Starch basics
Starch basics
BakingBusiness.com, May 01, 2006
by FoodBusinessNews.net Staff

Bakers know that selecting the right starch for their applications can be a complex task. The variety of starches available — wheat, corn, waxy, potato, tapioca — and their range of functionality provides unlimited options.

A few similarities can be found among the different types of starch. For instance, all starches consist of granules ranging in size from 1 micron to 100 microns, and all starch granules contain chains of two glucose molecules: amylopectin and amylose. Amylose chains, which are straight, are less viscous and more soluble than amylopectin chains, which are more branched. High-amylose starches impart the crispy crunch of snacks and cereals. Because they are slow to hydrate, high-amylose starches can extend the bowl life of cereal.

Granular starches are insoluble in cold water, but when heated to approximately 140°F to 158°F (60°C to 70°C), the granules begin to swell and gelatinize. As the granules begin to hydrate, they become thicker and more viscous, developing a paste-like texture.

During storage, the solubility of the gelatinized molecules decreases, and they begin to crystallize or retrograde. Retrogradation contributes to the firming of crumb structure in bread.

It is here that the similarities end, and the characteristics of individual starches take over. Because each starch has a different crystalline organization in its granules and vary in their amylose content, they swell in different ways and offer various forms of viscosity.

Corn starch can withstand high levels of heat and stress and has strong adhesive properties, making it well suited for snack products.

Waxy starches, which resemble hard, opaque wax, consist mostly of amylopectin. They form clear, thick and tacky pastes.

Waxy maize starch is noted for its good expansion properties. It is well suited for puffed cereals, baked chips and cakes. In filling applications where boil-out and heat stability are issues, waxy maize starch is recommended because it is thicker than other starches, which helps reduce boil-out. Using a modified waxy maize starch in snacks yields a crunchy texture and eliminates the risk of starch breakdown during processing.

Tapioca starch is glossy and more brittle. In products where a bland flavor is required, such as creme-based fillings, tapioca starch is recommended.

Waxy rice starch is preferable in all-natural products, especially if the product will be frozen or there is a risk of starch retrogradation. Rice starch is also being used in extruded applications, where it reduces moisture migration, improves batter viscosity and imparts a crisp texture to snack foods.

Modified wheat starch imparts rapid meltdown, or a melt-in-your mouth sensation, and provides a better flavor release.

Potato starch is often used in potato-based extruded snacks because it provides high expansion during extrusion, imparts a crisp texture to the finished product and acts as a shelf life extender.

TERMINOLOGY

Unmodified starch. Also known as native starches, unmodified starches are not chemically altered and therefore can be labeled in their generic terms: corn starch, wheat starch or tapioca starch. Unmodified starches may be physically altered to produce the desired effects and are used in applications that require little shear, low baking temperatures or short bake times.

As the interest in clean labeling increases, suppliers are trying to find ways to use starch to get the same functionality as modified starches or those that have been chemically altered.

Modified starch. Modified starches have undergone chemical modification to yield desired characteristics not found in native starches. Modification can stabilize a starch, preparing it for activities such as freezing and shearing.

Fruit fillings and icings often require a modified starch that can impart high viscosity to hold fruit pieces in position. Since fruit fillings have a low pH level, modified starches that have a tolerance for a low pH environment, process shear and high temperature stability are well suited for filling applications.

Too, in baked products with a high moisture content, moisture migration is a common problem, leading to an over-saturated crust. In such applications, modified starches are used to provide a sheen to the filling, bind and retain moisture and deliver a short paste texture, which eliminates tailing.

Instant starches. Instant starches, which can be either modified or unmodified, disperse easily in baking applications. They impart stability and act as shelf life extenders in fillings for pies, toaster pastries and cereal bars. Instant starches are also used in cake mixes, muffins and quick bread. Because they go directly into a system, shear and breakdown are avoided.

Instant starches are often used in baked snacks where oven temperatures increase slower than with other cooking equipment. These starches also produce a crispy, crunchy texture and can eliminate the drying time before or during the production process. They are better suited for foods baked at low temperatures, such as in a microwave.

Pre-gelatinized starch. Pre-gelatinized starch, often referred to as a pre-gelled or cold water swelling starch, is processed to swell in cold water, unlike regular starch. A starch paste is heated to its gelatinization temperature, dried on a drum dryer and ground into a powder. When added to water, this pre-cooked starch is thinner than other starches and gels more easily.

Many low-moisture products require pre-gelled starches. For example, cake mixes use finely ground waxy maize starch for its rapid hydration and viscosity-building characteristics. According to one supplier, the pre-gelled starch at a 1% to 3% usage rate yields a more uniform cell structure, bake and a higher volume in the final product.

Pre-gelled starch contributes moisture retention among other functions and is typically used in applications that require rapid hydration or room temperature preparation, such as instant fruit fillings, cream fillings, cake mixes, bread, muffins, icings, cookies and reduced-fat baked foods.

Cook-up starch. Cook-up starches require additional heat to reach their full functional temperature. They are often used in products that will reach 180°F for at least 10 minutes. In fresh and frozen applications, cook-up starches add viscosity, are resistant to acid, heat and shear, increase overall stability, provide clarity and remain stable in cold storage.

Resistant starch. Resistant starches act like fiber in that they resist to digestion in the small intestine and fermentation in the large intestine. While they have fiber contributions, these starches do not have the typical off flavor or negative effect on baking as fiber.

Resistant starches are used mainly in low- to moderate-moisture products, such as high-fiber bread, bran muffins and breakfast cereals. According to studies conducted by one starch supplier, resistant starch yields a better product appearance, texture and mouthfeel than conventional fiber and increases expansion and crispness.