Choosing a starch no longer is as cut and dried as it used to be. Previously, the native properties of a starch would dictate the application in which it would be used. Now, it is not just the starch source, but the source plus the various modifications and physical processes used on the raw material that determine which starches will be appropriate, says David S. Jackson, professor and interim head of the department of food science and technology at the University of Nebraska (Lincoln, Neb.).
“The base starch is a very initial starting place,” he says. “Some of the generalities concerning native starches from ten years ago aren't even true anymore.” Corn starches can take on the properties of other starch materials and vice versa. Sometimes manufacturers can modify a starch and get the exact viscosity they want using an [atypical] starch source with different commercial preparations.
For instance, root starches and tubers like cassava (also known as tapioca) and potato tend to expand better in extrusion operations, but given a certain process condition, a corn starch will expand extremely well also. “When modified, the different starch bases that contribute to unique functionality and textures in food systems are virtually limitless,” says Joseph Light, senior director of customer solutions at a starch ingredient supplier.
Although most modifications are proprietary, physical modifications such as pre-cooking or pre-gelatinization and cold water-swelling (which create good dispersibility) are standard. There are also modifications that produce resistant starch. Waxy and high-amylose starches are from genetic mutants, created using conventional breeding techniques.
Nevertheless, choosing a starting base material still is very essential because, in their native states, all starches have slightly different cooking temperatures, viscosities and amylose-to-amylopectin ratios. Physical, chemical or genetic modifications still are based on the inherent properties of the starch. Corn starch, cassava, wheat, or potato starches differ in their granular structure, amylose and amylopectin contents, as well as polymer length and branching patterns. These differences substantially contribute to the gelling, filming and viscosifying properties of starches.
As the amylopectin level increases, the viscosifying/thickening potential increases. Waxy corn starch containing 100% amylopectin generally forms weaker gel systems, but is an excellent starch base for specialty starches, which provide viscosity in food applications. Starches that contain 50% to 80% amylose molecules form very rigid gel systems and are more difficult to fully cook. “In certain applications, such as extrusion, for example, those different starch types will have different expansion properties at different moisture levels,” explains Jackson. Depending on how much expansion is needed and the percent of moisture during extrusion, a different ratio of amylose or amylopectin might be chosen.
Waxy-based starches can be used to emulsify flavor oils which are dispersed in water or thicken beverage systems. Tapioca-based products with amylose contents closer to 20% are known for their low protein level and bland taste along with a quicker mouth “meltaway” when compared to other starches. As such, tapioca-based starches are ideally suited for delicately flavored dairy products.
Native potato starch tends to be very high in viscosity and very clear when freshly cooked; however, it typically performs better in systems with low salt concentrations, says Light. Native potato starches retrograde quickly to form a firm gel on storage.
A fair amount of native common starch is used in stovetop applications and products that will be directly consumed. “Native common starch is a very economical thickener that is used quite widely in dry mix applications,” says Jane Gottneid, a technical service specialist who works with starch in convenience foods at a starch supplier.
ModificationsAcidifiers, water availability, lipids and other ingredients will impact how a starch functions. For example, sugar, gums and proteins will compete with starch for water. Fats and oils can coat the starch granule delaying gelatinization, while acids disrupt the starch granule, thus aiding in gelatinization but potentially increasing the starch breakdown rate. To avoid viscosity loss in the presence of heat and acid, a more highly cross-linked starch will better tolerate abuse in a low-pH range.
Cross-linking increases starch's stability during processing conditions such as heat and mechanical shear. It reinforces hydrogen bonding of starch chain-to-starch chain with a covalent chemical bond, which effectually alters texture and viscosity.
Substitution is accomplished when the hydrogen atom of the hydroxyl groups at carbon atoms 2, 3 and 6 are removed and replaced by acetic anhydride or hydroxypropyl groups. “Substitution basically provides a steric hindrance to the starch chains hydrated with water, while preventing them from hydrogen bonding with a neighboring starch chain,” explains Gottneid. “The result of starch substitution is a lowered cook temperature and increased clarity. Additionally, it improves water-holding capacity, thereby decreasing retrogradation and increasing long-term cold storage stability.”
“The chemical modification of starch is regulated and limited by the FDA, but we can use physical modification to improve functionality and meet various applications,” says Wen-Juin Shieh, the site manager for applied science and support group at a starch supplier. The FDA specifies what reagents manufacturers can use, in what combinations and at what use levels in 21 CFR 172.892. The FDA allows acetylated substitution only up to 2.5%. “In order to go up to a higher substitution level and attain a more functionally effective starch, higher levels of a hydroxypropyl substitution are allowed by the FDA,” says Gottneid. “Typically, as you go higher in the degree of substitution, you get a lower gelatinization temperature, a higher clarity and sheen, and enhanced water-binding ability.”
If manufacturers want the starch to contribute functionally in a frozen, microwaveable, hand-held convenience food item, viscosity and process tolerance are very important. In addition, the low pH of tomato or barbecue-type sauces add to starch abuse during heating. Native starches are not tolerant enough to withstand long-term freezer storage and a recurrent freeze-thaw cycle in such frozen convenience products.
Dual-modified, waxy starches--such as a starch that is both cross-linked and substituted--are best suited for frozen applications. This dual-modified, waxy starch will compensate for lack of viscosity, stability and retrogradation, which are attributes prevalent in the use of flour.
High-performance, cold water-swelling starches are appropriate for microwave applications. These are starches which disperse rapidly (no lumps) and can suspend particulates in instant soups, which allow for uniform heating during microwaving. Sometimes modified food starch can replace the egg in sauces, dressings and bakery applications.
“Specialty starches can be used to provide structure to food applications where shape retention is necessary,” says Light. Retention of shape is normally held more strongly by quick-gelling, high-amylose products. “Gummy and chewy candies are examples where starch helps to set the system quickly during processing and then provides a chewy texture upon consumption,” he adds.
Modified starches have added functionality over unprocessed native starches, but native starches make labels appear cleaner. “Products have recently been developed that match the functionality of modified starches but are labeled with the native starch base used,” notifies Light. Processes exist to improve a native starch's gelling, emulsification, molding and water-binding characteristics, allowing them to mimic the properties of expensive functional ingredients like dairy proteins, gums and eggs.
Encapsulation and GumsStarch has the ability to “grab” onto a particular flavor, color component or vitamin. Once it is in a food and subsequently in the mouth, starch plays a role in how a flavor is released. Some starches have film-forming properties and can provide protection against oxidation and evaporation. Additionally, they reduce the heat damage for heat-sensitive compounds like flavors and vitamins.
Shieh uses starch derivatives to encapsulate and protect limonene, a volatile component in orange oil that oxidizes easily. Once spray-dried, the flavored oil powder has a very glassy surface which will provide a barrier against oxidation and evaporation during storage. “With that protection, the shelflife of the flavor compounds can be extended,” reports Shieh.
Starch derivatives are used widely in beverage emulsions to replace gum Arabic. An ester modification introduces a hydrophobic functional group into the starch molecule that will then interact with lipophilic compounds. Such a modification enhances not only the flavor encapsulation, but also the encapsulation of lipophilic vitamins like vitamins E, D and A. “This type of starch can provide the functional equivalent of gum Arabic and sodium caseinate in various food systems,” explains Shieh. Most gum Arabic is produced in African countries where supply, quality and price fluctuate often, due to political or weather conditions.
Companies in Far Eastern developing countries are looking to introduce essential fat-loving vitamins into non-dairy beverage applications. “Most dairy-based applications use sodium caseinate, but for religious reasons or health concerns, these countries can't utilize the sodium caseinate--since it is derived from milk.” Emulsifying starch can provide the same functionality as sodium caseinate and deliver essential vitamins in the food products.
Compared to gum Arabic, lipophilic starches act to provide multiple benefits such as consistent quality from batch-to-batch, quick dispersion and lower homogenization pressures. Depending on the starch selected and the processing conditions, a range of emulsion particle sizes meeting product requirements can be obtained.
When applying both starches and gums together, it is possible to more finely tune the viscosity in a particular product, address price differentials and adjust subtle mouthfeel features that are characteristic of both ingredients. For instance, interesting combinations of gum and starch systems can mitigate the slimy mouthfeel associated with some gums and starches. Some starches complement xanthan gum and, together, they provide clarity, a light mouthfeel and cling onto the food matrix. Using starch and xanthan gum in combination is functionally and economically beneficial in a wide variety of convenience food applications.
Gum Arabic is a highly branched structure. Waxy maize starch containing 100% of amylopectin also is highly branched and its derivative will be a good substitute for gum Arabic in such products.
Resistant Starches“Resistant starch has been a critical ingredient in the last year to support the development of high-quality, low-carb products,” says Light. The nutritional value of resistant starch also lowers the glycemic index. High-amylose starches tend to be a key raw material for manufacturers looking to produce resistant starch. Because of the white color, bland taste and low moisture binding ability, resistant starch can produce organoleptically pleasing bakery and snack products, when compared to other fibers. “Natural resistant starch has over 140 clinical studies showing the physiological benefits of resistant starch,” informs Light.
Most commercially prepared resistant starches are made in a proprietary process--by taking a high-amylase starch, partially depolymerizing it and then allowing the smaller amylose chains of starch to reassociate and retrograde into a strong crystalline structure that melts at a high temperature.
The processor should be sure the crystalline structure that makes resistant starch resist human digestion has not melted during processing and subsequent consumer preparation. As the temperature of certain extrusion processes increases, a situation can occur where the resistance starch converts to standard carbohydrate. “There are definitely certain products where resistant starch [as a] dietary fiber has been partially destroyed, if not completely,” offers Jackson.
Gottneid tells customers that the more specifically a manufacturer defines the desired the final product, the better her team will be at identifying the proper starch. Questions and answers that should be top of mind include: How will the starch perform under process conditions? What is the desired clarity and texture? And what are the effects of the other ingredients? She suggests formulators not only evaluate the processing conditions, but that they also predict packaging, storage and shelflife requirements as well as consumer reconstitution and use. “They need to begin with the end in mind.”
Sidebar:Waxy-based corn starch is popular in the U.S, while potato starch has been a popular choice for Europeans and tapioca is commonly used in East Asia. “Hundreds of specialty starches exist in the market, each one of those providing unique functional benefits,” says Light. Between December 2003 and November 2004, more than 12,000 food and beverage product introductions contained the word “starch,” reports Mintel's Global New Products Database (GNPD, Chicago).
PurSoup's Soup Creative by Liebig (Le Pontet, France) is a shelf-stable vegetable soup with wheat germ. It contains fat-soluble vitamin A and natural flavorings. Oishii Obento brand Shrimp and Tofu Hamburgers by Katokichi (Kanonji City, Japan) come with mayonnaise-flavored and ketchup starch-based sauces. Gelled particulates are gaining status as Bubble tea, which has starch balls in a sweetened tea beverage, has found its way across the Pacific from Asia to influence the Americas. Foods from other regions using starches are growing in popularity in the U.S.
Examples include starch as a thickener in Asian sauces (oyster or chili sauce) and starch as a texturizer in a Brazilian cheese bread. Surimi is a popular food where starch has been used for years. Mexico's NutriVerde Corn, Chili and Cheese Medallions by Frigorizados La Huerta (Aguascalientes, Mexico) contain bleached wheat flour, corn starch and guar gum.
Apple-flavored Oat Sensations Hot Cereal by Jordans (Biggleswade, Bedfordshire, U.K.) utilizes potato starch for this microwaveable vegetarian meal. Jotis' (Athens, Greece) Milhojas is a vanilla slice dessert with instant cream, topping and icing sugar. Along with carrageenan and corn starch, modified starch is used in the cream and topping.
PHOTOS COURTESY OF MINTEL INTERNATIONAL'S GNPD