Chapter 7 Determination of acidity Section 1 General

1. Concept of acidity • 1. Total acidity • 2. Effective acidity • 3.

2. Significance of acidity • Organic acid affects color, aroma, taste and stability of

3. Organic acid kinds and distribution of foods • There are organic acid and

1. Determination of total acidity • 1. 1 Principle : RCOOH + Na. OH

2. Determination of p. H • p. H test paper • p. H meter

3. Determination of volatile acid • Volatile acid: mainly acetic acid, along with trace

• Direct determination: Separating volatile acid by distillation or solvent extraction, and then

Section 3. Separation and determination of organic acids in foods

Determined methods • Gas chromatography (GC) • Ion-exchange chromatography (IEC) • High pressure liquid

Slides: 14

Download presentation

Chapter 7. Determination of acidity

Section 1. General

1. Concept of acidity • 1. Total acidity • 2. Effective acidity • 3. Volatile acid • 4. Acidity of milk

2. Significance of acidity • Organic acid affects color, aroma, taste and stability of foods. • Quality of foods can be judged by acidity. • Mature degree of some fruits can be judged by acidity.

3. Organic acid kinds and distribution of foods • There are organic acid and inorganic acid in foods, and mainly organic acid. • Familiar organic acids in foods: citric acid, malic acid, tartaric acid, oxalic acid, lactic acid and acetic acid.

Section 2. Determination of acidity

1. Determination of total acidity • 1. 1 Principle : RCOOH + Na. OH = RCOONa + H 2 O Indicator: phenolphthalein, PH 8. 2 • 1. 2 Applying range : Foods of slight color

2. Determination of p. H • p. H test paper • p. H meter

p. H meter

3. Determination of volatile acid • Volatile acid: mainly acetic acid, along with trace of formic acid, not including lactic acid, CO 2, SO 2, etc. • Content of volatile acid would increase because of fermentation of sugar. So content of volatile acid is an indicator of some foods’ qualities.

• Direct determination: Separating volatile acid by distillation or solvent extraction, and then titrate using standard alkali. • Indirect determination: removing volatile acid, and then titrate unvolatile acid.

Section 3. Separation and determination of organic acids in foods

Determined methods • Gas chromatography (GC) • Ion-exchange chromatography (IEC) • High pressure liquid chromatography (HPLC) • Thin layer chromatography (TLC)