الفهرس 
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Abstract
A total of 100 random samples of marine water fish represented by Barboni, Morgan, Mackerel and Balameta (25 of each) were collected from local markets in Alexandria Governorate, Egypt. Samples were collected in semi chilled state and moderate weight and kept in a separate sterile plastic bag and transferred in an ice box as soon as to the laboratory of the Food Hygiene Department, Faculty of Veterinary Medicine, Alexandria University under possible aseptic conditions. Samples were subjected to the following chemical examinations to evaluate their freshness through determination of proteolytic and lipolytic indices as well as their histamine content and the obtained results were summarized as follow:
7.1. Determination of pH value:
pH value is not suitable index for freshness assessment and it can be useful as a guideline for quality control of fish.
It was recorded that pH values of the examined frozen fish samples ranged from 5.9 to 6.39 with mean value of 6.11±0.05 for Barboni fish and it was 6.1 to 6.31 with mean value of 6.17 ± 0.03 for Morgan fish while it was 6.2 to 6.34 with mean value of 6.15 ± 0.04 for Mackerel fish and it was 6.12 to 6.29 with mean value of 6.25 ±0.7 for Balameta fish.
Also, it was noticed that the highest mean of pH values was determined in samples of Balameta fish followed by Morgan fish then Mackerel and lastly Barboni. Moreover, it was noticed that all of the examined samples were within the permissible limit (6.5) recommended by Egyptian Organization for Standardization (EOS), (2005).
7. 2. Determination of Total volatile nitrogen:
Total Volatile Nitrogen (TVN) (mg %) as proteolytic index of spoilage was measured. It was found that the mean of TVN values for examined fish samples was 22.29 ± 0.26, 23.27 ± 0.24, 27.38 ± 0.33 and 24.19 ±0.23 for Barboni, Morgan, Mackerel and Balameta fish samples, respectively. In addition, it was noticed that the highest mean of TVN values was determined in samples of Mackerel fish followed by Balameta, Morgan and lastly Barboni. Moreover, it was noticed that all of the examined samples were within the permissible limit (25 mg %) recommended by Egyptian Organization for Standardization (EOS), (2005).
7.3. Determination of Trimethylamine:
Trimethylamine (TMA) (mg %) as proteolytic index of spoilage was determined for fish samples. It was found that the mean of TMA values for examined fish samples was 5.22 ± 0.23, 4.18 ± 0.18, 3.32 ± 0.33 and 4.90 ±0.49 for Barboni, Morgan, Mackerel and Balameta fish samples, respectively. In addition, it was noticed that the highest mean of TMA values was determined in samples of Barboni fish followed by Balameta, Morgan and lastly Mackerel. Moreover, it was noticed that all of the examined samples were within the permissible limit (10 mg %) recommended by Egyptian Organization for Standardization (EOS), (2005).
7.4. Determination of Thiobarbituric acid:
Thiobarbituric Acid (TBA) (mg %) as lipolytic index of spoilage was estimated for fish samples. It was found that the mean of TBA values for examined fish samples was 3.9± 0.13, 3.6 ± 0.12, 4.8 ± 0.14 and 4.1 ±0.11 for Barboni, Morgan, Mackerel and Balameta fish samples, respectively. Also, it was noticed that the highest mean of TMA values was determined in samples of Mackerel fish followed by Balameta, Barboni and lastly Morgan. Moreover, it was noticed that all of the examined samples were within the permissible limit (4.5 mg %) recommended by Egyptian Organization for Standardization (EOS), (2005).
7.5. Determination of peroxide value (mg/kg):
It was found that the mean of peroxide values for examined fish samples was 0.47 ± 0.06, 0.41 ± 0.05, 0.43 ± 0.04, 0.48 ±0.06 meq O2/kg for Barboni, Morgan, Mackerel and Balameta fish samples, respectively. Also, it was noticed that the highest mean of PV values was determined in samples of Balameta fish followed by Barboni, Mackerel and lastly Morgan.
7.6. Determination of Free fatty acids (mg %):
It was found that the mean values of FFA for the examined fish samples was 0.28 ± 0.03, 0.26 ± 0.02, 0.31 ± 0.04 and 0.29 ±0.05 for Barboni, Morgan, Mackerel and Balameta fish samples, respectively. Also, it was noticed that the highest mean of PV values was determined in samples of Mackerel fish followed by Balameta, Barboni and lastly Morgan.
7.7. Determination of histamine level (mg %):
It was found that the mean values of histamine level FFA for the examined fish samples was 15.6 ± 1.3, 14.2 ± 1.6, 17.4 ± 1.3 and 16.5 ± 2.1 for Barboni, Morgan, Mackerel and Balameta fish samples, respectively. Also, it was noticed that the highest mean of histamine level was determined in samples of Mackerel fish followed by Balameta, Barboni and lastly Morgan. In addition, it was found that all of the examined samples of fish are accepted based on their levels of histamine according to permissible limit stipulated by EOS, (2005).