Richard G. Bailey

Comparative study of the reversed-phase high-performance liquid chromatography of black tea liquors with special reference to the thearubigins

Abstract New high-performance liquid chromatographic methods for the analysis of black tea phenolic pigments, using Hypersil ODS, Hypersil octyl wide-pore, and Hamilton PRP-1 columns, and several new results arising from them are presented. Very good resolution of a wide range of phenolic tea pigments, was obtained using a Hypersil ODS column with a citrate buffer, and, for the first time, eight theaflavins were observed in a single chromatogram. Unresolved brown phenolic pigments (thearubigins), ran as a convex broad band on the Hypersil wide-pore and Hamilton PRP-1 columns, and the Hamilton PRP-1 column showed an anthocyanidin to be a significant contributor to liquor colour. The pigments were classified into three groups by chromatographic behaviour: group I, pigments running close to the void volume of the columns; group II, resolved pigments; and group III, unresolved pigments. Group II pigments were divided into four Sub-Groups by their photodiode-array UV—VIS spectra, as follows: sub-group II.1, theaflavins; sub-group II.2, theaflavic acids; sub-group II.3, type I resolved pigments; and sub-group II.4, type II resolved pigments. Pigments in sub-groups II.3 and II.4 were designated as resolved thearubigins, and those in group III as unresolved thearubigins.

An Analysis of the Non-Volatile Reaction Products of Aqueous Maillard Model Systems at pH 5, using Reversed-Phase HPLC with Diode-Array Detection

An HPLC-diode array detection (HPLC-DAD) method was developed for the direct analysis of reaction products of aqueous Maillard model systems. The method was applied to mixtures of xylose or glucose refluxed with glycine or lysine for up to 120 min with the pH maintained at 5 throughout heating. Four types of chromatographic behaviour were apparent, ie unretained peaks, resolved peaks and two broad bands. Glycine systems were dominated by unretained peaks while systems based on lysine showed all four types of behaviour. By reference to HPLC-DAD data for standard compounds, some of the resolved peaks were tentatively attributed to pyrrole-like and furanone-like compounds.

Separation of Maillard reaction products from xylose—glycine and glucose—glycine model systems by capillary electrophoresis and comparison to reverse phase HPLC

Abstract Capillary electrophoresis (CE) and reverse phase HPLC were used to analyse Maillard reaction products (MRPs) formed in refluxed, aqueous xylose—glycine and glucose—glycine model systems. CE was shown to resolve many more components than reverse phase HPLC. Ultrafiltration was used to separate the MRPs into three molecular weight fractions, nominally > 3000, between 3000 and 1000, and

The influence of pH on the non-volatile reaction products of aqueous Maillard model systems by HPLC with diode array detection

Abstract Aqueous solutions of sugar (xylose or glucose) and amino acid (glycine or lysine monohydrochloride), one molal with respect to each reactant, were heated without control of the pH for up to 120 min. Total reaction products were analysed by HPLC with diode array detection and the data obtained were distinctive and different from those of the corresponding model systems maintained at pH 5 throughout heating. Less unresolved material and variations in its chromatographic behaviour suggested differences in the melanoidins formed. Resolved peaks from the xylose-lysine and glucose-lysine systems were grouped into spectral families, based on their diode-array spectra. For xylose-lysine, seven of these peaks were common to the systems heated both with and without pH control for 15min (based on retention time and spectral matching). No peaks were common to both glucose-lysine systems heated for 120min.

Analysis of the non-volatile Maillard reaction products formed in an extrusion-cooked model food system

Abstract An enzymic method was developed to extract the total non-volatile Maillard reaction products from a model starch–glucose–lysine extrudate. This method, coupled with HPLC using a diode array detector, was used to compare the profiles of Maillard reaction products in extrudates prepared from feedstocks with added citric acid (CA) or sodium hydrogen carbonate (SHC). The chromatograms revealed the presence in both samples of material that was unretained by the HPLC column as well as resolved peaks, but the chromatograms of the SHC sample were more complex. Diode array spectra were obtained for three and seven resolved peaks, respectively, from the CA and SHC extrudates. All three peaks from the CA sample were also present in the SHC sample and one was 5-hydroxymethylfurfural (HMF).

Identification of New Heterocyclic Nitrogen Compounds from Glucose-Lysine and Xylose-Lysine Maillard Model Systems

Aqueous sugar (glucose or xylose)-lysine model systems were heated at 80 degrees C for 6 h with the pH maintained at a predetermined value (3, 4, or 5). Selected compounds were isolated by combinations of solvent extraction and semipreparative HPLC, prior to identification by NMR and mass spectrometry. Two compounds were identified from the pH 5 glucose system and were identified as epsilon-[2-formyl-5-(hydroxymethyl)pyrrole-1-yl]-L-norleucine (pyrraline) and the new compound, 1-(5-carboxy-5-aminopentyl)-2-formyl-3-(1,2,3-trihydroxypropyl)pyrrole. A third compound was partially characterized. 2-Acetyl-5-hydroxymethyl-5,6-dihydro-4H-pyridinone was identified in the pH 3 xylose system, and the new compound, 8-furan-2-yl-methyl-5-hydroxymethyl-5,6-dihydro-indolizine-1,7-dione, was identified in the pH 4 xylose system. 2-Furfurylidene-4-hydroxy-5-methyl-3(2H)-furanone was identified in both xylose systems. Mechanisms of formation are proposed for the novel compounds.

Play and Problem-Solving in a New Light.

This article presents a model of childrens play, explored from an evolutionary perspective. Surprisingly, an evolutionary approach has only recently been introduced into this field, especially as far as learning is concerned, and is virtually unknown in educational studies. However, such an approach seems entirely reasonable if one accepts that cognitive activities are a product of evolution and selection. Moreover, there is some urgency in stressing the contribution biological sciences can make to the study of childrens early development, since there exists an enormous amount of research of immediate relevance to educators that has apparently been ignored.

Recent Advances in the Analysis of Coloured Maillard Reaction Products

Summary The objective of the work was to separate and identify low molecular weight heterocyclic reaction products from xylose-glycine and glucose-glycine model systems refluxed for 2 h with the pH maintained at 5. Diodearray spectra and HPLC retention times were obtained for the resolved peaks of these model systems and for a series of standard compounds. Two peaks (one of which was coloured) were isolated from the xylose system and five peaks (two of which were coloured) were isolated from the glucose system. They were subjected to 1H- and 13C-NMR and mass spectral analyses. The colourless peaks were identified as the known structures 4-hydroxy-5-methyl-3(2H)-furanone (from xylose), 4-hydroxy-2-(hydroxymethyl)-5-methyl-3(2H)-furanone (from glucose), 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (from glucose) and 5-hydroxymethylfurfural (from glucose). The coloured compounds were the novel structure, 2-acetyl-5-hydroxymethyl-4,5-dihydropyridin-4-one (from xylose) and two isomers of a related acetyldi(hydroxy-methyl)dihydropyridinone (from glucose).