Xylose-glycine

The primary cell walls of most higher plant species contain XGs of the XXXG type, which bear trisaccharide side chains (8) on the backbone [247]. The seeds of many plants contain XXXG-type XGs, in which about 30% of the xylose units possess a /3-D-Galp residue attached to position 2. Several plant species produce XGs that lack fucose and galactose, and have a-L-Ara/ attached to 0-2 of some of the Xylp side-chains, such as XG isolated from olive fruit [262] and soybean (Glycine maxima) meal [263]. However, a-L-Ara/ residues occur also 2-linked directly to some of the Glcp residues of the backbone [154]. 

An effort has also been made to determine the structure of products providing coloration in the Maillard reaction prior to melanoidin formation. The reaction between D-xylose and isopropylamine in dilute acetic acid produced 2-(2-furfurylidene)-4-hydroxy-5-methyl-3(2/f)-furanone (116). This highly chromophoric product can be produced by the combination of 2-furaldehyde and 4-hydroxy-5-methyl-3(2//)-furanone (111) in an aqueous solution containing isopropylammonium acetate. The reaction between o-xylose and glycine at pH 6, under reflux conditions, also pro-duces " 116. Other chromophoric analogs may be present, including 117,... 

Fig. 49. Hypothetical arrangement of organic layers in the diatom cell wall Gl glucose, M mannose, Fu fucose, X xylose. Ser serine, Asp aspartic acid, Gly glycine, Thr threonine hatched lines represent hydrogen bonds (Hecky etal54 ))...

Being a biochemist, Maillard (20) studied the reaction of glycine with xylose or glucose at 40° and then at 34°C, in order to know the possibility of the change in vivo. 

Yamaguchi, N. Koyama, Y. Fujimaki, M. Fractionation of antioxidative activity of browning reaction products between D-xylose and glycine. Prog. Food Nutr. Sci. 1981, 5, 429-39. 

Colored Compounds Formed by the Interaction of Glycine and Xylose... 

Colored compounds were isolated and characterised from the reaction products of xylose (1M) and glycine (1M), refluxed for 2 h, initial pH 6. The solubles in light petroleum ether (b.p. 60-80°) were fractionated into at least 13 peaks by semipreparative reverse-phase HPLC, using a water-methanol gradient. 

High-performance liquid chromatography has been used for the separation of Amadori products (2 ) and for the isolation of 3,8-dihydroxy-2-methylchromone from the products of xylose degradation at 100° (J3). In 1981 (4j we reported an HPLC separation scheme for the colored products of the xylose/glycine reaction. 

Preparation of browning product mixtures Xylose (15 g) and glycine (7.5 g) were dissolved in Sorensen s phosphate buffer (ji) (1/151 1 pH 8.2, 100 ml) and heated under reflux for 2 h. On 250-fold dilution with water, the absorbance at 450 nm was 0.75 i 0.05. The preparation was also carried out in the absence of buffer, initial pH 6.0. Larger amounts were prepared on 5 and 10 times this scale. 

Here we are solely concerned with the light petroleum solubles (designated Fraction A), derived from a xylose/glycine model system. Fraction A was obtained as a yellow solid in 0.05 yield. Analysis by HPLC at 450 nm showed it to consist of at least 25 components (Figure 1), and examination at 315 and 260 nm further increased the number detected. 

On the other hand, Yamaguchi, et al. (5) found most of the antioxidative effect in the melanoidin fraction. By various chromatographic methods they purified an antioxidative product from glycine and xylose having a molecular weight of approximately 4500. 

D-xylose-glycine (1 5) mixture at 65° showed that maximum browning is reached when the water content is about 30 %. If the water content is zero, or above 90 %, no browning is observed at 65°. Kato160 has similarly shown... 

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