Table 3 Main materials used to form capsule shell

Polysaccharides

 Alginate

• Low toxicity

• Bio inert material

• Low cost encapsulation process

• Limited changes on mechanical properties

• Instability caused by ion-leaching

Biotic

[155, 168, 169]

 Carrageenan

• Not toxic

• Biocompatible

• Biodegradable

• Potential reaction with bioactive molecules

Abiotic / Biotic

[170,171,172]

 Chitosan

• Not toxic

• Enhanced biocompatibility

• High stability

• Expensive dosing is prevented

• Method of preparation depends on the PHs used

Abiotic / Biotic

[157, 173, 174]

 Gum Arabic

• Abundant availability

• Excellent core protection ability

• Limited availability

• High cost

Abiotic

[175, 176]

 Modified starch

• Fully biodegradable

• Inexpensive material

• Can be easily modified

• Loose structure due to its poor resistance to shearing and stirring

• Toxicity of several derivative products

Biotic

[159, 177, 178]

 Maltodextrin

• Low hygroscopicity

• Protect bioactive compounds from oxidation

• Poor stability

• Low retention

Biotic

[179, 180]

 Pectin

• Low cost encapsulation process

• Possibility to modify its structure

• High swelling degree in unfavourable environments

Biotic

[181,182,183]

Inorganic

 Amorphous silica

• Biocompatible

• High uptake capacity

• Controlled drug release system

• Low toxicity

• Improved loading and releasing properties

• Difficult to predict successful amount of encapsulated drug

Abiotic/Biotic

[162, 184]

Synthetic and natural polymers

 Polyvinyl alcohol

• Biodegradable

• Not toxic

• Biocompatible

• Low stability

• Chemical modification

Abiotic

[185, 186]

 Polyacrylamide

• High stability

• Toxic

Abiotic

[187, 188]

Fats and waxes

 Hydrogenated vegetable oils

• Controlled release

• Multiple steps in the preparation process

Biotic

[189, 190]

 Bees wax

• Highly diverse

• Adaptable material to changes in different conditions

• Degradable

• Low encapsulation capacity

Abiotic

[191, 192]

 Paraffin wax

• Structure does not change over time

• Not adjustable

• Not adoptable

• Toxic

Abiotic

[193, 194]

Proteins

 Soft gelatine capsule (SGC)

• High accuracy

• Reduces dustiness during manufacturing

• Expensive to produce

• Not adaptable

Biotic

[195, 196]

 Hard gelatine capsule (HGC)

• Rapid drug release

• Problems with cross-linking

• Not suitable with hygroscopic compounds

Biotic

[195, 197]

 Sodium caseinates

• Oxidative stability

• Biocompatibility

• Increases encapsulation efficiency

• Requires a significant amount of bioactive compound

Abiotic

[166, 198, 199]