Goldthwaite has reported that, when tartaric and citric acids w^ere used to
acidify fruit juices deficient in acid, tartaric acid gave better results, the
texture and flavor being better than when citric acid was used. Tarr's
results confirm Goldthwaite's observations. Spencer explains this difference
in the following manner. Since pectin sols are partially stabilized by a
negative charge, the preferential absorption of one anion above that of
another would increase the stability of the pectin sol. In other words, the
citrate ion is more strongly absorbed than the tartrate ion, hence increases
the negative charge on the pectin to a greater extent, making it more stable,
less easily precipitated, so that a weaker jelly is obtained with citric acid
than tartaric, if the same concentrations of pectin and sugar are used.
Methods of reporting acidity of fruit juices. Investigators have
reported concentration of acids required for jelly in different ways. The
/»H gives the concentration of hydrogen ion or ionized part of the acid.
Some report acid as number of cubic centimeters per 100 grams of jelly.
However, work done some time ago was usually reported in percentage of
ROLE OF SALTS IN JELLY FORMATION 163
some acid, not necessarily the one found in the fruit. It has often been
reported as sulfuric acid. The concentration of the acid is determined by
titration with an alkali ; from the quantity of alkali required the percentage
of acid is calculated. Campbell states that 0.3 per cent as sulfuric acid
is required to produce a jelly of good quality, the minimum being 0.27
and the maximum 0.5 per cent. Goldthwaite has reported from 0.154 to
1.892 per cent as sulfuric acid. Singh has reported still lower percentages
of acids than these, but his jellies with a very low percentage of acid
contain an unusually high percentage of pectin.
The Effect of Temperature to Which Pectin Is Heated
on Jelly Strength
Olsen states that the abnormally high jelly strength with pectin heated
to only 55°, shown in Table 22, is not the result of the time factor alone.
To prove this he recovered the pectin from duplicate batches of jelly, one
of which had been heated to 100° and poured; the other poured at 50°C.
The recovered pectins were remade into jelly at 50°. Both gave jellies test-
ing as high in strength as the original jelly poured at 50 °C. This proved
that the lesser strength of the pectin heated to 100° was not due to hydrol-
ysis of the pectin but the effect of temperature upon the gel structure. From
these results Olsen concludes that "the structure of jelly is fundamentally
different when slowly set from the hot solution than when rapidly set from
the cool sirup. If we assume that pectin exists in two states of hydration;
that is, if the amount of water bound by the pectin fibrils differs depending
upon the temperature at which the pectin is precipitated, then a ready ex-
planation is at hand."
These results are not to be interpreted as showing that hydrolysis of the
pectin does not occur with long boiling but that none takes place with a
short-boil process.
The Role of Salts in Jelly Formation
The role salts play in jelly formation is not emphasized as much as
that of pectin, acid, and sugar, but it is an important one. All fruit juices
contain salts of the acids found in the fruit. In addition to these, other
salts may be found.
Page 132
Presented as published in 1932. Historical recipes may not meet modern food-safety standards. Cook from the modern interpretation, not the original instructions.
AI-modernized reading of the original text
A modernized reading is not available for this page yet. You are seeing the original text.
Goldthwaite has reported that, when tartaric and citric acids w^ere used to
acidify fruit juices deficient in acid, tartaric acid gave better results, the
texture and flavor being better than when citric acid was used. Tarr's
results confirm Goldthwaite's observations. Spencer explains this difference
in the following manner. Since pectin sols are partially stabilized by a
negative charge, the preferential absorption of one anion above that of
another would increase the stability of the pectin sol. In other words, the
citrate ion is more strongly absorbed than the tartrate ion, hence increases
the negative charge on the pectin to a greater extent, making it more stable,
less easily precipitated, so that a weaker jelly is obtained with citric acid
than tartaric, if the same concentrations of pectin and sugar are used.
Methods of reporting acidity of fruit juices. Investigators have
reported concentration of acids required for jelly in different ways. The
/»H gives the concentration of hydrogen ion or ionized part of the acid.
Some report acid as number of cubic centimeters per 100 grams of jelly.
However, work done some time ago was usually reported in percentage of
ROLE OF SALTS IN JELLY FORMATION 163
some acid, not necessarily the one found in the fruit. It has often been
reported as sulfuric acid. The concentration of the acid is determined by
titration with an alkali ; from the quantity of alkali required the percentage
of acid is calculated. Campbell states that 0.3 per cent as sulfuric acid
is required to produce a jelly of good quality, the minimum being 0.27
and the maximum 0.5 per cent. Goldthwaite has reported from 0.154 to
1.892 per cent as sulfuric acid. Singh has reported still lower percentages
of acids than these, but his jellies with a very low percentage of acid
contain an unusually high percentage of pectin.
The Effect of Temperature to Which Pectin Is Heated
on Jelly Strength
Olsen states that the abnormally high jelly strength with pectin heated
to only 55°, shown in Table 22, is not the result of the time factor alone.
To prove this he recovered the pectin from duplicate batches of jelly, one
of which had been heated to 100° and poured; the other poured at 50°C.
The recovered pectins were remade into jelly at 50°. Both gave jellies test-
ing as high in strength as the original jelly poured at 50 °C. This proved
that the lesser strength of the pectin heated to 100° was not due to hydrol-
ysis of the pectin but the effect of temperature upon the gel structure. From
these results Olsen concludes that "the structure of jelly is fundamentally
different when slowly set from the hot solution than when rapidly set from
the cool sirup. If we assume that pectin exists in two states of hydration;
that is, if the amount of water bound by the pectin fibrils differs depending
upon the temperature at which the pectin is precipitated, then a ready ex-
planation is at hand."
These results are not to be interpreted as showing that hydrolysis of the
pectin does not occur with long boiling but that none takes place with a
short-boil process.
The Role of Salts in Jelly Formation
The role salts play in jelly formation is not emphasized as much as
that of pectin, acid, and sugar, but it is an important one. All fruit juices
contain salts of the acids found in the fruit. In addition to these, other
salts may be found.