Cooking starch

Bioavailability of starch. Cooked rice was administered to colectomized rats by gastric intubation and the recovery of starch in the ileal digesta measured after 10 hours of ingestion. Significant starch (11-15%) was recovered from animals fed peas, lima beans, or kidney beans 0.2-0.4% of starch from rice. Oligosaccharide extraction, the size of the test meal, and the amount of starch did not affect starch biovailability . cAMP accumulation. Methanol extract of the grain, in cell culture at a concentration of 1 mg/mL, was active on mast cells " . 

Salts and organic by-products, mostly the diol resulting from hydrolysis of the epoxide, from dry cationization are left in the starch. Trimethylamine, if formed, can be detected by its odor. It can be neutralized by subsequent addition of acid. Addition of a slightly soluble organic acid, such as fumaric or adipic acid, during the cationization both eliminates the odor and aids scale control in starch cooking equipment.44... 

Controlled crosslinking of cationic starches improves performance in microparticle-containing papermaking systems.84-86 Superior performance over cationic potato starch was achieved with crosslinked cationic or amphoteric waxy maize, tapioca or potato starch in microparticle systems when the starch cooking was optimized to produce the proper colloidal dispersions.86... 

The products of starch cooking with retention are similar to those obtained by dispersion with excess steam. Retention of starch paste for several minutes under pressure requires that all steam is condensed otherwise false body of uncondensed steam will shorten the retention. Jet cooking with retention is practiced for on-site chemical starch modification. 

Cationic starch must be thermally dispersed before it is added to the papermaking furnish. In batch cooking, a slurry with up to 4% starch content is heated to a temperature of 93-96°C (200-205°F) for 20-30 minutes. In jet cooking, the solids can be raised to 6% and the temperature to 102-116°C (215-240°F) with short retention. For waxy maize starch, the cooking temperature should not exceed 107°C (225°F). The starch cook must be diluted to <1% solids before addition to the paper stock. 

Uncooked starch slurries are sometimes added at the wet-end, intending that the starch cooks in the dryer section. This procedure is satisfactory only if the temperature of the web is high enough to gelatinise the starch granules in situ, otherwise no value is derived from the uncooked starch granules they merely act as filler and lower the strength of the paper [3]. 

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. 

Chem. Descrip. Hydrophobic silica/hydrocarbon oil-based defoamer Uses Defoamer for latex mfg., paper coatings, adhesives, detergents, starch cooking, textiles, metalworking fluids Features Rapid bubble-break time and persistence Regulatory FDA compliance... 

Fig. 7.16 Starch cooking processes (a) discontinuous, (b) continuous (source BVG).

Fig. 7.17 Continuous starch cooking and converting process (source Metso).

Table 2. Cook Characteristics of Native Starches (cooked 1 part in 15 parts water...

Foam Blast 335NS defoamer, starch coatings Foam Blast 240 defoamer, starch cooking... 

Starch, cooked in the paper mill or supplied as - pregelatinized starch, is used also. Modified starches (- oxidized starch, - cationic starch or - starch ethers) are common in that application. Sodium - carboxymethyl cellulose is also effective, but as an anionic polymer, it requires a retention aid such as alum. 

---