The Effect of Some Extraction Solvents on the Chemical Structure of the Starches from tobacco Leaf and Potato Tubers

Abstract

Tobacco leaf starch has been isolated as granules by mechanical extraction, and the viscosity, amylose content, f3-amylolysis limit, starch-iodine complex absorption spectrum, and apparent chain length compared with samples extracted by perchloric acid, sodium hydroxide, and chloral solution and purified as the starch-iodine complex. The efficiency of extraction of these methods was also compared. The same comparisons were made with potato granules and potato granules treated with these extracting reagents.Evidence is presented that the most efficient method of extraction of tobacco leaf starch is with perchloric acid but all solvent extraction methods give a degraded starch with low viscosity. The f3-amylolysis limits are similar, while the starchiodine absorption spectra and apparent amylose contents of the extracted starches and granules may differ slightly, but solvent·extracted starches show a quite different pattern of acid release on oxidation with periodate ion which makes estimation of apparent chain length difficult.EFFECT OF SOLVENTS ON STARCH 313 starches isolated by chemical methods has not been reported. Starch can be brought into solution, after gelatinization by boiling, by a number of agents that disperse the swollen grains. The most common extraction solutions used have been chloral at 80°C (Meyer and Bernfeld 1940), perchloric acid at or below room temperature (Pucher, Leavenworth, and Vickery 1948), and sodium hydroxide at room temperature (MacWilliam, Hall, and Harris 1956). It is well known that degradation of starch by alkali and hot water (Greenwood 1956; Machell and Richards 1958) and by acids (Greenwood 1956;Cowie and Greenwood 1957a) occurs. These solvents are not selective but remove other polysaccharides, e.g. cell wall polysaccharides, proteins, and inorganic salts, so that further purification is necessary. This is usually carried out by precipitation of the starch as the iodine complex in the presence of iodine-potassium iodide solution. Starch content can be estimated by hydrolysing this complex and estimating the glucose produced (Pucher, Leavenworth, and Vickery 1948). To make structural studies, e.g. apparent chain length of amylopectin fraction by estimation of formic acid produced on periodate oxidation of the whole starch (Anderson, Greenwood, and Hirst 1955) or isopotential absorption of iodine by potentiometric titration (Bates, French, and Rundle 1943) it is necessary to remove inorganic ions. This is usually carried out by decomposition of the starchiodine complex by alkali followed by dialysis, a process that involves the possibility of further degradation.

Starch Changes in Developing and Senescing Tobacco Leaves

“…The iodine affinities and ,$-amylolysis limits of these iodine precipitates (Table 4) are typical of starch. Matheson and Wheatley (1962) have shown that these properties for granules approximate those of a perchloric extract prepared from granules. Thus no evidence could be found for the presence in tobacco leaves of significant amounts of a glucan that was not starch, apart from structural cellulose.…”

“…The method of Pirt and Whelan (1951), modified as described by Matheson and Wheatley (1962), was used for these estimations.…”

Isolation and Purification of Leaf Starch Components

“…A similar technique was used by Adkins and Greenwood (1), but the fate of contaminants smaller than 75 Pm was unknown. Matheson and Wheatley (22) tried to purify starch granules from tobacco leaves by the procedures of Porter and Martin (26). They subjected an aqueous suspension of crude starch granules to gravity sedimentation.…”

“…Amylopectin was then separated from the coloidal ceDl wall contaminants by its specific interaction with concanavalin A. Purities of starch components were verified by specific biochemical and enzymic tests in addition to their iodine-binding capacity. This procedure should also be suitable for purification of starch components from other plant sources.In the purification of starch from either seeds or leaves for physicochemical studies, no specific processes have been employed to remove cell wall contaminants (1,3,11,12,15,22,24). In these procedures dispersed starch has been treated with various precipitants such as butanol (24), butanol plus pentasol 27 (Pennsalt Chemical Corp.)' (9,15), thymol (13), and others (14,28).…”

“…In the purification of starch from either seeds or leaves for physicochemical studies, no specific processes have been employed to remove cell wall contaminants (1,3,11,12,15,22,24). In these procedures dispersed starch has been treated with various precipitants such as butanol (24), butanol plus pentasol 27 (Pennsalt Chemical Corp.)' (9,15), thymol (13), and others (14,28).…”