gum is extracted from the seeds of the leguminous plant Cyamopsis tetragonolobus [171].
Starch can be consumed alone and it is an important energy source in the human diet. Unlike starch, some polysaccharides cannot be digested in the upper gastrointestinal tract of humans, but they are used in food technology as food additives in small quantities (usually less than 2%) relative to the total food composition: In the European Union, 40 food additives among the 334 permitted ones are polysaccharide-based. The function of biopolysaccharides as food ingredients are: (i) they bind water, thereby increase viscosity and stabilize food structures, (ii) they form networks and gels, and (iii) through lowering the surface tension between water and oil and increasing the viscosity of the continuous phase, they act in emulsions as emulsifiers and emulsion stabilizers. For instance, arabinoxylans, β-glucan, and gums do not have nutritional value, but they are used as thickeners, emulsifiers, emulsion stabilizers, gelling and encapsulating agents in the food industry [171].
Non-starch polysaccharides are carbohydrate fractions other than starch and free sugars. Non-starch polysaccharides include cellulose, hemicellulose, pectins and oligosaccharide. They are found both intra- and extra-cellularly, but the majority of non-starch polysaccharides present in the cell wall. Xylans, arabinoxylans (pentosans), β-glucan and cellulose are non-starch polysaccharides found in cereal grains while the stem and leaves include a small amount of pectic polysaccharides. The cotyledon of legumes also contains pectic polysaccharide [172]. Wood biomass which is used in pulping traditionally is the main source of cellulose [173]. However, woody tissue offers an attractive source also for food additives such as methylcellulose (E461) and hydroxypropyl methylcellulose (E464) which are used for film formation and barrier properties, binding and shape retention, and preventing boil-out and bursting at higher temperatures; hydroxypropyl cellulose (E463) which offers good surface activity exploited in the use of lower viscosity grades of toppings for whipping or dispensing from aerosol cans; methyl ethyl cellulose (E465) and sodium carboxymethyl cellulose E466 which are used to enhance viscosity [174]. Non-starch polysaccharides also include hemicelluloses that are miscellaneous non-cellulosic polysaccharides. Hemicelluloses are partially soluble in water and most often they found as heteropolymers and less commonly as homopolymers of monosaccharides [172]. Hemicelluloses include xyloglucans, xylans, mannans, glucomannans, and β-(1→3, 1→4)-glucans [175]. Hemicelluloses can be hydrolyzed into fermentable sugars, but they can also be used to fabricate high-value products such as prebiotics, food additives, films, gels, coatings, and biodegradable components in composite materials [171]. But still, the number of hemicellulose-based products is limited, mainly because of the degradation of hemicelluloses during traditionally important alkaline processes, such as kraft and soda pulping, for separation of the wood polymers and production of cellulose-based products [176]. Galactoglucomannan, also known as spruce gum, is water-soluble hemicellulose consisting of galactose, glucose, and mannose. Bhattarai et al. showed that galactoglucomannan behaves as an excellent emulsifier and stabilizer of oil-inwater emulsions [177]. However, it is not currently in the list of accepted food ingredients, since its safety has not been evaluated, yet [171]. In addition to galactoglucomannan, birch xylan is another hemicellulose as a promising food ingredient. Rosa-Sibakov et al. evaluated the potential of birch xylan as a food hydrocolloid and dietary fiber. It showed a slower fermentation rate by fecal microbiota compared to the reference compounds inulin, fructooligosaccharide and xylooligosaccharide. In addition, texture and stability of acid milk gels were improved with birch xylan addition compared to control (no hydrocolloids) or the references [178].
Even though the vast majority of polysaccharides used as food ingredients are plant-based, polysaccharides of microbial origin have proved themselves as new polymeric materials because of their some advantages: (i) microbial polysaccharide production is independent of regional and climatic conditions, (ii) polysaccharide recovery from microorganisms is an easy process, (iii) microorganisms can be produced in large scales and their growth conditions can be controlled, (iv) microorganisms can be modified genetically to produce polysaccharides with desired properties, and (v) microbial growth media ingredients are simple and safe to use [179]. Microbial polysaccharides are used as viscosifying, stabilizing, emulsifying, or gelling agents in food. For example, it has been almost 30 years since the FDA has approved the use of xanthan gum, an anionic exocellular exopolysaccharide secreted by Xanthomonas campestris, as a food-grade thickener and stabilizer [180]. Another example of bacteria-derived polysaccharides used as a food ingredient is gellan gum. It is used as a thickener, binder, and stabilizer in food products particularly in confectionery products, jams, jellies, fabricated foods, and dairy products such as ice cream, milkshakes, and yogurt [181]. As another bacterial polysaccharide, dextran is used as a thickener for jam and ice cream since it prevents sugar crystallization, improves moisture retention, and maintains flavor and appearance of food items [182]. Finally, both algal and bacterial alginate act as a stabilizer, thickener, and gelling agents, and emulsifiers in a wide range of beverages, jelly, ice cream, and dessert products. Additionally, dietary alginate was suggested to reduce the rate of nutrient absorption, and potentially lowers risks associated with the glycemic response, gastrointestinal diseases, and cardiovascular diseases [183]. Dietary alginate was also shown to be a natural heavy metal absorbent that can lower the toxic effects of metals that cause chronic diseases [184, 185]. Although microbial polysaccharides are generally added to foodstuffs to obtain specific properties in the food, there are several bacterial fermentation processes, such as milk fermentation to obtain yogurt, during which polysaccharide is produced. The thick gel-like texture seen in fermented milk products formed by the exopolysaccharides synthesized by the bacteria during the fermentation. Polysaccharide generation during bacterial growth enhances the smoothness and mouthfeel properties of the yogurt [179].
Another application area of natural polysaccharides in the food industry is biopackaging [186]. Dairy products, like fresh and semi-hard cheeses, are complex food products comprising mainly of water, casein, and, fat, so oxidative reactions and microbial spoilage reduce the shelf life of this kind of perishable foods [187]. New technologies have been applied to counteract these negatives effects. Active packaging is an advanced and creative approach to conserve food products or prolong the shelf‐life of food products while preserving their integrity, quality, and safety [188]. Furthermore, an increase in ecological awareness and a dramatic decrease in fossil resources, research has turned towards the elaboration of more natural materials [186]. As defined in the European regulation (EC) No 450/2009, active packaging interacts with the food and the interior environment in such a way as to “deliberately incorporate components that would release or absorb substances into or from the packaged food or the environment surrounding the food” [189]. Active food packaging may involve oxygen and moisture absorption agents, ultraviolet barriers, compounds that deliver flavoring, antioxidants, or antimicrobial agents [188]. Among the packaging systems, polysaccharide-based edible films and coatings have appeared as a good alternative for improving the quality and safety of foods. Previous studies have shown that various polysaccharides-based films and coatings, including chitosan, alginate, carrageenan, pectin, starch, cellulose derivatives, and apple puree, can be utilized as superior carriers of antimicrobial agents for protecting the quality and safety of foods in the industries of meat, poultry, seafood, dairy, fruits, and vegetable. In addition, to prevent food oxidation and browning, antioxidant compounds were incorporated into polysaccharide-based edible coatings and films. Furthermore, different polysaccharides-based coatings, such as alginate, gellan, chitosan and gum-based coatings, have been reported to be excellent carriers of nutraceutical compounds, such as vitamin E, calcium, probiotics [187].
In sum, natural polysaccharides are abundant renewable bioresources as food or food ingredients, but to be used as active food ingredients, the safety of polysaccharides has to be evaluated about their origin, purity, isolation method, stability, composition, immunogenicity, and toxicity. As mentioned above, the packaging is a demand for food preservation. Natural polysaccharides arise as suitable materials for biopackaging. However, polysaccharide-based systems have to be improved for commercial purposes to carry and release bioactive agents, such as antimicrobial, antioxidant agents. Packing systems relying on the “release on time” concept seems to be the future concept of the food industry. Therefore, polysaccharide-based biopackaging systems should be developed to respond to environmental changes such as changes in pH or temperature to liberate their bioactive agent contents.