Analysis c4

• Moisture analysis

  The determination of the amount of water present in a food sample
• Total solids


  The dry matter that remains after moisture removal
• Importance of moisture analysis

  • Legal and labeling requirements
  • Economic importance
  • Microbial stability
  • Food quality
  • Food processing operations
• Moisture content requirements

  • Cheddar cheese ≤ 39% moisture
  • Pineapple juice ≥10.5° Brix soluble solids
  • Black pepper powder ≤ 12% moisture
  • Wholemeal flour ≤ 15% moisture
• Microbial stability

  Moisture content affects the growth of microbes in foods like dehydrated vegetables, dried milk, powdered eggs, spices and herbs
• Moisture as a quality factor

  Affects the texture, taste, appearance and stability of foods
• Moisture content of selected foods

  • Wheat flour, whole grain 10.3% moisture
  • Milk 88.0% moisture
  • Margarine 16.7% moisture
  • Watermelon, raw 91.5% moisture
• Moisture content equation

  % Moisture = (mass of water / mass of sample) x 100
• Forms of water in foods

  • Bulk water or free water
  • Adsorbed water
  • Chemically bound water or water of hydration
• Sample preparation for moisture determination

  • Ensure sample is representative
  • Prevent changes in sample properties
  • Prevent loss or gain of water
  • Avoid exposure to atmosphere
  • Minimize temperature fluctuations
  • Minimize heating from friction during grinding
  • Minimize headspace in storage container
• Techniques for moisture determination

  • Oven drying methods
  • Distillation methods
  • Chemical methods
  • Physical methods
• Oven drying methods


  • Moisture content depends on oven type, conditions, time and temperature
  • AOAC approved ovens include forced draft, vacuum, microwave, and infrared
• Removal of moisture by oven drying

  • Boiling point of water is 100°C
  • Dissolved solutes raise the boiling point
• Factors influencing moisture removal

  • Particle size and distribution
  • Sample size
  • Surface area during drying
• Sand pan technique

  Uses sand to prevent surface crust formation and disperse the sample
• Decomposition during oven drying

  • Carbohydrate decomposition can generate additional water
  • Sucrose hydrolysis can utilize moisture
  • Loss of volatile compounds
  • Oxidation can cause weight gain
• Temperature control in ovens

  • Non-convection ovens have greatest temperature variations
  • Forced draft ovens have least temperature differential
• Types of oven drying

  • Forced draft oven
  • Vacuum oven
  • Microwave oven
  • Infrared drying
• Forced draft oven

  • Fan forces air movement, rapid drying in 0.75-24 hrs
  • Suitable for high carbohydrate foods
• Vacuum oven

  • Wider temperature spread, drying under reduced pressure in 3-6 hrs
  • Suitable for high sugar products at 70°C
• Microwave oven

  • Rapid, precise technique, results similar to 5 hrs in vacuum oven
• Infrared drying

  • Penetrates sample, rapid analysis but not AOAC approved
• Distillation procedures

  Co-distill moisture with high boiling solvent, less thermal decomposition than oven drying
• Karl Fischer titration

  Coulometric or volumetric titration to determine trace water, rapid and sensitive
• Physical moisture determination methods

  • Electrical (dielectric, conductivity)
  • Hydrometry
  • Refractometry
  • Infrared spectroscopy
  • Freezing point
• Water activity (aw)

  Ratio of vapor pressure of water in a food to the vapor pressure of pure water, indicates microbial stability and physical properties