12
Preparation
Sample preparation is critical to achieving precise and accurate test results. The
sample should be properly prepared to achieve repeatable moisture results between
duplicate analyses of the same sample. Sample preparation is either a physical or
chemical modification of the sample. Physical modification may be as simple as
stirring or shaking the sample to ensure homogeneity or more complex such as
particle size reduction, dilution or deaeration.
Chemical modification is the addition of an enzyme to hydrolyze chemically
bound fat. The objective is to create a homogeneous sample and to improve the
correlation of the test method to standard methods. Some products, such as a beef
emulsion or comminuted poultry, may require no additional preparation. Other
materials will require particle size reduction, dilution or dearation prior to testing.
Samples should be kept cool and in sealed containers to prevent loss of moisture.
If repeatable results cannot be obtained on the same sample, re-blend the sample to
improve the homogeneity and repeat tests. Sample preparation methods include:
1.
Mixing of Sample – Thoroughly stir or shake sample to ensure
homogeneity.
2.
Particle Size Reduction – Many products require particle size reduction
prior to being applied to the glass fiber pad. Reduction, based on product
sample, can be accomplished with a meat grinder, either an industrial or
consumer grade food processor, a coffee mill or a cheese grater. The
meat grinder is the best choice for all meat products. USDA procedure
specifies three to four passes through a
1
/
8
” or
5
/
64
” blade with mixing
between grinds. A USDA inspector or outside laboratory can make
recommendations. An industrial grade food processor is a good
alternative for grinding meat products. A consumer grade food processor
is ideal for grinding frozen potatoes, breaded products, or “dry” snack
foods such as cookies, crackers, and chips. A coffee mill can be used to
grind or mix “dry” snack foods. A cheese grater can be used to grate
small quantities of hard cheese samples or soap.
3.
Dilution – Products with a high carbohydrate content are strong
microwave absorbers and have a tendency to burn. These samples may
require either a water or salt dilution.
A. Water Dilution – A specified amount of sample is diluted with a
specified amount of water and mixed in a blender. Typical samples
include doughs, cheese powders, corn syrups, dried meat bases and
sauces. An external balance and a blender are required for this
procedure.
(1)
Interface an external balance with the SMART System
5
.
(2)
Tare the blender cup on the external balance.
(3)
Add product sample to the blender cup.