Educational Materials - Alginate Gel
How To Make Fun & Colorful Gel Beads With Alginate
What is alginate? Alginate is a polysaccharide, made up of chains of sugar units that can be thousands of sugars long. Sugars in alginate consist of guluronate (G), mannuronate (M) or guluronate-mannuronate blocks, and the proportion of the different sugars determines how strong a gel is formed. An excellent, illustrated reference to the structure, discovery (late 1800s), history of use, and chemistry of alginate can be found at here. FMC (Fine Marine Colloids) is a major world wholesaler of two algal polysaccharides, alginate from brown seaweeds and carrageenan from certain red seaweeds.
What seaweeds contain alginate? Alginate is found in the cells walls of brown marine algae such as kelps and rockweeds; photos of kelps are on the PSA's "Algae and Biodiversity" and "Algae and People" bookmarks (also on this webpage).
What do alginates do in brown seaweeds? Different parts of the same seaweed often contain different types and quantities of alginate in their cell walls. These alginates provide flexible, mechanical structure to the seaweeds and cushion them from possible injury when the seaweeds are subjected to strong water motion (waves, currents).
What products use alginate? Alginate is used to keep ingredients in foods from separating from each other (i.e., it is used as an emulsifier or stabilizer) and to create a tasty, smooth texture--- from "creamy foods" to "gelled foods". For example, alginate is commonly found in ice creams, salad dressings, fruit juices, and yogurt. Alginate is also used as an emulsifier or gelling agent in the manufacture of papers, textiles, pet foods, and pharmaceuticals. Alginate touches nearly every person's life, nearly every day.
How do I make a gel with alginate for fun? If you are a teacher or professor, the information in this exercise and its links will let you use alginate to teach students about hydrocolloids, polymers, diffusion, and the power of a chemical transformation (i.e., calcium bridges formed between alginate chains) to alter the shape and texture of a material.
And, if you want to have a birthday party with cool stuff, this is for you!
Here's what you'll need:
Materials:
1. Sodium alginate (don't use alginic acid). This is available as a dry powder from a number of sources (just Google "sodium alginate").
A supplier we've tested the exercise with is Modernist Pantry (469-443-6634; York, Maine), because this company sells food-grade sodium alginate in inexpensive quantities ($7.00 for 50 grams of sodium alginate [checked 6/1/12]).
2. Calcium chloride. This is available as a dry powder from many chemical companies (and the Modernist Pantry); just Google "calcium chloride". It is also inexpensive.
3. Pure water (e.g., distilled water or reverse osmosis-prepared water) to make the solutions. This is available at most grocery stores in inexpensive jugs.
4. Something to color the sodium alginate. This is optional, but the gel, although visible, will be transparent unless you make and use colored solutions of sodium alginate.
We used Crayola's Washable Kids' Paint, which has 6 plastic bottles of different colors of paint in the box (6/1/12). Any "color" will do, as long as it doesn't contain calcium; however, food dyes (e.g., McCormick's Assorted Food Color) are so small in size that they move out ("diffuse") of an alginate gel over time, ---but it is fun to see the liquid begin to turn color, too!
How to Make a Gel:
Step 1. Mix the dry, powdered sodium alginate with distilled water.
For a great gel, use 100 milliliters of distilled water and 1 teaspoon of sodium alginate (this is a 2% sodium alginate solution).
It is handy to mix this up in a kitchen measuring cup, and it will take nearly 30 minutes of stirring with a spoon to dissolve the sodium alginate. At first, it will form dry-looking "globs" in the water, but as you continue to stir, it will begin to dissolve and form a viscous, syrupy solution (a "hydrocolloid"). If this is a party, everyone can take a turn stirring!
Step 1: Measuring cup with dissolved sodium alginate, note viscous drop on end of chopstick; dry sodium alginate powder on blue saucer; package of calcium chloride (for step 2) and purple Kid's Paint bottle (step 3 ) in background.
2. In another container, mix the calcium chloride with distilled water.
Use a heaping teaspoon of calcium chloride in 100 milliliters of distilled water (this is a 5% calcium chloride solution).
The calcium chloride will dissolve in the water almost instantly. Put part of the solution in a glass or a bowl or a flower vase---something clear that will let you see the gel you make (in Step 4).
3. Make colored solutions of sodium alginate.
Pour some of the colorless sodium alginate solution you've made into each of several clean tea cups (or beakers or plastic tubes). Then, stir some children's paint or food dye into the sodium alginate solution (just enough to get a good color, e.g., 1/4 teaspoon Kids' Paint to 2 tablespoons of your sodium alginate solution).
Step 3: The three tea cups of dissolved sodium alginate are colored as follows: red food dye (left), uncolored (middle), purple Crayola Kid's Paint (right).
4. Make a gel by adding dissolved alginate to the calcium solution
Using a spoon or a dropper, add (i.e., drop or squirt) a little of the colored sodium alginate solution into the calcium chloride solution---PRESTO! In an instant, the calcium reacts with the sugar units in the alginate to pull the long flexible chains of alginate into a gel.
Step 4: Both glasses had calcium chloride solution (Step 2) poured into them. The sodium alginate with red food dye was added to the left glass; Kid's Paint colored socium alginates were added to the right glass. Notice that the food dye dissolves out of the red gel into the solution.
Gels (on hand) collected with colander from the calcium chloride solutions.
Other references (find these in your library or through interlibrary loan):
Chapman, V. J. & D. J. Chapman. 1980. Seaweeds and Their Uses (3rd ed). London: Chapman & Hall. 334 pp. (Chapter 6 is on alginates and p. 214 shows the calcium bridges between the alginate chains).
Graham, L. E., Graham, J. M. & L. W. Wilcox. 2009. Algae (2nd ed). San Francisco: Benjamin Cummings Publ., 616 pp. (pp. 71-72 has information on alginate and other algal cell wall materials used as gelling agents; pp. 278-308 has information on the brown algae (Phaeophyceae)).
Acknowledgements: This exercise was first used by the Phycological Society of America at its booth at the 2nd National Science and Engineering Festival in Washington, D. C. (April 26-28, 2012).