Cell wall phenolics and polysaccharides in different tissues of quinoa (Chenopodium quinoa Willd)

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Mode of action of RG-hydrolase and RG-lyase toward rhamnogalacturonan oligomers. Characterization of degradation products using RG-rhamnohydrolase and RG-galacturonohydrolase

The mode of action of RG-hydrolase and RG-lyase toward purified linear rhamnogalacturonan (RG) oligomers has been studied. Major tools in the characterization of the degradation products were the exo-acting RG-rhamnohydrolase and RG-galacturonohydrolase. They were used to prepare a series of standards of RG oligomers for HPAEC. H-1 NMR spectroscopy confirmed the structure assignment made using HPAEC for a selection of isolated degradation products. Identification of degradation products from purified RG oligomers was then performed by comparing retention times of HPAEC peaks with those of standards. RG-hydrolase was able to cleave RG oligomers which contained five Rha units or more, i.e. DP 9 with a Rha unit at both, nonreducing and reducing end. Its preferential cleavage site was at four units from the first nonreducing Rha. RG-lyase was active toward oligomers that contained at least six GalA units, i.e. DP 12 with a GalA at the nonreducing and a Rha at the reducing end. The preferential cleavage site was for the smaller oligomers four residues, and for the largest oligomer six residues from the reducing Rha. From the observed cleavage patterns it can be speculated that in hairy regions, the RG stretches have to be at least 13 residues long for RG-hydrolase and 16 residues long for RG-lyase in order to produce one tetramer. (C) 1998 Elsevier Science Ltd. All rights reserved

Isolation and structural characterisation of rhamnogalacturonan oligomers generated by controlled acid hydrolysis of sugar-beet pulp

Controlled acid hydrolysis was applied to a deesterified beet pulp and the resulting soluble fraction was fractionated on a Biorad AG 1X8 column eluted by ammonium acetate pH 6 from 0.05 to 2 M. Eight retained fractions were obtained, containing almost exclusively GalA and Rha. Three types of oligomers could be identified: homogalacturonans, of which mono-, di- and tri-GalA were isolated as individual components, and two series of rhamnogalacturonan (RG) oligomers. One RG oligomer, isolated after ion-exchange chromatography, was identified as alpha-D-GalA p-(1 --> 2)-alpha-L-Rhap-(1 --> 4)-alpha-D-GalA p-(1 --> 2)-L-Rhap. The major peak contained oligomers of dp 6 to more than 20, of which dp 6 to 16 could be isolated on Bio-Gel P-6 + P-4. NMR of the oligomers of dp 6 to 10 showed the following structure: alpha-D-GalA p-(1[ --> 2)-alpha-L-Rhap-(1 --> 4)-alpha-D-GalA p-(1](n) --> 2)-L-Rhap. A second, quantitatively minor, series of RG oligomers eluted at higher ionic strength. These oligomers, which could be hydrolysed by RG-hydrolase and RG-lyase, were based on the alternating RG structure. Their non-reducing end was GalA, susceptible to hydrolysis by RG-galacturonohydrolase, and their reducing end might have more than one consecutive GalA. (C) 1998 Elsevier Science Ltd

Some preliminary results on the action of rhamnogalacturonase on rhamnogalacturonan oligosaccharides from beet pulp

Sugar-beet pulp was saponified and then hydrolysed with 0.1 M HCl at 80 degrees C for 72 h, and a rhamnogalacturonan fraction was isolated by ion-exchange chromatography on AG 1X8 resin. Four individual oligomers, and a mixture of oligomers with higher degrees of polymerization, were obtained by chromatography on BioGel P-4. They all presented the alpha-D-GalAp-(1[-->2)-alpha-L-Rhap-(1-->4)-alpha-D-GalAp-(1](n)-->2)-L- Rhap structure (with n greater than or equal to 2) The five fractions were submitted to hydrolysis with rhamnogalacturonase. The enzyme was active on oligomers with degrees of polymerization greater than or equal to 10, and gave as main products alpha-L-Rhap-(1-->4)-alpha-D-GalAp-(1-->2)-or-L-Rhap(1-->4)-D-GalAp and alpha-D-GalAp-(1-->2)-alpha-L-Rhap-(1-->4)-alpha-D-GalAp-(1-->2)-alpha-L -Rhap-(1-->4)-D-GalAp

In vitro gastrointestinal digestion of pea protein isolate as a function of pH, food matrices, autoclaving, high-pressure and re-heat treatments

This study investigated the influence of pH and processing conditions (autoclave at 93 °C/13 min or high pressure processing (HPP) at 600 MPa/5 min without/with follow-up reheating at 80 °C/30 min) on the digestibility of pea protein isolate. Both aqueous solutions and real food matrices (apple and carrot purees) containing pea protein was examined at 37 °C. In vitro gastrointestinal digestion was followed using sodium dodecyl sulphate polyacrylamide gel electrophoresis, titrimetric techniques and theoretical calculations. Pea protein with HPP followed by re-heating showed the highest rate of proteolysis in gastric conditions. In case of sequential intestinal digestion of the gastric chyme, pea protein at pH 6.2 demonstrated higher degree and rate of digestibility as compared to that at pH 3.6, the latter being close to the isoelectric point of pea protein. However, autoclave treatments overshadowed such pH effects. Processing-induced enhancement in digestibility might be attributed to the unfolding of the globular pea protein subunits. Pea protein in the carrot puree was more digestible than in the apple puree, due to apple procyanidins binding to pea protein. These new findings might have important implications in designing the process parameters and selection of appropriate food matrices for delivering pea protein

Fungal bioconversion of agricultural by-products to vanillin

The ester-linked ferulic acid of wheat bran and sugar beet pulp can be converted to vanillin using biological transformation. Free ferulic acid from sugar-beet pulp and from wheat bran was almost quantitatively obtained by extensive degradation of the cell-walls using enzyme mixtures complemented with specific ferulic acid esterases. The Basidiomycete Pycnoporus cinnabarinus then converted the released ferulic acid to vanillin. The selection of stable and highly productive strains was achieved using formal genetics. The use of cellobiose as an activator of the vanillin pathway and the sequential addition of a precursor (ferulic acid) in cultures of selected P. cinnabarinus strains, allowed 90 and 300 mg/L of vanillin to be obtained fi om ferulic acid enzymically released from wheat bran and sugar-beet pulp, respectively. This process was adapted into a two-step process involving two filamentous fungi, Aspergillus niger and P. cinnabarinus, with complementary capabilities of transformation