Derived from animal sources, gelatin has been produced traditionally from bovine bones and pork skin. It is widely used in food, pharmaceuticals, dying, tanning and other industries. In the pharmaceutical industry, some of the key reasons gelatin has remained the principal ingredient for fabricating hard capsule shells include its excellent gelling properties over a wide pH range, its rheological behaviour demonstrating temperature-dependent reversible sol-gel transition, its non-toxic and inert nature and its ability to form robust, flexible films. However, despite its manifold advantages to the pharmaceutical industry, gelatin obtained from its traditional sources can pose serious risk of BSE (bovine spongiform encephalopathy) contamination. Moreover, its sources may also not be acceptable to all due to religious or cultural reasons.
Fish gelatin has been identified as a viable alternative to both pork and bovine gelatin, because of its parallel physicochemical properties. It also has low melting point that greatly helps in rapid dissolution.
Characteristics of Fish Gelatin
The most important attribute for gelation is the gelling point, which for most varieties of fish gelatin is significantly lower than bovine or pork gelatin. The reason for low setting point of fish gelatin is the lower occurrence of hydroxyproline (9%) in this gelatin variety than that contained in the bovine or porcine variety (13-15%). However, by virtue of its low setting point, fish gelatin shows poorer gelling property. This results in high occurrence of outflow of fish gelatin solution from the mold pin during the manufacturing of capsule shells. But this challenge can be resolved by employing different gelling agents.
Approaches to Enhance the Gel Strength of Fish Gelatin
A mixture of horse mackerel fish gelatin with egg albumin (3:10) has been studied to produce synergistic association and compatible gel structure that increases its gel strength. Addition of polysaccharides like gellan and κ-carrageenan also demonstrates an increase in the melting point of the fish gelatin. This is because gellan forms coupled networks with the gelatin molecule that depicts formation of new heterolytic junction zones between anionic segments of gellan and cationic segments of gelatin molecules. This helps elevate the gelation temperature, rate and improve the gel strength. Gel strength of gelatin can also be enhanced by the use of chemically modified dialdehyde polysaccharides (starch or dextrin), wherein the dialdehyde starch (degree of substitution of at least 0.005) synergistically improves the gel strength and hardness.
Takeaways
The use of natural cross-linking agents can help enhance the gel strength of fish gelation to match-up against mammalian gelatin. Possibilities of replacing mammalian gelatin with fish gelatin, can therefore be explored with its ability to offer vying, unparalleled characteristics like other biopolymers and the potential to satisfy the requirements of the global market.
