High-Velocity Viscosity

Starch is one of nature’s most abundant compounds. In food systems, starches can control texture, consistency, density, opacity and moisture migration, and can stabilize emulsions and films. Many starches rely on a product’s thermal processing to develop functionality but, in many applications, heating damages or destroys the finished product. It is in these processes where instant starches find their niche.

Children of the corn, etc.

Corn, potato, tapioca, rice and wheat are the most common sources of instant starch. “Native” starch is extracted by wet milling, which separates out pure starch from fiber, oil and protein.

All starches begin as combinations of two long-chain polysaccharides. Amylose ranges from 200 to 20,000 glucose units joined by alpha 1,4 linkages, mainly in linear configurations. Amylopectin has 1,4 linkages plus occasional 1,6 linkages that result in branches. Although its linear sections rarely exceed 25 to 30 glucose units, amylopectin has as many as 2 million glucose units in a compact molecule. Typically, cornstarch has 25% to 30% amylose, with amylopectin making up the difference. Tapioca has approximately 17% amylose, while waxy maize has almost none.

The functional characteristics usually occur in two phases. In water, starch granules can swell and hold up to 30% of their dry weight in water. Applying heat to the water drives gelatinization, a progressive, irreversible hydration. Viscosity increases rapidly during this phase, as does clarity. Upon cooling, higher amylose contents tend to yield gels. Often referred to as “waxy,” starches high in amylopectin are typically nongelling, providing thick pastes.

However, not all applications require heating, but still call for rapid development of a starch’s functionality.

The need for speed 

To obtain a pregelatinized (pregel) starch, a starch slurry is heated to gelatinization, then dried—often in one step using a drum dryer and ground. Virtually any kind can be pregelled to obtain the characteristics of the cook-up form in an instant. The degree of retention of the original starch is variable. Particle size affects the dispersability and subsequent hydration. Coarse grinds exhibit less lumping, but can impart a less smooth, more pulpy texture. Finely ground starches typically yield a smoother texture, provided they are thoroughly dispersed and completely hydrated.

Pregel starch particles, by nature, hydrate quickly. However, too-rapid hydration leads to lumping, which hinders the complete development of the starch’s functionality and causes undesirable texture and appearance. To avoid these problems, Michelle Kozora, food scientist-technical service, Tate and Lyle, Decatur, IL, suggests using dry ingredients already present in the system, such as sugar, maltodextrin and spice, to individualize the starch particles and facilitate uniform dispersion before hydration begins. “For a dry mix or sugar, developers should use a 4:1 ratio, dry to starch,” she suggests. Proper ratios provide sufficient dispersion without creating competition for water that might hinder the starch’s ability to hydrate completely. Stabilizing gums in a dry mix can also compete with starch for water. In these formulations, ingredient addition order may need to be considered.

In systems where oil is a component, the pregel starch may be dispersed into the oil phase to improve dispersion and slow hydration. “If you’re using an oil or a liquid fat, the oil to starch ratio is 3:2,” Kozora says. “If you have a liquid sweetener— corn syrup or high fructose corn syrup—it’s three parts liquid sweetener to one part starch.”

Pregelatinizing fragments the granules, resulting in reduced sheen and flexibility, and increased graininess, compared to cook-up starches. However, coldwater- swelling (CWS) starches offer the benefits of a pregel, without sacrificing performance. Specialized heating systems swell starches without drum-drying’s irreversible alterations. Granular integrity is maintained, yielding smooth texture and glossy appearance, and improved processing tolerance. Amylograms show CWS starches maintaining viscosity through extended heating that causes breakdown of traditional pregel material.

“A key segment for CWS starches is bakery,” notes Shana Brewer, principal food scientist, National Starch Food Innovation, Bridgewater, NJ. “In baked goods, instant starches help to provide a more uniform cell structure, extend shelf life and contribute to softer crumb and moister texture. Instant starches also provide additional viscosity in the batter before baking. This viscosity helps with suspension of particulates (chocolate chips, blueberries, etc.) so that they are uniformly distributed within the baked product and not all sitting on the bottom.”

Other applications include replacing solids in tomato sauces or fruit fillings. “The texture of the starch simulates that of the tomato or fruit, while providing substantial cost savings for the sauce or filling manufacturer,” Brewer says. “An instant starch based on tapioca can function as a fat mimetic in both low- and high-moisture applications. It works very well in low-fat products to provide the mouthfeel and lubricity similar to that of a full-fat product.”

Kozora describes agglomeration, a process for facilitating the dispersion of pregel and CWS starches, as “sticking individual starch particles together with pockets of air in between them,” so the larger particles have less surface area than individual particles. Agglomeration delays hydration and improves dispersability in systems without a suitable diluent, such as instant sugar-free pudding.

New horizons 

As demand for “natural” and “organic” products grows, manufacturers are developing new starches with functionality similar to that of a chemically modified product, but with a clean or native label declaration. “Unlike traditional native starches, which would typically break down, these instant products exhibit heat, acid and shear tolerance in a variety of applications,” Brewer says. “One such product, based on waxy maize, provides a smooth, creamy texture in many applications and is simply labeled as ‘corn starch.’” 

R.J. Foster is a communications specialist with over 15 years of experience in the food industry, ranging from technical service, research & development, quality control, regulatory, and technical sales. He can be reached by email at [email protected].