Food Chemistry. Dennis D. Miller
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Название: Food Chemistry
Автор: Dennis D. Miller
Издательство: John Wiley & Sons Limited
Жанр: Техническая литература
isbn: 9781119714606
isbn:
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.