Of whole starch

Another common method for determination of alpha-samylase involves measurement of the diminution of the iodine-stainability of whole starch or amylopectin )8-limit dextrin. These methods are useful, as very small quantities of alpha-amylase may be estimated in this way. They are comparative, and cannot be used to determine rates of bond scission, unless they are carefully calibrated by a method that measures reducing end-groups. Such a calibration has been made for the action of hog-pancreas alpha-amylase on waxy-maize starch, although the validity of the reducing-power determinations, made with iodine and thiosulfate, has been confirmed for maltose only thus, it is not yet known whether the calibration is actually valid for the experimental system in which larger oligomers, for example, the triose and tetraose, are also formed. 

As amylopectin predominates in all known starches, the poor film-forming properties of whole starch acetates become understandable. Artificial mixtures of amylose and amylopectin triacetates (acetylated fractions A and B) show increasingly poor film-forming properties as the proportion of amylopectin acetate in the mixture is increased. 

The continuing interest of Bourne in the chemistry of polysaccharides and associated enzymes originated from the work of Haworth and Peat directed towards the enzymic synthesis and degradation of starch. The impetus for this work was given by the discovery, made by C. S. Hanes in 1940, that a phosphorylase isolated from the potato and pea effects the synthesis, from D-glucosyl phosphate, of starch, later shown (by Haworth, Heath, and Peat) to be amylose. In his first paper (with Haworth and Peat) in 1944, Bourne described the isolation of the Q-enzyme which, in conjunction with phosphorylase, effects the conversion of D-glucosyl phosphate into the major component of whole starch, namely, amylopectin. He had discovered the Q-enzyme in a fraction discarded by previous workers. Already, the quintessence of his mind was revealed in this work meticulous attention to detail, and perception of essentials. 

Mandamba, L.S.P., Bustrillos, A.R., and San Pedro, E.L. 1975. Sweetpotato starch Physicochemical properties of whole starch. Philippine Agric. 58, 338-350. 

In preparing derivatives of whole starch, the granules are reacted directly only at the risk of extensive degradation. Consequently, it is desirable to swell or disorganize the granules by some type of pretreatment employing either water, aqueous chloral hydrate, aqueous pyridine, formamide, or alkali. A readily reactive form of whole starches or of the components is obtained by precipitation of their aqueous solutions with ethanol. 

The two highest concentrations of tannic acid (0.051 and 0.034%) resulted in a linear increase of virus titer up to 21 days after inoculation, even though the reduction of starch lesion formation was 91 and 64%, respectively. Thus, the virus must have replicated beyond the limitation of starch lesions. Further experiments indicated that a systemic spread of the virus into the primary leaves in cucumber plants could be obtained by daily brushing the noninoculated primary leaves (only the cotyledons were inoculated) with tannic acid following a vacuum infiltration of whole plants with 0.051% tannic acid 24 hours after virus inoculation. Primary leaves were shielded by tinfoil during the inoculation of the cotyledons to prevent accidental infection. Aerosol O.T. (0.1%) was incorporated in tannic... 

Pectinase from Rhizopus sp. 26R showed high efficiency in enhancing the digestion of raw starch from whole cassava tuber when it was mixed with the glucoamylase. At the 1 hour of the reaction, the mixed enzymes gave the most efficient digestibility with hydrolyzation rate twice faster, than that when glucoamylase was used alone and about 3 times faster than when pectinases... 

According to the ability of the pectinase of Rhizopus sp. 26R that could efficiently enhance the hydrolyzation of raw starch from whole cassava tuber. 

It is obviously important that the fractionation products should be adequately characterized. The only accurate method for ascertaining the purity of the starch components, and also the amylose/amylopectin ratio in whole starch, is to determine potentiometrically the amount of iodine bound.8 38 Colorimetric methods which have been suggested37 38 are useful for comparative measurements, but are often not absolute. The yield of... 

Early investigations on whole starch established the presence of 4 —> 1-a-D-linkages between the D-glucopyranose units involved. Two chemical... 

Table I shows the results of periodate oxidation and methylation applied to amylopectins from various sources. If the percentage of amylose in a whole starch is known, the length of unit chain of the amylopectin component can be calculated from the results of periodate oxidation of the whole starch (see Table II). The length of unit chain appears to depend on the botanical species, but not the variety, from which the starch wras isolated. In the case of tapioca and corn amylopectins, sub-fractionation of these by precipitation with methanol, followed by periodate oxidation, showed the sub-fractions had the same degree of branching as the original amylopectins.71 The action of periodate on whole starches and amylopectins is now so well established and accurate, that it may well completely supersede the methylation technique for pure starches, in view of its many advantages.

Obtaining Different Properties in the Starch. One method of obtaining a starch with different properties is the biological method of using a different type of plant. The best example of this is waxy maize, which yields a starch that is nearly pure amylopectin. The other method is to chemically modify the starch. Chemically modified starch is normally declared as modified starch . A whole range of modified starches are available. There is of course no bar to chemically modifying a starch from a special source. 

Tapioca.—This substance is tho meal from tho roots of the above-mentioned plant, scraped, washed, and rasped into flour. Whilst still moist It is dried upon hot plates, by which treatment some 1 of the starch grains swell to bursting, and the amylaceous matter thus liberated cements the whole into small irregular masses. Hence tapioca is partially soluble iu water. In boiling water it swells up and constitutes a transparent jelly-like mass. 

Figure 3.23. Starch-gel electrophoresis of whole milk samples in urea and mercaptoethanol. Letters on the bottom half of the photograph refer to the genetic types of the milk proteins. (Photograph courtesy Dr. W. Michalak, Warsaw, Poland). (From Thompson 1970. Reprinted with permission of the American Dairy Science Association.)...

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