Chitosan (85% deacetylated, viscosity > 400 MPa, and molecular weight of 570.3 kDa)/squid gelatin hydrolysates (SGH) were prepared by incorporating SGHs (10%, 20%, and 40%) into chitosan films. SGH were obtained from squid skin gelatin by hydrolysis with Alcalase. The effects of adding SGH on the physical, chemical structure, mechanical, degradability, antioxidant, and antifungal properties of the chitosan films were evaluated. Films containing SGH were opaquer and more colored than the reference. Scanning electron microscope imaging showed that the surface sections of the CH/SGH films were smooth and homogeneous, though a small amount of insoluble microparticles was observed. Atomic force microscopy indicated that the surface roughness of the chitosan films increased with the addition of SGH. Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy suggested an excellent compatibility of the components due to hydrogen bonding. The flexibility and in vitro degradability of the films increased as the SGH content increased. The 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate acid and 1,1-diphenyl-2-picrylhydrazyl scavenging rate of films increased with the addition of SGH. Moreover, films containing 20% SGH improved the fungistatic activity against Aspergillus parasiticus of chitosan films. The chitosan/SGH composite films have the potential for use in food packaging.

Ultrasonic pulses are considered green technology for the improvement of the functional properties of proteins. In this study, four high-intensity ultrasound pulse treatments (ultrasound-pulsed gelatin (UPG)-42, UPG-52, UPG-71, UPG-84, and non-pulsed control gelatin (CG)) were applied to tilapia (Oreochromis niloticus) skin gelatin in order to study their effect on its physicochemical and antioxidant properties; a non-treated gelatin was used as a control. UPGs showed a significant increase in soluble protein and surface hydrophobicity compared to the control gelatin, and no significant difference was found in the electrophoretic profiles. The effects on the secondary structure were studied by circular dichroism and infrared spectra, and these showed that the random coil conformation was the main component in all treatments and the ultrasonic treatments only affected the α-helix and β-sheet proportion. Finally, the ABTS ((2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid)) and FRAP (ferric reducing ability) assays demonstrated that ultrasound treatments could improve the antioxidant activity of gelatins as free radical scavengers and electron donors. These results suggest that high-intensity ultrasound pulse technology is useful to improve fish gelatin antioxidant properties, which could be associated with secondary structure disruption.

The optimal alkaline and acid conditions for insoluble collagen extraction from jumbo squid fin (JSF) were established by factorial analysis. Dependent variable: protein concentration; independent variables: NaOH and HCl concentrations. The antioxidant properties of JSF collagen hydrolysates obtained by two protease systems were studied. Moreover, jumbo squid skin (JSS) collagen was obtained and hydrolysated under optimal conditions. The optimal extraction condition was 0.5 M NaOH followed by 0.2 M HCl. Collagen α-chains were detected in both JSF and JSS. Collagen β-component was detected only in JSS. JSS collagen showed higher levels of polar and hydrophobic amino acids. The JSF hydrolysates produced by subtilisin showed a lower degree of hydrolysis and higher antioxidant activity (2,2-diphenyl-1-picrylhydrazyl (DPPH), Trolox equivalent antioxidant capacity (TEAC), and oxygen radical absorbance capacity-fluorescein (ORAC_FL)) than those produced by a mixture of trypsin, chymotrypsin, and peptidase. The JSS hydrolysates showed a higher antioxidant capacity. We have thus established a suitable process to improve the utility of JSF.

This study evaluated the effect of ultrasonic pulse-assisted extraction on the yield and antioxidant activity of essential oils from grapefruit (Citrus paradisi) by-products using hydrodistillation and Soxhlet solvent extraction (hexane, acetone, ethanol). Ultrasound was applied at 40% amplitude for 20 min before extraction. Results showed that ultrasound significantly increased extraction yield with hexane (from 2.6 ± 0.58% to 7.6 ± 1.5%) and acetone (from 8.6 ± 0.96% to 12 ± 1.4%), while ultrasound-assisted hydrodistillation nearly doubled the yield (from 0.7 ± 0.03% to 1.5 ± 0.49%). In contrast, ultrasound decreased yield with ethanol by 3%. Antioxidant activity measured by TEAC assay was highest in acetone extracts without ultrasound (13,366.5 ± 7.66 mmol TE/g) and ethanol extracts (12,606.8 ± 0.51 mmol TE/g). However, ultrasound combined with ethanol increased DPPH scavenging activity from 1073.5 ± 1.07 µg/mL to 4933.3 ± 0.71 µg/mL and maintained high flavonoid content (9.41 ± 0.15 mg/mL) and phenolics (5.33 ± 0.09 mg/mL). Ultrasound-assisted hydrodistillation also enhanced antioxidant capacity, with DPPH values rising from 51.82 ± 5.56 µg/mL to 2413.03 ± 3.17 µg/mL. These findings demonstrate that ultrasound effectively enhances essential oil extraction and antioxidant activity depending on the solvent used, underscoring the potential of this clean technology for valorizing citrus by-products.