Food & Nutrition: Nutrients, Labeling, and Chemical Testing Notes on-Biochemical Testing

Learning Objectives for Food & Nutrition

• Recall Nutrients: Identify the various nutrients required for a healthy human diet.
• Interpret Nutrition Labels: Understand and extract data from nutritional information labels found on food packaging.
• Recall Nutrient Tests: Identify and describe the chemical tests used to detect the presence of specific nutrients in food samples.

Understanding Diet and Food Sources

• Definition of Diet: In a scientific context, a diet refers to the total amount of food and drink consumed by an individual or organism.
• Specific Food Sources:   - Chicken: This is a significant source of protein, which is essential for growth and repair.   - Potatoes: These are primarily a source of complex carbohydrates (starch) providing energy.
• Food Packaging Requirements: Companies are legally mandated to create food packaging labels for all products to inform consumers about the nutritional content and potential allergens.
• Allergen Warnings:   - Cereal boxes frequently state "May contain traces of nuts."   - Rationale: This warning is critical for the safety of individuals with nut allergies, as even minute amounts can trigger severe reactions.

The Seven Categories of Nutrients

Every human body requires food containing seven specific types of nutrients to function, grow, and remain healthy:

1. Carbohydrates

• Primary Function: To provide energy for the body.
• Types of Carbohydrates:   - Simple Carbohydrates (Sugars): These provide a quick, immediate source of energy.   - Complex Carbohydrates (Starch): Found in foods like pasta and potatoes; these are broken down more slowly by the body providing sustained energy.

2. Proteins

• Primary Function: Essential for the growth and repair of body tissues.
• Common Sources: Includes meats, nuts, eggs, tofu, quorn, and certain vegetables.

3. Lipids (Fats and Oils)

• Primary Functions:   - Provide a concentrated source of energy.   - Act as an energy store within the body.   - Provide thermal insulation to keep the body warm.   - Protect internal organs from physical damage/impact.
• Sources: Found in various oily and fatty foods.

4. Vitamins

• Primary Function: Required in small amounts for growth, development, and maintaining normal bodily functions.
• Specific Examples:   - Vitamin A: Essential for maintaining good eyesight.   - Vitamin C: Crucial for building and maintaining a healthy immune system.   - Vitamin D: Necessary for the maintenance of healthy teeth and bones.
• Sources: Primarily found in fruits and vegetables.

5. Minerals

• Primary Function: Required for growth, development, and the normal functioning of biological processes.
• Specific Examples:   - Iron: Critical for blood health (specifically hemoglobin production for oxygen transport).   - Calcium: Essential for the development and maintenance of healthy teeth and bones.
• Sources: Integrated into various foods, particularly fruits and vegetables.

6. Fibre

• Characteristics: Unlike other nutrients, fibre cannot be broken down or digested by the human body.
• Primary Function: Provides bulk to the food, which is essential for a healthy digestive system and the prevention of constipation.

7. Water

• Significance: The human body is composed of over $70\%$ water.
• Primary Function: Needed within cells and for various bodily fluids.
• Requirement: Water lost through sweat and other excretions must be constantly replaced.
• Daily Recommendation: Individuals should drink over $1\,\text{liter}$ of water every day.

Nutrition Information Label Analysis: Label B

Nutritional labels are mandatory on all shop-bought food. Below is a detailed breakdown based on "Label B" for a breakfast cereal:

• General Calculations:   - Label B Data (Typical values per $100\,g$ vs. per $45\,g$ serving):     - Energy: $1570\,kJ$ ($375\,kcal$) per $100\,g$; $710\,kJ$ ($170\,kcal$) per $45\,g$ serving.     - Protein: $10.3\,g$ per $100\,g$; $4.6\,g$ per $45\,g$ serving.     - Carbohydrate: $73.8\,g$ per $100\,g$; $33.2\,g$ per $45\,g$ serving.       - Sugars: Of the total carbs, sugars account for $15.0\,g$ per $100\,g$ and $6.8\,g$ per serving.       - Starch Calculation: In a $45\,g$ serving, starch is calculated by subtracting sugar from total carbohydrates: $33.2\,g - 6.8\,g = 26.4\,g$ of starch.     - Fat: $2.0\,g$ per $100\,g$; $0.9\,g$ per $45\,g$ serving.       - Saturates: $0.3\,g$ per $100\,g$; $0.1\,g$ per serving.     - Fibre (determined by AOAC): $8.2\,g$ per $100\,g$; $3.7\,g$ per $45\,g$ serving.     - Sodium: $0.2\,g$ per $100\,g$; $0.1\,g$ per serving.     - Salt equivalent: $0.6\,g$ per $100\,g$; $0.3\,g$ per serving.
• Health Notes: Adding a handful of fruit to this cereal serving will count as one of your "5-a-Day."

Energy, Body Mass, and Health

• Energy Measurement: Energy obtained from food is measured in Joules ($J$).
• Energy Balance:   - If energy intake is higher than the energy used by the body, the individual will gain body mass.   - If an individual becomes Fat, the risk of heart disease increases.   - An underweight person is often described as anorexic (in clinical contexts).

The Food Standards Agency (FSA)

The FSA is a UK government agency with three primary roles to ensure public health and safety regarding nutrition:

1. Safety: Ensuring that all food available for consumption is safe to eat.
2. Authenticity: Ensuring that food products are exactly what they claim to be on their labels.
3. Sustainability and Health: Ensuring that food production is healthier for the consumer and more sustainable for the environment.

Laboratory Food Tests

The following procedures are used to verify the presence of major nutrients in food samples:

1. Test for Starch (Carbohydrate)

• Reagent: Iodine solution.
• Procedure:   1. Add a food sample to a spotting tile.   2. Add a couple of drops of iodine to the sample.
• Positive Result: If starch is present, the iodine will change from its original orange-brown color to blue-black.

2. Test for Sugar (Carbohydrate)

• Reagent: Benedict’s reagent.
• Procedure:   1. Add approximately $10\,\text{drops}$ ($2\,ml$) of Benedict’s reagent to a test tube containing the food sample.   2. Heat the solution in a water bath for $3-5\,\text{minutes}$.
• Results/Observations:   - Blue: No protein/sugar (Note: worksheet indicates blue for no protein, but standard Benedict's start is blue).   - Green: Small amount of sugar present.   - Orange/Red: High concentration of sugar present.

3. Test for Protein

• Reagents: Biuret A and Biuret B.
• Procedure:   1. Add a few drops of Biuret A to the food sample.   2. Add a few drops of Biuret B.
• Positive Result: If protein is present, the solution will turn purple.

4. Test for Lipids (Fats)

There are two primary methods for testing for fats:

Method A: Ethanol (Emulsion Test)

1. Add the food sample and ethanol to a test tube.
2. Secure the tube with a bung and mix/shake thoroughly. (Note: Solid foods must be crushed first).
3. Pour the resulting ethanol solution into a test tube containing water.

• Positive Result: If fat is present, a cloudy white layer (emulsion) forms at the surface.

Method B: Paper (Grease Spot Test)

1. Take a sample of the food and rub it directly onto a piece of paper.

• Positive Result: If fat is present, the paper will become translucent, allowing light to pass through the spot.

Questions & Discussion

Progress Check & Plenary

• Q: What is the role of the Food Standards Agency?   - A: To ensure food is safe, authentic (what it says it is), and to promote healthier/sustainable food.
• Q: Why is it important that food we buy has food labels?   - A: To allow consumers to monitor their nutrient intake and avoid allergens like nuts.
• Q: Match the nutrient to the test:   - Starch: Iodine.   - Sugar: Benedict’s.   - Protein: Biuret.   - Fat: Ethanol or Filter Paper.
• Q: Name the nutrient found in pasta.   - A: (Starchy) Carbohydrates.
• Q: What chemicals are needed to test for protein?   - A: Biuret A and Biuret B Reagents.
• Q: Application - Spaghetti Bolognese:   - Expected Nutrients: Carbohydrates (from pasta), Protein and Lipids (from meat), Vitamins and Minerals (from tomato sauce/vegetables).   - Testing methodology: One would use the chemical tests (Iodine, Benedict's, Biuret, and Ethanol) on the specific components or a prepared sample of the dish to confirm their presence.