1. Acids and Bases (Acidity and Alkalinity)

2. Acidity Have more hydrogen ions (H+) Make foods acid Examples include:
Lemon juice
Vinegar
Other characteristics of acidic foods:
Sour taste
Sting when touched
React strongly when combined with metals
A Acids and Bases

3. Bases /Alkalinity Have more hydroxide ions (OH)
Makes foods more alkaline
Examples include:
Soap
Egg whites
Other characteristics of a alkaline:
Bitter taste
Feel slippery to touch
Do not react when combined with metals
A Acids and Bases

4. Acids and Bases identified by:
Taste sour
Turn red when tested
pH between 0 and 6.9
BASES
Taste bitter
Turn blue when teted
pH between 7.1 and 14
A Acids and Bases

5. Effects of pH on food
pH is a measure of acidity or alkalinity of food.
Changes in pH effect quality.
Color
Texture
Stability
Changes in pH effect safety
Foods are generally acidic (pH less than 7.0)
Low acid foods have a pH between 4.6 and 7.0 (potentially hazardous food)
High acid foods have a pH of 4.6 or less. (non-potentially hazardous food)
A Acids and Bases

6. A Acids and Bases

7. Methods for Reliable and Accurate Measures of pH
pH Measurement
Methods for Reliable and
Accurate Measures of pH

8. Definition of pH
A way to measure acids (acidic) and bases (alkalinity) in food.
Expression of the concentration of hydrogen (H+) and hydroxide ions (OH-) in an aqueous solution (water-based).
Uses a scale between 0 and 14
A Acids and Bases

9. Measurement Method– Litmus Paper
1. Used by dipping litmus paper into solution
2. Turns yellow to red in acidic solution (acid)
3. Turns green or blue in alkaline solution (base)
4. Easy method
5. Not completely accurate
A Acids and Bases

10. Measurement Method – Indicator Strips
Dip the strip into the aqueous (liquid) food being tested for a few seconds.
Remove strip from test solution and compare color segments to center color printed on the strip.
A Acids and Bases

11. Measurement Method – Indicator Dye
Organic dyes
Done with dropper
Acidic (acid) -- pink or red
Alkaline (base) -- green or blue
Neutral solution may turn lilac
Not totally accurate
A Acids and Bases

12. Measurement Method – pH Meter
Digital reading
Accurate
Some units are expensive
Easy and sanitary
A Acids and Bases

13. Measure Method – Titratable Acidity
1. Add base with know pH to an acid.
2. Use burette.
3. More difficult to calculate.
4. Use if have chemistry knowledge.
A Acids and Bases

14. A Acids and Bases

15. Chemical Properties Of Food
A Acids and Bases

16. Chemical Properties pH – measure of acidity and alkalinity
Total solids -- total content of suspended and dissolved solids in water
Ash -- mineral content of the food
Titratable acidity -- approximation of a solution's total acidity
Total sugars – approximation of all carbohydrates
Total fatty acids
A Acids and Bases

17. Chemical Changes
Occurs whenever new substances with different chemical and physical properties are formed.
Chemical changes result in:
Changes in color – enzymatic browning, carmelization of sugar
Changes in odor – cooked cabbage smell
Flavor changes – cooked onions, fermented foods.
Release of gas – mixing baking soda and vinegar, alcoholic beverages
A Acids and Bases