NUTR 405
Proximate Analysis Lecture
, Proximate Analysis Lecture
1. List the five proximate components, their importance to food analysts, and the various methods/apparatus that each
can be determined. **just the methods/apparatus that we covered in lab-not the numerous other methods of analysis that
are covered in the text book
Proximate Analysis: quantitative analysis of any food to determine the percentage of its components
o Determine moisture, ash, fat, protein and carbohydrate content of a food
o Conducted with official methods – Association of Official Analytical (AOAC), American Association for
Clinical Chemistry (AACC), American Oil Chemists Society (AOCS)
Moisture: food item – moisture = total solids – natural food (~70%), fruits and veggies (~95%)
o Role of water in food: texture – either the presence or absence of water
o States of water in food: free water, bound water, adsorbed
o Relevance of measuring water: determine food quality, food stability and preservation, microbial stability, legal
requirements/labeling (QC and QA, flour 12-15%), economic
o Method to determine: oven drying (vacuum or convection ovens), freeze drying (sublimation)
o How to calculate: (amount lost/original wet weight) * 100 = % moisture
Fat: relevance of measuring lipids – nutritional information/labeling, lipid oxidation, physical characteristics of foods, food
quality
o Methods to determine fat content:
1. Goldfisch – continuous, gold standard, food analysis
2. Soxhlet – semi continuous
3. Mojonnier – discontinuous
o How to calculate: (weight of lipid extracted/sample weight) * 100 = % fat
Protein: relevance of measuring protein – determine total protein/individual AAs, investigate functional properties,
nutrition labeling
o Methods to determine protein content:
1. Kjeldahl – gold standard
2. Dumas – combustion reduction purification detection, much faster than kjeldahl (4min v. 1-2hrs)
• Actually measuring nitrogen – nitrogen conversion factor (5.3)
3. Bradford – not very conclusive, can be time consuming
Ash: ash content v. mineral content, relevance of measuring ash – nutrition labeling, quality of raw products, microbial
stability, nutrition, processing
o Method to determine ash content:
1. Wet ashing – strong acids + heat
2. Dry ashing – muffle furnace (500-600 C for > 24 hours (AOAC)
o How to calculate: (dry weight/original wet weight) * 100 = % ash
Carbohydrate: classification of CHOs, sweetness appearance, texture
o Relevance of measuring CHOs – nutritional labeling, standards of identity, food quality, economic
o Methods to determine carbohydrate content:
1. Indirect measurement – total % carbohydrate by difference (100 – (%fat + %protein + %ash + % h20 in
100 g food))
2. Direct measurement – sum of weight of individual CHO + fiber via
• Chromatographic + electrophoretic methods
• Chemical methods
• Titration methods
• Enzymatic methods
Equipment Overview
Proximate Analysis Lecture
, Proximate Analysis Lecture
1. List the five proximate components, their importance to food analysts, and the various methods/apparatus that each
can be determined. **just the methods/apparatus that we covered in lab-not the numerous other methods of analysis that
are covered in the text book
Proximate Analysis: quantitative analysis of any food to determine the percentage of its components
o Determine moisture, ash, fat, protein and carbohydrate content of a food
o Conducted with official methods – Association of Official Analytical (AOAC), American Association for
Clinical Chemistry (AACC), American Oil Chemists Society (AOCS)
Moisture: food item – moisture = total solids – natural food (~70%), fruits and veggies (~95%)
o Role of water in food: texture – either the presence or absence of water
o States of water in food: free water, bound water, adsorbed
o Relevance of measuring water: determine food quality, food stability and preservation, microbial stability, legal
requirements/labeling (QC and QA, flour 12-15%), economic
o Method to determine: oven drying (vacuum or convection ovens), freeze drying (sublimation)
o How to calculate: (amount lost/original wet weight) * 100 = % moisture
Fat: relevance of measuring lipids – nutritional information/labeling, lipid oxidation, physical characteristics of foods, food
quality
o Methods to determine fat content:
1. Goldfisch – continuous, gold standard, food analysis
2. Soxhlet – semi continuous
3. Mojonnier – discontinuous
o How to calculate: (weight of lipid extracted/sample weight) * 100 = % fat
Protein: relevance of measuring protein – determine total protein/individual AAs, investigate functional properties,
nutrition labeling
o Methods to determine protein content:
1. Kjeldahl – gold standard
2. Dumas – combustion reduction purification detection, much faster than kjeldahl (4min v. 1-2hrs)
• Actually measuring nitrogen – nitrogen conversion factor (5.3)
3. Bradford – not very conclusive, can be time consuming
Ash: ash content v. mineral content, relevance of measuring ash – nutrition labeling, quality of raw products, microbial
stability, nutrition, processing
o Method to determine ash content:
1. Wet ashing – strong acids + heat
2. Dry ashing – muffle furnace (500-600 C for > 24 hours (AOAC)
o How to calculate: (dry weight/original wet weight) * 100 = % ash
Carbohydrate: classification of CHOs, sweetness appearance, texture
o Relevance of measuring CHOs – nutritional labeling, standards of identity, food quality, economic
o Methods to determine carbohydrate content:
1. Indirect measurement – total % carbohydrate by difference (100 – (%fat + %protein + %ash + % h20 in
100 g food))
2. Direct measurement – sum of weight of individual CHO + fiber via
• Chromatographic + electrophoretic methods
• Chemical methods
• Titration methods
• Enzymatic methods
Equipment Overview
