Idee della chimica - I saggi di riconoscimento degli alimenti

Summary

This video demonstrates how to detect common food frauds such as the addition of starch in cheese or unexpected proteins in certain foods through simple chemical tests. It explains three key experiments to identify the presence of proteins, simple sugars, and complex sugars in food using colorimetric assays. The tests involve chemical reactions with copper sulfate, sodium hydroxide, and iodine, revealing the presence of these substances through changes in color, such as purple for proteins and black for starch. The demonstrations highlight how basic lab techniques can be used to identify hidden ingredients.

Takeaways

• 🧪 The script discusses laboratory tests to uncover food fraud, such as adding starch to cheese or proteins to foods that should not contain them.
• 🔍 Chemical tests can reveal the presence of fats, proteins, sugars, salts, minerals, and vitamins in food.
• 🌈 Colorimetric tests are mentioned, which use the chemical properties of substances to be detected.
• 🥛 An example is given where water and milk are used in test tubes to demonstrate the presence of proteins.
• 💧 A 10% sodium hydroxide solution and a 1% copper sulfate solution in water are added to the test tubes to reveal proteins.
• 🟣 The test tube with milk turns violet due to the reaction of copper with proteins, while the water test tube remains blue.
• 🍇 The Fehling's test is described for reducing sugars, using copper sulfate and sodium potassium tartrate in a sodium hydroxide solution.
• 🍎 Reducing sugars like glucose and fructose react with copper, forming a red-brick precipitate of copper oxide upon heating.
• 🌾 For complex sugars, a solution of iodine and iodide is used, which turns blue-black when it reacts with sugar chains, as demonstrated with flour.
• 🧬 Starch, a complex sugar, turns blue-black in the presence of iodine due to the reaction with its sugar chains.

Q & A

What is the purpose of the laboratory tests described in the transcript?

The purpose of the laboratory tests is to detect food frauds, such as the addition of starch in cheese or proteins in foods that should not contain them. The tests reveal the presence of fats, proteins, sugars, salts, and vitamins in foods.

What type of tests are used to detect the presence of proteins, sugars, and other substances in food?

Colorimetric tests are used, which exploit the chemical properties of the substances to be detected. These tests change color based on the reaction between the chemical reagents and the food components.

What are the substances tested for in the experiment described?

The experiment tests for the presence of proteins, simple sugars (reducing sugars), and complex sugars (starch).

How is the test for proteins conducted?

The protein test is performed by adding a 10% sodium hydroxide solution and a 1% copper sulfate solution to two test tubes, one containing water (negative control) and the other containing milk (positive test). The reaction between copper and proteins in the milk causes the solution to turn purple, while the control remains blue.

What is the purpose of using water in the test tubes?

Water is used as a negative control to ensure the test is valid. It allows comparison with the sample that contains the substance being tested.

What is the test for reducing sugars and how is it performed?

The test for reducing sugars, like glucose and fructose, is performed using Fehling's solution. Copper sulfate and sodium-potassium tartrate are added to the test tubes, one with water (control) and the other with fruit juice. Reducing sugars react with the copper, and upon heating, a red-brown precipitate of copper oxide forms if sugars are present.

Why is heat necessary in the reducing sugar test?

Heat accelerates the reaction between reducing sugars and copper ions, facilitating the formation of the red-brown copper oxide precipitate.

How is the test for complex sugars (starch) conducted?

For the complex sugar test, iodine-iodide solution is added to two test tubes, one with water (control) and the other with a suspension of flour in water. If starch is present, the solution turns a deep blue-black color due to the reaction between iodine and the starch chains.

What is the visual indicator for the presence of starch in the test?

The presence of starch is indicated by the solution turning a deep blue-black color when iodine reacts with the starch.

What are the key differences between the tests for reducing sugars and complex sugars?

The test for reducing sugars requires heating and results in a red-brown precipitate if sugars like glucose or fructose are present. In contrast, the test for complex sugars (starch) uses iodine-iodide solution and results in a deep blue-black color without the need for heating.