Development of Karl Fischer Reagents

III-2. Foodstuffs
Chapter III: Applications - 2
The food category encompasses a wide range of substances with varying
properties.
It includes agricultural, livestock and marine products and processed
products, as well as food additives. The moisture content of these items also
varies widely. It is necessary, therefore, to select the most appropriate
sample handling procedures and measurement method for each individual
product.
Test methods for foodstuffs are mostly stipulated in the JAS standards. In
most cases moisture content is measured using heating and drying
methods, but Karl Fischer titration is specified for some items. In the case of
chemically defined foodstuffs, such as sugars and additives, Karl Fischer
titration can be applied using the same methods as for normal chemicals.
Food items with complex structures, such as cereals and meats, contain not
only adhesion moisture but also moisture incorporated within cells.
Measurement results for these items are provided for your information.
Because many food items do not dissolve in organic solvents, the moisture
vaporization method is used extensively. However, foodstuffs commonly
become unstable when heated, and water may be formed as substances
break down. Care must be taken, therefore, when setting analytical
conditions.
1. Food Additives and Flavorings
Key Points
Food additives are substances used in the manufacture, processing
and preservation of foodstuffs. There are many types with varying
attributes. Most are solid, but those that dissolve in dehydrated solvents
or electrolytes can be titrated directly using Karl Fischer titration.
However, it is necessary first to determine whether or not interference
substances are present. Direct titration should be avoided in the case
of insoluble substances, and the moisture vaporization method is
recommended. As the moisture content of these substances is
generally high, volumetric titration is used.
However, coulometric titration can also be used if the sample quantity is
kept small.
When using moisture vaporization, it is necessary to set the
measurement conditions after determination of the heating temperature.
Official specifications for food additives commonly stipulate the loss-ondrying
method, so conformance with that method should be checked.
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