Analysis c3

• pH


  Measure of the acidity or basicity of a solution
• Titratable acidity

  Measurement of the total acid concentration contained within a food

  
• Titratable acidity is a better predictor of an acid's impact on flavour than pH
• Molarity (M)

  The number of moles of the solute per liter of solution
• Normality (N)


  A concentration unit representing the number of equivalents (Eq) of a solute per liter of solution
• Percentage concentrations


  The mass amount of solute or analyte per 100 mL of 100 g of material
• Preparation of solution in %

  1. 1 g sugar diluted to 100 g solution

  2. 1 g salt diluted to 100 ml solution

  3. 4 ml ethanol diluted to 100 ml solution
• Equivalents

  The molecular weight divided by the number of equivalents in the reactions
• Examples of molarity vs normality


  • 1 M H2SO4 = 2N H2SO4
  • 1 M NaOH = 1 N NaOH
• Acid

  A substance capable of donation protons (A proton donor)
• Base


  A substance capable of accepting protons (A proton acceptor)
• Neutralization

  The reaction of acid with a base to form a salt
• Neutralization reaction


  • HCl + NaOH → NaCl + H2O
• Phenolphthalein

  Used to approximate the equivalent point in titrations
• Indicators and their pH ranges

  • Thymol blue (first transition): Red (1.2 – 2.8) to Yellow

  Methyl red: Red (4.4 – 6.2) to Yellow

  Bromothymol blue: Yellow (6.0 – 7.6) to Blue

  Thymol blue (second transition): Yellow (8.0 – 9.6) to Blue

  Phenolphthalein: Colorless (8.3 – 10.0) to Fuchsia
• Standard Alkaline (NaOH)


  • Very hygroscopic, often contains sodium carbonate, can react with CO2, glass containers should be avoided
• Standard Acid

  • Potassium acid phthalate (KHP) is commonly used, HCl is also commonly used
• Sample Analysis

  An aliquot of sample (often 10 ml) is titrated with a standard alkaline solution (often 0.1 N NaOH) to a phenolphthalein endpoint

  Potentiometric endpoint is used when sample pigment makes use of a color indicator impractical
• Acid can exist at levels below detection limits or can be the preeminent substance present in the food
• The contribution of acids to food flavour is not indicated by acid content alone
• Brix / Acid Ratio

  Better predictor of food tartness than acid content alone
• Acids tend to decrease with the maturity of fruit while sugar content increases