Lecture 2 Flashcards
What is food analysis?
The development, application and study of analytical methods for characterizing foods and their constituents
Why is food analysis important?
Information about foods, produce foods that are safe and nutritious, allow the consumer to make informed decisions
Government regulations ensure quality of the foods, ensure food industry makes safe foods with high quality, there is fair competition between companies, eliminates economic fraud
Quality control ensure food composition doesn’t change, characterize raw materials
What are the six components to proximate analysis?
- Moisture
- Ether extract
- ASH
- Nitrogen
- Crude Fibre
- NSE
What is the formula for moisture?
%Moisture = [(wet weight - dry weight)/wet weight] x 100%
What is the formula for %Dry Matter?
%Dry Matter = 100% - %Moisture
Why is determining water content in feed important?
Water weight (price and shipping)
Moisture in storage
Too much - food spoils quickly
Too little - food is less palatable
Moisture dilutes energy and nutrients in food
Moisture is important for optimum intake/performance of animals
How is the first component (moisture) created?
Feed sample is air dried to separate the dry matter and moisture
What are the potential error/limitations of moisture?
Drying can remove other volatile compounds (SC FA, minerals) which can cause a slight under-estimation of dry weight
How is ether extract created?
Feed sample is air dried to create moisture and dry matter, an organic solvent (ether) is incorporated into the dry matter and separates it into two precipitates and the one on top is used to extract the fat
What is the formula for ether extract/crude fat %?
%Crude fat = [(weight of their extract)/wet weight of sample] x 100%
What are the potential sources of error in the ether extract/crude fat component?
- other things are soluble in organic solvents such as chlorophyll, resins, waxes, plants which could over-estimate crude fat determination
- newer and more sensitive methods now exist
How is ASH extracted?
From the precipitates created from the organic ether solvent, the bottom precipitate is ignited (to get rid of anything w carbon = organic)
Why is it important to measure ASH content?
Nutritional labelling
Quality/taste of food
Microbiological stability
Nutritional requirements
Manufacturer processing
What is the formula for ASH (mineral content)
%ASH = [(weight of ASH)/wet weight of sample] x 100%
What are the potential sources of error/limitations for ASH (mineral content)?
- volatile minerals may be lost when burning the residue
- no information about the individual minerals
(It is now mandatory for food labels to indicate sodium content)
How is the nitrogen component extracted?
Kjedal’s analysis
What are the two assumptions made for Kjedahls analysis?
- All nitrogen is in protein
- All protein contains 16% nitrogen
What are the three steps for Kjeldahls analysis?
- Digestion - a food sample is mixed with sulfuric acid, which converts nitrogen to ammonia
- Distillation - separates the ammonia
- Titration - quantifies the amount of ammonia
What is the formula for % crude protein?
%Crude Protein = [(N in sample x 6.25)/wet weight of sample] x 100%
6.25 is the conversion factor, it is calculated by 100% (total protein) / 16% nitrogen percentage = conversion factor
What are the potential sources of error in the Kjeldahl analysis?
- Assumes proteins have 16% nitrogen, the actual range is 13-19% therefore the conversion factor could change
- Other sources of nitrogen are found in nitrites, urea, nucleic acids etc. therefore this would slightly over-estimate crude protein content
What is the process in extracting crude fibre?
Ether extraction of dry matter is then boiled in acid, the residue is then boiled in alkali, lastly the product of that is ASH + Crude fibre, this is ignited to separate ASH and crude fibre, the crude fibre is then analyzed
What is the formula for crude fibre content?
%Crude fibre = [(weight of ASH + Crude Fibre) - (weight of ASH)/wet weight of sample] x 100%
What is the difference between crude fibre and dietary fibre?
Crude fibre tells us about the cellulose and lignin content (insoluble fibres) Dietary fibres is used to describe all fibres (both soluble and insoluble)
What is the potential source of error in crude fibre?
Unable to distinguish different fibre components. Measuring crude fibre under-estimates the actual dietary fibre content of feed by up to 50%
What are insoluble vs. Soluble dietary fibres?
Insoluble: Cellulose, lignin, hemicellulose
Soluble: Pectins, Gums, Mucilages
What are the benefits of insoluble vs soluble dietary fibres?
Insoluble: regulates bowel movements, maintains pH, removes toxins, reduces constipation, does not dissolve in water, remains intact through intestinal tract
Soluble: regulates blood sugar, reduces cholesterol, forms gel, does dissolve in water
What is the formula for Nitrogen free extract (NFE)
Digestible Carbohydrate content = %NFE = 100% - (%moisture + %crude fat + %ASH + %crude protein + %crude fibre)
What are the potential sources of error/limitations in NFE?
NFE accumulates all of the errors that exist in other components
What are the pros and cons to proximate analysis?
Pro: still used as the basis for human food labelling and animal feed analysis, has prompted the development of more advanced analytical assays to improve food characterization
Cons: No information on the digestibility of food/feed, no information on specific amino acids, minerals, lipids, carbs
What is the formula for digestible carbohydrates in grams
(Total wet weight) x (NFE percentage in decimal form)
What are the two more accurate fibre analyses to complement the proximate analysis?
- Van Soest method
- Southgate method
What is the Van Soest method?
Fibre analysis in feeds, not used in human food analysis, differentiates between insoluble fibres (cellulose and hemicellulose) and (lignin), determines fermentable and non-fermentable CHO
What is the Southgate Method?
Provides information about sugars, starch and various fibres, useful for human nutrition and food labeling, does not differentiate sufficiently between various insoluble fibre components adequately, so this method is not used for agricultural applications
