Step 1: Understanding the Problem:
The question asks to identify the most appropriate size reduction equipment for milling heat-sensitive food materials, such as spices (which lose volatile oils at high temperatures) or bioactive nutraceutical compounds.
Step 2: Detailed Explanation:
• The Heat Problem in Milling: Traditional milling equipment (such as hammer mills, ball mills, or roller mills) relies on physical mechanical impact, compression, or attrition. A large fraction of the mechanical energy supplied is dissipated as heat, raising the product temperature. This thermal stress causes the loss of volatile oils in spices or the degradation of thermolabile vitamins and active compounds.
Fluid Energy Mill (Jet Mill) Principle:
• In a fluid energy mill, size reduction occurs through high-velocity collisions between the product particles themselves (inter-particle attrition), driven by high-pressure, high-velocity streams of gas or compressed air introduced through nozzles.
• Because there are no moving mechanical grinding parts (like hammers or rollers), friction-generated heat is minimized.
• Additionally, the rapid expansion of the compressed gas as it exits the nozzles causes a Joule-Thomson cooling effect, which lowers the temperature inside the milling chamber.
• Suitability: This cooling effect makes the fluid energy mill suitable for ultra-fine grinding of heat-sensitive materials down to the micrometer range without thermal damage.
Step 3: Final Answer:
The fluid energy mill is the most suitable equipment for heat-sensitive food materials due to its cooling gas expansion and low mechanical friction, making option (C) the correct choice.