Coating of Oral Solid Dosage Forms in the Nutraceutical Sector

Tablet coating is a pharmaceutical technique used to apply a protective or decorative layer around a solid core such as tablets, capsules, softgels, and pellets.

It is now a well-established practice in the nutraceutical sector, aimed at enhancing both the functional properties and the appearance of products. Originally adopted from the confectionery industry in the form of “sugar coating,” the process has evolved over time—from the use of sugars to more advanced film-forming materials, such as synthetic and natural polymers. This evolution has led to significant improvements in the delivery and preservation of dietary supplements, making coating a crucial step in the production cycle.

Types of Coating

1. Sugar Coating: Historically the first type of coating, imported from the confectionery industry, it improves the appearance and taste of tablets. However, it has several limitations, such as long production times and a significant increase in tablet weight.

2. Film Coating: introduced in the 1930s, this method offers a faster process and a thinner, more resistant coating. It can be applied using organic solvents or aqueous dispersions, enhancing drug protection and allowing for controlled release of the active ingredient.
   Film coating is typically categorized into three main types:

   • Cosmetic: Improves the visual appearance of the product.

   • Protective: Shields the product from external agents such as light, moisture, and oxygen.

   • Functional: Enables the controlled release of nutraceutical ingredients.

3. Dry Coating: Dry coating involves the application of a second compression layer without the use of solvents. It offers advantages in terms of stability, especially for moisture-sensitive ingredients. However, it is less commonly used due to its production complexity and the need for specialized equipment.

4. Hot Melt Coating:This technique uses waxes and other meltable materials to create a durable coating. 

Advantages of Coating

• Protection of the Active Ingredient
  Coating protects active substances from external factors such as moisture, light, and oxygen, preserving their effectiveness and extending shelf life.
• Controlled Release
  It allows modulation of the release rate and site of the active ingredient, ensuring optimal absorption by the body.
• Taste and Odor Masking
  It conceals unpleasant tastes or odors of active ingredients, enhancing consumer acceptability.
• Aesthetics and Branding
  Provides a uniform and attractive appearance, facilitating product identification and reinforcing brand image.
• Gastroprotection
  Reduces the irritating effects of certain actives on the gastric mucosa.
• Increased Robustness
  Helps protect the product during handling and packaging processes.

Limitations of Coating

• Adds cost to the manufacturing process.
• The use of organic solvents raises concerns regarding safety and waste disposal.
• Requires tablets to have specific physical characteristics, such as low friability and sufficient mechanical strength.

Coating Process

Sugar Coating

1. Sealing
   Application of an insulating film to protect the tablet core from moisture and other environmental factors.

2. Subcoating
   Layers of sugar and powders are added to give the tablet its initial shape and structure.

3. Smoothing
   The surface is smoothed using sugar syrup to eliminate irregularities.

4. Coloring
   Pigments or lakes are used to improve the visual appeal and allow product identification.

5. Polishing
   Waxes are applied to give the tablet a shiny, glossy finish.

Film Coating

The film coating process includes several key stages:

1. Preparation of the Coating Solution
   The selected materials (e.g., polymers, plasticizers, colorants) are mixed with suitable solvents to create a homogeneous solution or suspension.

2. Application of the Coating
   The solution is sprayed onto solid dosage forms using specialized equipment (such as a coating pan) that rotates to ensure even distribution across all surfaces.

3. Drying
   The solvent is evaporated through the application of heat or airflow, leaving behind a solid film adhered to the surface.

4. Quality Control
   Final checks include verification of:

   • Uniformity of the coating

   • Thickness

   • Adhesion

   • Mechanical resistance