Laboratory 5
Carbohydrate chemistry - pectin and gelation
Introduction
Carbohydrates in foods are important for their structural, functional and nutritional properties as well as
for their participation in many types of chemical reactions. Polysaccharide exist in foods as a diverse
array of naturally occurring polymers and a wide variety of chemically modified forms. The physical state
and chemical nature of polysaccharide influence the texture, appearance and mouth feel of foods.
Gels are semi-rigid, elastic colloidal solutions which entrap large amounts of water. They are
important in the food industry for such products like jellies, jams, puddings, etc. Jelly texture is influenced
by a number of ingredients and conditions such as pectin - type and concentration; sugar - type and
concentration; acid - influences charges of the molecules in the system; and water.
The purpose of this exercise is to learn how to make jelly and to explain how the ingredients function in
a pectin gel system. Also to compare and contrast product with different treatment variables and evaluate
the difference between sensory and physical evaluation techniques.
Jelly Formulation and Procedures
Materials
- mason jars with lids (48) - lemon juice (140 mL)
- apple juice, canned unsweetened - thermometers
(6,000 - 8,000 mL) - saltine crackers
- Certo liquid pectin (4 boxes) - Instron
- aspartame or Nutrasweet - pH meter
- 2 large cooking pans or pots (8 qts) - 1 large kettle for sterilizing jars & lids
-sugar -refractometer
-ladles & large spoons -balance
-gloves (heat & water resistant) -paper plates, cups, spoons
Procedure (from: Applied Food Science Laboratory Manual, D.B. Ott, Pergamon Press, pp. 35-45)
a. Basic formulation for pectin gel: apple juice (946 mL); sucrose (1,400 g); and pectin (180 mL). This
formulation will be used as the base and all other ingredients will be substituted as described
below.
b. Weigh or measure all ingredients according to the direction of the instructor.
c. Begin sterilization of jars and lids - make sure there are no defects. Wash, drain and then place in a
large container of boiling water for 10 min (keep the jars hot). You will need to use special gloves
so you don’t get burned. [Note: Jars can also be sterilized by autoclaving.]
d. Record initial juice pH. Place juice and sugar into saucepan. Note: For acid and aspartame
treatments, do not add these ingredients at this time; they will be added after boiling is completed,
“step h”.
e. Bring mixture to full boil, stirring constantly.
f. Stir in liquid pectin at once.
g. Stir and bring to full rolling boil. Check oBrix of solution. Boil with constant stirring until sample reaches
>64 oBrix. (Note: some jelly formulations may not reach the desired Brix.)Brix.)
h. Remove from heat and skim foam with a spoon. Add lemon juice or aspartame at this time; mix well.
I. Take 25 mL in a beaker, allow to cool to 40C, and then measure the pH of the mixture (should be
between 2.8 - 3.5). Record the pH measurements.
j. Ladle the hot mixture into the jars, leaving Brix.)½” space at the top. Place lids on jars and seal by
tightening.
k. Invert jars for 1 min and then wipe jar of any spills with a damp cloth.
l. Re-invert the jars and label each jar according to the treatment being performed.
m. Store jars in a cool, dry area for the next lab section.
Variables
