# Marine Gelatine from Rest Raw Materials
## 2 Properties and Applications of Marine-Derived Gelatine
### Comparison of Fish and Mammalian Gelatine  
Physical and chemical properties of mammalian gelanes have been extensively researched and although fish-derived gelatines have also been extensively studied, the majority of results have been published recently [17; 21]. Fish derived gelatine is a viable alternative to mammalian sourced gelatine. There is however a number of limitations to widespread use of fish gelatine, and they are related to difference in physical and chemical properties in comparison to mammalian-sourced gelatines. Odour, colour, techno-functional and film forming properties, as well as consistency of amino acid composition may significantly vary depending on the gelatine source. Therefore, great care should be paid to optimization of the production process in order to obtain a product with the best properties for intended applications. Gelatine quality is rated based on numerous parameters, such as solubility, transparency, colour, odour and taste, and functional properties including rheology, moisture, ash, protein, pH, setting point and time, melting point and time, gel strength and viscosity. Physical and chemical properties of gelatine are mostly influenced by the animal species from which they are derived. It is known that, in general, fish-based gelatines have lower melting temperatures and strengths compared to their commercial pig skin and bovine counterparts [29]. Warm water fish gelatine is reported in the literature to have better functional properties than cold-water fish gelatines [30; 31]. The principal reason for these differences is that, in general, fish gelatines have a lower content of imino-acids (hydroxyproline and proline) than mammalian gelatines. Therefore, gelatine with low levels of imino acids tends to have lower gel strengths and melting points. The molecular weight distribution is also important in determining the gelling behaviour of gelatine. [PERSON] et al. [32] reported that the content of hydroxyproline and proline is approximately 30% in mammalian gelatines, 22-25% in warm water fish gelatines, and only around 17% in cold water fish gelatines (such as cod). Relative lack of these amino acids is partially compensated for by higher concentrations of serine and threonine. For this reason, gelatines obtained from cold water fish act as viscous liquids at room temperature, limiting their use in the food industry [30]. Higher amount of hydrophobic amino acids can, however, be a potential advantage in certain scenarios. [PERSON] et al. [30] have investigated water vapour permeability of cold- and warm-water fish skin gelatines films and compared them with different types of mammalian gelatines. Films obtained from cold-water fish species (_Alaskan Pollock_ and salmon) gelatines showed lower water vapour permeability compared to warm water fish and mammalian gelatines. The authors concluded that, although physical properties of these gels were inferior, the lower water vapour permeability of fish gelatine films can be useful particularly for applications related to reducing water loss from encapsulated drugs and refrigerated or frozen foods. However, a contrasting report has been published by Atma [31] on the comparison of amino acid and proximate composition in several warm water fish species. Among the investigated fish species, King weakfish and Lizard fish were found to have the highest hydroxyproline and protein content, which did not correspond to their respective gel strengths. The author has concluded that imino acid content may not be the main factor influencing gel strength in all cases, and that multiple other factors, including other amino acids, extraction conditions and molecular weight distribution may also play an important role in gelatine production. The most widespread application of gelatine in the food industry is the use in formulation of water-based gel deserts, owing to its unique property of melting at body temperature [7; 21]. Fish-based gelatines have a disadvantage in this regard due to their lower gel strength and melting temperature.