Food Acids, pH, Total Acidity, and Buffer systems

What is the importance of acids in foods?

• taste: sourness/tartness

• appearance: some pigments change color

• safety: microbial inhibition

• emulsions and foams: influences stability

• gel formation: pectin gels, cheese

• carbohydrate hydrolysis (acid + heat)

• leavening: reacts with base to form CO2

• buffering: ability to resist changes in acidity

How can you recognize the general structure of food acid?

• look for hydrogens that can dissociate

• COOH

• R-COOH

• hydrogen ions

What is the difference between an acid and a base?

• an acid is a proton donor and a base is a proton acceptor

• acids have a tendency to release (H⁺) and bases have a tendency to capture (OH^-)

What is pH?

• a scale developed for convenience in working with the extremely small numbers representing hydrogen ion concentration

• negative log og the hydrogen ion concentration

How do you calculate pH?

pH = -log(H⁺)

How can you calculate (OH^-)?

• [H⁺][OH^-] = 1 × 10-14

• [OH^-] = 1 × 10-14/[H⁺]

How do you calculate [H⁺] from pH?

[H⁺] = 10^-pH

What is a weak acid?

• have at least one H⁺ that does not completely ionize

• most food acids are weak acids

What is a strong acid?

• have at least one H+ that completely ionizes

• examples: hydrochloric, nitric, phosphoric, sulfuric

What is total acidity?

• concentration of both ionized H+ and unionized H+

• normality is the concentration term used

• measured by titration with a base

• also known as titratable acidity

What is active acidity?

• concentration of ionized H+ present at a given time

• pH is the concentration term used for active acidity

• measured electronically (pH meter) or by color change (litmus paper)

What is a buffer system?

• a chemical system that resists changes in hydrogen ion concentration (pH0

• examples

  • a weak acid and its salt

  • proteins, because some amino acid side chains have ionizable groups

Why are buffers important?

• used to achieve similar “sour” levels at different pH values

• protein solubility and functionality is affected by pH

• many chemical reactions, especially those in biological systems, proceed best at a particular pH

How does a buffer system work?

• when an acid is added: The conjugate base in the buffer reacts with the extra H⁺ ions, preventing a significant pH drop.

• when a base is added: The weak acid in the buffer donates H⁺ ions, neutralizing the OH⁻ and preventing a large pH increase.