Starch treatment

FIGURE 5.12 X-ray diffraction patterns of annealed rice starch (treatment conditions are indicated above each profile) [adapted from Nakazawa etal. (1984) with permission from Japan Science and Technology Agency]. 

Surface sizing with cationic starches offers the added property of substantivity to the cellulose fiber. Most mills will use broke in their furnish. Repulping of broke that previously had a starch treatment can mean loss of the starch to the mill effluent and subsequent BOD treatment. Cationic surface sizes are substantive to the fibers and are not lost to the effluent. Thus pollution problems are minimized. 

Refining. After saccharification, the hydrolyzate is clarified by precoat filtration, or possibly membrane filtration, to remove traces of insoluble fat, protein, and starch. Treatment with powdered carbon, granular carbon, and/or ion-exchange resins is then used to remove residual trace impurities, color, and inorganic constituents. The refined hydrolyzate can be dried to a solid product, evaporated to a high dextrose syrup, or processed to crystalline monohydrate or anhydrous dextrose. A typical process for production of crystalline dextrose is shown in Figure 2(7). 

Modified wheat starch Treatment or substituent Amylograph viscosity, BU... 

The manufacture of pyrodextrins and British gum-like products requires addition of some kind of catalyst. Among them, the acidic catalysts, hydrochloric, phosphoric, and nitric acid, are the most frequently used. Comparative studies have shown that phosphoric acid (the weakest of the three) exerts the least effect on farina starch. Treatment of starch with sulfuric acid, sulfurous acid, sulfur dioxide, hydrochloric acid, mixtures of hydrochloric... 

Of the esters, starch phosphate is produced by reaction with phosphorus oxychloride, polyphosphates, or metaphosphates a cross-bonded product results. Total degree of substitution is determined by measuring the phosphorus content, and the mono- to disubstitution ratio can be calculated by potentio-metric titration. Allowance is made for the natural phosphorus content of the starch. Treatment of starch with acetic anhydride produces starch acetate, which has improved paste stability over native starch. The acetyl group is very labile, and hydrolyses readily under mild alkaline conditions. When a known amount of alkali is used, the excess can be titrated and the ester function measured. This is not specific, however, and a method based on an enzymatic measurement of the acetate has been developed in an ISO work group. The modified starch is hydrolyzed under acidic conditions, which releases acetic acid and permits filtration of the resulting solution. Acetic acid is then measured by a commercially available enzyme test kit. Both bound and free acetyl groups can be measured, and the method is applicable... 

The aerosol container has enjoyed commercial success ia a wide variety of product categories. Insecticide aerosols were iatroduced ia the late 1940s. Additional commodities, including shave foams, hair sprays, antiperspirants, deodorants, paints, spray starch, colognes, perfumes, whipped cream, and automotive products, followed ia the 1950s. Mediciaal metered-dose aerosol products have also been developed for use ia the treatment of asthma, migraine headaches, and angiaa. 

Polymers. AH nitro alcohols are sources of formaldehyde for cross-linking in polymers of urea, melamine, phenols, resorcinol, etc (see Amino RESINS AND PLASTICS). Nitrodiols and 2-hydroxymethyl-2-nitro-l,3-propanediol can be used as polyols to form polyester or polyurethane products (see Polyesters Urethane polymers). 2-Methyl-2-nitro-l-propanol is used in tires to promote the adhesion of mbber to tire cord (qv). Nitro alcohols are used as hardening agents in photographic processes, and 2-hydroxymethyl-2-nitro-l,3-propanediol is a cross-linking agent for starch adhesives, polyamides, urea resins, or wool, and in tanning operations (17—25). Wrinkle-resistant fabric with reduced free formaldehyde content is obtained by treatment with... 

The concept and use of food polymer science in describing the behavior of starch during and after thermal treatment has been developed (20,21). In... 

In industrial production of acid-modified starches, a 40% slurry of normal com starch or waxy maize starch is acidified with hydrochloric or sulfuric acid at 25—55°C. Reaction time is controlled by measuring loss of viscosity and may vary from 6 to 24 hs. For product reproducibiUty, it is necessary to strictly control the type of starch, its concentration, the type of acid and its concentration, the temperature, and time of reaction. Viscosity is plotted versus time, and when the desired amount of thinning is attained the mixture is neutralized with soda ash or dilute sodium hydroxide. The acid-modified starch is then filtered and dried. If the starch is washed with a nonaqueous solvent (89), gelling time is reduced, but such drying is seldom used. Acid treatment may be used in conjunction with preparation of starch ethers (90), cationic starches, or cross-linked starches. Acid treatment of 34 different rice starches has been reported (91), as well as acidic hydrolysis of wheat and com starches followed by hydroxypropylation for the purpose of preparing thin-hoiling and nongelling adhesives (92). 

Cationic Starches. The two general categories of commercial cationic starches are tertiary and quaternary aminoalkyl ethers. Tertiary aminoalkyl ethers are prepared by treating an alkaline starch dispersion with a tertiary amine containing a P-halogenated alkyl, 3-chloto-2-hydtoxyptopyl radical, or a 2,3-epoxypropyl group. Under these reaction conditions, starch ethers are formed that contain tertiary amine free bases. Treatment with acid easily produces the cationic form. Amines used in this reaction include 2-dimethylaminoethyl chloride, 2-diethylaminoethyl chloride, and A/-(2,3-epoxypropyl) diethylamine. Commercial preparation of low DS derivatives employ reaction times of 6—12 h at 40—45°C for complete reaction. The final product is filtered, washed, and dried. 

Low DS starch acetates ate manufactured by treatment of native starch with acetic acid or acetic anhydride, either alone or in pyridine or aqueous alkaline solution. Dimethyl sulfoxide may be used as a cosolvent with acetic anhydride to make low DS starch acetates ketene or vinyl acetate have also been employed. Commercially, acetic anhydride-aqueous alkaU is employed at pH 7—11 and room temperature to give a DS of 0.5. High DS starch acetates ate prepared by the methods previously detailed for low DS acetates, but with longer reaction time. 

Acid-modified starches are used in the manufacture of gum candies because they form hot concentrated pastes that form strong gels on cooling. ThermaUzed starches are used in foods to bind and carry flavors and colors. Sweetening agents (com symp, HFCS) are made from starch by enzymatic or acid treatment as previously noted. 

Enzyme—Heat—Enzyme Process. The enzyme—heat—enzyme (EHE) process was the first industrial enzymatic Hquefaction procedure developed and utilizes a B. subtilis, also referred to as B. amjloliquefaciens, a-amylase for hydrolysis. The enzyme can be used at temperatures up to about 90°C before a significant loss in activity occurs. After an initial hydrolysis step a high temperature heat treatment step is needed to solubilize residual starch present as a fatty acid/amylose complex. The heat treatment inactivates the a-amylase, thus a second addition of enzyme is required to complete the reaction. 

In the EHE process, a starch slurry is prepared and calcium, as the chloride or hydroxide, is added as a cofactor to provide heat stabiUty to the enzyme. The starch slurry is passed through a stream injection heater and held at temperature for about one hour. The resulting 4—8 DE hydrolyzate is then subjected to a heat treatment in a hoi ding tube, redosed with enzyme, and allowed to react for one hour to a DE level of 10—15. 

In these processes, the starch slurry is prepared in the same manner as in the low temperature process. In a dual-enzyme/dual-heating process, the steps ate the same as the low temperature process until the completion of the second-stage reaction. Then, a 2—5-min heat treatment foUowed by a second enzyme addition and another reaction step is employed. In a dual-enzyme/single-heating process, the starch slurry is immediately heated to 145—150°C for one minute or less. Although the enzyme is rapidly inactivated, sufficient hydrolysis takes place to provide a partially thinned hydrolyzate that can be pumped to a second stage where additional enzyme is added and the reaction continued at 95—100°C for 20—30 minutes. The temperature is then lowered for the remainder of the reaction. 

Phosphate—Polymer Control. Phosphate treatment results are improved by organic supplements. Naturally occurring organics such as lignins, tannins, and starches were the first supplements used. The organics were added to promote the formation of a fluid sludge that would settle in the mud dmm. Bottom blowdown from the mud dmm removed the sludge. 

---