Vegetarian and conventional Gummy Bears

Demonstration Experiment on Video

Vegetarian and conventional Gummy Bears

Objective: Swelling Capability of the Biopolymer Gelatin

Peter Keusch

German version

Supermarket products:
	UFO Gummy Bears - Gummy Bears made of gelatin, produced for Plus Vertriebs GmbH, Mühlheim an der Ruhr (Germany)
	Gummy Bears made of starch, Firm: Bears & Friends

Glass wares:
	4 snap-cap vials 20 mL

Experimental procedure:

A gummy bear made of gelatin is placed into a snap-cap vial. The other vial contains a gummy bear made of starch. The vials are filled with dist. water until the gummy bears are covered. The gummy bears remain in the water over night.

Results:

Substances in the gummy bear that give it solidity are: glucose, starch and gelatin.

The gummy bear made of gelatin swells in water and grows to a multiple of its original size. On the other hand, the gummy bear made of starch changes neither the shape nor the size,

Video clip (Download RealPlayer .rm file)

Discussion and background:

Gelatin (denatured collagen) is a heterogeneous mixture of proteins derived from animal collagen by hydrolysis. Collagen is the fibrous protein constituent of skin, cartilage, bone, and connective tissue.

Collagen consists of left-handed polypeptide chains each containing about one thousand amino-acid residues. The amino acid content of collagen is about one third glycine and a further 22% proline and hydroxyproline. The peptide helix is composed of repeats of the amino acid sequence Gly - X - Y, where X and Y are often proline and hydroxyproline. There are 3.3 amino acid residues per turn in the helix. The presence of glycine in every third position is essential because this amino acid is small enough to fit in the restricted space in the centre of the helix. The bulky side chains of proline and hydroxyproline face outward.

The tertiary structure of collagen consists of three left-handed helices twisted into a right-handed coil. The structure of the triple helices is stabilized by intermolecular hydrogen bonds between the peptide backbone NH - and CO - groups of the the three polypeptide chains, and by the presence of many proline and hydroxy proline residues. Because proline and hydroxyproline are rigid cyclic amino acids they limit rotation of the polypeptide backbone and thus contribute to the stability of the triple helix.

Triple helix

Many three-strands molecules pack together side-by-side, generating a strong fibril (quaternary structure). The collagen fibers formed by intermolecular interactions between collagen triple helices are stabilized by cross-links between lysine and hydroxylysine residues. Lysine residues (or hydroxylysine residues) are post-translationally modified to aldehyde derivates (allysines or hydroxyallysines) by the enzyme lysine oxidase. Two aldehydes react to form a aldol group, which is dehydrated to a a, b - unsaturated group. A very stable covalent cross-link is formed that join the nonhelical amino- and carboxy-terminal ends of one strand to the helical portion of an adjacent strand.

When collagen is heated and denatured with acid or base it becomes water soluble. Gelatin is produced. The triple-helical configuration of collagen is disrupted by heating. Upon cooling the hydrogel, gelatin partially regains triple helix structure and creates interchain crosslinks. The chains fall into a random arrangement.

Gelatin is multi-functional: gelling, thickening, water-binding, emulsifying, foaming. These properties are due to the steric structure of the polymer and depend on the type of the biopolymer, its concentration, pH and operating conditions of temperature and pressure. As gelatin binds with water, it swells. Gelatin can absorb a tremendous amount of water - up to 5-10 times its weight. The water binding capability of gelatin is based on the formation of hydrogen bonds between water molecules and the hydrophilic groups in the biopolymer sided chains.

References:
Collagens
Tertiary and Quaternary Structure

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