Application of the Gadidae Fish Processing Waste for Food Grade Gelatin Production

Physiochemical and functional properties of gelatin obtained from frigate mackerel (Auxis thazard), skipjack tuna (Katsuwonus pelamis), Longtail tuna (Thunnus tonggol) and yellowfin tuna (Thunnus albacares) skin

This study conducted a systematic investigation into the physicochemical and functional properties of gelatin extracted through alkaline methods from the skins of four commercially significant tuna species: frigate mackerel (Auxis thazard), skipjack tuna (Katsuwonus pelamis), longtail tuna (Thunnus tonggol), and yellowfin tuna (Thunnus albacares). Comparative analyses revealed notable species-specific variations in gelatin yield, amino acid composition, molecular weight distribution, and functional performance. Notably, yellowfin tuna skin gelatin (YSG) exhibited the highest melting point (28.09 °C), gel strength (271 g), and proline content (14.3 %), along with superior foaming capacity (20.43 %), water retention, and emulsification stability. Molecular weight profiles obtained via SDS-PAGE confirmed the presence of α- and β-chains characteristic of type I collagen, with YSG demonstrating enhanced structural integrity and thermal stability attributed to its elevated proline content. Additionally, Fourier-transform infrared spectroscopy (FTIR) and circular dichroism (CD) analyses indicated stronger hydrogen bonding and preservation of the triple-helix structure in YSG. While longtail tuna yielded the highest extraction rate (21.5 %), skipjack tuna showed the highest protein content (86.7 %). In contrast, frigate mackerel gelatin displayed darker coloration (ΔE* = 53.09) due to residual pigments. Rheological assessments highlighted YSG's optimal viscoelasticity and melting behavior, aligning with its robust interfacial properties. These findings underscore the potential of yellowfin tuna skin gelatin as a viable alternative to mammalian gelatin in food and biomedical applications, offering enhanced functional performance while valorizing underutilized fishery by-products.