The optimization of antioxidant and anti-tyrosinase activity during jellyfish hydrolysate preparation was studied using a response surface methodology (RSM) with a face-centered composite design. The influence of the hydrolysis duration and the enzyme concentration on the IC₅₀ of the DPPH and ABTS radical scavenging activity, ferric-reducing antioxidant power (FRAP), the degree of hydrolysis (DH), yield, and the IC₅₀ value of tyrosinase inhibitory activity were determined. The optimum conditions for the production of jellyfish hydrolysate using alcalase (JFAH), flavourzyme (JFFH), or papain (JFPH) were achieved at hydrolysis times of 360, 345, or 360 min, respectively, and at an enzyme concentration of 5.0%. JFFH had the highest antioxidant and tyrosinase inhibitory activity. JFAH, JFFH, and JFPH concentrations of 2.5 mg/mL resulted in HaCaT cells (IC₈₀) having a survival rate of 80%. The amino acid profile of JFFH contained about 43% hydrophobic and 57% hydrophilic amino acids, comprising Gly, Cys, Glx, Asx, which were dominant. The isolation of a peptide fraction from JFFH was carried out using ultrafiltration membranes (10, 3, and 1 kDa) and gel filtration chromatography. Fraction-III (1–3 kDa) showed the highest antioxidative and tyrosinase inhibitory activity.

Mantis shrimp (Oratosquilla nepa) exoskeleton, a leftover generated after processing, was used as a starting material for chitosan (CS) production. CS was extracted with different deacetylation times (2, 3 and 4 h), termed CS−2, CS−3 and CS−4, respectively, and their characteristics and antimicrobial and film properties with agarose (AG) were investigated. Prolonged deacetylation time increased the degree of deacetylation (DDA: 73.56 ± 0.09–75.56 ± 0.09%), while extraction yield (15.79 ± 0.19–14.13 ± 0.09%), intrinsic viscosity (η: 3.58 ± 0.09–2.97 ± 0.16 dL/g) and average molecular weight (M_ν: 1.4 ± 0.05–1.12 ± 0.08 (×10⁶ Da)) decreased (p < 0.05). FTIR spectra of extracted CS were similar to that of commercial CS. Among all the CS samples prepared, CS−3 had the best yield, DDA, M_ν and antimicrobial activity. Therefore, it was chosen for the development of composite films with AG at different ratios (CS−3/AG; 100/0, 75/25, 50/50, 25/75 and 0/100). As the proportion of AG increased, the tensile strength (29.96 ± 1.80–89.70 ± 5.08 MPa) of the composite films increased, while thickness (0.056 ± 0.012–0.024 ± 0.001 mm), elongation at break (36.52 ± 1.12–25.32 ± 1.23%) and water vapor permeability (3.56 ± 0.10–1.55 ± 0.02 (×10⁻⁷ g m m⁻² s⁻¹ Pa⁻¹)) decreased (p < 0.05). Moreover, lightness of the films increased and yellowness decreased. CS−3/AG (50/50) composite film exhibited high mechanical and barrier properties and excellent compatibility according to FTIR and SEM analyses. According to these finding, mantis shrimp exoskeleton could be used to produce CS. The developed bio-composite film based on an appropriate ratio (50/50) of CS−3 and AG has potential for being used as food packaging material.

Tuna blood (TB) was subjected to enzymatic hydrolysis. The effects of the relationship of hydrolysis time (30–180 min) and enzyme concentration (0.5–3.0% w/w protein) on the degree of hydrolysis (DH), yield, antioxidant and angiotensin-I-converting enzyme (ACE) inhibitory activities were determined. The response surface methodology (RSM) showed that TB hydrolysis’s optimum conditions were hydrolysis for 180 min and Alcalase, Neutrase or Flavourzyme at 2.81%, 2.89% or 2.87% w/w protein, respectively. The hydrolysates with good DH (40–46%), yield (3.5–4.6%), the IC₅₀ of DPPH (0.8–1.6 mg/mL) and ABTS (1.0–1.4 mg/mL) radical scavenging activity, ferric reducing antioxidant power (FRAP) value (0.28–0.65 mmol FeSO₄/g) and IC₅₀ of ACE inhibitory activity (0.15–0.28 mg/mL) were obtained with those conditions. The TB hydrolysate using Neutrase (TBHN) was selected for characterization in terms of amino acid composition, peptide fractions and sensory properties. The essential, hydrophobic and hydrophilic amino acids in TBHN were ~40%, 60% and 20% of total amino acids, respectively. The fraction of molecular weight <1 kDa showed the highest antioxidant and ACE inhibitory activities. Fishiness and bitterness were the main sensory properties of TBHN. Fortification of TBHN in mango jelly at ≤ 0.5% (w/w) was accepted by consumers as like moderately to like slightly, while mango jelly showed strong antioxidant and ACE inhibitory activities. TBHN could be developed for natural antioxidants and antihypertensive peptides in food and functional products.