Unmodified starches

Starch is often modified by hydrolysis with hydrochloric or sulfuric acid (93). The resulting product is resistant to syneresis, keeps food in suspension after cooking, and exhibits much greater free2e—thaw stabUity than unmodified starch. Modified starch is commonly used in baby food, fro2en prepared foods, pie fillings, meat products, and candy. 

Binders. Paper-coating biaders are either polymers derived from aatural sources or syathetic polymers. The largest volume, aaturally derived biader is starch (qv) (99). Starch is provided ia derivatized form or unmodified form pead com starch is used predomiaanfly for the latter. Unmodified starch is solubilized by thermal conversion or enzyme conversion. The most common derivatized products are acetylated [9045-28-7] oxidized, and hydroxyethylated starches. 

An aqueous dispersion of an unmodified starch containing amylose wiU gradually form an insoluble precipitate through association of linear segments. This process is called retrogradation or set-back. 

Using acetic acid, starch acetates are formed, which are used as film-forming polymers for pharmaceutical products, and as the polymer in biodegradable packing-foam peanuts. Starch acetates have a lower tendency to create gels than unmodified starch. 

Oxidized starch, usually oxidized with sodium hypochlorite, is whiter than unmodified starch it has increased clarity and lower viscosity. 

Amylopectin is the polymeric component of starch and consists mainly of glucose units joined at the 1,4-positions. Relative molar mass tends to be very high, e.g. between 7 and 70 million. A variety of modified starches are used commercially which are produced by derivatisation to give materials such as ethanoates (acetates), phosphates, and hydroxyalkyl ethers. Modified and unmodified starches are used in approximately equal tonnages, mainly in papermaking, paper coatings, paper adhesives, textile sizes, and food thickeners. 

A principal advantage in thermal conversion is the potential for using unmodified starch at a cost saving over pre-converted, viscosity controlled starches. 

The properties of corresponding native (unmodified) starches are given in brackets, starches from different potato cultivars. 

The presence of unconverted starch may be detected also by treating the dextrin with concentrated caustic potash solution, which gives a clear solution if only soluble starch is present, but a kind of paste if unmodified starch remains. 

Special attention should be paid to the dietary composition when the test material itself is a nutrient, (e.g., an industrially treated protein or starch, singlecell protein, irradiated food products). This is because some products are usually incorporated into the diet at levels as high as 20% to 60% at the expense of corresponding regular and normal nutrients. Examples are, modified versus unmodified starch and single-cell protein versus soybean meal. 

Starches may be used directly as feedstocks, or in more technical uses in modified form (typically as starch esters and ethers), or simply converted to glucose syrups for use in industrial fermentation processes or for onward conversion to isoglucose (fructose). After use of unmodified starches in ethanol production, the largest industrial user of both unmodified and modified starches is the papermaking... 

A chemically stabilized and viscosity adjusted starch will have predictable rheological properties. For modified starches, the logarithm of viscosity correlates directly with starch concentration, as shown for hydroxyethylated starches in Figure 18.2. In contrast, unmodified starch might produce very noticeable changes in rheological behavior with only a slight variation in concentration. 

In past practice, native (unmodified) starch was added to the papermaking furnish in order to increase internal and surface strength of the product. The presence of starch in the papermaking furnish allows lower levels of pulp refining for... 

Most frequently, com or potato starches are used, but there are also applications of wheat starch, rice starch, tapioca starch and others. Recently, waxy maize starch has found commercial application in the manufacture of paper. Thermally dispersed or pregelatinized unmodified starches are used for paper strength improvement by addition to the furnish or by spraying onto the papermaker s wire. 

Use of unmodified starches in combination with mild acids and carbonates has been claimed.214 Starch moisture content should be no greater than 25%. Acids such as tartaric, citric or malic acids are added at levels between 0.2% and 7%, while the carbonate level is 0.1% to 2%, both based on total starch composition. The acid is stated to serve a two-fold function it depolymerizes the starch during extrusion via hydrolysis, improving expansion at the same time, it liberates carbon dioxide, which acts as a blowing agent, from the carbonate. A typical formula extruded in a twin-screw extruder at 170-195°C yielded a product with a density of approximately 1 lb/ft3 (16kg/m3) and resilience of 60-85%. The foam had a continuous skin with a closed cell structure. 

---