The impact of other ingredients on the performance of starch in foods is often ignored. This article will explain how common food ingredients affect the function of starch.
Most foods have a pH between 4 and 7, which does not affect starch viscosity much during heating. However, foods with a pH of 3 or less, like salad dressings and fruit fillings, can cause starch to swell and break down, especially when heated. This can be compensated for with high crosslinking, which can increase viscosity during baking. In canning, fill-viscosity starch is used with less than 0.2% ascorbic acid, araboascorbic acid, or dihydroxymaleic acid to achieve lower final viscosities. Potato starch pastes have maximum viscosity at pH 8.5, while tapioca starch is not affected by pH. Mild heating at a pH greater than 11 can cause gelatinization.
Potato starch has a small amount of anionic phosphate groups, making it sensitive to other ions. Increasing the ionic strength of the solution decreases the dynamic viscosity of potato starch, especially with divalent cations. This property can cause potato starch to be affected by residual minerals during processing. Salt can also have complex effects on starch, such as increasing then decreasing gelatinization enthalpy and onset temperature. Other salts, like calcium chloride and sodium sulfate, also have interesting effects on starch. Salt can also reduce the tendency of starch to retrograde.
Sugars like sucrose, glucose, and glucose syrups can delay and prevent starch swelling by competing for water. They affect gelatinization temperature and decrease the rate of thickening and enthalpy of gelatinization. High concentrations of sugar can increase the gelatinization temperature, and adding sugar after starch cooking may be necessary to develop viscosity. Sugars also make swollen granules less sensitive to mechanical disruption and can reduce opacity and syneresis.
Fats and Surfactants
Fats and emulsifiers can affect the texture and mouthfeel of starch pastes. They can interfere with granule swelling, but when mixed vigorously with starch, their effects are minor. Certain types of surfactants can form a complex with starch, delaying its swelling and solubilization and increasing gelatinization temperature. This complexation can improve the texture of processed foods, such as dehydrated potatoes and retorted pasta, and prevent stickiness in rice kernels. It can also be used to control the firmness of bread and improve the texture of aseptic puddings.
Proteins and starch interact in specific ways that can increase viscosity. When cooked together, starch and milk protein can create a greater viscosity than if cooked separately and mixed. Blends of starch and caseinate were found to be synergistic in terms of viscosity formation. Starch also increases the rigidity of surimi at elevated temperatures. Proteins can absorb onto the surface of gelatinized granules with varying degrees of tightness. Starches also vary in protein binding. Mixed gels are affected by the respective transition temperatures and rates of gelation of the components.
Starch and gums can be combined to achieve specific flow properties or reduce cost. For example, carrageenan can be used with starch in a refrigerated dairy dessert to manipulate thixotropy and viscosity after shear. In some cases, gums and starches interact unexpectedly, such as when adding modified starch to derivatized celluloses or when adding methylcellulose to sweet potato starch. Adding rice starch to gellan can increase G, while adding gelatinized starch can reinforce the gel and bind water. Different amounts of starch can be added to vary viscosity, while kappa-carrageenan concentration can be varied to independently vary tan delta. Interactions with CMC can improve freeze-thaw stability, stability under acidic conditions, retort conditions, and mechanical shear.
Starches and dextrins can help reduce the evaporation of aromatic compounds, like limonene and beta-ionones.
Some food ingredients contain enzymes called amylases, which can break down starch and make it lose its texture, such as its ability to thicken or gel. Examples of such ingredients are blue cheese in salad dressings, blueberries in pies, and flour used for dusting baked goods. To prevent this, it is best to cook the amylase-containing ingredient along with the starch, as the enzyme is denatured before it can break down the starch. For cold processes using pregelatinized starches, it is more difficult to prevent this, so amylase-free ingredients are needed. If ingredients are added to cooked starch, even low levels of enzyme may cause a delayed effect, especially if high temperatures are encountered during distribution or if the ingredient contains microbes producing amylase activity. To avoid this issue with dusting flours, unmalted flour should be used.