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Agar hydrolysate (AH) from Gracilaria tenuistipitata was prepared using hydrogen peroxide (H₂O₂) scission and assessed as an antioxidative gel enhancer in surimi. Hydrolysis conditions were optimized via response surface methodology, considering time (0–3 h) and H₂O₂ concentration (2–4% w/w). Optimal hydrolysis (2.64% H₂O₂, 3 h) yielded a degree of hydrolysis (DH) of 30.49 ± 3.18% with high antioxidant activity. Both variables positively affected DH and antioxidant properties ( P  < 0.05). To test the potential of AH, agar/AH blends (100:0 to 50:50) were incorporated as 3% supplements in surimi gels, subjected to repeated freeze-thaw (F-T) cycles (0, 3, and 6 cycles). The 60:40 ratio significantly improved gel strength, reduced expressible moisture content, and prevented F-T-induced lipid oxidation ( P  < 0.05), while whiteness remained unchanged. Microstructural analysis confirmed the presence of finer gel networks and lower TBARS values ( P  < 0.05), indicating enhanced oxidative stability. These findings demonstrate that H₂O₂-generated agar hydrolysate, combined appropriately with native agar, serves as an effective natural multifunctional ingredient that simultaneously enhances gel properties and stabilities as well as provides antioxidative protection in surimi-based products. This approach advances sustainable production processes and enhances the utilization of fisheries resources.

Antioxidant and sensory properties of Nile tilapia protein hydrolysates prepared by one- and two-step hydrolysis using commercial proteases were investigated. Hydrolysates prepared using single protease including Alcalase (HA), Flavourzyme (HF), Protamex (HPr) and papain (HPa) had increases in antioxidant activities as the degree of hydrolysis (DH) increased up to 40 % ( P  < 0.05). Amongst all hydrolysates, HA having 40 % DH showed the highest antioxidant activities. When HA was further hydrolysed by papain, the resulting hydrolysate (HAPa) exhibited the highest antioxidant activities for all assays tested ( P  < 0.05). ABTS radical scavenging activity and metal chelating of HAPa generally remained constant in a wide pH range (1–11) and during heating at 30–100 °C. Both activities increased in the simulated gastrointestinal tract model system, especially in intestine condition. HAPa (100–1,000 ppm) could retard lipid oxidation in β-carotene-linoleate and lecithin-liposome model systems in a dose dependent manner. Peptides in both HA and HAPa with molecular weight of 513 Da and 1,484 Da possessed the strongest ABTS radical scavenging activity and metal chelating activity, respectively. The amino acid profile of both HA and HAPa contained a high amount of hydrophobic amino acids (38.26–38.85 %) and had glutamic acid/glutamine, lysine and aspartic acid/asparagine as the dominant amino acids. However, HAPa showed a higher acceptability than did HA, owing to the lower bitterness. Therefore, the use of Alcalase in combination with papain for hydrolysis of protein isolate rendered the hydrolysate with antioxidant properties and reduced bitterness, which could serve as the functional supplement.

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.

Saltwater crocodile (SC; Crocodylus porosus) bone, an underutilized by-product, can be converted into high-value bio-calcium (Biocal), serving as a potential source of calcium and minerals. This study aimed to produce SC bone Biocal as functional gel enhancer for fish bologna development and to increase calcium intake. The resulting bone powder was evaluated for physicochemical, microbiological, and molecular properties. Additionally, the textural, physicochemical, structural, and sensorial properties of the formulated fish bologna incorporating Biocal at varying levels (0–10% w/w) were also evaluated. Biocal, obtained as a fine white powder, had a 16.83% yield. Mineral analysis showed 26.25% calcium and 13.72% phosphorus, with no harmful metals or pathogens detected. X-ray diffraction confirmed hydroxyapatite with 69.92% crystallinity, while calcium bioavailability was measured at 22.30%. Amino acid analysis indicated high levels of glycine, proline, and hydroxyproline, essential for collagen support. The findings confirmed that SC bone Biocal is beneficial and safe for food fortification. Incorporating SC Biocal (2–10% w/w) significantly affected the fish bologna characteristics (p < 0.05). As the Biocal level increased, the gel strength, hardness, and shear force also increased. The addition of 6% (w/w) Biocal significantly improved the textural property, without a detrimental effect on the sensory attributes of the bologna gel (p < 0.05). SDS-PAGE analysis showed TGase-enhanced myosin heavy chain (MHC) cross-linking, particularly in combination with Biocal. Moreover, the enriched Biocal–bologna gel exhibited a finer and denser microstructure. Thus, SC Biocal, particularly at 6% (w/w), can serve as a functional gel enhancer in surimi-based products, without compromising organoleptic quality.

The aim of this study was to develop plant-based yogurt from a mixture of waxy corn and soy milks that mitigated the nutritional deficiencies of typical plant-based products with desirable sensory characteristics and nutritional value by fortifying them with pea protein isolate (PPI) and bio-calcium (Bio-Ca) from Nile tilapia bone. Firstly, different concentrations of PPI (1.0%, 3.0%, and 5.0%) were applied to enhance protein content of plant-based yogurt. Their impacts on the fermentation, physicochemical, and sensory characteristics of developed plant-based yogurts were studied. During fermentation at 40 °C (14 h), the pH of PPI-supplemented samples was higher than that of the control (without PPI) in the first period of fermentation (0–6 h), indicating buffering property of PPI. Titratable acid content (TTA) of yogurt with PPI showed higher TTA than control ( p  < 0.05) after 14 h of incubation. With good acceptance (score ≥ 6) and high protein content (5.41%), the yogurt with 5% PPI was then selected for a study on Bio-Ca fortification. The results showed that adding Bio-Ca (0.5%, 1.0%, and 1.5%) changed the way yogurt fermented and its physical and chemical properties, especially when Bio-Ca levels were higher than 0.5%. After fermentation, the sample with Bio-Ca exhibited a higher total titratable acidity (TTA) and increased viscosity, indicating enhanced metabolic activity of lactic acid bacteria and the formation of salt bridges, respectively, due to Bio-Ca. Sensory evaluation showed that the addition of Bio-Ca had no adverse effect on all attributes tested. In addition, fortification of Bio-Ca at 1.5% showed that calcium content in yogurt was 206.5 mg/100 g sample. Thus, yogurt with 5.0% PPI and 1.5% Bio-Ca was selected for stability evaluation under cold storage for 21 days. The selected yogurt showed a great stability with > 6 log CFU/mL of probiotics throughout the storage period with a lowered syneresis (78.8%), compared with control (72.0%) ( p  < 0.05). This study emphasizes a novel formulation of plant-based yogurt, which provides a rich source of protein and calcium, thereby suggesting its potential advantages over both conventional dairy and plant-based yogurts. Graphical Abstract Highlights • Adding pea protein isolate governed yogurt fermentation and characteristics. • Adding Bio-calcium impacted yogurt fermentation and viscosity. • Novel plant-based yogurt showed great stability during cold storage. • Novel plant-based yogurt provided a rich source of protein and calcium. • Novel plant-based yogurt showed advantages over conventional yogurts.

Sea cucumber is rich in protein that can be used to prepare a potential derived bioactive peptide for antioxidant and protective effect against UV-B induced skin cell damage. This study aimed to optimize preparation of sea cucumber hydrolysate with both UV-B protective and antioxidant activities using three commercial enzymes using response surface methodology (RSM) with a face-centered central composite design (face- centered CCD). Hydrolysis time and concentration of enzyme effects on the degree of hydrolysis (DH), yield, antioxidant and UV-B protective activities of sea cucumber hydrolysates were determined. The optimum conditions for sea cucumber hydrolysis using papain (SCP), alcalase (SCA), or flavourzyme (SCF) were 3.6, 5.0, and 4.1% (w/w protein), respectively, and a hydrolysis time of 360 min. The resulting hydrolysates had a DH of 81-91%, yield of 13-14%, IC 50 for DPPH radical scavenging activity of 0.3-4.1 mg/mL, FRAP of 0.5-0.6 mmol FeSO 4 /mL, and IC 50 for ABTS radical scavenging activity of 1.3-1.6 mg/mL. The UV-B protective activity was reported as the HaCaT cell viability percentage after UV-B treatment. The SCP, SCA, and SCF hydrolysates showed 72.4, 74.5, and 71.3% cell viability, respectively. The concentration of hydrolysates with 80% survival of HaCaT cells was 0.21, 0.15 and 0.20 mg/mL for SCP, SCA and SCF, respectively. Thus, the SCP was selected for bioactive peptide isolation and characterization. The SCP contained hydrophilic and hydrophobic amino acids of 42.4 and 57.6%, respectively. The ultrafiltration and Sephadex G-25 gel filtration chromatography were done for peptide isolation from the SCP. Six potential peptides were identified using LC-MS/MS as Leu-Val-Asn-Glu-Leu-Thr-Glu-Phe-Ala-Gln (1163 Da), Leu-Val-Asn-Glu-Val-Thr-Glu-Phe-Ala-Gln (1149 Da), Phe-Val-Asp-Ser-Ser-Ala-Thr-Thr (826 Da), Phe-Asn-Asp-Leu-Gly-Ala-Trp (821 Da), Phe-Pro-Asp-Thr-Thr-Thr-Leu (793 Da), and Lys-Phe-Gly-Glu-Gly-Lys (664).

Microbiological, chemical and sensory changes of sea bass slices wrapped with fish protein isolate (FPI)/fish skin gelatin (FSG) films incorporated with 3 % ZnO nanoparticles (ZnONP) (w/w, based on protein content) and 100 % basil leaf essential oil (BEO) (w/w, based on protein content) during storage of 12 days at 4 °C were investigated. Sea bass slices wrapped with FPI/FSG-ZnONP-BEO film had the lowest growth of psychrophilic bacteria, lactic acid bacteria and spoilage microorganisms including Pseudomonas , H₂S-producing bacteria and Enterobacteriaceae throughout storage of 12 days in comparison with those wrapped with FPI/FSG-BEO, FPI/FSG-ZnONP, FPI/FSG film, polypropylene film (PP film) and the control (without wrapping), respectively (P < 0.05). Lowered increases in pH, total volatile base, peroxide value and TBARS value were found in FPI/FSG-ZnO-BEO film wrapped samples, compared with others (P < 0.05). Sensory evaluation revealed that shelf-life of sea bass slices was longest for samples wrapped with FPI/FSG-ZnONP-BEO film (12 days), as compared to the control (6 days) (P < 0.05).

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 (Mν: 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, Mν 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.

Antioxidant activities of protein hydrolysate prepared from Nile tilapia protein isolate using Alcalase (HA), Alcalase followed by papain (HAPa) and their Sephadex G-25 fractions (FHA and FHAPa) were investigated in both chemical and cellular based models. Amongst all samples, FHAPa showed the highest chemical antioxidant activities, however it had no metal chelation activity. Cellular antioxidant ability of HA, HAPa and their fractions against H 2 O 2 and AAPH induced oxidative damage of HepG2 cell and DNA were tested. When cells were pretreated with all hydrolysates or fractions at different concentrations (0.5–2 mg/mL) in the absence and presence of 50 μM Trolox, cell viability was in the range of 91.10–111.40 %. However, no difference in cell viability was observed among samples having various concentrations ( P  > 0.05). Cell reactive oxygen species (ROS) generation as mediated by H 2 O 2 and AAPH decreased with treatment of hydrolysates or their fractions, especially in combination with 50 μM Trolox. FHAPa effectively inhibited H 2 O 2 and peroxyl radical induced DNA scission in a dose dependent manner. Therefore, Nile tilapia protein hydrolysates could serve as a functional food ingredient.