Carbohydrates

Abstract

Carbohydrates are the most abundant biomolecules on Earth. Carbohydrates are (together with proteins and fats) macronutrients, meaning they are one of the three main ways the body obtains energy, or calories. Inside cell walls they form a major portion of the supporting tissue and thus supply structural support. The cellulose polymer retains its structural properties outside of living nature when it is used as timber for construction, as pulp for paper and paperboard, or cellulose fibre for textiles. Starch, polygalactomannans and other natural gums do so, when they thicken or jellify water or other liquids. Polysaccharide hydrocarbons are large high-molecular weight molecules constructed by joining monosaccharide units together by glycosidic bonds. A key factor in carbohydrates are the free hydroxyl groups on each monosaccharide unit in the polysaccharide chain. These allow extensive changes in structural properties and rheological behaviour through esterification or etherification, grafting, or other polymer analogue reactions. By hydrolysis of the glycosidic bonds, the polysaccharides can be reduced to oligosaccharides or monosaccharides, which, in turn, can undergo a variety of chemical reactions known as sugar chemistry. However, the sugar-rich carbohydrates through direct microbial fermentation processes or through the hydrolysis of polysaccharides into fermentable sugars are also used as feedstocks for biochemical value chains to produce bio-products such as alcohols, organic acids, microbial oils, and hydrocarbons, biosurfactants, and biopolymers.