Food Tests - GCSE Science Required Practical

Summary

In this video, Dr. Sheffield from Mars Beauty School Science demonstrates food tests for detecting sugars, proteins, fats, and starch in different foods such as apple, biscuit, and cheese. The process includes preparing food samples, filtering them, and conducting Benedict’s test for sugars, iodine test for starch, ethanol test for lipids, and Biuret’s test for proteins. Each test shows specific color changes to indicate the presence of these chemicals. The video also highlights the importance of knowing test methods, expected results, and offers additional resources for teachers looking to improve practical science skills.

Takeaways

• 🔬 The video covers required food tests, including testing for sugars, proteins, fats, and starches.
• 🥐 The food samples used in the test are biscuit, apple, and cheese, with biscuit being tested first to minimize mess.
• ⚗️ Preparing the samples involves grinding the food, adding distilled water, stirring, and then filtering the mixture to remove solids for clearer results.
• 🧪 The Benedict's test is used to detect sugars (glucose). The reagent starts blue and, when heated, changes color depending on sugar levels, with the final color being brick red.
• 🌾 The iodine test is for starch, commonly used in questions about photosynthesis. If starch is present, iodine turns from orange to blue-black.
• 💧 The test for lipids (fats) involves adding ethanol and distilled water, then shaking. A cloudy white color indicates the presence of fats.
• 🥚 The Biuret test detects proteins, where the solution starts blue and turns pink or purple if proteins are present.
• 🍎 Results for the apple sample showed glucose was present (orange color in Benedict's test), but no starch, fats, or proteins were detected.
• 🍪 The biscuit sample had positive results for sugars, starch, and fats, but no proteins.
• 🧀 The cheese sample gave unexpected positive results for starch due to a food additive in grated cheese. It also tested positive for fats and proteins, but negative for sugars.

Q & A

What is the purpose of the food tests in this practical?

The purpose of the food tests is to identify different chemicals, such as sugars, proteins, and fats, found in various food types like apple, biscuit, and cheese.

Why is it important to filter the food samples?

Filtering the food samples removes solid food particles, helping to make the results of the color-change tests clearer and easier to interpret.

Why does Dr. Sheffield suggest testing biscuit, apple, and cheese in that specific order?

The food samples are tested in order of increasing messiness, starting with the biscuit, followed by the apple, and leaving cheese for last as it is the messiest to handle.

What is the Benedict’s test used for, and what color changes indicate a positive result?

The Benedict’s test is used to test for glucose and other short carbohydrates. A positive result shows a color change from blue to green, yellow, orange, or brick red, depending on the amount of sugar present.

How is the iodine test for starch performed, and what result indicates the presence of starch?

The iodine test for starch involves adding iodine to the food sample. A positive result is indicated by a color change from orange to a blue-black color.

What is the procedure for testing lipids (fats) using ethanol?

To test for lipids, ethanol is added to the food sample, followed by distilled water. The tube is shaken vigorously, and a positive result is indicated by a cloudy white suspension.

What does the Biuret test detect, and what result shows the presence of proteins?

The Biuret test detects proteins. A positive result is shown by a color change from light blue to pink or purple.

Why might grated cheese give a positive result for starch in the iodine test?

Grated cheese may give a positive result for starch because manufacturers often add starch powder to keep the grated pieces separate.

Why is it necessary to clean the pestle and mortar between preparing different food samples?

The pestle and mortar need to be cleaned between food samples to avoid cross-contamination, ensuring that the results of the tests are accurate.

What should you include in an exam answer when describing the Benedict’s test for sugars?

In an exam, you should describe adding Benedict’s solution to the food sample, heating the mixture in a hot water bath, and observing the color change, which can range from blue to brick red depending on the amount of sugar present.