Acids/Bases in cooking

Why be concerned?

pH Acids and Bases

• What are the characteristics of Acids?• Think of foods that are acidic & taste:– Lemons and other citric fruit– Vinegars

• What are the characteristics of Bases?– Baking soda

• What is the reaction when you mix them?

pH scale

History

• For thousands of years people have known that vinegar, lemon juice and many other foods taste sour. However, it was not until a few hundred years ago that it was discovered why these things taste sour - because they are all acids. The term acid, in fact, comes from the Latin term acere, which means "sour".

• Bases taste bitter.

[H+] pH Example  

Acids

1 X 100 0 HCl

1 x 10-1 1 Stomach acid

1 x 10-2 2 Lemon juice

1 x 10-3 3 Vinegar

1 x 10-4 4 Soda

1 x 10-5 5 Rainwater

1 x 10-6 6 Milk

Neutral 1 x 10-7 7 Pure water

Bases

1 x 10-8 8 Egg whites

1 x 10-9 9 Baking soda

1 x 10-10 10 Tums® antacid

1 x 10-11 11 Ammonia

1 x 10-12 12 Mineral lime - Ca(OH)2

1 x 10-13 13 Drano®

1 x 10-14 14 NaOH

NAMES TO KNOW

• Here are a couple of definitions you should know:Acid: A solution that has an excess of H+ ions. It comes from the Latin word acidus that means "sharp" or "sour". Base: A solution that has an excess of OH- ions. Another word for base is alkali.Aqueous: A solution that is mainly water. Think about the word aquarium. AQUA means water.

• http://chemistry.about.com/

Acid and Bases

• Effect of Acids and Bases on the Browning of Apples - Chemistry Experiments

• By Anne Marie Helmenstine, Ph.D., About.com

Supplies for the experiment

• Five slices of apple (or pear, banana, potato, or peach)

• Five plastic cups or other clear containers • Vinegar (or dilute acetic acid) • Lemon juice • Solution of baking soda • Solution of milk of magnesia and water• Water • Graduated cylinder or measuring cups

Day 1

• Label the cups: – Vinegar – Lemon Juice – Baking Soda Solution – Milk of Magnesia Solution – Water

• Add a slice of apple to each cup. • Pour 50 ml or 1/4 cup of a substance over the apple in its

labeled cup. You may want to swirl the liquid around the cup to make sure the apple slice is completely coated.

• Make note of the appearance of the apple slices immediately following treatment.

• Set aside the apple slices for a day.

Day 2

• Observe the apple slices and record your observations. It may be helpful to make a table listing the apple slice treatment in one column and the appearance of the apples in the other column. Record whatever you observe, such as extent of browning (e.g., white, lightly brown, very brown, pink), texture of the apple (dry? slimy?), and any other characteristics (smooth, wrinkled, odor, etc.)

• If you can, you may want to take a photograph of your apple slices to support your observations and for future reference.

• You may dispose of your apples and cups once you have recorded the data.

Results

• What does your data mean? Do all of your apple slices look the same? Are some different from others? If the slices look the same, this would indicate that the acidity of the treatment had no effect on the enzymatic browning reaction in the apples. On the other hand, if the apple slices look different from each other, this would indicate something in the coatings affected the reaction. First determine whether or not the chemicals in the coatings were capable of affecting the browning reaction.

Sharing results

• If an effect was observed (results), draw a conclusion about the type of chemical (acid? base?) capable of inactivating the enzymatic reaction.

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[H+] pH Example  

Acids

1 X 100 0 HCl

1 x 10-1 1 Stomach acid

1 x 10-2 2 Lemon juice

1 x 10-3 3 Vinegar

1 x 10-4 4 Soda

1 x 10-5 5 Rainwater

1 x 10-6 6 Milk

Neutral 1 x 10-7 7 Pure water

Bases

1 x 10-8 8 Egg whites

1 x 10-9 9 Baking soda

1 x 10-10 10 Tums® antacid

1 x 10-11 11 Ammonia

1 x 10-12 12 Mineral lime - Ca(OH)2

1 x 10-13 13 Drano®

1 x 10-14 14 NaOH

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