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INTERNATIONAL RESEARCH JOURNAL OF PHARMACY www.irjponline.com ISSN 2230 – 8407

Review Article

A REVIEW ON XYLOOLIGOSACCHARIDES

Gupta Praveen Kumar*, Agrawal Pushpa, Hegde Prabha Department of Biotechnology, R.V College of Engineering Bangalore-560059 India

Article Received on: 18/05/12 Revised on: 29/06/12 Approved for publication: 17/07/12

*Email: praveenkgupta@rvce.edu.in

ABSTRACT: Xylan is an important structural component of plant biomass left in agricultural wastes. It is the most abundant of all of the hemicellulosic materials in the world. A number of economically valuable products such as xylose and xylitol can be made from Xylan, but one category of emerging importance is Xylooligosaccharides (XOS). Xylans are present not only in wood but also in various other plants such as grasses, cereals, and herbs. They constitute 5-35% of the dry tissues of lignocellulosic materials and occur up to 50% in some cereal grains. Non-digestible oligosaccharides are low molecular weight carbohydrates of intermediate in nature between simple sugars and polysaccharides. They can be obtained by direct extraction from natural sources or produced by chemical processes hydrolyzing polysaccharides or by enzymatic and chemical synthesis from disaccharides. XOS have great prebiotic potential and can be incorporated into many food products. XOS seem to exert their nutritional benefits in various animal species, which by definition have an intestinal tract populated by a complex, bacterial intestinal ecosystem. KEYWORDS: Lignocellulosic materials, xylan, xylooligosaccharides, prebiotic, bifidobacteria. INTRODUCTION: Diet is an important determinant of disease risk in all population groups. There is emerging evidence that functional food ingredients can have an impact on a number of gut-related diseases and dysfunctions associated with changing lifestyle and age. The words of Thomas Alva Edison “The doctor of the future will give no medicine, but will have interest in the care of the human frame, in diet and in the cause and prevention of disease” are relevant in the present scenario where each individual desires to live longer in a healthy manner1. The importance of the colonic microbiota in human health and well-being is a major breakthrough in both medical and nutrition research. The symbiosis between prokaryotes and the colon is increasingly recognized as a major player in health and well-being and to achieve this, the concept of prebiotics has been suggested.2 Prebiotics are nutrients that have the potential to considerably influence the physiology of whole body and, consequently, health, and well-being.3 However, because prebiotics specifically and selectively affect the gut microflora, their importance is likely to become greater and greater. As biomedical research progresses, it is proposed to go further and to classify a “prebiotic” as an essential, specific colonic nutrient. Xylooligosaccharides (XOS) are relatively new type of oligomers which have gained a lot of interest because of many technological and health benefits and lot of research is going on to explore their dietary and physiological roles.2,3

OLIGOSACCHARIDES: Oligosaccharides are an important group of polymeric carbohydrates that are found either in free or combined forms in all living organisms. According to the IUB-IUPAC nomenclature, oligosaccharides may be defined as oligomers which are composed of 2–10 monosaccharide residues structurally linked by glycosidic bonds that are readily hydrolyzed to their constituent monosaccharides either by acids or specific enzymes.4 They are found naturally in fruits, vegetables, milk and honey. Most oligosaccharides have a mild sweet taste and the mouth-feel they lend to food that has drawn the interest of the food industry to use them as a partial substitute for fats and sugars in foods. Moreover, oligosaccharides can be used as functional food ingredients that have a great

potential to improve the quality of many foods. It has been reported that these have various physiological functions.1,4 Different types of oligosaccharides along with their sources are given in Table.

Table: Dietary oligosaccharide with their natural sources and industrial production processes (adapted from Murphy, 2001).

Types of Oligosaccharides

Natural Occurrence

Industrial Production Process

Lactulose Cow milk Isomerization of lactose

Lactosucrose, glycosucrose

Beet Extraction and transglycosylation of

sucrose Xylooligosaccharide Soyabean Hydrolysis of

polyxylans Stacchyose, raffinose Beet, soyabean Synthesis from starch Fructooligosaccharide Fruits,

vegetables Synthesis and

extraction from saccharose

Galactooligosaccharide Human milk, cow milk

Enzymatic synthesis from lactose

Xylooligosaccharides are sugar oligomers made up of xylose units. These are naturally present in fruits, vegetables, bamboo, honey and milk and can be produced at industrial scale from xylan-rich materials. Of particular interest are those sources of residual origin, such as forestal, agricultural or industrial wastes of lignocellulosic nature. Processing of residual vegetable biomass as raw material offers economic and ecological benefits, since it is a biorenewable, widely distributed and abundant resource The growing commercial importance of these non digestible oligosaccharides is based on their beneficial health properties, particularly the prebiotic activity.6,7

PROPERTIES OF XYLOOLIGOSACCHARIDES:8,9

Physico-chemical property: Sweetness, bitterness, hygroscopically, reinforcement agent for drinks, stabilizing agents of active substances etc. They are stable over a wide range of pH and temperatures and have organoleptic characteristics suitable for incorporation into foods. Biological property: Digestibility, non-digestibility, non-carcinogenicity, bacteriostatic action, selective proliferation of bifidobacteria, improvement of serum lipids and blood, glucose etc. Moreover it also shows activity as enzyme

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inhibitors. XOS favor the selective growth of bifidobacterium spp, which have important biological effects since they; i) suppress the activity of entero putrefactive and pathogenic

intestinal bacteria due to the production of short chain fatty acids.

ii) facilitate the absorption of nutrients. Xylooligosaccharides are advantageous over other nondigestible oligosaccharides in terms of both health and technological related properties. However, the comparatively high production costs require further development of processing and purification technologies. CHEMISTRY OF XYLOOLIGOSACCHARIDES: Depending upon various xylan sources used for XOS production, the structures of XOS vary in degree of polymerization (DP), monomeric units and types of linkages. Generally, XOS are mixtures of oligosaccharides formed by xylose residues linked through β-(1→4)-linkages. The number of xylose residues involved in their formation can vary from 2 to 10 and they are known as xylobiose, xylotriose, and so on. For food applications, xylobiose (DP = 2) is considered to be a xylooligosaccharide. In addition to xylose residues, xylan is usually found in combination with other side groups such as α-D-glucopyranosyluronic acid or its 4-O-methyl derivative, acetyl groups, or arabinofuranosyl residues. The presence of these side groups results in branched XOS with diverse biological properties.9,10,11

BASIC STRUCTURES OF XYLOOLIGOSACCHARIDES:12

PRODUCTION OF XYLOOLIGOSACCHARIDES: LCM affluent in xylan, such as agriculture residues (corncobs, bagasse, cornstalks, sunflower, rice hulls and almond shells), hardwoods, and algae can effectively be used to produce xylooligomers through fractionation processes.13 There have been a number of approaches divulged for fractionation of LCM mainly:14,15 I. Isolation or solublization of xylan through chemical fractionation and enzymatic hydrolysis

II. Direct enzymatic hydrolysis of xylan rich material

Figure 1:15 Hydrolysis of xylan to xylooligosaccharides and xylose by different enzymes

III. Autohydrolysis: Hydrolytic treatments based on aqueous/steam processing and chemical and/or enzymatic hydrolysis. The combined chemical and enzymatic extraction of XOS is performed in two stages i.e. the xylan extraction from LCM and enzymatic hydrolysis of that xylan into xylooligomers. Isolation or solublization of xylan through chemical fractionation and enzymatic hydrolysis. The xylan fraction is usually treated with low concentrated solutions and mild conditions. This can be obtained by treatment of the LCM with dilute acids alkali (i.e. solutions of ammonia, Ca(OH)2, NaOH, KOH or mixture of any of these), the stable pH of xylan supporting this treatment.9,10,11

Feed stock material can be pretreated with oxidizing agents, alcohols or salts to remove lignin/pectic substances depending upon the nature of material. From the alkali treated LCM, recovery of degraded hemicellulosic byproducts can be made by precipitation with organic compounds. Further degradation of isolated xylan can be achieved by hydrolysis with xylanases, which can be added directly to the reaction media, immobilized, or may be produced in situ by microorganisms. The xylanases play a key role in xylan hydrolysis to XOS.16

Purification of Xylooligosaccharides:17,18

APPLICATIONS: The growing demand of functional foods and the potential for products development open promising markets for xylooligosaccharides in many fields, including food and feed, agricultural and pharmaceuticals applications. Food Applications: Among the main use of oligosaccharides, these are used in beverages including fruit drinks, coffee, cocoa, tea, soda, health drinks and alcoholic beverages and milk products e.g. instant powders, powdered milk and ice cream, fermented milks. Further, existing uses in the food industry take in desserts such as jellies, puddings and sherbets; confectionary products such as candy, cookies, biscuits, breakfast cereals; chocolate and sweets; breads and pastries; table spreads such as jams and marmalades; and meat products such as fish paste.5,6,10 Agricultural and feed Applications: It is used as yield enhancer, ripening agent, growth stimulator and accelerator and Feed for pets and fishes. Xylooligosaccharides can be used as ingredients of functional foods, cosmetics, pharmaceuticals or agricultural products.6,7

High selective proliferation of bifidobacterium : Its effect is 20 times of other polymer sugars; it can hardly be digested and absorbed, but directly enters large intestine and is preferably utilized by bifidobacterium to proliferate beneficial bacterium for human body and inhibit growth and proliferation of other harmful bacterium.19,20

Pharmaceutical Applications: Xylooligosaccharides have been reported for having the immunomodulatory activity, anti-cancerous activity, anti-microbial activity, growth regulator activity and other biological activity like antioxidant, ant-allergic, anti-inflammatory, antihyperlipidaemic activity and cosmetics and variety of other properties. It is also used in preparation of micro or nanoparticles and hydrogels for drug delivery and treatment and prevention of gastrointestinal disorders.9,23

Other health benefits: these have non-carcinogenic properties and save insulin secretion from the pancreas, thus stimulating intestinal mineral absorption. Xylooligosaccharides as these oligosaccharides are mildly laxative by stimulation of bacterial growth and fermentation. The xylooligosaccharide intake has been reported as highly effective for reducing severe constipation in pregnant women without any adverse effects. Nutritional formula for infants

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comprising xylooligosaccharides has been claimed to improve gut barrier maturation and provides synergistic effects all along the intestinal tract. Nutritional infant formulae containing XOS have been claimed to have synergistic effects all along the intestinal tract, improving gut

barrier maturation. XOS can be mixed with other prebiotics to achieve synergistic effects or make part of synbiotic preparations together with probiotic microorganisms. Recent patents have been issued on this latter topic.21,22,23

Figure 2: Steps involved in purification of xylooligosaccharides

Figure 3: A systematic diagram on different application of xylooligosaccharides

ECONOMIC AND MARKET CONSIDERATIONS: XOS offer an array of other dietary benefits to consumers including fiber-like properties, reducing cholesterol, improving uptake of calcium, and acting as antioxidants. With an estimated market price of $22/kg in 2004, there is potential to create some economic value from agricultural waste.22,23 CONCLUSIONS: Available experimental evidence supports the hypothesis that XOS and other prebiotics can offer an opportunity to prevent or mitigate gastrointestinal disorders. Even though encouraging results have been obtained for other prebiotics in preliminary clinical trials, the data on XOS are limited.19,20 More investigations are required to further elucidate the mechanisms involved in the reduction of cancer risk and in the cancer chemo- and/or radiotherapy-potentiating effects of XOS.21,22,23 However, these effects need to be confirmed in

other experimental models as well as in clinical trials before XOS can be recommended as nontoxic and easily applicable adjuvants for cancer therapy without any additional risk for the patients. The properties of XOS offer a new dimension for the development of functional foods.6,10 One approach that may be encouraged for future research is the combination of prebiotics and probiotics (as synbiotics). Opportunities exist in exploring the improved knowledge of the synbiotic relationships between colonic microbiota, XOS, and whole body physiopathology. XOS have great potential as agents to maintain and improve a balanced intestinal microflora for enhanced health and well-being. XOS can be incorporated into many food products.5,6 There are however, several questions that still need to be answered. The observations made in this review and published information on nutritional, physiological, and microbial benefits of XOS give a distinct direction to future

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research. Furthermore, the challenge of the future exploitation of these benefits into authentic health issues remains a challenge ACKNOWLEDGMENTS: The authors wish to express their appreciation to Dr B.S. Satyanarayana, Principal RVCE and Dr S Mahesh Head Department of Biotechnology RVCE Bangalore for granting permission for this research. REFERENCES: 1. Aachary AA. Prebiotics: specific colonic nutrients. In:

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