juice is poured into 3 to 5 tablespoons of alcohol. Sometimes equal quantities
of juice and alcohol are used, but the larger amount of alcohol gives a
better test. Turn the container gently from side to side. If a test tube or
graduated cylinder is used it can be turned slowly upside down and back
to bring all the juice in contact with the alcohol. If the pectin comes down
in a solid mass there is a sufficient quantity to make jelly. If the pectin is
flocculent or in small flakes the juice needs boiling down to concentrate the
pectin.
Johnston and Denton have reported that the amount of alcohol precipi-
tate in citrus pectin extracts does not indicate the jellying power. It may
also be possible that the amount precipitated in different juices will show
different jellying strengths. Of course, alcohol precipitates such substances
as gums and starch in addition to the pectin. The precipitated mass becomes
firmer after standing in the alcohol a few minutes, so the estimate should
be made just after mixing.
For the pectin test, straight ethyl alcohol, denatured, or wood alcohol
can be used. The denatured alcohol is better to use than the wood alcohol
and usually gives a satisfactory test. When wood alcohol is used, the
precipitated pectin may be redissolved after standing a few minutes. This
may also be true of some denatured alcohol.
Pectin test by viscosity. Based on the observed correlation of the
viscosity of pectin solutions with the jellying power of the pectin, Baker
has developed a jelmeter. The viscosity of the fruit juice is determined
by the rate of flow of the juice through a given orifice compared with the
time of flow of an equal quantity of water at the same temperature. The
viscosity or thickness of the fruit juice is dependent principally upon its
pectin concentration, although sugars, starches, and proteins influence it
slightly. If the approximate viscosity is known, then the amount of sugar
to use and the weight to which the jelly should be cooked can be determined.
Baker has prepared such tables.
The jelmeter is similar to a graduated pipette. The test is easy to make
and practical. It works satisfactorily with the fruit juices that have been
tested.
Effect o£ high temperatures and a long period of heating upon
pectin. Numerous investigators, among them Johnston and Denton,
Sucharipa, and Tarr, have found that high temperatures decrease the jelly-
ing power of pectin. Myers and Baker state that "Prolonged heating of
pectin solution has a deleterious effect on the jellying power of the solution.
The higher the temperature the greater the decrease in jellying power
of the pectin." They find that heat has the same effect on the powdered
pectin as upon the pectin in solution.
The boiling of a pectin solution with acid decreases the amount of pectin
in the solution because of the formation of pectic acid by hydrolysis. Some
of Tarr's data seem to indicate that, if the sugar is in the juice during
COMMERCIAL PECTIN
159
Page 128
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juice is poured into 3 to 5 tablespoons of alcohol. Sometimes equal quantities
of juice and alcohol are used, but the larger amount of alcohol gives a
better test. Turn the container gently from side to side. If a test tube or
graduated cylinder is used it can be turned slowly upside down and back
to bring all the juice in contact with the alcohol. If the pectin comes down
in a solid mass there is a sufficient quantity to make jelly. If the pectin is
flocculent or in small flakes the juice needs boiling down to concentrate the
pectin.
Johnston and Denton have reported that the amount of alcohol precipi-
tate in citrus pectin extracts does not indicate the jellying power. It may
also be possible that the amount precipitated in different juices will show
different jellying strengths. Of course, alcohol precipitates such substances
as gums and starch in addition to the pectin. The precipitated mass becomes
firmer after standing in the alcohol a few minutes, so the estimate should
be made just after mixing.
For the pectin test, straight ethyl alcohol, denatured, or wood alcohol
can be used. The denatured alcohol is better to use than the wood alcohol
and usually gives a satisfactory test. When wood alcohol is used, the
precipitated pectin may be redissolved after standing a few minutes. This
may also be true of some denatured alcohol.
Pectin test by viscosity. Based on the observed correlation of the
viscosity of pectin solutions with the jellying power of the pectin, Baker
has developed a jelmeter. The viscosity of the fruit juice is determined
by the rate of flow of the juice through a given orifice compared with the
time of flow of an equal quantity of water at the same temperature. The
viscosity or thickness of the fruit juice is dependent principally upon its
pectin concentration, although sugars, starches, and proteins influence it
slightly. If the approximate viscosity is known, then the amount of sugar
to use and the weight to which the jelly should be cooked can be determined.
Baker has prepared such tables.
The jelmeter is similar to a graduated pipette. The test is easy to make
and practical. It works satisfactorily with the fruit juices that have been
tested.
Effect o£ high temperatures and a long period of heating upon
pectin. Numerous investigators, among them Johnston and Denton,
Sucharipa, and Tarr, have found that high temperatures decrease the jelly-
ing power of pectin. Myers and Baker state that "Prolonged heating of
pectin solution has a deleterious effect on the jellying power of the solution.
The higher the temperature the greater the decrease in jellying power
of the pectin." They find that heat has the same effect on the powdered
pectin as upon the pectin in solution.
The boiling of a pectin solution with acid decreases the amount of pectin
in the solution because of the formation of pectic acid by hydrolysis. Some
of Tarr's data seem to indicate that, if the sugar is in the juice during
COMMERCIAL PECTIN
159