La Gambidieta - The prawn diet

This is the project that my pupils, Lola Padilla Medina, Raquel Garrido Ceacero, María Jesús Jódar Montoro and Jorge Rubio Ramírez, and I, have carried out.
Our secondary school is called IES Andrés de Vandelvira, which is located in Spain, specifically, in a charming Andalusian town called Baeza.

Our project is called La Gambidieta, translated as ”the prawn diet”

The target of which is to study the effectiveness of some products called fat finders.

There are a lot of these products in the market, and especially at Christmas when a massive advertising campaign starts.

They promise an easy solution to weight loss without a change to diet

If we think about this, these products are fantastic, because thanks to them, we can eat fat without gaining weight.

You only have to take one or two pills with your meal, and the fat is bound by the product to form a fat-fibre complex or a viscous solution, that cannot be absorbed by the body and it is eliminated naturally.

It is such a good idea that we wanted to test it.

The first step is to study the composition of these products.

They can be classified into two major types:
those that are composed of vegetable fibre, and the others whose main compound is chitosan.

Then, we wondered, what is chitosan?

Chitosan is a compound produced by deacetylation of the chitin.

After cellulose, chitin is the most widespread biopolymer in nature.

Where can we find chitin?

We chose prawns.

Why prawns? Because they are easy to get, cheap and above all we have a previous evidence, because everyone who has prepared paella, has noticed that from the very moment prawns are put into the pan, they start absorbing all the floating oil.

Hands to work!

We decided to obtain chitin of prawn exoskeletons.

There is a simple method which consist of two basic steps, deproteinisation and demineralization. Then, deacetylation of chitin to obtain chitosan.

We have a poor laboratory equipment and we couldn´t ensure that the temperature and stirring conditions were correct, so we decided to buy chitosan.

Then, we work with three products:

XLS- Medical
Chitosan
Raw prawn exoskeletons washed, dried and reduced a fine powder.

1 kg of prawns provides about 40 g of dried exoskeleton for only 20 cents/g,

XL-S Medical is 58 cents/g and Chitosan is 50 cents/g

So our prawn shells choice is cheaper per gram and besides, we get to eat “Gambas al pil pil” or spicy garlic prawns, a delicious Spanish dish.

Olive oil is the chosen fat, because it is an easy liquid to manipulate.

And living in Jaén, we really felt obliged to used it , considering that Jaén, the province in which I live, is the main producer of olive oil in the world.

Experimental design

2 g of chitosan put into a beaker with 10 mL of olive oil. Mixture kept stirring for 40 minutes.

This process is repeated with 2 g of XLS and 2 g of prawn exoskeletons respectively.

Then, the mixtures are filtered with a fluted filter paper, and the oil not absorbed by products is collected on a graduated cylinder in order to know the volume.

Prawns!!!

We were so surprised that we repeated the whole process several times, and the same result was obtained.

Prawn exoskeletons absorb 6.5 mL.
Chitosan absorbs 3.4 mL.
XLS Medical absorbs 3.7 mL.

But, we wondered

Maybe stomach conditions could be important to make these products effective.

So, we repeated the experiment simulating stomach conditions, 37 ºC and a pH of 1.5.

Experimental design

2 g of chitosan put into a beaker with 10 mL of olive oil and 50 mL of 0,03 M hydrocloric acid solution

Mixture was heated to about 37 ºC and kept stirring for 40 minutes.

This process was repeated with 2 g of XLS and 2 g of prawn exoskeletons respectively.

Then, the mixtures were filtered with a fluted filter paper, and the oil not absorbed by products was collected on burets in order to know the volume.