Proximate analysis Flashcards
what is food analysis and why is it important?
- the development, application and study of analytical methods for characterizing foods and their constituents
- important for allergies, health consequences, optimal performance, optimal health, safe and nutritious foods and consumer trust
how is food analysis applied in government regulations and quality control?
Government regulations: maintain the quality of foods, ensure the food industry makes safe food with high quality, fair competition between companies producing the same product, eliminate economic fraud
Quality control: ensure that food composition doesn’t change (decrease), characterize raw material
Nutrient Density
Nutrient-dense foods: lots of value, little calories
empty calorie foods: little value, lots of calories
- need nutrient-dense foods in a nutritious diet
true or false caloric content predicts nutrient content in food
false
What is proximate analysis?
analytical determination of moisture content, ether extract (fat content), Ash content (mineral content), nitrogen (protein content) and crude fibre
why is determining the water content in feed important?
- water is weight (part of the price of feed)
- more water weight = higher shipping cost
- storage conditions: how long food can sit on the shelf and how safe it is on the shelf
- too much moisture and food will spoil quickly
- too little moisture and the food will be less palatable
- moisture dilutes energy and nutrients in food
- moisture is important for optimum intake and performance of animals
how do you isolate the moisture content in a feed sample
- start with the feed sample (wet weight) and air dry it to get dry matter
- what you removed is the moisture (water content)
potential sources of error / limitations for determining moisture content
- drying can remove other volatile compounds like SCFAs and some minerals
- can cause a slight underestimation of drying weight
how can you mathematically determine % moisture
% moisture = (wet weight - dry weight) / (wet weight) x 100
how can you determine the % dry matter from a feed sample
dry matter = 100% - % moisture
What are the differences between human and agricultural applications of moisture content
- the agricultural industry is more interested in the composition of dry matter (animal feed)
- human food labelling is based on wet weight
how do you isolate ether extract (fat content) from a feed sample?
-treat the dry matter with an organic solvent (ether extraction) to yield the fat content
- the solution is transferred to a new tube and then dried. the solution is the fat and anything not fat would have precipitated out
how can you calculate % crude fat?
% crude fat = (weight of ether extract / wet weight of sample) x 100%
Potential source of error / limitations determining crude fat
- other things are soluble in organic solvents such as chlorophyll, resins, waxes in plants
- could over-estimate crude fat determination
why is it important to measure ASH (mineral) content?
- nutritional labelling
- quality and taste of food
- microbiological stability
- nutritional requirements
- manufacturer processing
How do you gather Ash content from a feed sample?
after the ether extraction of the dry matter, a residue is taken and ignited
- using the same solution from determining fat content, the precipitate will be used to determine mineral content
- when the tube is ignited everything that is organic is burnt off
how do you calculate ash (mineral) content?
%ASH = (wight of ASH/weight of sample) x 100%
potential sources of error / limitations for calculating ASH conctent
- volatile minerals like iron may be lost during the high-temperature burn
- no information about individual minerals (which is now mandatory) just the total
How can you isolate nitrogen (protein content) from a feed sample
- after the dry matter is produced we use it to carry out the Kjeldahl analysis to determine the nitrogen
2 assumptions are made when carrying out Kjeldahl
1. all nitrogen in the sample is in protein
2. all protein contains 16% nitrogen
STeps in the Kjeldahl 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
how can you calculate the % crude protein
% crude protein = (N in sample x 6.25)/wet weight of sample x 100%
what equation is used to estimate crude protein
nitrogen x 6.25
where do we get 6.25 from in the Kjeldahl analysis
- we assume all protein has 16% nitrogen
100%(total protein) / 16%(nitrogen) = 6.25
assume 6.25 unless given a different % nitrogen
possible sources of error / limitations of the Kjeldahl analysis
- assumes all protein has 16% nitrogen
- actual range is 13%-19% - other sources of nitrogen could be present in the sample
- nitrates, nitrites, urea, nucleic acids etc. would be in the crude protein calculation
- slightly over-estimates crude protein content
How can we isolate crude fibre from a feed sample?
- after the dry matter is collected an ether extraction is taken and boiled in acid
- a residue is taken then boiled in alkali to yield ASH + crude fibre
- the ASH + crude fibre sample is ignited and and the 2 are able to be seperated
how can you calculate crude fibre content?
%crude fibre = ((weight of ASH + crude fibre)-(wt of ASH after ignited) / wet weight of sample x 100%
what is crude fibre?
- mainly tells us about the cellulose and lignan content (insoluble fibres)
- ## we lose dietary fibres in the crude fibre analysis
difference between crude and dietary fibre
crude: tells us about insoluble fibres
dietary: describes all fibre both soluble and insoluble
Potential sources of error/limitations when calculating crude fibre
- unable to distinguish the different fibre components
- measuring crude fibre under-estimates the actual dietary fibre content of feed by up to 50%
- since dietary fibre includes a variety of components, soluble fibres are lost
What is NFE (digestible carbohydrate content?)
NFE = nitrogen free extract
- estimates starch and sugar content (digestible carbs)
how can we calculate NFE%
%NFE = 100% - (5 components added together)
Potential sources of error/limitations when calculating NFE
- NFE accumulates all previous errors from analytical analysises
What does the proximate analysis lack to provide information on?
- No info on the “digestibility” of food/feed
- don’t know what will actually be absorbed by the organism - No info on specific amino acids, minerals, lipids, or carbohydrates
- this has prompted the development of more advanced assays
what is the difference in calculations starting from wet weight vs. dry matter in proximate analysis?
wet weight: account for the original weight of the feed
dry matter: the % composition values will change but not the absolute amount in grams
what are more accurate fibre analyses that can be used to complete the proximate analysis?
- Van Soest Method
- Southgate method
Van Soest method for fibre analysis in feed
- differentiates between insoluble fibres - Cellulose and hemicellulose - lignan (poorly fermented, prevents fermentation of other fibres)
- determines fermentable and non-fermentable CHOs
- not used for human food analysis because it poorly differentiates sugars, starches and soluble fibres
- important for agriculture
Southgate method for fibre analysis in feed
- provides information about sugars, starch and various fibres
- useful for human nutrition food labelling
- doesn’t differentiate sufficiently between various insoluble fibre components adequately (therefore not used for agriculture)
What component in the proximate analysis does each group on the food label come from?
fat = crude fat (ether extract)
carbohydrate = digestible CHO (NFE)
fibre = southgate analysis
protein = crude protein (Kjeldahl)
