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 (<i>Auxis thazard</i>), skipjack tuna (<i>Katsuwonus pelamis</i>), longtail tuna (<i>Thunnus tonggol</i>), and yellowfin tuna (<i>Thunnus albacares</i>). 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.