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Aims: Skipjack tuna has the highest level of catch rate among tuna all over the world. Its head contains about 64% protein. Many Protein Hydrolysates and peptides obtained from various marine sources have a high antioxidant power. The aim of this study was to investigate the antioxidant activity of Protein Hydrolysate in Skipjack tuna head.
Materials & Methods: In this experimental study, 30 Skipjack tunas were investigated. At first, the amount of different compounds (protein, fat, ash, and moisture) was evaluated in the raw material; then, the hydrolysis process was performed by Alcalase enzyme and the hydrolysis degree of the protein hydrolysate was evaluated at different times. The antioxidant activity of the protein hydrolysate mixture was measured by DPPH radical scavenging activity, iron revival power, and ABTS radical inhibitory activity. For data analysis, the analytical tests were used.
Findings: The main part of the fish head was protein and it had high levels of ash. The degree of hydrolysis increased with increasing time and was it significant at 15, 60, and 120 minutes (p<0.05), but not significant at 120 and 240 minutes (p<0.05). DPPH radical scavenging activity increased with increasing hydrolysis time and there was a significant difference in all samples obtained from different times (p<0.05). The iron reduction capacity of the protein hydrolysate samples increased with increasing the hydrolysis time, and the highest amount was at 240 minute. The samples obtained from different times had a significant difference in iron reduction capacity (p<0.05). Increasing the concentration of protein hydrolysate increased inhibitory activity (p<0.05).
Conclusion: Protein hydrolysate in Skipjack tuna head has a high antioxidant activity and can be used in food products to increase oxidation stability.

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Diabetes mellitus is a major health problem in the worldwide. Inhibition of DPP-IV is one of the methods to control diabetes type 2. Inhibition of this enzyme may improve glycemic control in diabetics by preventing the rapid breakdown and there by prolonging the physiological action of incretin hormones. Furthermore, improving the antioxidant system in diabetic patients can prevent the occurrence of secondary disease caused by oxidative stress. Therefore, the head of skipjack tuna was hydrolyzed with alcalase enzyme (1/5% of raw material weight) for 4 hours, in order to produce a product with antidiabetic and antioxidant activities. The DPP-IV inhibition activity, DPPH radical scavenging activity and reducing power of hydrolysate were measured. The results showed that the skipjack tuna head protein hydrolysate possess bioactive properties in a concentration dependent manner and increasing the protein concentration leads to a significant increase in bioactive properties of hydrolyzed product (p≤0.05). The IC50 of protein hydrolysate in DPP-IV inhibition and DPPH radical scavenging activities were obtained 1.016±0.02 mg/ml and 0.297±0.015 mg/ml, respectively. Also the reducing power of hydrolysate was 0.176±0.002 in 2.5 mg/ml protein concentration. Overall, according to the obtained results, it can be concluded that protein hydrolysate of skipjack tuna head possess high antioxidant and antidiabetic activities in vitro, and can be used as a food additive to enhance health level if additional research be conducted.

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The present study was conducted with the aim of protein isolate production from the muscle of grass carp (Ctenopharyngodon idella) and investigation of the effect of extraction pH on different properties of isolated protein. Proteins were produced by pH-shift method in two treatments including dissolution in alkaline pH (11.5), and acidic pH (3), and then evaluated in terms of nutritional value, functional properties, and structural changes. According to the results, the yield of protein production was significantly higher in alkaline conditions than in acidic conditions. The evaluation of emulsifying and foaming capacity and water absorption capacity showed that the protein obtained from alkaline pH was better than acidic treatment. Also, the extracted proteins contained all essential amino acids within the recommended limit for daily consumption of adults. The evaluation of color indices showed that the protein obtained from acidic pH had a brighter and whiter color than alkaline pH. The images obtained from the scanning electron microscope and the FTIR spectra of samples showed that the pH-shift method did not lead to extensive destruction of the protein structure and both protein isolates had all the absorption peaks related to the main bonds of the proteins structure. In general, it can be concluded that the pH-shift method is an efficient method for extracting high quality protein from grass carp tissue, and different alkaline and acidic conditions lead to the production of proteins with different characteristics that can be used based on the application that is intended for the final product.

 

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 In the current study, fish-isolated protein (FPI) was extracted by alkaline pH method from the wastes of the head and fins of Siberian sturgeon (Acipenser baerii) and Iranian sturgeon (Acipenser persicus) and its composition, functional and structural characteristics were investigated. The results showed that the extraction efficiency according to the wet weight, the protein recovery of FPI, and the dry matter recovery of FPI from the Siberian sturgeon was higher than that of Iranian sturgeon. The results showed 91-94% protein in FPI of two species. The results did not show any significant differences between the proximate analysis and TVB-N (P> 0.05). The water absorption capacity, foaming capacity, and stability of FPI were shown at 30, 50, and 50%, respectively. The whiteness and transparency index of the FPI extracted was low. The results of particle size and zeta potential (P< 0.05) showed that the size of FPI particles in both samples is about a micron and they have a negative charge, so they can be easily used in colloidal systems. FTIR spectroscopy in both samples showed all the absorption peaks related to the main bonds of the protein structure. In general, considering the large amount of sturgeon waste in processing, and the amount of protein, functional properties, and nutritional value of FPI extracted from two species of sturgeon, there is the possibility of using them in human food and sports supplements.

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In the present study, the antioxidant properties of different molecular weight fractions and different concentrations of protein hydrolysate from Common carp (Cyprinus carpio) head were investigated. Fish heads were hydrolyzed by Alcalase enzyme (1% v/w) at 55˚C and pH 8 during 180 min. The supernatant was fractionated to three different molecular weight fractions of <3, between 3 and 10 and >10 KDa by ultrafiltration. The results showed a significant difference between DPPH radical scavenging activity of the different molecular weight fractions, and the highest and the lowest values ​​were observed in the fractions of 3-10 and less than 3 KDa, respectively (p <0.05). The fraction with molecular weight of 3-10 KDa showed the lowest IC₅₀ (1.15±0.015 mg/ml) for DPPH scavenging activity.  As the concentration increased, ferric ion reducing power of all molecular weight fractions were increased, and the highest value was observed in the molecular weight of more than 10 kDa (p <0.05). Significant differences of ABTS radical scavenging activity were observed between the different molecular weight fractions at all concentrations, and the highest and the lowest values ​​were observed in the molecular weight fractions of 3-10 and less than 3 kDa, respectively (p <0.05). The molecular weight fraction of 3-10 kDa, exhibited the lowest IC₅₀ value for ABTS radical scavenging activity (1.1±0.01 mg/ml). In general, according to the positive function of Common carp head protein hydrolysate at different concentrations and different molecular weights on DPPH and ABTS radical scavenging activity and ferric ion reducing power, it can be stated that this protein hydrolysate can be considered as a natural antioxidant for use in the food industry or animal, poultry and aquatic feed.

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The purpose of this study was to investigate the effect of microwave pretreatment on the degree of hydrolysis and antioxidant activity of Beluga (Huso huso) viscera protein hydrolysate. For this purpose, the samples were hydrolyzed after two conditions of pretreatment including no treatment with microwave or after ten minutes treatment with microwave (frequency 2450 Hz and temperature 90 °C), by alkalase enzyme with a concentration of 2%, temperature of 55°C and pH 8, and then the degree of hydrolysis and antioxidant activity of the produced samples were evaluated. According to the results, the degree of hydrolysis after microwave treatment was significantly higher than the sample without microwave treatment (p<0.05). Also, the sample produced after microwave treatment showed higher antioxidant activity (DPPH and ABTS radicals scavenging activity and Fe reduction capacity) compared to the control treatment (p<0.05). The IC₅₀ values ​​of this treatment in inhibiting DPPH and ABTS radicals scavenging activity were obtained as 1.25 mg/ml and 1.63 mg/ml, respectively, which was significantly lower than the control treatment (p<0.05). Also, in both samples, antioxidant activity increased significantly with increasing concentration (p<0.05). In general, it can be stated that 10 minutes of microwave pretreatment at 90 °C has a favorable effect on the properties of Beluga viscera protein hydrolysate which can indicate the applicability of this technology in the production process of fish protein hydrolysate.