Arabitol production

The major change in yeast metabolism induced by casamino acids supplementation was the marked increase in xylitol production, being the major metabolic product by D. hansenii grown in supplemented concentrated medium (Fig. 2B). Both arabitol and xylitol production in yeast are described to be augmented under stress conditions. Arabitol is usually found as a product of arabinose metabolism in oxygen-limited conditions (8,22), but arabitol production is not restricted to arabinose metabolism,... 

Thus, the relatively constant arabitol production in all tested conditions can probably be explained by a combination of factors, such as high oxygen limitation and possible osmotic effects (e.g. induced by sulfate ions not fully precipitated with calcium) that may act synergistically. Arabitol yields and productivities found in the present work are similar to reported values in the literature (8,22). 

Little attention has been focused on the fermentation of L-arabinose to ethanol. Recently, McMillan and Boynton [100] evaluated eight fungal and six yeast strains for ethanol production from arabinose under oxygen-limited conditions. None of the strains tested produced ethanol from arabinose. They utihz-ed arabinose for cell biomass and L-arabitol production. 

The aldehyde and ketone units appear in some biologically important systems. The ketone unit appears in many carbohydrates (sugars), including ribulose (85), fructose (86), and sorbose (87). d-Ribulose is an intermediate in the fungal pathway for d-arabitol production as the l,5-6is(phosphate), d-ribulose combines with carbon dioxide at the start of the photosynthetic process in green... 

Products were analyzed via Waters Model 515 HPLC Pump fitted with a Waters model 2410 refractive index detector. Separations was performed via an Aminex HP-87H 300mm column at 65°C using 0.005M H2SO4 as the mobile phase. Compounds calibrated for this work included xylitol, arabitol, erythritol, threitol, PG, EG, glycerol, lactate, 1-propanol, 2-propanol, ethanol, methanol, and the butanetriol isomers. Any compounds not visible by RID were not quantified in this work. 

The d,L-arabitol pentaacetate was hydrolyzed by refluxing it for three hours with methanol containing an excess (7 moles) of hydrogen chloride. After concentration to one-half its volume the solution crystallized spontaneously. By collecting the product before crystallization was too far advanced and washing it with a little fresh methanol, crystals melting at 105-106° were obtained. This is the melting point of d,L-arabitol as first recorded by Ruff.1 ... 

This liquid was hydrolyzed under conditions similar to those employed with d,L-arabitol pentaacetate and yielded a sirup which crystallized spontaneously on standing, or immediately if seeded with ribitol. The crude product melted at 96-104° upon recrystallization from ethanol the melting point and mixed melting point with an authentic sample of ribitol was 101.5-102°. 

The selectivity was enhanced by adding small amounts of anthraquinone-2-sulfonate (A2S), which decreased the formation of deoxy by-products. Thus, by adding 260 ppm of A2S with respect to arabinonic acid the selectivity to deoxy-products decreased from 4.2 to 1.6%. A2S acted as a permanent surface modifier since the catalyst was recycled with the same selectivity without further addition of A2S. The highest selectivity to arabitol was 98.9% at 98% conversion, with a reaction rate of 73 mmol h 1 gRU 1 at 80 °C. 

Polyols, namely arabitol and xylitol, have potential chemical, pharmaceutical, and food applications. The latter polyol is currently produced by chemical means, in spite of xylitol bioproduction receiving increased interest (40). Previously it was shown (22) that D. hansenii CCMI 941, under oxygen limitation conditions, coproduces both of arabitol and xylitol in chemically defined medium. In the present work, we evaluated the polyol production by D. hansenii grown on the BSG acid posthydrolysate. 

Fig. 1. Time course of substrates, cell dry weight, and metabolic products in fermentation of BSG OCL posthydrolysate (H medium) (A) and concentrated posthydrolysate (CH medium) (B) by D. hansenii CCMI941. ( ) Glucose, (O) xylose, (A) arabinose, ( ) cell dry weight, ( ) ethanol, ( ) xylitol, and (A) arabitol.

Maximal Volumetric Production Rates and Yields for Cell Biomass, Ethanol, Arabitol, and Xylitol Obtained with D. hansenii CCMI941 Yeast for Different Tested Conditions... 

Besides biomass and C02, no significant amount of extracellular products was detected. Xylitol and arabitol were only accumulated in small amounts, with a maximum of 2.0 and 3.8 g/L, respectively. Other metabolic products usually associated with the pentose metabolism of D. hansenii, such as ethanol and glycerol (46,47), were only found in trace amounts, less than 0.5 and 0.3 g/L, respectively. 

Hemicelluloses can be hydrolysed into their component sugars and used as a fermentation feedstock for the production of ethanol and other alcohols (e.g. butanol, arabitol, glycol and xylitol), organic acids (e.g. acetic acid), acetone and gases (e.g. methane and hydrogen). The wider monosaccharide profile offers opportunities to develop different products to those derived from glucose alone. 

Benzylidene-D-threitol (VII) was prepared by Haskins, Hann and Hudson79 by hydrogenation of 2,3-benzylidene-D-threose, a product of the periodate oxidation of 2,3-benzylidene-D-arabitol. The tetritol was proved to be D-threitol, rather than erythritol, by the fact that hydrolysis of VII and subsequent treatment with benzaldehyde afforded the known dibenzylidene-D-threitol. The acetal group was allocated to the 2,3-position on the basis of independent evidence concerning the structure of the parent benzylidene-D-arabitol (see page 152). For the physical constants of acetals of threitol see Table VIII. 

Product Arabitol Xylitol Mannitol Sorbitol Galactitol... 

Scheme 5.56. The synthetic utility of transketolase has been demonstrated by its application in the synthesis of several natural products including (+)-exo-brevicomin, l,4-dideoxy-l,4-imino-D-arabitol, fagomine, and A-hydroxypyrrohdin.

Bicyclic trans diacetals with one axial residue will be considerably less stable than the acetals with equatorial residues this is shown by the absence of 3,5 4,6-diacetals of glucitol, 1,3 2,4-diacetals of mannitol and 2,4 3,5-diacetals of arabitol from the products of acetalation of the free glycitols. However, by suitable masking of hydroxyl groups, some trans diacetals with axial substituents should be obtainable. The most interesting will be 2,4 3,5-di-0-methylene-D-talitol (LIII), in which one terminal group is axial and the other equatorial (see p. 43). 

Hallborn et al. [115] cloned a short-chain dehydrogenase gene from P. stipitis CBS 6054 that has its highest activity with D-arabinitol as substrate. The D-arabinitol dehydrogenase activity is not induced by xylose but it can use xylitol as a substrate. D-Ribulose is the final product for this enzyme. This enzyme is similar to an NAD+-dependent D-arabitol dehydrogenase cloned from Candida albicans [116]. 

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