Carbohydrate Gels
FST 605 - Laboratory 7
Introduction
Complex carbohydrates can be added to food for a number of reasons. In many applications, they are added to provide structure. In this laboratory we will examine the effects of using various modifications or types of carbohydrates on the properties and stability of gels.
1. Pectin gels
We will use two forms of pectin that differ in the degree of methylation. There is a low methoxy pectin with about 5% methylation and a normal with about 70%. We will examine the ability of these samples to form gels as affected by sugar content.
A. Low methoxy pectin.
Prepare two samples by adding 0.5 of pectin and 0.05 g of CaCl2 very slowly to 30 ml of cold water and mix for 10 minutes. To one, add 1 g of sugar to the other add 45 g of sugar while heating. When the sample begins to boil, add 0.5 ml of citric acid solution (286g citric acid in 300 ml H2O) and cool.
B. High methoxy pectin
Prepare three samples. Blend 0.3 g pectin with 4.5 g of sugar. Heat 30 ml of water and add the mixture while stirring. When the sample has been completely dissolved, add 41 g of sugar to one, 30 g to one and no sugar to the other. Boil for a minute or two and add 0.5 ml of the acid solution.
Allow the samples to cool and compare the gels formed.
2. Starch Gels:
Prepare samples according to the following table
| Starch Type | Starch (g) | Water | pH | Sugar (g) | Heat |
| Corn Starch | 1.75 | 25 ml | 7 | 0 | Boil |
| Corn Starch | 1.75 | 25 ml | 7 | 0 | Autoclave |
| Corn Starch | 1.75 | 25 ml | 7 | 10 | Boil |
| Corn Starch | 1.75 | 25 ml | 7 | 10 | Autoclave |
| Corn Starch | 1.75 | 25 ml | 4 | 0 | Boil |
| Corn Starch | 1.75 | 25 ml | 4 | 0 | Autoclave |
| High amyolpectin | 1.75 | 25 ml | 7 | 0 | Boil |
| High amyolpectin | 1.75 | 25 ml | 7 | 0 | Autoclave |
| High amyolpectin | 1.75 | 25 ml | 4 | 0 | Boil |
| High amyolpectin | 1.75 | 25 ml | 4 | 0 | Autoclave |
| High amyolpectin - crosslinked | 1.75 | 25 ml | 7 | 0 | Boil |
| High amyolpectin - crosslinked | 1.75 | 25 ml | 7 | 0 | Autoclave |
| High amyolpectin - crosslinked | 1.75 | 25 ml | 4 | 0 | Boil |
| High amyolpectin - crosslinked | 1.75 | 25 ml | 4 | 0 | Autoclave |
For each sample note the texture and appearance of the gel formed. Compare the samples heated to boiling to those that were autoclaved. Place the samples that were boiled at pH 7.0 in the freezer and examine again in 30 minutes. Compare the starch gel that contained sugar to those that did not.
3. Carrageenan Gels
Samples of kappa and iota carrageenan have been prepared. They contain 0.5 g of each carrageenan in 20 ml of water. Prepare to two 20 ml samples of each carrageenan. Add 5.0 ml of potassium solution to a sample of kappa and iota carrageenan. Add 5 ml of calcium solution to the other beakers of each carrageenan. Measure the strength of the gels with the texture analyzer.
Questions
1. Why were the gels formed by the three types of starch different in texture and appearance. What were the differences in the gels formed at pH 7.0 verses those formed at 3.0? Explain the differences noted in heating of the pH 4.0 starch samples.
2. How is low methoxy pectin prepared? What are its food uses? Explain the results observed.
3. What was the effect of the addition of calcium and
potassium to each type of carrageenan? What were the relative
strengths of the gels formed. What type of product could a
carrageenan gel be used in?