Unit 2: Processing Food by Sugar Concentration
Topic: Testing Pectin Content
Learning Outcomes:
1. Identify the different test to know the pectin content
of fruit juices.
2. Explain the importance of testing the pectin and acid
content of fruits and fruit juices
Concept Digest (Discussion)
Definition of Terms
For better understanding of the lesson, take a look at the
word meanings below.
1. Acid – a substance that makes the structure of jelly is
firm and rigid.
2. Denatured Alcohol- a type of alcohol from wood that is
used to determine the pectin content of fruit/vegetable
juice. It is usually available in hard ware shops.
3. Gel – a colloidal dispersion of a solid in a liquid which
may range from the nearly liquid to the solid state, but is
typically a semi-solid and a jelly-like consistency.
4. Gel meter - is an instrument similar to a graduated
pipette, where fruit juice is allowed to run down the Gel
meter tube for one minute to test the pectin content.
Testing Pectin Content
To find out if a fruit has high or low pectin content, any
of the following tests may be performed:
1. Cooking test – Boil a small amount of juice with sugar.
If gel sets, then it is rich in pectin.
2. Alcohol test – mix one tablespoon of fruit juice and two
tablespoons of 95% denatured alcohol. The following
result will determine the pectin content of the fruit
juice.
a. Rich in pectin – a transparent jelly – like lump is
formed Fruit juice rich in pectin
b. Moderate amount of pectin – a jelly-like clot is not
very firm and could be broken into two or more lumps.
c. Very little pectin content –The clot could be broken
into numerous small pieces or the juice is cloudy.
3. Gel meter test – in this test, fruit juice is allowed to
run down into tube for one minute to test the pectin
content.
There are two indications in a gel meter that will show if
the fruit has high or low pectin content.
a. Rich in pectin content - the juice is thicker and runs
down into the tube more slowly.
b. Low in pectin content - the juice runs below one-half
(½) mark of the gel meter after one minute.
Testing the Fruit Acidity
To test the acidity of fruits, mix one tablespoon of
calamansi juice and ½ cup of water. The following result
will determine the acidity of the fruit juice.
a. High acid content - if the taste is as sour as the
solution of calamansi and water.
b. Lack acid content – if the taste of the solution is
less sour.
*jellying may be improved by adding acid in the form of
calamansi or lemon juice and or commercial citric or
tartaric acid.
Combining juices that has low acidity to juices with high
acidity will proportion the sour taste and correspond to
desired quality.
Adjustment of Sugar and Acid Concentration
Jams, jellies and syrups must have the right sugar
concentration. Fruit juices on the other hand, must have the
desired sugar acid proportion to give the best quality
products. Hence, knowing how to determine and adjust the
sugar and acid concentration is important he preparation of
products.
Brix/Acid Ratio
The Brix/acid Ratio is sweetness – to – tartness
relationship. It gives a ratio compared with unity which
forms a comparative scale for the acceptability of juice
concentrates. The Brix unit is the concentration of
dissolved solids in an aqueous solution or the % Soluble
solids (%SS). The acid unit is the concentration of
citric acid in the citric juice.
Degrees Brix (symbol °Bx) is the sugar content of an
aqueous solution. One degree Brix is 1 gram of sucrose
in 100 grams of solution and represents the strength of
the solution as percentage by mass.
Acid Concentration
The % acid of fruit juices is called tritable acidity.
Tritable is an important factor for flavor quality. The
product may be rejected if too high in acid, if too
low, the flavor is bland and unappealing. Hence,
adjusting fruit juices to the desired acidity is
important.
The acidity of fruit juices can be determined by
titration. A certain weight of sample is tritable with
0.1 normal sodium hydroxide solutions gives light pink
color.
Let us Remember:
It is important to test the pectin and acid content of
fruits because the amount of sugar to be added will depend
on the acid and pectin content of juice. As a general rule,
the higher the acid content, the less sugar required; the
higher the pectin content, the more sugar to add. For fruit
juices that are rich in pectin, add ¾ to 1 cup sugar per cup
of fruit juice is recommended. If fruit juices have moderate
amount of pectin, add less sugar, Fruit juices with small
pectin content should not be utilized for jelly making
unless added with concentrated pectin that are available in
the market.
To produce a product of good quality, one must test the
pectin and acid contents of fruits when processing food by
sugar concentration.
