the applied methods on physico-chemical and sensory characteristics of fermentation media were investigated. The average salt concentrations of the brines were determined as 5.718, 5.769 and 4.825%, for T I, T II and T III, respectively. Salt content of T III was found lower than other treatments. TIII olives displayed the lowest acidity (0.270%) with the highest pH (5.96) depending on removal of most of the sugars and nutrients by lye treatment and following washings. The pH presented a sharp decrease, on the contrary to acidity, within the first days of fermentation in all treatments. The average reducing sugar concentrations of treatments were determined as 0.748, 0.692 and 0.441% for T I, T II and T III, respectively. Although the lowest oleuropein values were obtained in T III olives, the overall liking scores revealed that T II olives had higher organoleptic acceptability (as 27.9). T II and T III olives were found to be more typical to consumers. The correlations of the different sensory attributes with overall acceptability indicated that the panel was negatively influenced by bitterness and skin separation. It appears that the panelists preferred olives with a acidic/bitter taste and firm appearance.
15 citations
Cites methods from "Chemical and enzymatic oxidation of..."
...Oleuropein content was realised according to the absorbance values of samples at 345 nm (Tzika et al., 2004; Mastorakis et al., 2004)....
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TL;DR: In this article, the debittering of green table olive by vacuum impregnation (VI) was carried out at atmospheric conditions and under vacuum (68 kPa). The results of these applications on some physicochemical properties (total dry matter, total ash, titratable acidity, salt, protein, oil, oleuropein, total phenolics, antioxidant activity and colour) of the processed samples were determined.
Abstract: The aim of this research was to assess the possibility of shortening the length of the debittering process for green table olive ‘Domat’ cultivar by vacuum impregnation (VI). For this purpose, debittering was carried out with NaCl (3 %), NaOH (1.5 %) and NaOH (1.5 %) + NaCl (3 %) solutions at atmospheric conditions and under vacuum (68 kPa). The effects of these applications on some physicochemical properties (total dry matter, total ash, titratable acidity, salt, protein, oil, oleuropein, total phenolics, antioxidant activity and colour) of the processed samples were determined. Total dry matter, titratable acidity, salt, protein and oil contents of the samples changed between 24.23 and 27.90, 0.22 and 0.45, 2.27 and 2.58, 0.50 and 1.26 and 6.79 and 9.42 % (w/w), respectively. Colour parameters (lightness (L*); redness (a*); yellowness (b*)) of the processed olives were measured as between 41.72 and 51.29, 15.09 and 13.30 and 22.79 and 34.84, respectively. Hue angles of the processed samples were changed between 59.78 and 68.52. VI was a useful tool for the shortening of the period of debittering process. Use of NaOH combined with NaCl in VI process caused the debittering period to decrease to 6 h. However, reduction of the amount of total phenolic compounds was the highest (21.43 %) in this condition. Use of alkali for debittering caused more dry matter diffusion from olive to the solution. There was no statistically significant difference between the oleuropein and total ash contents of the processed samples (p < 0.01). Alkali treatment also caused more oil loss from the olives. Antioxidant activity of the samples reduced up to 59.89 %. This research was the first using VI for debittering of olives; further studies are necessary to optimise process conditions of debittering for limiting loss of natural antioxidants and other components and to ensure maximum benefits to the consumer.
13 citations
Cites methods from "Chemical and enzymatic oxidation of..."
...Oleuropein content was measured according to the absorbance (ABS) values of samples at 345 nm by Shimatzu UV/VIS 1800 (Japan) model spectrophotometer (Tzika et al. 2004; Mastorakis et al. 2004)....
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TL;DR: Addition of l-proline as a coupling reactor did not succeed in preventing enzyme inactivation in the microemulsions, probably owing to substrate localization and product accumulation around the entrapped enzyme molecules in the micellar interface.
Abstract: Microemulsions consisting of olive oil as the non-polar solvent, lecithin as surfactant, 1-propanol as cosurfactant, and water were prepared. The choice of the compositions of the microemulsions used was based on the pseudo-ternary phase diagrams of the system determined at 30°C, for different weight ratios of lecithin/olive oil. Lecithin solubilization and water incorporation in these microemulsion systems was limited. Tyrosinase, an oxidizing enzyme present in olives, was successfully incorporated in the water core of these microemulsions. Enzymatic oxidation of oleuropein, the most abundant olive phenolic compound, in the restricted aqueous environment of olive oil microemulsions was studied. Formation of oleuropein oxidation products was followed spectrophotometrically at 30°C for several minutes. An absorption maximum was observed at 415 nm. When the enzymatic reaction was considered at different tyrosinase and oleuropein concentrations, a rapid inactivation of the enzyme was observed. Addition of l-proline as a coupling reactor did not succeed in preventing enzyme inactivation in the microemulsions, probably owing to substrate localization and product accumulation around the entrapped enzyme molecules in the micellar interface.
13 citations