الفهرس 
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Abstract
7. SUMMARY
In recent years, the demand for natural antioxidants has been increased mainly because of the adverse effects of synthetic antioxidants, which have been confirmed for their toxicological and carcinogenic effects. The, most of the recent investigations have been directed towards the identification of natural antioxidants from various plant sources. They will offer increased consumer acceptability, decreased potential health risks, They can often achieve the same degree of oxidation prevention as Synthetic antioxidants.
The results of the studies demonstrated that the addition of seaweeds, in extract form, can improve the nutritional and textural properties of food products. Additionally, low-fat products with less calories and less saturated fatty acids can be prepared using seaweeds. Moreover, the addition of seaweeds also affected the health properties of food products. The results of these studies demonstrated that the health value, shelf-life and overall quality of foods can be improved through the addition of either seaweeds or seaweed extracts.
Seaweeds, by virtue of their bio-diverse nature, possess abundant quantity of bioactive compounds including polysaccharides, peptides, omega-3 fatty acids, carotenoids, phenolics, vitamins and minerals. These compounds have been demonstrated to have potential for improving human health and imparting various physiological functions.
Therefore, the aim of this study was to evaluate algae aqueous extract (Dictyota,Sargassum and Hormophysa) for their phenolic, flavonoid, antioxidant and antimicrobial potentials. Furthermore the Dictyota extract was applied to fish fingers with three different concentrations (5% and 10%) compared with negative control and positive control (BHT). Their impact on shelf life was assessed through chemical, physio-chemical and microbiological analysis through a storage period of 12days and at 4 °C, to recommend the most appropriate concentration as a natural preservative replacing the artificial preservative (BHT).
This aim was achieved by:
1. Preparation of algae aqueous extracts.
2. Evaluating algae extracts for their phenolic, flavonoid, antioxidant and antimicrobial potentials.
3. Assessment of algae extract impact on shelf life of fish fingers with two different concentrations (5% and 10%) compared with negative control and positive control (BHT) through a storage period of 12 days and at 4 °C, through the evaluation of chemical, physio-chemical and microbiological analysis every three days of the storage period.
The obtained results can be summarized as follow:
The mean values for phenolic content was (142.78±2.36, 127.37±1.29 and 108.48±2, 29 mg/g sample), respectively, for (Dictyota, Sargassum and Hormophysa). The Dictyota extracts showed the highest phenolic content.
The mean values for flavonoid content were (114.42±0.68, 105.88±2.05 and 103.56±1.24 mg/g sample), respectively, for (Dictyota, Sargassum and Hormophysa). The Dictyota extracts showed the highest flavonoid content.
Results of antioxidant activity represented in the IC50 and EC50 which was (10.55±0.14, 69.44±0.13, 77.04±0.11 and 101.01±0.18 μg/ml), respectively, for (Ascorbic,Dictyota,Sargassum and Hormophysa) The Hormophysa showed the highest antioxidant potentials.
The Dictyota show a remarkable antimicrobial activity with MIC of 25mg/ml with the pathogenic strains (Staphylococcus aureus EMCC1351, Streptococcus pyogenes EMCC1772, Bacillus cereus EMCC1006, Escherichia coli ATCC25922 and with MIC 100 mg/ml with Candida albicans EMCC105) which was higher than the antimicrobial potentials of other extracts.
The Dictyota extract has the highest antioxidant and antimicrobial potentials than other extracts. So the Dictyota extract was applied as natural preservative in fish finger at two concentrations (5% and 10%) and compared with negative control and positive control (BHT) and the pH value, WHC, TBARS, DNPH and microbial load was evaluated through a storage period of 12 days and at 4 °C.
During storage the treatment with Dictyota extract on fish finger samples showed results superior to that of the synthetic antioxidant with a lower significant change on pH value and WHC value at 12 days of storage with a mean values of (6.55, 6.65, 6.86 and 6.90) for pH in Tilapia finger samples and with a mean values of (6.27,6.18,6.28 and 6.42) for pH in Mugil finger samples . The WHC showed a mean values of (73.45, 76.63, 74.27 and 76.80%), respectively, for ( negative control, positive control (BHT), BAE5% and BAE10%) for Tilapia fingers samples and The WHC showed a mean values of (74.59 76.46, 77.45and 79.29%), respectively, for ( negative control, positive control (BHT), BAE5% and BAE10%) for Mugil fingers.
The Dictyota extract showed high antioxidant potential on both lipid and protein oxidation through the storage period expressed in TBARS value and carbonyl content at 12 days of storage with a mean values of (1.80, 1.02, 0.71 and 0.65 Mg MDA\ Kg) for TBARS and, a mean values of (18.03, 10.15, 7.11 and 6.53 Nmol carbonyl content/mg protein) for DNPH, respectively, for ( negative control, positive control (BHT), BAE5% and BAE 10%) for Tilapia finger samples and also period expressed in TBARS value and carbonyl content at 12 days of storage with a mean values of (1.48, 1.03, 0.44 and 0.31Mg MDA\ Kg) for TBARS and, a mean values of (14.81, 10.27, 4.37 and 3.14 Nmol carbonyl content/mg protein) for DNPH, respectively, for ( negative control, positive control (BHT), BAE 5% and BAE 10%) for Mugil finger samples.
The microbial load at 12 days of storage showed a result with a mean values of (2.1x105, 1.2x104 , 2.8x104 and 1.1x103 Cfu/g) for aerobic bacterial count, respectively, for ( negative control, positive control (BHT), BAE 5% and BAE 10%) for Tilapia finger samples .While the microbial load at 12 days of storage showed a result with a mean values of (1x105, 1.1x104 , 1.9x104 and 1.3x103 Cfu/g) for aerobic bacterial count, respectively, for ( negative control, positive control (BHT), BAE 5% and BAE 10%) for Mugil finger samples . While coliform count and yeast and mould count the BAE extract 10% was able to keep the counts without significant increase in comparison with the negative control, positive control and other concentrations of the mix for both Tilapia and Mugil finger samples.
The TVB-N in fish finger samples at zero day there was significant difference (p<0.05) in TVB-N value between the fish finger samples showing the results of negative control, positive control, BAE 5% and BAE 10% (1.30, 1.88, 1.50 and 1.24 mg/100 g), respectively, and at 12 days of storage it increase reaching (36.06, 20.30, 14.22 and 13.06 mg/100 g), respectively, for Tilapia fish finger samples, also the TVB-N in fish finger samples at zero day there was significant difference (p<0.05) in TVB-N value between the fish finger samples showing the results of negative control, positive control, BAE 5% and BAE 10% (1.30, 1.30, 1.60 and .98 mg/100 g) ,respectively, and at 12 days of storage it increase reaching (29.62, 20.54, 8.74 and 6.28 mg/100 g) respectively.
The fish fingers treated with algae extract or without extract (PC and NC) gained no a significant difference (P >0.05) in all sensory criteria including appearance, taste, color, flavor, taste and overall acceptability after processing, but there was a significant difference in the overall grade with the highest score for BAE 10% group 7.53 followed by BAE 5% group 6.87 then the negative control group 7.53 and the lowest scores were for the positive control group 7.13 for Tilapia, also the fish fingers treated with algae extract or without extract (PC and NC) gained no a significant difference (P >0.05) in all sensory criteria including appearance, taste, color, flavor, taste and overall acceptability after processing, but there was a significant difference in the overall grade with the highest score for BAE 10% group 7.53 followed by BAE 5% group 6.80 then the negative control group 7.53 and the scores were for the positive control group 7.47 for Mugil which considered appositive results as the treatment were acceptable to the consumer.
These findings show that this algae extract is very effective against lipid and protein oxidation, and a powerful antimicrobial in different fish products and is a promising natural antioxidant and antimicrobial replacing the synthetic preservatives in fish processing. These biological activities could be attributed to phenols present in these algae. Further research is needed for the isolation and identification of individual phenolic compounds in addition to In-Vivo studies that can introduce better understanding of their mechanism of action.