Retro Starches…Back to the Future?
Early formulation efforts were often judged on the ability to find the “optimum” ingredients. This required a clear definition of each required function in the food, and consideration of all the available ingredients capable of delivering those functions. “Optimum” was originally defined as ingredients that perfectly deliver the desired functional requirements at the lowest ingredient cost. As a result, a slightly different starch might be used in each formula.
By the mid-80s, the business definition of “optimum” was changing. Corporations understood that each ingredient in the system carried hidden costs of inventory, quality management, etc., and the process of ingredient consolidation began. The huge number of starches specified so carefully into formulas were compared and grouped by common features. The most versatile and cost-effective option in the group was tested for acceptable function in all the formulas. The result was a considerably pared down list of specified starches that tended to be chemically and physically modified for maximum performance at minimum cost. Introducing a new starch to the group required justifying its necessity to a senior manager.
The next focus was on Total Quality and Sources of Variation. During this period, it was discovered that formulating “too close to the edge” could result in significant variation in finished product quality. This understanding led to yet another aspect to “optimum” ingredient functionality...the concept of “robust” performance. Meanwhile, significant advances in the understanding of fundamental structures in foods, such as glass transition theory, resulted in new tools to solve formulation and quality problems, and provided a rational basis for anticipation of these quality “cliffs.” At the end of this period, the concept of “lowest cost” was expanded to include lowest total delivered cost, and included not only ingredient cost, but the effect the ingredient might have on other ingredient, processing and distribution costs.
Current Expectations for Starch PerformanceOver the last 15 years, the industry has made a number of forays through low-fat/fat-free, high-fiber, low-carb, glycemic index (GI) and other marketing trends. Delivering products to meet the needs of each of these trends has added to the technical toolkits used by suppliers. As consumers continue to become more label savvy, driven by a desire for food to aid in health maintenance, they avoid perceived “bad” ingredients such as allergens, trans fats, etc. The current emerging trends of whole grains, chef-inspired, and organic/natural/clean labels are inspiring new focus on starches and other ingredients.
For a new starch ingredient to meet a formulator's needs today, there is a tough list of requirements, including:
* Fit to formula and processing system requirements,
* Delivery of critical sensory and performance attributes,
* Lowest cost possible, at the concentration used in the final formula,
* Statistically consistent in-plant performance and quality through distribution and shelflife,
* Allergen status,
* Broadest range of functionality possible, permitting the fewest ingredients to be used in a formulation and the fewest inventoried starches to meet a company's starch ingredient needs, and
* As close to “nature” as possible, using consumer-friendly labels that feature ingredients with understandable names rather than “additives” or “chemicals.”
Starch OptionsRegardless of the plant from which a starch is derived, it is composed of glucose units, variously joined together by a-1, 4 or a-1,6 glycosidic bonds. The result is two polymer types: the basically linear amylose, and the larger and more branched amylopectin. The length of linear regions between branches, the number and placement of the branches, overall starch molecule size, the packing arrangement between molecules in the starch granule and other features all contribute to create significant differences in functionality. (See chart “Amylose and Amylopectin Characteristics.”) These functional differences long have been considered in starch applications but become more important when formulating for “clean labels” where chemical modification is not desired.
Traditional native starches currently have limited use in formulated foods because they have significant disadvantages in processed food systems. These include: poor processing tolerance to heat, shear and acid; undesirable textures; and poor stability during storage or holding. Poor processing tolerance results from the fragility of fully gelatinized, swollen, hydrated starch granules. As the starch slurry is held at high temperatures, the granules begin to fragment, and the viscosity breaks down. High shear or extreme pH conditions also tend to disrupt the granules, again leading to a rapid breakdown from the initially high viscosity. Poor texture results from the naturally viscous quality and gel structure characteristics of some of these starches. Poor freeze/thaw stability and a tendency toward gel syneresis occur due to the starch polymers' ability to associate with each other and re-form networks. The ability to associate is hindered in some modified starches where functional groups have been added to the molecules to interfere with their ability to do so.
However, when classic chemical modifications are inappropriate, the desirable attributes of chemical modification can be achieved by a variety of other approaches.
* Hybridization or Variety Selection
Just as in oilseeds, starch-producing plants are more likely to be viewed as the “manufacturing plant” that provides a range of characteristics without chemical or genetic modification techniques. Methods of hybridization and selecting naturally occurring varieties of corn, potato, tapioca, rice and other starches results in products with different percentages of amylose and amylopectin. High-amylose starches have unique properties for gelling and film-forming and can be used to provide structure and barrier properties. High-amylopectin starches have built-in viscosity stability, due to the branched nature of the polymer molecule, which provides freeze/thaw and syneresis stability.
* Utilization of Unique Characteristics of Starch
Certain starch types are known to have special characteristics. Again, these become more important to consider when formulating for “clean labels.”
Rice, tapioca and potato starch have particularly bland flavor because of the low protein and lipid contents present in the starch.
Although rice starch has more branches in its amylose and amylopectin polymers, the starch molecules have shorter chains, and the granule is uniquely small. This results in better resistance to processing stresses than most other native starches, very slow retrogradation and smooth texture in the mouth.
Wheat starch contains two distinct populations of granule sizes, accounting for the very wide range of granule sizes and the wide gelatinization temperature range. The high phospholipid content of wheat starch also explains its performance as a fat emulsion stabilizer.
Potato starch has extremely large granules, and molecules with phosphate monoester groups attached to the amylose and amylopectin molecules. These two factors contribute to its tendency to swell at low temperatures and hold very high amounts of water, and its resistance to retrogradation during storage.
* Standardization of Native Starches
When using native starches, the natural variation in key processing characteristics must be considered. The specification for the starch should include key processing attributes, such as viscosity, under relevant conditions. The manufacturer should use some process to achieve “standardization.” Since native starches may be purchased from less sophisticated suppliers, it is crucial to assure the expected level of consistency of processing characteristics will be delivered. Variation in key characteristics within or between lots of starch can result in difficult processing issues.
* Alternate Processing Approaches
Formulators and process engineers have benefited from ingredient tolerance provided by chemical modifications that permit the development of highly efficient lines running highly convenient processes. One approach to utilizing “clean label” starches might be to eliminate as many stress points in the formula and process as possible. Some newer manufacturing systems are designed with greater consideration for more “gentle” processing. This makes it inherently easier for these manufacturers to use “clean label” ingredients.
These newer approaches include reducing shear input wherever possible. To that end, pipe runs can be shortened, and mixers and pumps can be selected to impart less shear. The order of ingredient addition also can be changed to minimize high-temperature contact between starches and acid, or to permit full hydration of starch before the addition of gelatinization-delaying ingredients such as high concentrations of sugar. Cook time sometimes can be reduced by separately heating ingredients before combining them with the starch material.
* Physical Modifications
When the properties of native starches alone are insufficient to meet formulation requirements, alternative strategies can be employed.
Starches are pregelatinized by gelatinizing the starch and then recovering it as a dry power. Most pre-gelled starches have lost granule integrity, however, because the granules are usually in fragments.
Particle size can be used to alter properties such as smooth texture or pulpiness, tendency to form lumps during dispersion and speed of hydration.
Cold water swelling is an alternative to pregelatinization that provides the convenience of a pregel with granule integrity of a cook-up starch. The granule integrity provides a smoother gel appearance than a pregel and greater tolerance to extended hold at high temperatures.
Some manufacturers consider enzyme modification—where enzymes are used to hydrolyze starches in various ways to achieve specific end properties—a physical modification. Enzyme modification provides starches with characteristics normally provided by “conversion” with acid. These traits include the ability to use starches at higher percentages, increased water solubility, controlled gel strength, or modified stability.
Heat Treatments—The New NativesThe impetus for new physical modifications arose initially in Europe, where manufacturers were driven by a demand for functional ingredients that could be considered ingredients and not additives under European labeling regulations.
Heat-treating starches under controlled conditions provides them with a range of textural and viscosity properties characteristic of chemically crosslinked starches. There are numerous variations of processes described in patent literature but, basically, starch is heated under conditions that tightly control pH, time, temperature and moisture content. The resulting starch granules are more resistant to viscosity breakdown from heat, shear, pH and high temperatures. A range of characteristics can be achieved by varying the degree of heat treatment. By combining the heat treatment with use of certain native starches, and by non-chemical pre-treatments, the cold storage stability of products using the heat-treated starch also can be improved. Gradually, as these new technologies are being developed, starches simply labeled with their base material name provide the range of properties previously delivered via modified starch.
Specialty starches can benefit from being combined with different hydrocolloids. If the current starches available to meet formulation criteria are limited or if cost constraints exist, food gums can be added to improve manufacturing, shelflife performance, finished product preparation and consumer appeal. As many food gums are derived from plant sources (seeds, fibers, seaweed, tree fruits, etc.) or produced via fermentation, they may well be positively perceived by the consumer.
As examples, xanthan gum can be added to provide increased heat viscosity and emulsion stabilization during processing at higher temperatures. Freeze/thaw stability can be enhanced by the addition of cold-soluble food gums for moisture control. Ice crystal growth during frozen food storage and subsequent moisture release can be controlled in this fashion. Well-characterized synergies also can be leveraged. For example, iota carrageenan and xanthan gum can yield much higher than predicted viscosities when combined with food starches.
Ironically, the food industry appears to be returning to its original emphasis on using simple ingredients. But fortunately, the advances made over the years in understanding starch composition and behavior while trying to reduce costs now allows the industry to meet consumers' desires without sacrificing taste or performance.
Website Resources:www.foodinnovation.com — Information from a dictionary of starch-related terms to starch science is provided
www.excelon-inc.com — Information on starch and gum availability
www.PreparedFoods.com — In the LINX search field type in “starch functionality” and change the right box from “All BNP Media” field to “Prepared Foods” for archived articles on this subject
www.abingredients.com — Site which discusses some starch applications
www.cargill.com — Searchable website with some starch information
www.tateandlyle.com — Searchable website with some starch attributes