Partially hydrolyzed guar gum characterization and sensitive quantification in food matrices by high performance anion exchange chromatography with pulsed amperometric detection--validation using accuracy profile.

Interest concerning functional ingredients and especially dietary fibres has been growing in recent years. At the same time, the variety of ingredient accepted as dietary fibres and their mixing at low level in complex matrices have considerably complicated their quantitative analysis by approved AOAC methods. These reasons have led to the specific development of an innovative analytical method performed by high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) to detect and quantify partially hydrolyzed guar gum (PHGG) in fruit preparation and dairy matrices. The analytical methodology was divided in two steps which could be deployed separately or in conjunction. The first, consists in a complete characterization of PHGG by size exclusion chromatography (SEC) with multi-angle light scattering and refractive index detection and HPAEC-PAD to determine its physico-chemical properties and galactomannans content, and the second step is the development of a new HPAEC-PAD method for PHGG direct quantification in complex matrices (dairy product). Validation in terms of detection and quantification limits, linearity of the analytical range, average accuracy (recovery, trueness) and average uncertainty were statistically carried out with accuracy profile. Overall, this new chromatographic method has considerably improved the possibility to quantify without fractionation treatment, low level of dietary fibres emerging from specific galactomannans, in complex matrices and many foodstuffs.

Analysis of hydroxyproline and hydroxyproline-arabinosides of plant origin by high-performance anion-exchange chromatography-pulsed amperometric detection.

The plant cell wall hydroxyproline-rich glycoprotein (HRGP), also called extensin, contains arabinose and oligoarabinoside side chains O-glycosidically linked to hydroxyproline (Hyp). We present a highly sensitive method for determining both the glycosylation pattern and the Hyp content of HRGP requiring only nanomole amounts of each Hyp-compound for accurate determination. This method is based on anion-exchange chromatography followed by pulsed amperometric detection of the Hyp-oligoarabinosides and Hyp released from HRGP by 0.22 M Ba(OH)2 hydrolysis, which cleaves only peptidyl bonds. A sodium acetate gradient (0-250 mM) in 150 mM NaOH elutes Hyp and the Hyp-oligoarabinosides Hyp-(Ara)1-5 in less than 40 min. We have used this procedure to determine the glycosylation pattern of Hyp in plant cell walls, without prior isolation of HRGP.

Purification and characterization of cinnamyl alcohol dehydrogenase isoforms from Phaseolus vulgaris.

Cinnamyl alcohol dehydrogenase (CAD) catalyses the reduction of hydroxycinnamaldehydes (p-coumaryl, coniferyl, sinapyl) to the corresponding alcohols which are the monomeric precursors of lignins. We have demonstrated the occurrence of two isoforms of CAD (CAD1 and CAD2) in bean which differ in terms of subunit Mr, specific activity, substrate affinity and antigenicity. The most abundant polypeptide in bean pods, organs with very limited lignification, is a low affinity CAD isoform (CAD1). This enzyme which is distinct from a benzyl alcohol dehydrogenase with broad substrate specificity, was purified to apparent homogeneity and partial amino acid sequencing was carried out using internal peptides obtained by trypsin cleavage.

Purification and Characterization of Cinnamoyl-Coenzyme A:NADP Oxidoreductase in Eucalyptus gunnii.

Cinnamoyl-coenzyme A:NADP oxidoreductase (CCR, EC 1.2.1.44), the entry-point enzyme into the monolignol biosynthetic pathway, was purified to apparent electrophoretic homogeneity from differentiating xylem of Eucalyptus gunnii Hook. The purified protein is a monomer of 38 kD and has an isoelectric point of 7. Although Eucalyptus gunnii CCR has approximately equal affinities for all possible substrates (p-coumaroyl-coenzyme A, feruloyl-coenzyme A, and sinapoyl-coenzyme A), it is approximately three times more effective at converting feruloyl-coenzyme A than the other substrates. To gain a better understanding of the catalytic regulation of Eucalyptus CCR, a variety of compounds were tested to determine their effect on CCR activity. CCR activity is inhibited by NADP and coenzyme A. Effectors that bind lysine and cysteine residues also inhibit CCR activity. As a prerequisite to the study of the regulation of CCR at the molecular level, polyclonal antibodies were obtained.