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Xylitol

Xylitol is a natural sugar alcohol appearing in many forest and agricultural materials containing hemicelluloses. It belongs to polyol group which consists of sweeteners that are carbohydrates and not sugars. The xylitol molecule contains five carbon atoms and five hydroxyl groups which qualify it as a pentitol. The sweetness of xylitol is equal to that of sucrose. The food energy contained in xylitol is 2.4 kcal/g which is roughly equivalent to 2/3 of that present in sucrose thus making it a low-calorie alternative to table sugar. Xylitol is also called “birch sugar” because it also comes from the cellulose of birch tree bark.

Xylitol was discovered in 1891 by a German chemist named Emil Fischer. Xylitol was first derived from birch trees in Finland in the 20th century and was first popularised in Europe as a safe sweetener for people with diabetes that would not impact insulin levels. During World War II an embargo prevented Finland from getting sugar. To prevent the country from going through sugar withdrawal, the government built a factory to produce xylitol. After the war xylitol production was discontinued because it was cheaper to again import cane sugar.

Xylitol with the sweetening property matching that of sucrose (sugar) enjoys good applications as sugar substitute for food processing and medicine industry. In food, xylitol has been found particularly attractive as a non sugar sweetener for chewing gums, hard candies, mints, sugar-less chocolates, gelatin, puddings, jams, baked products and ice-creams whereas in medicine it has been used as a non sugar sweetener for chewing vitamins, tablets, cough syrups, mouth washes and tooth pastes. Xylitol produces a perceived sensation of coolness in mouth as it comes in contact with the saliva for its negative heat of solution. This property makes it quite desirable in certain food products, especially beverages.

Another significant property of Xylitol has been the prevention of dental cavities as established by the dental cavities prevention     studies thus making it the best nutritive sugar substitute with respect to cavities prevention. Years after Finland stopped producing xylitol, Finnish dentists noticed that there were fewer cavities in the children whose teeth had erupted during the sugar embargo of WWII. This was confirmed by other Scandinavian countries that had gone through the embargo and substituted xylitol for sugar. Xylitol is a five-carbon alcohol sugar as opposed to other types of sugars which are six-carbons. Bacteria in plaque “feed” on six-carbon sugars and produce acid that erodes tooth enamel resulting in cavities. Because of its five-carbon structure xylitol doesn’t “feed” Streptococcus mutans which then can’t produce damaging acid. Xylitol reduces the ability of bacteria to stick to teeth which allows for saliva to wash it away more easily.

Industry Application / Use
Food Confectionery, cakes, bread, ice cream, special food, tobacco, chewing gums, sugar free sweets
Cosmetics & Pharmaceuticals Ointments, creams, tooth pastes, coated tablets
Other Wax paper, textiles, adhesives, dyes, shoe creams

Xylitol has virtually no aftertaste, and is advertised as "safe for diabetics and individuals with hyperglycemia". This tolerance is attributed to the lower impact of xylitol on a person's blood sugar, compared to that of regular sugars. Xylitol easily metabolizes (independent of insulin) in human body and produces the same amount of energy (4 cal/gm) signifying its application in all diabetic foods. Apart from the above, the adhesive properties of xylitol have been reported to replace phenolic resin for plywood bonding.

Production process

Xylitol can be found in small quantities in a various plants, fruits and vegetables. The primary sources are raspberries, strawberries, yellow plums, cauliflower, spinach and others.  Although widely distributed in nature, its presence in low concentration makes it uneconomic to produce xylitol on commercial scale from such natural sources.  Lately technology has been developed to extract xylitol from bagasse which has made the commercial production of xylitol economically feasible. Xylitol is also produced by fermenting an aqueous solution containing xylose and other free hexoses with a yeast strain. It may also be produced by converting polysaccharides of Hemicellulose to monosaccharides which on fermentation with a hexose fermentation yeast and hydrogenation of the aqueous medium produce xylitol. Another process for the production of xylitol employs recombinant microbial hosts. The production processes of xylitol from pentosans and bagasse are briefly explained in the following lines.

Xylitol from pentosans: Over the time, different methods to produce xylitol from pentosans or xylan have been used. In the most commonly used process, the synthesis of xylitol from natural products is based on the chemistry of pentosans occurring in many plants. Xylan, a constituent of pentosan, is a polysaccharide; this can be hydrolized into D- xylose.  Xylitol is produced as a result of hydrogenation of xylose.

Xylitol from Bagasse: This is relatively new technology where xylitol is extracted from bagasse, corn cob, rice and cotton seed hulls, corn stalks or coconut shells. Currently Taiwan and China are offering technologies for extraction of xylitol from bagasse. The Taiwanese manufacturing process involves shredding of bagasse into smaller particles (size: max. 1.5 cm long) and removal of pith by thoroughly washing with water to remove the dissolved mineral matters. Drying of bagasse reduces its moisture content to 10 percent and the ash content is maintained at maximum 1 percent. Hydrochloric acid liquor and bagasse are fed into a mixer and are mixed thoroughly by agitation in a stirred tank reactor and passed on to a rotary kiln (autoclave) fitted with a school feeder. The acid liquor and bagasse are steam heated to 100-125°C with a residence of 40-75 minutes in the rotary kiln. This treatment helps in pre-hydrolysis of hemicellulose content of a bagasse. The output from the rotary kiln is post-hydrolized continuously on a screen conveyor where the mixture is sprinkled with hot water (100°C) to leach the liquor. The leached liquor is collected at conical bottomed vessels placed under the screen conveyor and is recycled. The post-hydrolysis step completely extracts the xylose content of bagasse. The hydrolysate, collected at conical bottomed vessels, containing 17-20% of xylose, is taken up for xylose separation. Water is removed from the spent bagasse in a screw press and the residue is used for pulp making.

In the Chinese process has little impact on environment and does not produce any waste gas. The waste dredge produce during the process can be used as fuel or culture for mushroom cultivation. After neutralization, waste water can be drained away or an aerobically treated if it contains organic substances.

The World Secanrio

In the 1990s Danisco, the largest xylitol producer from Denmark, identified xylitol for leverage in the Asian chewing gum market. The firm launched a 'value network' to bolster awareness of the ingredient. They talked to regulatory bodies, media, dentists, universities et al to promote the product. Today 80 to 90 per cent of chewing gum sold in Asia has xylitol in their formulations.

The start of 21st century saw tremendous growth in the production and consumption of xylitol. Nowadays, xylitol is produced in many countries around the world, such as Russia, Finland, France,  Italy, India, China etc. China has become the largest xylitol production base and supplier in the world. Chinese xylitol industry has witnessed significant development from 2004 to 2007.

Year Imports Exports
2006 343,356 385.193
2007 396,362 460,192
2008 370,293 461,890
2009 306,332 210,072
2010 322,297 288,038

The above table depicts the global trade of xylitol for last five years. In 2010, China, USA, Finland, France and Italy were the top exporters respectively whereas Japan, USA, Korea, Poland and Canada were the top importer for the same period.

Recommendation:

Although the exports of xylitol came down in 2008 due to global economic crisis but it is now picking up again and new manufacturers are also entering the field and the global market is expected to regain and grow by over 50 percent from 2010 as more people become health-conscious.

The absence of any manufacturer of xylitol in Pakistan offers an opportunity for the aggressive entrepreneurs to capitalize on the opportunity. Absence of competition in local market is an edge for the early entrants in this field.

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