Molecular characterisation, gelation kinetics and rheological enhancement of ultrasonically extracted triggerfish skin gelatine

Abstract

Improper fish skin disposal raises environmental and health concerns, highlighting the need for sustainable waste management. Turning discarded fish skins into marketable products like gelatine benefits both the economy and ecology. This study aims to investigate the feasibility of employing ultrasonic technique for the recovery of gelatine from the collagen-rich titan triggerfish skin following a preliminary pretreatment. The applied ultrasonic parameters included 100 W power, 40 kHz frequency, and a temperature held at 50 °C over a 3 h duration, resulting in a maximum gelatine yield of 20.5 ± 0.3 % (w/w) based on wet weight measurements. The biochemical and functional attributes of the extracted triggerfish gelatine (TFG) were compared to those of commercial bovine gelatine (CBG). TFG exhibited a substantial protein content (92.2 ± 0.2 %), along with low levels of moisture (7.4 ± 0.1 %), fat (0.2 ± 0.1 %), and ash (0.2 ± 0.04 %). SDS-PAGE showed that the primary elements of TFG were β- and α-chains (MW ∼ 150 to 220 kDa). While both gelatine types displayed predominant FTIR bands in the amide area (amide-I, amide-II and amide-ІІІ), TFG spectra, however, suggested that the ultrasonic treatment had no discernible effect on its triple helical structure. Significant variations in the gross amino acid profiles were found in both TFG and CBG. Nevertheless, compared to CBG, TFG had lower levels of proline and hydroxyproline residues. Additionally, TFG exhibited relatively lower gel strength; however, the optimal inclusion of microbial transglutaminase (MTGase) increased its gel strength (394±4 g) and melting temperature (Tmp = 31.9 °C), while reducing gelation time (<50 min at 20 °C). Functionally, TFG demonstrated higher foaming but marginally lower emulsifying properties than CBG. The finding underscores the potential of ultrasonication to mitigate fish skin waste emissions and efficiently retrieve high-quality gelatine within a shorter time frame.