Elementary plant Biochemistry and Biotechnology (2+1)

Non-reducing disaccharides

Trehalose
 
• Trehalose, a non-reducing disaccharide., occurs as a major constituent of the circulating fluid (hemolymph) of insects and serves as an energy storage compound. It is also present to a limited extent in the fat body of a variety of insects. It gives twice the amount of energy as that of glucose and at the same time maintains the osmotic balance. It has been described as an important adaptation of insects engaged in flight. The anomeric carbons of both glucose moieties are involved in the formation of glycosidic bond

Sucrose

• Sucrose, a sugar of commercial importance, is widely distributed in higher plantsn. Sugarcane and sugar beet are the sole commercial sources. It is made up of glucose and fructose. The anomeric carbon atom of glucose (C-1) and fructose (C-2) are involved in linkage and is therefore a non-reducing disaccharide. Sucrose is a major intermediate product of photosynthesis and it is the principal form in which sugar is transported from the leaves to other portions of plants via their vascular systems.


Invert sugar

• The hydrolysis of sucrose when followed polarimetrically the optical rotation changes from positive (dextro-) to negative (levo-). The dextrorotatory sucrose on hydrolysis yield levorotatory mixture of glucose and fructose. The levorotaion is due to the presence of fructose which is by itself more levorotatory (-92°) than dextrorototary glucose (+52.2). This phenomenon is called inversion and the mixture of glucose and fructose is called invert sugar.This reaction is catalysed by the enzyme invertase. Invert sugar is more sweeter than sucrose. Honey contains plenty of invert sugar and therefore is very sweet.

Sucrosyl oligosaccharides

• The degree of polymerization (DP) of sucrosyl oligosaccharides normally ranges from 3 to 9. Though sucrose is found at higher concentration in all plants, members of the sucrosyl oligosaccharides occur at least in traces in each plant family. The main accumulation of surosyl oligosaccharides is found in storage organs such as roots, rhizomes and seeds. The important members of sucrosyl oligosaccharides are raffinose (DP-3), stachyose (DP-4), verbascose (DP-5) and ajugose (DP-6).All sucrosyl oligosaccharides are non-reducing in nature.

Raffinose

• It occupies the second position next to sucrose in abundance in the plant kingdom. Raffinose occurs only at low concentration in the leaves of leguminous plants, but accumulates in the storage organs such as seeds and roots. Most of the leguminous seeds contain these oligosaccharides in large amounts. Bengal gram has higher amounts of raffinose. Red gam and green gram have significantly high amounts of verbascose and stachyose than Bengal gram and black gram. These sucrosyl oligosaccharides are responsible for flatulence following the consumption of these legumes. It serve as reserve material. It also contributes to frost resistance.