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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.

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 , H 2 S-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).

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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.

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Effect of whey protein concentrate (WPC) in combination with calcium chloride (50 mmol/kg) on the gel properties of surimi produced from goatfish (Mulloidichthys martinicus) was investigated. Breaking force and deformation of both kamaboko (40/90C) and modori (60/90C) gel increased with increasing WPC (0-3%) (P < 0.05). Myosin heavy chain (MHC) band intensity of all gels was more retained as WPC concentration increased. The coincidental increase in water-holding capacity was obtained, however, the whiteness was slightly decreased. At all levels of WPC added, kamaboko gels added with CaCl 2 exhibited the superior properties to those without CaCl 2 (P < 0.05). On the other hand, CaCl 2 addition resulted in the poorer gel properties of modori gel, regardless of WPC addition. The microstructure of surimi gels added with 3% WPC generally became denser and more ordered, compared with the control gel, irrespective of CaCl 2 addition. PRACTICAL APPLICATIONSGoatfish is the new raw material for surimi production; however, it yields the gel with poor quality. The addition of WPC and CaCl 2 at the appropriate levels can be a promising means to improve the gel quality via the inhibition 3 Corresponding 341 of endogenous proteinases and the enhancement of setting phenomenon, respectively. As a consequence, surimi industry is able to produce surimi from goatfish with the quality equivalent to that of surimi from commonly used species. Thus, the greater benefit can be gained from goatfish, especially for the surimi industry.

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