## 2 Overview of Mechanical Processes in the Food Industry  
### Classification of Mechanical Unit Operations  
Mechanical unit operations in food engineering encompass a broad range of processes that involve the application of mechanical forces to transform raw or intermediate food materials into products with desired properties. These operations are integral to the structure formation, compositional uniformity, and functionality of food products, and are typically classified based on the type of mechanical action applied and the intended processing goal. Below is an overview of the main categories:  
* Size Reduction and Comminution This group includes mechanical operations that decrease the particle size of solids or droplets to improve processability or modify texture. Subtypes include: cutting, slicing, grinding, and milling (e.g., in vegetable or meat processing), emulsification (e.g., in sauces or dairy systems), pulping and refining (e.g., in fruit/vegetable purees). These operations often involve high energy input and require control to avoid overheating or structural damage to sensitive ingredients [12].
* Mixing and Homogenization These processes involve the mechanical agitation of multiple components to achieve a uniform composition or distribution. They can be further classified as: solid-solid mixing(e.g., blending powders or granular ingredients), liquid-liquid mixing (e.g., emulsification), solid-liquid mixing (e.g., batter or dough preparation), gas-liquid or gas-solid mixing (e.g., aeration of foams or whipped products). Key mechanisms include convective transport, diffusion, and shear-induced deformation. Equipment examples: ribbon blenders, planetary mixers, high-shear homogenizers [13].  
(c) Shaping and Forming  
Mechanical shaping processes confer the final geometry to food products and often influence their internal structure. Examples include: extrusion--combining mechanical and thermal energy to texturize and shape, moulding, sheeting, and stamping--common in bakery and confectionery, encapsulation and pelletizing--for controlled release or convenience [14].  
(d) Mechanical Drying Assistance  
Mechanical forces are often used to enhance drying kinetics by improving mass and heat transfer or preventing agglomeration. These include: fluidized bed drying--where gas flow suspends and agitates particles, vibratory drying--where mechanical vibrations promote uniform drying and prevent sticking, spouted beds or mechanically stirred dryers--improving contact between food particles and hot air [15].  
(e) Mechanical Separation  
This group involves the use of mechanical energy to separate components based on size, density, or phase. Major types include: centrifugation--separation of immiscible liquids or clarification, sieving and screening--classification of powders and particles, membrane-assisted mechanical filtration (e.g., tangential flow filters with dynamic agitation). Although typically considered physical separation techniques, these operations rely on carefully controlled mechanical parameters to be effective [16].  
(f) Transport and Conveyance  
Mechanical handling systems are essential for moving raw materials and products throughout processing lines. Although not directly transforming product properties, these operations affect residence time, mechanical stress, and product integrity. Systems include: screw conveyors, belt conveyors, and pneumatic transport systems, often modeled with CFD for pressure drop and flow optimization [17].