Starch viscosity

Gum arabic, standard starch dextrins and laboratory prepared low viscosity starch octenylsuccinates were used for all encapsulation work. 

Emulsions of lemon oil stabilized with gum arabic, a conventional starch dextrin and a low viscosity starch octenylsuccinate were spray-dried and evaluated for encapsulating efficiencies. Oil retentions and surface oil determinations were made according to the Materials and Methods section. TABLE 3 demonstrates the superiority of the starch octenylsuccinate in flavor retention and surface oil to gum arabic and a starch dextrin (5) ... 

As can be seen from the data in TABLE 5 the low viscosity starch octenyl-succinate closely matches the oxidation resistance of gum arabic. This product would offer improved shelf-life over a standard starch dextrin and similar stability to a gum arabic encapsulated flavor. 

Converted starches, also called thin-boiling starches, are produced by degradation of the starch chains into small segments. They can be cooked in water at higher concentrations than native starches. Low-viscosity starches are needed in applications where a high solid starch paste with a pumpable and workable viscosity is required. There are four classes of commercial converted starches dextrins (hydrolysis in solid-state) acid-modified starches (hydrolysis in a slurry) oxidized starches and enzymically depolymerized starches. 

FIG. 32. Viscosity as a function of shear rate for three starch solutions (Race, 1993). A, starch solution A B, starch solution B C, starch solution C. (a) Measured at 70°C in the high pressure cell, (b) Measured at 130°C in the high pressure cell. Note that in (a) the viscosity was measured at 70°C, the starch solution A behaves similar to B but significantly smaller than starch solution C in (b) the viscosity was measured at 130°C, the viscosity starch solution A was significantly greater than that of solution B and C, while solution B and C behaves in a similar way. 

Cross-linking is employed when a stable, high viscosity starch paste is needed, and particularly when the dispersion is to be subjected to high temperature, high shear, and/or low pH (137). 

Starch is added at the calender stack for curl control, surface strength, laying of surface fuzz, clay coating holdout, printing characteristics, and grease or oil resistance. Solids vary from 2 to 24%, depending on the starch type used and on the paper requirements. Low viscosity starches, hydroxy ethylated converted starches, and oxidized starches are used in this application. 

Mounting Rapid tack, good open time, nonwarp Dextrin and low viscosity starches 50 3800 (RV 4/20/75)... 

Within this process, hand builders (give a firmer, bulkier hand to fabrics), based on low-viscosity - starch derivatives, are used. 

Gums and starches were used in early attempts to replace the viscosity and lubricity of oils in foods. These were not well received by consumers because they assumed fats merely suppHed mouthfeel and a bit of flavor. On closer examination, it became evident that fats in food and in the diet performed many roles, some simple, some extremely complex, some understood, and some not understood. 

Konjac flour, derived from the konjac plant tuber, has a long history of use in the Ear East, but is a newcomer to the United States. It reacts with many starches to enhance the viscosity of both, and is used in gels that are stable in boiling water. 

The main raw material required for the production of viscose is ceUulose (qv), a natural polymer of D-glucose (Fig. 1). The repeating monomer unit is a pair of anhydroglucose units (AGU). CeUulose and starch (qv) are identical but for the way in which the ring oxygen atoms alternate from side to side of the polymer chain (beta linkages) in ceUulose, but remain on the same side (alpha linkages) in starch. 

Spray Drying. Spray-dry encapsulation processes (Fig. 7) consist of spraying an intimate mixture of core and shell material into a heated chamber where rapid desolvation occurs to thereby produce microcapsules (24,25). The first step in such processes is to form a concentrated solution of the carrier or shell material in the solvent from which spray drying is to be done. Any water- or solvent-soluble film-forming shell material can, in principle, be used. Water-soluble polymers such as gum arable, modified starch, and hydrolyzed gelatin are used most often. Solutions of these shell materials at 50 wt % soHds have sufficiently low viscosities that they stiU can be atomized without difficulty. It is not unusual to blend gum arable and modified starch with maltodextrins, sucrose, or sorbitol. 

Starches are quite hydrophilic and the granules swell in water to several times their volume. In the preparation of starches for coating, the granules are heated at 93°C to ensure complete breakdown. The starch is then mixed with the pigment while it is fluid. Normal practice is to coat the paper at an elevated temperature to help control viscosity. 

Thixotropy and Other Time Effects. In addition to the nonideal behavior described, many fluids exhibit time-dependent effects. Some fluids increase in viscosity (rheopexy) or decrease in viscosity (thixotropy) with time when sheared at a constant shear rate. These effects can occur in fluids with or without yield values. Rheopexy is a rare phenomenon, but thixotropic fluids are common. Examples of thixotropic materials are starch pastes, gelatin, mayoimaise, drilling muds, and latex paints. The thixotropic effect is shown in Figure 5, where the curves are for a specimen exposed first to increasing and then to decreasing shear rates. Because of the decrease in viscosity with time as weU as shear rate, the up-and-down flow curves do not superimpose. Instead, they form a hysteresis loop, often called a thixotropic loop. Because flow curves for thixotropic or rheopectic Hquids depend on the shear history of the sample, different curves for the same material can be obtained, depending on the experimental procedure. 

The Hercules viscometer was originally designed for paper and paperboard coatings, but its use has been extended to paints, adhesives, mineral slurries, emulsions, and starch solutions. The iastmment, noted for being robust and rehable, is particularly well suited for quaUty control and product formulation. It is capable of measuting viscosity over a moderate range 1-10 mPa-s) up to high shear rates (115,000 ). A more recent model is the... 

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