Analysis of Feedstuff Flashcards
Nutrient
Chemical element in the diet that is required for normal reproduction, growth, lactation, or maintenance of life processes
Analytical standard
A purified, known material or solution made from an analyte that is used in an assay and against which all sample results are compared to
Gravimetric analysis
Technique through which the amount of an analyte can be determined through the measurement of mass
What are the 2 general types of feed assays
Chemical analyses (wet chemistry) Near infrared (NIR) reflectance spectroscopy
What are 3 examples of chemical analyses
Gravimetric, spectrophotometric, chromatographic
What are 2 subdivisions of chemical analysis
Empirical fractions and specific analytes
Empirical fractions are defined by
The “fraction” or “extract” being measured
Often a mixture of compounds
Empirical assays tend to be…
Gravimetric (no analytical standard that represents a pure compound)
Empirical assays must be run using…
Standardized methods
What are the two main organizations responsible for the standardization of feed analysis
Association of Analytic Chemists (AOAC)
National Forage Testing Association
Specific analytes measure…
Specific, identifiable compounds
What are used as standards in specific analytes
Purified analytes
What are 3 types of chemical analysis that specific analytes can be measured by
Colorimetric, chromatographic, or spectroscopic
What is a proximate analysis
A combinator of analytical procedure, outdated, many limitations from a nutritional standpoint, still used by legislations for the declaration of the composition of foods in many countries
The proximate analysis divides the food into what 6 components
Moisture, crude protein, crude fat, crude fiber, ash, nitrogen-free extract
Dry matter (DM)
Material remaining after removal of moisture
Why is accurate DM values important
Allows comparisons of the nutrient composition among different feeds
What is the most common method to measure the moisture content of feed
Drying a known weight of food to constant weight at 105C
How is crude protein content calculated
From the total nitrogen multiplied by a specific factor
How is total nitrogen often determined
By the Kjeldahl or dumas combustion method
What is the factor that N content is multiplied by to get crude protein
5.3-6.38 (originally 6.25 based on the assumption that proteins contain 16 percent N)
Why is crude protein not true protein
The methods for determining it use N from sources other than protein, such as free amino acids, amines and nucleic acids
Explain the Kjeldahl procedure
Organic matter is digested with concentrated sulphuric acid
Catalyst mixture is added
All N is converted to ammonia (except nitrate/nitrite)
Ammonia ionized to ammonium
Ammonium is collected and measured colorimetrically/by titration
Explain the Dumas/combustion method
Sample is combusted
N is converted to N gas
Other volatile compounds are trapped and separated
Measures N gas
What are some downsides to the Kjeldahl method
Time consuming and involves the use of hazardous chemicals
What are some downsides to Dumas method
Expensive
Ether extraction
Ground dry samples are extracted with diethyl ether for more than 4 hours
The residue after evaporation is the ether extract
Ether soluble materials include…
A large variety of organic compounds, many of which may not have nutritional significance
Crude fiber is determined by…
Using the ether extracted sample, boiling in dilute acid, dilute base, filtering, drying and burning in a furnace
Crude fiber fraction
Different in weight before and after burning
Crude fiber contains…
Cellulose, hemicellulose and lignin.
Ash
The residue after all combustible material has burned off - inorganic matter in feed
Ash in feed samples comes from…
Minerals in plant cells, added minerals, soil contamination, or from biogenic silica
Organic matter is calculated as…
The difference of its dry matter and ash content, expressed as a percent
Nitrogen free extract is determined by…
The difference between the original sample weight and the sum of the weight of moisture, crude protein, ether extract, crude fiber and ash
NFE is made primarily of…
Readily available carbs (sugars, starches, fructans, pectins and organic acids), and hemicellulose and lignin
What is a major drawback of NFE
It is calculated as a difference, so it is prone to large errors
Fiber commonly refers to…
Hemicellulose, cellulose and lignin
Neutral detergent extraction (NDF) contains…
Cellulose, hemicellulose, and lignin (major cell wall components)
In NDE, the nonsoluble material is…
The NDF
Why are amylase and sulfite used in NDE
Amylase removes starch and sulfite breaks disulfide linkages to remove proteins
This results in less contaminating material
When is sodium sulfite not used in NDE
To produce residue on which neutral detergent-insoluble nitrogen can be measured
Acid detergent fiber is composed of…
Cellulose, lignin and acid detergent-insoluble nitrogen (ADIN)
Why is ADF useful for forages
There is a good correlation between in and forage digestibility
ADIN an be used to estimate…
undigestible or heat-damaged protein in feeds
What are some properties of lignin
Reduces the digestibility of the cell wall carbs it is associated with
Linked to plant cell wall components
How do you determine acid-detergent lignin
The ADF fraction is treated with concentrated sulfuric acid, dissolving cellulose
The residue is ashed and determined crude lignin
What are 2 ways to determine amino acid composition in feedstuff
HPLC or IEC
Maillard reaction
Reduces biological value of protein, lysine becomes nutritionally unavailable
What 2 groups are used to measure the sugar fraction
WSC and 80% ESC (WSC preferred bc of fructans)
What is NIR spectroscopy
Involves shining NIR light on ground feed samples and detecting the reflected light
What is the wave length of NIR
730-2500nm
NIR should only be performed on feed samples for which…
Adequate calibrations (known curves) are available
What are some benefits to NIR
Useful, less time, less expensive than chemical analyses
