This manual is the product of the efforts of many people over a period of more than 40 years. First and foremost, we thank the students at Cornell University who enrolled in the Food Chemistry Laboratory course in the Department of Food Science over the 40 years it was offered as part of the Institute of Food Technologists‐approved curriculum for Food Science majors. Their enthusiasm, lab reports, presentations, questions, and gentle criticisms were an immense help in developing and refining the experiments in the manual. Another group of students who contributed enormously were the graduate and undergraduate teaching assistants who set up the laboratories, assisted students during the lab periods, graded lab reports, and offered suggestions for improving the exercises. In recent years, Aaron Jacobsen, Teaching Support Specialist at Cornell, has worked tirelessly to streamline the lab exercises and identify errors in the procedures. We also thank our colleagues at Cornell and Cal Poly for their comments, suggestions, and continual intellectual stimulation. We thank Drs. Alicia Orta Ramirez and Motoko Mukai who both took their turns in teaching the Food Chemistry Lab course at Cornell. We are especially grateful to Professors John Brady and Chang Lee for their friendship, encouragement, and support. Last but not least, we thank our editors at Wiley for their expert advice and support.
About the Companion Website
This book is accompanied by a companion website.
www.wiley.com/go/Miller/foodchemistry2
This website includes:
Preparations and solutions for all chapters
1 Acids, Bases, and Buffers
1.1 Learning Outcomes
After completing this exercise, students will be able to:
1 Explain the roles of acids and bases in food products.
2 Measure the pH of selected food products.
3 Prepare and evaluate a buffer system.
4 Measure the buffering capacity of a common beverage.
1.2 Introduction
Many food components may be classified as acids or bases due to their capacity to donate or accept protons (hydrogen ions). These components perform numerous important functions including flavor enhancement, control of microbial growth, inhibition of browning, alteration of texture, prevention of lipid oxidation, and pH control.
Acids and bases are key metabolites in living plant and animal organisms, for example as intermediates in the TCA cycle, and are mostly retained when the plant is harvested or the animal is slaughtered so they are naturally present in foods. They may also be added during processing or synthesized during fermentation to produce desired characteristics in the final food product.
The concentration and relative proportion of acids and bases determine the pH of a food, an extremely important characteristic. pH can affect the flavor, color, texture, stability, and behavior in food processing situations. For example, commercial sterilization of acid foods (pH less than 4.6) [1] can be achieved under milder processing conditions than in foods with a higher pH.
1.2.1 Acids
Acids serve a variety of functions in foods including flavor enhancement, control of microbial growth, protein coagulation, emulsification, control of browning, buffering action, and metal chelation (to control lipid oxidation). All acids have a sour taste but different acids produce distinctively different sour flavors. Thus, it is not enough to simply add any acid when attempting to produce a characteristic sour flavor in a food. Table 1.1 gives structures and pK values of some common food acids.
Table 1.1 Acids common in foods: structures and pKa values.
| Substance | Structure | pKa | Food found in |
|---|---|---|---|
| Acetic acid |
 |
pK = 4.75 | Vinegar, figs |
| Adipic acid |
 |
pK1 = 4.43 pK2 = 5.62 | Beets |
| Butyric acid |
 |
pK = 4.82 | Cheese, butter |
| Citric acid |
 |
pK1 = 3.06 pK2 = 4.74 pK3 = 5.40 | Oranges, lemons, apricots, tomatoes |
| Lactic acid |
 |
pK = 3.83 | Yogurt, buttermilk, cheese, beer |
| Malic acid |
 |
pK1 = 3.40 pK2 = 5.05 | Apples, apricots, grapes, oranges, tomatoes |
| Oxalic acid |
 |
pK1 = 1.27 pK2 = 4.27 | Spinach, potatoes, tomatoes |
| Phosphoric acid |
 |
pK1 = 2.12 pK2 = 7.21 pK3 = 12.32 | Tomatoes, acidulant used in soft drinks |
| Tartaric acid |
 |
pK1 = 2.98 pK2 = 4.34
|
