Starch in Frozen Sauces

Sauces are like icing for entrées. Whether thick and rich or light and delicate, sauces accent an array of foods and, in some cases, create the distinctive flavor or texture for which a product is known. And in sauces of all sortsfrom rich cream sauces that coat your mouth with lingering flavors to fiery marinades that transfer flavors of all sorts to meat, poultry and fishstarches have long been used for textural assistance.

Cold, hard facts

Growing interest in frozen products has, however, presented new challenges for developers. In general, starches are used in sauces to modify texture, increase emulsification and improve mouthfeel, says Denise Fallaw, technical manager for meat & convenience, Cargill Texturizing Solutions, Wayzata, MN. In frozen applications, it is important the starches have good freeze/thaw stability to maintain these characteristics through multiple cycles of temperature fluctuations. Temperature fluctuations and freeze/thaw cycles are far more numerous than you might think. Rachel Wicklund, food scientist, Tate & Lyle, Decatur, IL, explains that such temperature swings are as likely to be seen in the manufacturing facility as on a distribution vehicle, or in a grocery store display case. Each time the door to the case is opened, the temperature in the display case goes up and the food may begin to thaw. Then, when the door is closed, the product re-freezes. If you combine that with the repeated freezing and thawing of the food that occurred before the food even reached the display case, with the repeated freezing and thawing that can occur as that food sits in your shopping cart and then your car before ever reaching the freezer at home, it is easy to understand why freeze/thaw is such a concern.

Baseline

Regardless of origin, starches are made up of two primary components: linear amylose and branched amylopectin, arranged radially into granules. The ratio of amylose to amylopectin will affect the characteristics of the starch during processing. Starches with a higher proportion of amylopectin will thicken, but do not form a gel as their counterparts with higher levels of amylose, Fallaw says. Retrogradation, where starch reverts to a crystalline structure upon cooling, is more likely with higher amylose starches. Wicklund notes that the origin of a given starch will affect the amylose-to-amylopectin ratio, providing functionalities that make a starch more or less suitable for frozen sauce applications.

Waxy corn starches, which are essentially composed entirely of the branched-chain molecule amylopectin, are excellent low-cost thickeners for many foods, including frozen sauces, Wicklund says. Dent corn starches consist partly of the straight-chain molecule amylase, and the remainder amylopectin. The straight-chain amylose molecules can associate to create a more-firm, slightly gelled texture that is highly desirable for many sauces. Functionality of starches that contain both amylose and amylopectin is often affected by granule size. Larger granules often exhibit lower molecular bonding. This allows for more-rapid swelling and greater potential amounts of water absorption. Potato, rice and tapioca starches are examples of large granule starches that impart rich creamy textures to sauce products. Increased physical size, however, brings increased susceptibility to shear.

Upgrades

While native starches can provide texture and mouthfeel effects, usage is limited because viscosity becomes too great above 6% solids. Additionally, very few native starches can provide the level of stability required for modern frozen products, especially those that will be reheated by microwave oven. In such systems, manufacturers turn to modified starches to obtain the specific functionality they seek. By further processing and modifying the starches, starch manufacturers can change the viscosity, gelatinization temperature, pH stability and emulsification properties can be changed, reports Mark Purpura, technical service manager, Advanced Food Systems, Somerset, NJ. Starches can also be modified to become more resistant to shear and be cold-water-soluble. Side chains or groups can also be added to give the starch additional functionality. Cross-linking is a process by which bridges are formed between hydroxyl groups on the starch chains. These connections increase its tolerance to heat, acid and shear. Cross-linking strengthens the starch granule and provides stability at low temperatures, giving excellent freeze/thaw stability, Fallaw says. Cross-linking also yields a shorter texture. Stabilization blocks starch retrogradation and the syneresis that can result thereafter. Stabilization, she says, prevents shrinkage of the granule and provides stability at low temperatures, giving excellent freeze/thaw stability. Wicklund adds: It is also important to prevent boil-out of the sauce, which requires that the sauce not heat-thin excessively. The incorporation of a heat-stable cross-linked starch will maintain the sauce texture and viscosity during reheating and reconstitution. Substitution, reacting a starch with another compound, adds functionality that will vary with the reactant. Substitution opens and expands the starch granule structure, which adds viscosity, improves water holding and stabilizes the texture during the shelf life of a frozen sauce, Wicklund says. Acetylation increases water-holding capacity and is a cost-effective means to improve freeze/thaw stability, while high-hydroxpropyl substituted starches provide superior water-holding, as hydropropyl substitution is the go-to starch modification for water control and freeze/thaw stability. Pregelatinization is a physical modification by which a starch slurry is cooked-up, dried and ground. This process, according to Fallaw, yields a starch with greater process tolerance and increased ease of handling and dispersion. Grind size plays an important role in the starchs performance. Large-mesh material will show less lumping in water than a fine-mesh product. The former can, however, be used to provide a less-thin, more pulpy texture. Smaller mesh powders will, in general, provide smoother textures. Dispersion is more difficult, though, as rapid hydration can cause lump formation that will reduce the efficacy of the starch and create undesirable appearance and texture in the finished sauce.

R. J. Foster is a wordsmith with a B.S. in food science from the University of Wisconsin-Madison and over 15 years of experience in the food industry. He can be reached through his website, wordsmithingbyfoster.com.