Klaus Niemelä

Oxidative and non-oxidative alkali-catalysed degradation of L-ascorbic acid

Abstract Capillary gas—liquid chromatography—mass spectrometry was used to identify products from the oxidative and non-oxidative alkaline degradation of L -ascorbic acid. Over 50 compounds were detected, of which 32 carboxylic acids could be identified. In the presence of oxygen, oxalic, glyceric, L -threonic, pentulosonic, L -xylonic, L -lyxonic, and C-( L - threo -1,2,3-trihydroxypropyl)tartronic acids were the main products. Their formation routes via L - threo -2,3-hexodiulosonic (“diketogulonic”) acid (1) are outlined. It is believed that the conversion of 1 to urinary organic acids in man is mainly non-enzymic. The presence of some of the degradation products in human urine is expected, even if not yet proved.

The conversion of cellulose into carboxylic acids by a drastic oxygen-alkali treatment

Abstract Cotton cellulose was treated with 1 and 3 M sodium hydroxide at 170–190°C and the resulting mixtures were investigated by capillary gas-liquid chromatography-mass spectrometry. Up to 65 products were identified including mainly straight-chain and branched-chain hydroxy monocarboxylic acids and dicarboxylic acids, of which lactic, glycolic, 3-deoxytetronic, glucoisosaccharinic, 3,4-dideoxypentonic, and 3,4-dideoxyhexaric acids were the main compounds. Utilization possibilities of the acid mixtures are briefly discussed.

Alkaline degradation of alginates to carboxylic acids

Abstract Various dicarboxylic acids related to saccharinic acids, as well as several monocarboxylic acids, formed on treatment of alginates with alkali at 95° and 135° have been identified by capillary g.l.c.-m.s. Higher concentrations of alkali facilitated the formation of glucoisosaccharinaric, anhydroisosaccharinaric, and 2-deoxy-3-C-methyltetraric acids, whereas 2,3-dideoxypentaric acid was the major product at lower concentrations. The presence of Ca2+ promoted the formation of α-glucoisosaccharinaric, 3,4-dideoxyhexaric, and 2-hydroxybutanoic acids, especially at 135°. The nature of the reaction products indicates that the alginate chains are degraded end-wise either directly or after cleavage of internal linkages.

Conversion of xylan, starch, and chitin into carboxylic acids by treatment with alkali

Abstract Treatment of xylan, starch, and chitin with m and 3 m sodium hydroxide at 175° and 190° gave mixtures of non-volatile carboxylic acids in yields of 50–70%, 40–60%, and 5–13%, respectively, in which >60 hydroxy monocarboxylic acids and dicarboxylic acids were identified. The main compounds were glycolic, lactic, 2-hydroxybutanoic, 3-deoxypentonic, xyloisosaccharinic, and 3,4,5-trideoxyheptaric acids from xylan; glycolic, lactic, 3,4-dideoxypentonic, glucoisosaccharinic, and 3,4-dideoxyhexaric acids from starch; and glycolic, lactic, 2-hydroxybutanoic, and 3,4-dideoxyhexaric acids from chitin.

Non-oxidative and oxidative degradation of d-galacturonic acid with alkali

Abstract Degradation products from non-oxidative and oxidative treatment of d -galacturonic acid with alkali have been analysed by g.l.c.-m.s.; 13 hydroxy monocarboxylic acids and 26 dicarboxylic acids were identified in addition to several isomerisation products. In the absence of oxygen, the main degradation products were 3-deoxy- lyxo -hexaric, 3-deoxy- xylo -hexaric, malic, tartonic, C -methyltartronic, lactic, and 3-deoxytetronic acids. In the presence of oxygen, arabinaric, threaric, malic, tartronic, and glycolic acids were formed in large proportions. The routes of formation for most of the compounds are outlined.

Interactions of a Lignin-Rich Fraction from Brewer's Spent Grain with Gut Microbiota in Vitro

Lignin is a constituent of plant cell walls and thus is classified as part of dietary fiber. However, little is known about the role of lignin in gastrointestinal fermentation. In this work, a lignin-rich fraction was prepared from brewers spent grain and subjected to an in vitro colon model to study its potential bioconversions and interactions with fecal microbiota. No suppression of microbial conversion by the fraction was observed in the colon model, as measured as short-chain fatty acid production. Furthermore, no inhibition on the growth was observed when the fraction was incubated with strains of lactobacilli and bifidobacteria. In fact, the lignin-rich fraction enabled bifidobacteria to survive longer than with glucose. Several transiently appearing phenolic compounds, very likely originating from lignin, were observed during the fermentation. This would indicate that the gut microbiota was able to partially degrade lignin and metabolize the released compounds.

Non-oxidative and oxidative alkaline degradation of pectic acid

Abstract As alkaline degradation products of pectic acid, 6 hydroxymonocarboxylic, 16 dicarboxylic, and 2 tricarboxylic acids were identified by g.l.c.-m.s. as their trimethylsilyl derivatives. In the absence of oxygen, the most abundant degradation products are 3-deoxy-2-C-(hydroxymethyl)pentaric, 2,3-dideoxypentaric, 2-deoxy-3-C-methyltetraric, malic, and 21,4-anhydro-3-deoxy-2-C-(hydroxymethyl)pentaric acids, whereas, in the presence of oxygen, glycolic, oxalic, malic, 3-deoxypentaric, and 2-C-carboxy-3-deoxypentaric acids preponderate. The routes of formation of these acids show many similarities with those encountered in the alkaline degradation of cellulose.

OXIDATIVE DETOXIFICATION OF WOOD-DERIVED INHIBITORS BY GLUCONOBACTER OXYDANS

Abstract The inhibitory effects of four wood-derived aromatic aldehydes: vanillin, syring-aldehyde, 4-hydroxybenzaldehyde and 5-hydroxymethylfurfural were tested using Gluconobacter oxydans subsp suboxydans ATCC 621 as model organism. At low inhibitor concentrations G. oxydans was found to recover rapidly from the inhibition. The organism detoxified all the inhibitors except syringaldehyde by simultaneously oxidizing and reducing them to the corresponding acids and alcohols. The oxidation step was preferred in all cases. The enzymes responsible for the detoxification were apparently induced by the presence of the inhibitors.

Identification of the products of hydrolysis of carboxymethylcellulose

Abstract Hydrolysis of carboxymethylcelluloses, made from softwood and hardwood pulps, gave mainly glucose and its mono- and di-substituted derivatives, together with considerable amounts of products derived from hemicellulose constituents. Each hydrolysate contained 2- and 3- O -carboxymethylxylose; mono- and di-substituted mannose derivatives were also detected after hydrolysis of the carboxymethylated softwood pulp. 2,3,6-Tri- O -carboxymethyl derivatives of glucose and mannose were detected in hydrolysates of samples of higher degrees of substitution, and 2,3-di- O -carboxymethylxylose was found only after hydrolysis of hardwood-derived samples.

The formation of 2-hydroxy-2-cyclopenten-1-ones from polysaccharides during kraft pulping of pine wood☆

Abstract Small amounts (∮.1% of wood) of 2-hydroxy-2-cyclopenten-1-one (1) and its alkyl derivatives were identified by capillary g.l.c.-m.s. in the chloroform extract of the spent liquor obtained from kraft pulping of pine wood. Their formation from polysaccharides was confirmed by experiments on xylan, pectic acid, and hydrocellulose. The most abundant compounds were the 3-methyl and 3,4-dimethyl derivatives of 1.