Food Chemistry. Dennis D. Miller

with tap water and invert it in a pan of water as shown in Figure 2.2 (take care to avoid allowing air to get into the cylinder).

      3 Weigh out the specified amounts of each of the leavening agents (see Section 2.5.1.2).

      4 With the stirrer running on low speed, transfer the leavening agent to the flask and stopper immediately. (Note: The rate of stirring will affect the rate of the reaction, so always use the same setting on the stirrer.)

      5 Record the volume of displaced water in the cylinder every 30 seconds for five minutes.

      6 Now, set the flask in a water bath held at 65 °C and continue recording the volume for an additional five minutes. (Note: Temperature can have a marked effect on CO2 generation, so regulate the temperature carefully.)

      7 Measure the final pH of the solution in the filter flask.

      2.5.1.4 Data Analysis

      Note: A spreadsheet program will save you time on this exercise.

      1 For each data point, subtract the control value from the treatment value.

      2 Determine the total available CO2 in each of the treatments (express as moles of CO2). Assume that the baking powder contains 28% sodium bicarbonate.

      3 Determine the moles of CO2 evolved at each time point. (You will need to use the ideal gas law to calculate the moles of CO2.) Transform your data to % of total available CO2.

      4 Plot %CO2 evolved vs time for each of the treatments. Your plot should be similar to Figure 2.1. Be sure to indicate on your plot the point where you put the flask into the 65 °C bath.

      2.5.2 Chemically Leavened Biscuits

      2.5.2.1 Biscuit Formula

Ingredients	Amount
All‐purpose flour	100 g
Sugar	6 g
Sodium bicarbonate	1 g
Leavening acid	To be calculateda
Salt	1.5 g
Oil	23 g
Skim milk	80 ml

      ^a Use the appropriate neutralizing values to calculate the amount.

      Source: Adapted from [11].

      2.5.2.2 Treatments

      1 Control 1 (no leavening acid and no sodium bicarbonate)

      2 Control 2 (1 g sodium bicarbonate but no leavening acid)

      3 Fast‐acting leavening acid (use monocalcium phosphate monohydrate)

      4 Slow‐acting leavening acid (use sodium aluminum sulfate)

      5 Double‐acting leavening acid (use a 50 : 50 mixture of MCP monohydrate and SAS).

      6 Baking powder (3.8 g), no sodium bicarbonate.

      2.5.2.3 Protocol

      1 Mix the dry ingredients thoroughly in a mixing bowl.

      2 Add the milk, and oil and mix thoroughly (use 16 strokes) with a rubber spatula.

      3 Measure out 65 g aliquots of the dough and place on a baking sheet. Make sure there is 1‐inch separation between each biscuit.

      4 Bake at 218 °C (420 °F) for 15 minutes.

      5 Cool down.

      6 Compare volumes (see below) and textures of the various treatments.

      7 Calculate the density of each biscuit.

      2.5.2.4 Volume Determination of Biscuits

      1 Select a plastic container (e.g. margarine tub or yogurt carton) slightly larger than the biscuit.

      2 Fill the container level full with fine seeds (rapeseed or millet).

      3 Pour seeds in the container into a graduated cylinder and record volume.

      4 Place the biscuit in the empty container and refill with seeds.

      5 Measure the volume of the seeds and calculate the volume of the biscuit by difference.

2.6 Problem Set

      Note: These problems are designed to help you review concepts from introductory chemistry. Consult your introductory chemistry textbook for review.

      1 Calculate the volume (at 25 °C and 1 atmosphere) of available CO2 contained in 0.34 g NaHCO3.

      2 Explain why leavening rates differ between leavening acids.

      3 The bicarbonate ion contains a proton and yet bicarbonate acts as a base in most leavening systems. Explain why this is so.

      4 Why are double‐acting baking powders more effective in many baking applications than single‐acting baking powders?

      5 The recipe for a large batch of pancake batter specifies 1 pound of baking soda and MCP as the leaving acid. How much MCP should be used?

      6 Vinegar contains about 5% acetic acid (wt/vol). Calculate the normality of vinegar. What volume of vinegar would be required to neutralize 100 ml of 0.1 N sodium hydroxide?

      7 You are baking a batch of biscuits and are out of baking powder. You decide to improvise and use vinegar and baking soda. You decide to add 2 teaspoons of baking soda to your dough. What volume of vinegar will you use? Assume that 1 mole of acetic acid will neutralize 1 mole of baking soda. One teaspoon of baking soda weighs 5 g.

      8 The published neutralizing value of monocalcium phosphate monohydrate (MCP) is 80. Calculate the expected NV of monocalcium phosphate monohydrate based on stoichiometric relationships. Assume that the MCP is behaving as a monoprotic acid in this system. Does your result agree with the measured value of 80? If not, give a possible explanation. Note: To solve this problem, you will need to write balanced equations for the reactions between MCP and sodium bicarbonate (one with MCP acting as a monoprotic acid and the other with MCP acting as a diprotic acid).

      9 What volume of CO2 would be produced from the complete neutralization of 5 g sodium bicarbonate at 80 °C?

      10 Draw the structure of potassium acid tartrate. Write an equation to show why it is a leavening acid.

      11 What is the main leavening acid in cultured buttermilk? Draw its structure.

      12 What is the main leavening acid in lemon juice? Draw its structure.

      13 Explain how glucono‐delta‐lactone can act as a leavening acid.

      14 What is the minimum percentage of sodium bicarbonate in baking powder necessary to yield 12 g of CO2 per 100 g of powder? (Assume that all of the bicarbonate is converted to CO2 and H2O.)

      15 What volume of 1.0 molar sulfuric acid would be required to neutralize 100 ml of 1.0 molar sodium hydroxide?

2.7 Useful Formulas and Values