Food Chemistry. Dennis D. Miller

172 33 Slow Sodium aluminum sulfate (SAS) 484 104 Slow Fumaric acid 116 145 Fast Potassium acid tartrate 188 50 Medium Glucono‐delta‐lactone 178 45 Slow

      ^a Adapted from [4] and [7].

      ^b Rate of reaction with NaHCO₃ at room temperature.

      NV are used to determine the amount of acid needed to neutralize a given amount of NaHCO₃. For example, if a formula specifies 20 kg of NaHCO₃, the amount of SAS (NV = 104) required would be:

      (8)

      Baking powders and recipes are generally formulated to give baked products with near‐neutral pHs. There are, however, some exceptions to this:

      1 Devil's Food Chocolate Cake. Excess sodium bicarbonate is added to give an alkaline pH in order for the chocolate to form the characteristic deep red color.

      2 Buttermilk products. Excess acid (in the form of buttermilk) is added to give the characteristic flavor.

      3 Pretzels and Gingerbread. Alkaline pHs are produced to accelerate nonenzymatic browning reactions which are important for the deep brown color.

      2.2.3 Leavening Rates

      The rates at which doughs are leavened are important determinants of the quality of baked products. Leavening rates in dough systems are influenced by a variety of factors including the types and concentrations of the leavening agents, temperature, the availability of water, and pressure [8].

Leavening rates may be measured by trapping evolved CO₂ and plotting CO₂ volume versus time. The amount of CO₂ produced is usually expressed as a percentage of the total amount of CO₂ that would be released if all of the sodium bicarbonate were converted to CO₂ and H₂O. When measured in a dough system, leavening rates are called “dough reaction rates.” Typical dough reaction rates for some leavening acids are shown in Figure 2.1.

Figure 2.1 Rates of CO₂ production from mixtures of SALP and MCP‐H₂O, SAPP‐40, or SAS. Evolved CO₂ is expressed as a percentage of “available” CO₂ in the NaHCO₃.

      Source: Adapted from [9].

      Measurement of leavening rates must be carefully standardized with respect to temperature, time, agitation, and ingredients so that comparisons between laboratories and experiments will be valid [10]. The examples of leavening rates given above serve to illustrate the fact that rates differ considerably among leavening systems. It should be remembered that leavening rates for a given leavening acid can be manipulated by applying coatings and changing particle size. Also, other ingredients in the batter or dough may affect leavening rates. Thus, when purchasing leavening acids from suppliers, it is important to specify the leavening rate needed for a particular application.

      2.2.4 Effect of Leavening Acid on Dough Rheology

      Cations and anions from chemical leaveners may alter the elastic and viscous properties of the dough and the texture and resiliency of the crumb. Calcium and aluminum ions can prevent coalescence of air bubbles into larger cells so that the structure of the finished product remains fine. Thus, two leavening acids with similar leavening rates may produce products with different textures.

2.3 Apparatus and Instruments

      1 Filter flask, 125 ml

      2 Rubber tubing

      3 Rubber stopper

      4 Graduated cylinders, 100 and 500 ml

      5 Ring stand with holder

      6 Magnetic stirrer and stir bars

      7 Shallow pan

      8 pH meter and pH standard buffers

      9 Baking oven set at 218 °C (420 °F)

      10 Water bath, 60–70 °C

      11 Burettes

      12 Electric mixer

      13 Thermometer

2.4 Reagents and Materials

      1 Sodium bicarbonate

      2 Monocalcium phosphate monohydrate (MCP)

      3 Sodium aluminum sulfate (SAS)

      4 Commercial double‐acting baking powder

      5 All‐purpose flour

      6 Sugar

      7 Salt

      8 Skim milk

      9 Vegetable oil

      10 Millet seeds

2.5 Procedures

      2.5.1 Determination of Leavening Rates

      2.5.1.1 The Apparatus

Set up CO₂ measuring apparatus as shown in Figure 2.2.

Figure 2.2 Apparatus for collecting and quantifying the volume of gas released.

      2.5.1.2 Experimental Treatments and Controls

Note: When there is more than one ingredient, mix them together thoroughly before adding to the flask.

      1 Control (no leavening agent)

      2 Sodium bicarbonate (0.34 g)

      3 Sodium bicarbonate (0.34 g) + MCP‐H2O (0.42 g)

      4 Sodium bicarbonate (0.34 g) + SAS (0.33 g)

      5 Baking powder (1.21 g). Note: this assumes that baking powder is 28% NaHCO3.

      2.5.1.3 Protocol

      Note: This is a standard protocol for measuring leavening rates in a model system.

      1 Add 60 ml distilled water and a magnetic stir bar to a filter flask.

      2 Fill