General approach to measurements
of meat and meat products
1. Sampling
2. Analytical methods
Sampling – Composite sample consisting of several
sub-samples
– Combine sub-samples (slices, links,
packages, scoops, handfulls, etc.) ---grind,
mix, blend --- take test samples in duplicate
or triplicate for analyses. Calculate mean or
average of the test samples for product
value.
BUT…how many sub-samples are needed?
Number of sub-samples
– Determined by variation among the subsamples
– Need to know variance or standard
deviation
– Standard deviation essentially tells the
range of values
 1 std. Dev. = 67 % of values in a
normal distribution
 2s
 3s
= 95 %
= 99 %
Therefore 6 s = full range
Determining the number of
sub-samples needed
n= 3s
E
2
n = number of sub-samples
s = standard deviation of sub-samples
E = error tolerated
Example:
s = 1%
E = 1%
n= 3x1
1
2
= 9 sub-samples
More variability in sub-samples
s = 2%
E = 1%
n= 3x2
1
2
= 36 sub-samples
More accuracy (less error) desired
s = 1%
E = 0.5 %
n= 3x1
0.5
= 36 sub-samples
Preparation of sub-samples to
form composite
Sources:
1. American Society for Testing and
Materials (ASTM)
2. AOAC International
previously known as - Association of
Official Analytical Chemists
3. USDA
– Meat and Poultry
Recommended procedures for sample
prep. of meat and poultry products
– AOAC
1. meat grinder with 1/8 inch plate / mix 3-5 times
– dependent on product
2. bowl cutter
– chill all parts before use
3. Small food choppers with enclosed bowls
(cuisinart, Robot Coupe)
– 4 - 30s bursts with scraping the bowl between each
– USDA
– grind 3 times with 1/8 inch plate or smaller
– beware fat smearing, water evaporation
Sample prep - laboratory
– Liquid nitrogen / Waring Blender
• ultimate in uniformity
• excellent for research samples especially if
stored frozen
• beware rapid thawing and evaporation
Analytical methods
– Two choices ….
a. Official methods
• evaluated and endorsed by AOAC International and
others (American Society for Testing and Materials,
American Oil Chemists Society, etc.)
• accurate and precise but often tedious and time
consuming
• necessary for USDA accredited laboratories
Analytical methods (continued)
b. Rapid methods
• quick and easy, often not as accurate or precise
Methods evaluation
– Repeatability
• standard deviation of measurements done on
the same sample by the same individual /
laboratory
– Reproducibility
• standard deviation of measurements done on
the same sample by different individuals /
laboratories
– Bias
• constant high / low values