الفهرس 
ContentsOnly 14 pages are availabe for public view
 |  | from | 112 |  |  |
| | | from | 112 | | |
Abstract
Although fish is highly nutritious, yet it is one of the most rapid perishable foods because of its short shelf-life can be achieved by freezing, chilling, salting, smoking etc. Consumers usually buy fish in bulk and store in refrigerator. Deterioration of fish. quality in refrigerator storage have great impact on the nutritious value of fish and the health of consumers.
Considering the importance from consumer view point, the present study consists of two parts. First part, to study the nutritional value of some Nile fish (Tilapia nilotica, Lates niloticus, chrysichthys auratus and Mormyrus niloticus) present in Assiut market. Second part, to investigate the effect of preservation by chilling in crushed ice for interval periods on the fish quality of these fish.
One hundred samples of freshwater fish (Tilapia nilotica, Lates niloticus, chrysichthys auratus and Mormyrus niloticus) were collected (25 of each) from Assiut city. Transfer them into the laboratory. Measurement of the length and weight. Determination of moisture, protein, fat and ash. Calculation of carbohydrates and energy value. Determination of cholesterol and free fatty acids.
Chemical examination revealed that there is no relationship between the length, weight and the nutritional value of fish.
It is evident that the mean values of moisture% in T. nilotica, L. niloticus, C. auratus and M. niloticus were 79.27±0.22, 78.07±0.28, 74.76±0.47 & 74.97±0.37, respectively.
The mean values of protein% in T. nilotica, L. niloticus, C. auratus and M. niloticus were 80.73±0.3, 89.3±0.39, 69±0.69 & 65.88±0.77, respectively.
The mean values of fat% in T. nilotica, L. niloticus, C. auratus and M. niloticus were 5.64±0.34, 3.89±0.69, 21.96±0.97 & 25.46±0.7, respectively.
The mean values of ash% in T. nilotica, L. niloticus, C. auratus and M. niloticus were 11.82±0.45, 7.39±0.33, 7.62±0.46 & 7.57±0.43, respectively.
It is evident that the mean values of carbohydrate% in T. nilotica, L. niloticus, C. auratus and M. niloticus were 1.8±0.18, 0.61±0.12, 1.36±0.24 & 1.1±0.16, respectively.
The mean values of energy value(kcal/100g) in T. nilotica, L. niloticus, C. auratus and M. niloticus were 380.94±3.24, 383.89±2.44, 479.8±6.8 & 496.99±4.27, respectively.
The mean values of cholesterol(mg/100ml) in T. nilotica, L. niloticus, C. auratus and M. niloticus were 31±1.33, 22.86±1.63, 70.02±1.04 & 80.31±1.21, respectively.
It is evident that the mean values of free fatty acid% in T. nilotica, L. niloticus, C. auratus and M. niloticus were 1.48±0.07, 0.77±0.05, 1.79±0.08 & 2.24±0.06, respectively.
from the obtained results we found that T. nilotica and L. niloticus species contain high protein than C. auratus and M. niloticus but they are lower fat than the other. The four species contain low values of carbohydrates, high calories and low levels of FFA. T. nilotica and L. niloticus have low cholesterol level but C. auratus and M. niloticus have high cholesterol level.
Eighty four samples of freshwater fish (T. nilotica, L. niloticus, C. auratus and M. niloticus) were also collected (21of each) from Assiut city, then transfer them into the laboratory. The samples were immediately transferred to an icebox and kept in crushed ice. The zero time samples were composed of three fishes for each type of fish. Measurement of the length and weight. Determination of moisture, protein, fat and ash. Calculation of carbohydrates and energy value. Determination of cholesterol and free fatty acid. Determination of Total volatile base nitrogen. Determination of Thiobarbituric acid. Then carried out these tests at different times 5, 10, 15, 20, 25, 30 days.
There was significant decline in moisture% of T. nilotica, L. niloticus, C. auratus and M. niloticus with prolonged storage time, where the mean decreased from 79.8±1.1, 80.2±0.9, 76.2±1.0 & 72.9±1.1 to 64.3±1.0, 68.1±0.9, 67±0.5 & 66.2±0.9, respectively. The decrease% in water content in the four species of fish were 19.4, 15.1, 12.1 & 9.2%, respectively.
There was significant decline in protein% of T. nilotica, L. niloticus, C. auratus and M. niloticus with prolonged storage time, where the mean decreased from 79.8±0.8, 88.7±0.8, 68.7±0.7 &67.4±1.2 to 56.5±0.9, 61.2±1.0, 49.2±0.9 & 51.2±0.5, respectively.In chilled samples, there were 29.2, 31.0, 28.4 & 24.0% decrease during 30 days experimental for the four species, respectively.
Change of fat% in T. nilotica, L. niloticus, C. auratus and M. niloticus were from 6.2±0.6, 2.8±0.5, 21.5±0.3 & 23.3±0.7 to 4.1±0.5, 1.8±0.1, 7.8±1.2 & 11±0.9, respectively. There were 33.9, 35.7, 63.7 & 52.8% decrease for the four species.
Change of ash% in T. nilotica, L. niloticus, C. auratus and M. niloticus were from 13.8±0.3, 8.4±1.0, 9.6±1.3 & 9±0.6 to 8.2±0.4, 5.8±0.5, 5.2±0.2 & 4.1±0.5, respectively.The decreases were 40.6, 31.0, 45.8 & 54.4% for the four species, respectively.
There was significant raised in carbohydrate% of T. nilotica, L. niloticus, C. auratus and M. niloticusfrom0.03±0, 0.2±0.1, 0.2±0.1& 0.3±0.1 to 31.5±0.8, 30.2±1.0, 38.5±0.9 & 34.7±1.2, respectively.The increase values were 31.47, 30.0, 38.3 &34.4 for the four species, respectively.
Change of energy value(kcal/100g) in T. nilotica, L. niloticus, C. auratus and M. niloticus were from 375.4±0.9, 380.8±0.5, 469.1±1.8 & 483.2±1.1 to 388.9±0.9, 381.8±0.3, 421±1.2 & 442.6±1.3, respectively. The increase values were 13.5 & 1.0 in T. nilotica and L. niloticus, the decrease values were 48.1 & 40.6 in C. auratus and M. niloticus.
It is evident that there was significant increase of cholesterol(mg/100ml) in T. nilotica, L. niloticus, C. auratus and M. niloticus from 33.2±1.2, 24.2±0.3, 64.1±0.9 & 84.8±0.4 to 45.0±1.0, 35.3±0.7, 78.5±0.3 & 98.3±0.8, respectively. There were 35.5, 45.9, 22.5 & 15.9% increase during 30 days experimental for the four species, respectively.
It is evident that the mean values of free fatty acid content were increased from 1.5±0.4, 0.8±0.2, 2.0±0.1 & 2.2±0.3 in T. nilotica, L. niloticus, C. auratus and M. niloticus to 4.9±0.3 , 3.2±0.2 , 17.9±0.4 & 19.0±0.2, respectively. In chilled samples, there were 3.4, 2.4, 15.9 & 16.8 increase during 30 days experimental for the four species, respectively.
There were changes in mean TVBN (Total volatile base nitrogen) content in T. nilotica, L. niloticus, C. auratus and M. niloticus, the significant increase took place from the initial time (zero time) to the last time of chilling (30 days) and occurred from 7.2±1.1,8.5±0.3, 4.2±1.0 & 5.9±1.2 mgN/100g to 39.9±0.9, 40.2±1.0, 31.8±1.0 & 30.5±0.9 mgN/100g, respectively. There were 32.7, 31.7, 27.6& 24.6 increase during 30 days experimental for the four species, respectively.
TBA (Thiobarbituric acid) values (mg mal/kg) at zero day were found to be 0.07±0.02 for T. nilotica, 0.06±0.03 for L. niloticus, 0.3±0.12 for C. auratus& 0.49±0.06 mg mal/kg for M. niloticus, while the values at 30th day were found to be 1.4±0.3, 1.3±0.1, 3.4±0.3 & 3.9±0.2 for T. nilotica, L. niloticus, C. auratus and M. niloticus, respectively. In chilled samples, there were 1.33, 1.24, 3.1 & 3.41 increase during 30 days experimental for the four species, respectively.
The organoleptic examination showed that the fish were unfit for human consumption after 15 days of chilling preservation although that not exceed the permissible limits.<Preservation by chilling prolong shelf-life for 15 days in case of T. nilotica and L. niloticus, and 20 days for C. auratus and M. niloticus.