Q7. Describe in detail the following components of food commodities of both the animal and plant origin

Here are the solutions to your Food Science assignment:

Q7. Describe in detail the following components of food commodities of both the animal and plant origin

a) Carbohydrates
Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, serving as the primary energy source for living organisms.

• Plant origin: In plants, carbohydrates are abundant and include starch (a storage polysaccharide found in grains like wheat and rice, and tubers like potatoes), cellulose (a structural polysaccharide forming plant cell walls), and various sugars like glucose, fructose, and sucrose (found in fruits, vegetables, and sugar cane).
• Animal origin: In animals, carbohydrates are primarily stored as glycogen in the liver and muscles, providing readily available energy. Lactose, a disaccharide, is the main carbohydrate found in milk and dairy products.

b) Nitrogen containing substances
Nitrogen-containing substances in food commodities primarily refer to proteins, but also include free amino acids, nucleic acids, and other nitrogenous compounds. Proteins are large, complex molecules essential for structure, function, and regulation of the body's tissues and organs.

• Plant origin: Plants synthesize proteins from amino acids, which are abundant in legumes (e.g., beans, lentils), nuts, seeds, and grains. These proteins are vital for plant growth and development, and provide essential amino acids for human consumption.
• Animal origin: Animal products are rich sources of complete proteins, meaning they contain all essential amino acids. Examples include meat, fish, eggs, and milk. These proteins are crucial for muscle building, enzyme production, and tissue repair in animals and humans.

Q8. Explain any three causes of surface contamination.

Surface contamination of food refers to the introduction of undesirable substances onto the outer layer of food. Three common causes are:

1. Cross-contamination: This occurs when pathogens are transferred from one food item (often raw) to another (often ready-to-eat) via hands, utensils, cutting boards, or other surfaces. For example, using the same cutting board for raw chicken and then for vegetables without proper cleaning.
2. Environmental sources: Contaminants from the surrounding environment can settle on food surfaces. This includes dust, dirt, airborne microorganisms, pests (insects, rodents), and contaminated water used for washing or processing.
3. Improper handling by personnel: Food handlers with poor hygiene can transfer microorganisms from their hands, clothing, or respiratory droplets (from coughing or sneezing) directly onto food surfaces. This is a significant source of bacterial and viral contamination.

Q9. Describe freeze-drying as applicable to fruit and milk products.

Freeze-drying (or lyophilization) is a preservation method that involves freezing a product and then reducing the surrounding pressure to allow the frozen water to sublimate directly from the solid phase to the gas phase, bypassing the liquid phase.

• Applicable to fruit: Fruits are first frozen, then placed in a vacuum chamber. The ice crystals within the fruit sublimate, leaving behind a lightweight, porous, and crispy product. This method effectively preserves the fruit's original shape, color, flavor, and most of its nutritional content. Freeze-dried fruits (e.g., berries, apple slices) can be eaten as snacks or rehydrated for use in various dishes.

• Applicable to milk products: Milk (often skim or whole milk) is frozen and then subjected to the same sublimation process. This results in a highly stable milk powder that retains most of the original milk's nutritional value, flavor, and solubility. Freeze-dried milk products (e.g., powdered infant formula, instant coffee creamers) have a very long shelf life and can be easily reconstituted with water.

Q10. Explain any two bacterial infections of fish.

Bacterial infections in fish can lead to significant economic losses in aquaculture and impact wild fish populations. Two examples are:

1. Vibriosis: This disease is caused by various species of Vibrio bacteria (e.g., Vibrio anguillarum). It commonly affects marine and brackish water fish. Symptoms include skin lesions, hemorrhages (red spots), ulcers, fin rot, and internal organ damage. Vibriosis can lead to high mortality rates, especially in stressed or overcrowded fish populations.
2. Furunculosis: Caused by the bacterium Aeromonas salmonicida, this disease primarily affects salmonid fish (salmon, trout) but can also infect other species. It is characterized by the formation of boils or "furuncles" on the skin, which can rupture and lead to deep ulcers. Other symptoms include internal hemorrhages, spleen and kidney swelling, and lethargy. It is highly contagious and can cause severe outbreaks.

SECTION B: 30 MARKS

1. With various examples of food commodities processed, discuss thermal, physical and chemical methods of food preservation. (15 marks)

Food preservation involves techniques to prevent or slow down spoilage, maintain nutritional value, and extend the shelf life of food commodities. These methods primarily target microbial growth and enzymatic or chemical reactions.

• Thermal Methods: These methods involve the application or removal of heat to control spoilage.

  • Heating: High temperatures kill microorganisms and inactivate enzymes.
    • Pasteurization: A mild heat treatment (e.g., heating milk to $72^\circ\text{C}$ for 15 seconds) that kills pathogenic bacteria and reduces spoilage organisms, extending shelf life. Example: Milk, fruit juices.
    • Sterilization (Canning): More intense heat treatment (e.g., $121^\circ\text{C}$ for 15 minutes) that destroys all microorganisms, including spores. Food is then sealed in airtight containers. Example: Canned vegetables, meats, fish.
    • Blanching: A brief heat treatment applied to vegetables before freezing to inactivate enzymes that cause undesirable changes in color, flavor, and texture. Example: Broccoli, peas.
  • Cooling: Low temperatures slow down microbial growth and enzymatic activity.
    • Refrigeration: Storing food at temperatures between $0^\circ\text{C}$ and $4^\circ\text{C}$ slows down spoilage. Example: Fresh produce, dairy products, fresh meats.
    • Freezing: Storing food at temperatures below $-18^\circ\text{C}$ stops microbial growth and significantly slows down chemical and enzymatic reactions. Example: Frozen fruits, vegetables, meats, fish.

• Physical Methods: These methods alter the physical environment of the food to inhibit spoilage.

  • Drying (Dehydration): Removing water from food inhibits microbial growth, as microorganisms require moisture to survive.
    • Sun drying: Traditional method for fruits and fish. Example: Dried apricots, stockfish.
    • Mechanical drying: Using controlled heat and airflow. *Example: Grains, pasta