Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-11-01
2001-07-17
O'Sullivan, Peter (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C562S531000, C564S459000
Reexamination Certificate
active
06262318
ABSTRACT:
The invention relates to a method of producing polyols from xylan-containing hemicellulose, in particular the invention relates to a method of producing xylitol and erythritol from arabinoxylan-containing material.
Xylitol is a sugar alcohol which occurs in nature and which is most commonly produced by reducing xylose, and whose sweetness corresponds to “ordinary sugar”, but whose calorie content (2.4 kcal/g) is lower than that of ordinary sugar. Small amounts of xylitol occur in many fruits and vegetables, and it is also produced by the human body as a normal metabolic product. The metabolic, odontological and technical properties of xylitol make it an extremely good special sweetener for a variety of uses, such as chewing gums, sweets, bakery products, etc. An example is the independence of xylitol metabolism of insulin metabolism, allowing also diabetics to use xylitol. Xylitol also has a slowing effect on bowel function and reduces nutrient absorption, making it usable in slimming diets. Furthermore, it has been found that xylitol is noncariogenic, even anticariogenic.
Despite the numerous advantages of xylitol, its use has been rather limited. This is due to the relatively high price of xylitol, which in turn results from high production costs.
Previously xylitol was mainly produced by hydrolyzing a material rich in xylan. A monosaccharide mixture, containing large amounts of xylose, is thus obtained. Thereafter, xylose is reduced to xylitol by catalytic reduction (hydrogenation), in general in the presence of a nickel catalyst, such as Raney nickel. The literature of the field describes numerous methods of producing xylose and/or xylitol from xylan-containing material. As examples can be given U.S. Pat. No. 3,784,408 (Jaffe et al.), U.S. Pat. No. 4,066,711 (Melaja et al.), U.S. Pat. No. 4,075,406 (Melaja et al.), U.S. Pat. No. 4,008,285 (Melaja et al.) and U.S. Pat. No. 3,586,537 (Steiner et al.). Xylitol can also be produced from glucose as disclosed in U.S. Pat. No. 5,631,150 (Harkki et al.) or from hexose as disclosed in U.S. Pat. Nos. 5,563,303, 5,238,826 and 5,096,820 and from oses and uloses as disclosed in WO 9,720,860.
In several plants the majority of hemicellulose is xylan, which can be hydrolyzed to xylose. A primary raw material of xylan is the hemicellulose of e.g. hardwood, corn cobs and bagasse, which mainly consists of xylan. Recently, there has been an increasing interest in the utilization of xylan and xylose obtained as by-products in pulp industry. Xylose is formed, for instance, in acid sulphite cookings, in which typical bases are Mg
2+
, Ca
2+
, NH
4
+
and Na
+
. A cooking liquor of neutral sulphite cookings can also be used as a raw material after the xylo-oligomers of oligomeric and polymeric xylan have been hydrolyzed. In the cooking liquor of acid sulphite cookings the hemicelluloses are mainly in the form of monosaccharides.
When using sulphite cooking liquor as a raw material of xylose, the problem is the variability of cooking conditions. Depending on the conditions, hemicellulose of wood dissolves in different ways yielding smaller or greater amounts of xylose. Cooking conditions which yield little xylose, may yield considerable amounts of xylonic acid.
A drawback with the previous methods is that only the xylose-rich hemicellulose is utilized and the rest of the hemicellulose structures is left unutilized.
Like other sugar alcohols, erythritol is highly thermostable and acid stable. Like mannitol, it has poor solubility, and like xylitol, its solution heat is low.
Erythrtol is a polyhydroxyalcohol occurring widely in nature, for instance, as a metabolic product and storage material in algae and fungi. Fruits, for instance melons, grapes and pear, contain erythritol. Various micro-organisms, such as bacteria, fungi and yeasts, produce erythritol, and therefore it occurs in food products prepared by fermentation processes, such as wine and beer, and in processed vegetables, such as soya sauce.
Since erythritol is introduced into the system along with the food, it can be found in many tissues and fluids of the body, such as the lens tissue of the eye, blood serum, sperm, amniotic fluid and urine. In human urine it is the principal sugar alcohol.
Many osmophilic yeasts are able to produce polyhydroxyalcohols. Yeasts like this and yeast-like fungi are found as contaminants in substances with high sugar content, such as honey. Resistance against high sugar and salt content is typical of them.
Erythritol is prepared biotechnically by hydrolyzing wheat and corn starches to glucose which is fermented mainly to erythritol by means of an osmophilic yeast (
Moniliella pollinis
), as disclosed in EP 136,803, EP 136,802, EP 262,463, and EP 327,342. The yield of the fermentation process is about 50% and e.g. ribitol or glycerol is formed as a by-product. The osmophilic property of yeast has a consequence that the dry solids content of the reaction liquor is high. From purified and concentrated liquor, it is possible to crystallize pure erythritol. A variety of other yeasts having osmophilic properties produce erythritol together with glycerol and/or D-arabinitol, but the problem is separation and purification of erythritol from the reaction mixture. Moreover, it has been found that certain yeasts yield acetoin as a by-product, the removal of which is difficult. A. Jeanes (
J. org. Chem
20, 1565-1568, 1955) describes 15 preparation of erythritol from erythronic acid. The publication by W. J. Humphlett,
Carbohydrate Res.
4, 157-164, 1967, describes preparation of erythronic acid from L-arabinose.
Erythritol, like other sugar alcohols used as sweeteners, such as sorbitol, maltitol and lactitol, is tooth-friendly and suitable for diabetics. Because of the small molecular size, erythritol reacts in metabolism in a totally different manner from other sugar alcohols. Consequently, the most important differences are its considerably lower energy content in comparison with other sugar alcohols and the system's higher tolerance to said substance.
The nutritional value of erythritol is considerably lower than that of other special sweeteners. Only 20% of erythritol can continue from the small intestine to the large intestine and therein only half of the substance, at most, converts to volatile fatty acids and further to energy to be used by the body.
On the average, 50 to 60% of the original energy content of other special sweeteners remains for use in the body, but of erythritol the percentage is only about 10, which corresponds to 0.3 kcal/g of the energy content.
Oral bacteria cannot utilize erythritol, as they cannot utilize other polyhydroxyalcohols either. In the tests conducted, it was found that oral bacteria, in particular the main cause of caries,
Streptococcus mutans
, cannot use erythritol for growth. Hence, it is possible to avoid the formation of organic acids and plaque, which contribute to the emergence of caries. This is why the use of erythritol as a sweetener makes the food products tooth-friendly.
In a 10% solution, the sweetness of erythritol is 60 to 70% as compared with cane sugar. The taste profile of erythritol is very similar to that of cane sugar, and it has no bitter after-taste. Therefore it suits well for improving the taste of other sweetening agents, such as aspartame.
It has now been found that xylitol and erythritol can be produced in an advantageous manner from an arabinoxylan-containing material.
&bgr;-D-xylo-pyranose units linked with a 1-4 glycosidic bond form the main chain of D-xylans. These polysaccharides occur in all plants and almost all plant parts. Proper D-xylan, formed from D-xylose alone, occurs rarely, and most D-xylan structures have other sugars as side chains.
One of the common side chains is L-arabinose, which in most cases is in the form of furanose. L-arabinose often forms the side chain alone, even though the chain may even comprise a plurality of sugar groups. In different plants, the proportion of L-arabinose and D-xylose varies greatly, depending on how branched said molecul
Alen Raimo
Heikkila Heikki
Kauko Siru
Lindroos Mirja
Nurmi Juha
O'Sullivan Peter
Scully Scott Murphy & Presser
Xyrofin Oy
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