Properties of the gelatine


III) Features of gelatine

a) Gelatine, a physical gel

Experiment 2:

  Material : A saucepan
                    A bowl

1) Make a water-based jelly as we previously explained
2) As it's jellied, take it out of the fridge and melt it in a saucepan
3) When it has turned liquid, put it back into the fridge.

  Observations : The jelly which was melt is jellied again.
Interpretation : Gelatine is a physical gel or as well thermoreversible. This characteristic is very interesting : if you cool a solution of gelatin, its strength increases. On the contrary, if you heat such a solution, its strength would progressively decrease, until it becomes liquid again.

How can we explain this phenomenon?

  We know that inside of matter, atoms and molecules are constantly agitated. This perpetual motion, called the Brownian movement, is directly connected with the temperature. The higher the temperature, the faster the motion, and inversely the lower the temperature, the slower the motion.
This phenomenon is obviously the same in the water.
In a heated gelatine solution, the water molecule's motion is very fast and prevent the gelatine proteins from associating with each other

  In a cool gelatine solution, the water molecules' motion is slower than in a heated one and the attraction between the gelatine molecules is strong enough to resist the water molecules' motion disturbance.
Then, the gelatine proteins wind up their extremities with each other and form a kind of 3D net, which hold the water molecule and prevent them form pouring. A gel is thus formed, a matter between liquid and solid.

  It has to be said that the fusion temperature of gelatine is between 81 and 89 degree Fahrenheit (27 to 30°C) which enables a fusion in the mouth. It's a really interesting property for food using with for example
jellybeans or jelly desserts.

b) Gelatine, a not much pH-sensitive gel

  We tried to test the ph-sensitivity of the gelatine protein.

Experiment 3: the vinegar jelly

  Material :  a half gelatin leaf
                     2 tablespoons of vinegar
                     A small glass

 

1) Let the gelatine swell into the water during 10 minutes.
2) Heat the vinegar.
3) Mix the vinegar and the gelatin leaf into the small glass.
4) Once it isn't heat anymore, put the glass into the frigde for 16 hours.

  Observation:

A water-Jelly after 16 hours in the fridge

The vinegar-Jelly after 16h hours in the fridge

  Observation : The vinegar gelatine is more liquid than the water one but it has set as well.
Interpretation: The gelatine depends on the pH, but not so much.

The small ph-dependance of gelatine is interesting, because it allows to cook some fruit jellies without any problem.

We show that the gelatine depends on the PH, but does the set jelly depends of the pH?

Experiment 4 : The water-jelly with lemon juice.

  Material : a small glass
                  a gelatine leaf
                  ½ cup of water
                  lemon juice

1) Cook a water-jelly
2) Pour the lemon juice on the set jelly

  Observation:

Gelatine+lemon juice

Gelatine+lemon juice after 5 hours

  We can notice that the acid phase has began to enter into the jelly.

  Interpretation : Once the Jelly is set, it's not really sensitive to the pH
The gelatine swells when it is in touch with water.

  We can conclude that gelatine is not really sensitive to the pH even if it's strength is affected while the gelling.

c) Gelatine, a surfactant protein.

  We read while our researches that gelatine contains a lot of surfactant molecules. Nevertheless, the explication wasn't clear at all. In spite of our research, we didn't found out much documents of our level able to explain us the surfactants role for the setting of the jelly.

  Apparently, the stability of a colloid solution (just as a gelatine solution) depends on these much talked-about surfactants.
Their aim is to fix the hydrophobic particles in a hydrophilic solution like water. It makes a disperal. That is to say an aqueous suspension which contains tiny particles in suspension.
Then, we can allow the stability of an unsteady mixture which contains unmiscible particles due to the surface tension. This tension is obtained by the micelles : these aggregates of surfactant molecules which has its « head » regions in contact with surrounding solvant, sequestering the hydrophobic single tail regions in the micelle centre. The surface tension is as a necessary consequence proportional with the surfaces of solution in touch with the micella.

a micelle

Experiment 5 : the « gelatine mayonnaise »

  Material : a salad bowl
                    a whip
                    Oil
                    Water
                    2 gelatine leaves

1) Put the gelatine leaves into a bowl full of water.
2) Dissolve the gelatine leaves in the heated water.
3) Whip the gelatine solution with the oil until getting foam.

 

Oil and gelatine solution

Oil and water emulsion after an hour

  We can notice that the oil and water emulsion ins't an emulsion anymore contrary to the oil and gelatine solution's emulsion which after an hour is still foamed.

  Interpretation :  We can conclude the gelatine protein has surfactant properties because the gelatin solution and oil emulsion is stable.

 

               Through this scientific part, we showed what is the collagen. We tried to explain how we can obtain gelatine thanks to an experimentation.In top of that we tried to explain the gelatine manufacture mechanisms in order to understand its structure and its nature.
In the sequel, we attempt to prove that gelatine was a protein as well as collagen and that its structure allows the jelly's set.
Once, we succeed in doing that, we tested its properties. We took an interest on three of them : its thermo reversibility, its ph-sensitivity and finally its surfactant properties.

 

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