Dispersed starch

Dried flavoring wall material development conducted in this study was completed in two separate phases. Firstly, a water-dispersable starch polymer which 1) exhibited good flavor retention potential during spray drying and 2) was able to form a stable flavor-incorporated aqueous emulsion was examined. 

Fig. 32.—Change of temperature in the 20th min of heating of potato starch in a microwave field. 1, Native starch 2, amylose 3, amylopectin 4, dispersed starch and 5, gelatinized starch (from Ref. 284).

The quantity of starch transferred to paper by a size press depends on several factors concentration of dispersed starch in the surface size viscosity of the starch dispersion diameter of the size press rolls size press pond height cover hardness of the size press rolls size press nip loading pressure paper machine speeds wet-end sizing of the sheet and water content of the sheet. The concentration of starch in the surface size liquid can range from 2% to —15%, depending on product requirements. Frequently, pigments and other materials are added, which further increases total dispersed and suspended solids content. The viscosity ranges from water thin to several hundred cP (mPa-s). 

In the production of corrugating medium, linerboard and other unbleached (Kraft) paperboard grades, starch is added as a slurry spray to the fiber mat on the paper-maker s wire.205 This procedure provides better starch retention in the sheet than the addition of dispersed starch to the stock. According to the position of the spray boom, starch can be forced into the sheet for strength gain or held on the surface for improved surface quality. 

Fig. 62.—The variation of specific viscosity (tjs) with composition of mixtures of 0.5% aq. solutions of gelatin and dispersed starch. (By permission from Lipatov and Lipatov.988)...

Difficulties in dispersing starch to give homogeneous sols, due to persistence of the swollen granule. 

Premature flocculation can be an interference. Sodium silicate is used as a dispersant. Starch, casein, and glue are used to disperse both gangue and carbonaceous matter. They also serve as protective colloids to prevent reflocculation, such as in the flotation of gold. 

For food applications it is desirable to only partially cook starch so that some texture remains. In food terms, a fuUy dispersed starch is overcooked . For papermaking, only fully dispersed starches will release their full bonding power. Partial cooking of ionic starches will release only part of the starch charge, with resulting variability and difficulties in wet-end charge control. Partially cooked starches may be referred to as undercooked in papermaking applications. 

The development of micro-particle retention systems radically changes the chemistry. In these systems an overdose of cationic material is added to the thin stock, such that the system becomes cationically dispersed. An anionic micro-particle is later added to flocculate the stock. Under these circumstances a complete starch cook out may not be necessary - especially if the system is being over-charged with a polymer rather than starch. Cross-linked cationic starches that do not fully disperse may be used in such systems. The partially dispersed starch acts partly as a colloid and partly as a particle, having a larger active radius than a fully dispersed starch molecule. Benefits in starch retention are claimed. 

Jones DA, Eknquist LF. Dispersible starch graft copolymer blend. US 4,159,260. Henkel 1977. 

For starch to be effectively degraded it must first be heated above 65 °C. The starch grains then burst and they form a viscous gel. This must be thinned so that the viscosity is low enough for the dispersed starch to be handled. The a-amylase from barley is fairly stable to heat, and it is active at 65 °C. However some a-amylases from the organisms which grow at temperatures up to 80° or 90 °C (e.g. Bacillus stearothermophilus) are stable for short periods at temperatures above 100°C, and these heat-stable enzymes are very useful for the controlled thinning of starch gels. 

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