Comparison of rheological behaviors and nanostructure of bighead carp scales gelatin modified by different modification methods

Abstract

In this study, microbial transglutaminase (MTGase) and pectin were compared to modify bighead carp (Hypophthalmichthys nobilis) scale gelatin. The functional properties of modified fish scales gelatin (FSG) were largely improved, including melting temperature and rheological behavior. While, modification methods decreased the triple-helix content and destroyed the single left-hand helix chain of modified FSG as investigated by X-ray diffraction. MTGase could induce the denser and finer gels network, but had none significant effect on nanostructural properties of fish gelatin. Pectin inserted itself into the fish gelatin gels network and caused aggregations, forming crystalline peaks and various nanostructures. In particular, compared with pectin modified FSG, MTGase produced FSG with lower storage modulus and apparent viscosity, but higher gel points and melting points.

Gelation kinetics and characterization of enzymatically enhanced fish scale gelatin–pectin coacervate

“…Compared with the control, TG showed slightly lower proportions of bright regions, suggesting that the gelatin aggregates were denser . According to da Silva et al ., MTGase forms a denser gel network by inducing cross‐linking of non‐disulfide covalent bonds in the gel structure via catalysis of the ϵ‐amino groups of a lysine residue and the γ‐amide group of a glutamine residue . The microstructures of the gels were continuous protein with the addition of lower concentrations of pectin (1 g kg −1 ).…”

“…However, the stress values decreased to 13.2 ± 0.22 kPa as pectin was 16 g kg − 1 ( P < 0.05). Low content of pectin contributed to the electrostatic interactions and hydrogen bond interactions between pectin and gelatin molecules, which contributed to gelatin triple‐helix formation, while high content of pectin may make the interaction between pectin and gelatin change to phase separation and disturb the network of the mixed system. TG‐P 8 possessed the highest stress values, suggesting that it was harder to fracture and much more deformable .…”

“…The resulting mixtures were incubated at 40 °C under constant stirring for 2 h, and pH was adjusted to 6.5 using 1 mol L −1 HCl and NaOH solution. MTGase (0.6 g kg −1 ) was then added to the mixture and heated at 40 °C for 40 min . Subsequently, the enzyme was irreversibly inactivated (100 °C, 5 min), followed by cooling to room temperature.…”

“…In our previous studies, we found that high concentrations of pectin could form unstable fish gelatin-pectin coacervates with weaker thermal and mechanical properties. 18 According to our preliminary experiment (supporting information, Table S1), high concentration of MTGase could improve the gel properties of fish scale gelatin (FSG)-high methoxyl citrus pectin (HMP) coacervate gels sharply. Nevertheless, there is still a lack of basic information about MTGase-enhanced FSG-HMP coacervate gels.…”

“…[12][13][14] Nevertheless, there is a strong opinion that fish gelatin exhibits poorer gelling and rheological properties than mammalian gelatin due to its lower proline and hydroxyproline content, which limit its large-scale applications. The formation of fish gelatin-polysaccharide complex coacervates, such as fish gelatin-gum arabic, 2,4,15 fish gelatin-sodium alginate, 16 fish gelatin--carrageenan 17 and fish gelatin-pectin, 18 has been investigated and is regarded as a potential method to improve functional properties of fish gelatin. In our previous studies, we found that high concentrations of pectin could form unstable fish gelatin-pectin coacervates with weaker thermal and mechanical properties.…”