Hemicellulose foods

In the past, research activities in the field of hemicellulose were aimed mainly at utilizing plant biomass by conversion into sugars, chemicals, fuel and as sources of heat energy. However, hemicelluloses, due to their structural varieties and diversity are also attractive as biopolymers, which can be utilized in their native or modified forms in various areas, including food and non-food applications. 

The number of reports about hemicelluloses that have been covered by this review indicates the significantly increased importance of all types of hemicelluloses as plant constituents and isolated polymers during the last decade. Attention has been paid not only to known hemicelluloses but also to the primary structure, physicochemical, physical, and various functional properties of hemicelluloses isolated from hitherto uninvestigated plants. The efforts to exploit a variety of plant as potential sources of hemicelluloses were pointed out particularly for agricultural crops, wood wastes, as well as for by-products of pulp and rayon fiber technologies. Many studies were devoted to characterize seed-storage hemicelluloses from plants that have been traditionally applied in food and medicine of many underdeveloped countries to find substitutes for imported commercial food giuns. 

For thousands of years, nature has provided humankind with a large variety of materials for the most diversified applications for its survival, such as food, energy, medicinal products, protection and defense tools, and others. The pharmaceutical industry has benefitted from such diversity of biomaterials and has exploited the use of natural products as sources of both drugs and excipients. One example of a promising biomaterial for pharmaceutical use is xylan, a hemicellulose largely found in nature, being considered the second most abundant polysaccharide after cellulose. 

NORMAND F L, ORY R L, MOD R R (1987) Binding of bile acids and trace minerals by soluble hemicelluloses of rice The ability of rice fiber components to bind bile acids may play a role in lowering serum cholesterol. Food Technology, 41(2) 86-90. 

Figure 1.15 gives an overview of the main constituents of non food biomass. There are three components Cellulose, hemicellulose and lignin. Cellulose and hemicellulose are built form sugar-type monomers, but their cost-effective isolation through enzymatic depolymerization remains a challenge. 

Agricultural residues (stem, leaves, etc.) currently left in the fields after harvesting are made of cellulose, hemicellulose, and lignin. They are not competing with the feedstock for the food industry. 

Dietary Fiber. Dietary fiber is a broad term that encompasses the indigestible carbohydrate and carbohydrate-like components of foods that are found predominantly in plant cell walls (see Carbohydrates). It includes cellulose lignin, hemicelluloses. pentosans, gums, and pectins. 

Most of the cells of wood are long, narrow hollow fibers and tubular-shaped cells arranged with their long axes parallel to the axis of the tree trunk. Certain food storage cells lie in radial bands, termed wood rays, which are perpendicular to the tree axis. The walls of this complex system of plant cells form the basic framework and material of all wood substance, All wood substance is composed of two basic chemical materials, lignin, and a polysaccharidic system, which is termed holoceliulose. The latter embraces cellulose and the hemicelluloses, a mixture of pentosans, hexosans and polyuronides, and in some instances small amounts of pectic materials. Wood cell wall tissue also always retains small amounts of mineral matter (ash). 

The present utilization of carbohydrates as a feedstock for the chemical industry is modest, when considering their ready availability, low cost and huge potential [92], The bulk of the annually renewable carbohydrate biomass consists of polysaccharides, but their non-food utilization is still modest. The low-molecular-weight carbohydrates, that is, the constituent units of these polysaccharides, are potential raw materials for several commodity chemicals in fact, glucose (available from cornstarch, bagasse, molasses, wood), fructose (inulin), xylose (hemicelluloses) or the disaccharide sucrose (world production 140 Mtons year-1) are inexpensive and available on a scale of several ten thousands. 

Rao, M. V. S. S. T. S. and Muralikrishna, G. (2006b). Hemicelluloses of ragi (finger millet, Eleusine coracana, Indaf-15) Isolation and purification of an alkali-extractable arabinox-ylan from native and malted hemicellulose B. J. Agric. Food Chem. 54, 2342-2349. 

The hemicellulose fraction of plant food and feed materials appears to be of considerably greater importance in determining nutritional value of such foods and feeds than has been generally recognized. 

The food, feed, and paper industries use hemicellulase to convert hemicellulose to useful products (Wong and Saddler, 1993). At the concentrations found in vegetable waste matter, hemicellulose has been viewed intermit-tendy as a potential enzyme substrate and as feedstock for commercial ethanol and furfural production. 

Hemicellulose has a greater impact on food texture than do polysaccharides (Kim and Kim, 1988), because it is this group of natural compounds that differentiates crispiness in vegetables (Klockeman et al., 1991). The many physical changes it undergoes with time directly affect the texture of cooked plant tissues whose quality attributes remain resident more in the low DP than in the high DP component (Kim and Kim, 1988). 

---