Food Engineering

Step 1: Analyze the factors related to the material's properties for size reduction (comminution).
A. Friability: This is a measure of how easily a material fractures or crumbles. A highly friable food requires less energy for size reduction. It is a critical factor.
C. Moisture content: High moisture content can make materials sticky or elastic, making them difficult to grind and causing them to clog equipment. Dry materials are generally easier to reduce in size.
D. Heat sensitivity: Size reduction generates heat. For heat-sensitive foods (e.g., those high in sugar or volatile oils), this can cause melting, degradation, or loss of quality. This influences the choice of equipment (e.g., requiring a cryogenic grinder).
B. Bulk density: While important for equipment capacity and material handling (how much material fits in the grinder), it is less of a direct factor in the effectiveness of the physical breaking process compared to the intrinsic properties of the material itself like friability. The primary factors are how the material behaves under stress.
Therefore, A, C, and D are the most influential factors.

Step 1: Identify the topic of the question. The question relates to the principles of comminution (size reduction), which describes the energy required to break down particles. Three main theories describe this relationship: Rittinger's law, Kick's law, and Bond's law.
Step 2: Define the relevant laws of comminution.

Rittinger's Law: States that the energy required for size reduction is directly proportional to the new surface area created. This theory assumes that all energy is used to create new surfaces. It is most accurate for fine grinding where the increase in surface area is significant.
Kick's Law: States that the energy required is proportional to the reduction in volume of the particles. It's more applicable for coarse crushing of large particles where little new surface area is created.
Bond's Law: An intermediate theory stating that the energy used is proportional to the new crack length produced. It is often considered more practical as it applies to a wider range of particle sizes. \end{itemize}
Step 3: Match the question's statement to the correct law. The question explicitly states that the energy is "proportional to the change in surface area". This is the definition of Rittinger's law.

Step 1: Analyze how each factor influences the spray drying process.
A. Nozzle pressure: Directly affects the energy of atomization, which in turn controls the initial droplet size. Smaller droplets dry faster and result in smaller final particles.
B. Liquid viscosity & C. Surface tension: These are properties of the liquid feed that resist atomization. Higher viscosity and surface tension make it harder to form small droplets, leading to larger final particles.
D. Nature of the solids: The type of solid (e.g., crystalline vs. amorphous), its concentration, and its properties affect how the particle forms as it dries. It influences the final particle's density, shape (e.g., hollow or solid), and solubility. Since all four factors have a significant impact on the final particle characteristics, the correct answer includes all of them.

Concept: Vinegar is a widely used food preservative and condiment. Its preservative action is primarily due to the presence of a specific organic acid.
Step 1: Understanding vinegar composition.
Commercial vinegar typically contains about 4--5% acetic acid diluted in water.
Step 2: Role of acetic acid.

• Inhibits growth of spoilage microorganisms
• Lowers pH, creating an unfavorable environment for bacteria
• Enhances flavor and shelf life

Step 3: Comparison with other acids.

• Citric acid: Used in fruits and beverages
• Lactic acid: Produced during fermentation (e.g., curd)
• Benzoic acid: Used as a preservative but not the main component of vinegar

Step 4: Conclusion.
Thus, acetic acid is the preservative present at 4--5% concentration in commercial vinegar.