الفهرس 
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Abstract
There is a big gap between the production and consumption of vegetable oils in Egypt, where 90 % of consumed quantities is imported from the outside. Thus, the researchers and producers try to find substituted vegetable oils such as canola oil. Canola crop is distingued by its high content of oil. Also, it is a winter crop, not conflicting with crop rotation and short growing season crop.
This study was carried out as a comparing study between cottonseed oil and canola oil to evaluate:
A. The physical and chemical characteristics of the studied oils.
B. Fatty acid composition.
C. Effect of frying (at 180 oC for 12 hours) on physical and chemical characteristics as well as fatty acid composition.
D. Effect of storage period and antioxidants on physical and chemical characteristics as well as fatty acid composition.
The results obtained can be summarized as follow: -
A- The physical and chemical characteristics of cottonseed and canola oils:
The physical and chemical properties of cottonseed oil were 44.80, 1.4685, 35/6.8, 0.18, 103.00, 198.45, 1.07, 9.40 and 0.78 for viscosity (m.Pa.sec./25oC), refractive index, colour, acid value, iodine value, saponification value, unsaponifiable matter (%), peroxide value and thiobarbituric acid, respectively. The physical and chemical properties of canola oil were 57.00, 1.4691, 35/6.6, 0.53, 111.15, 191.80, 1.42, 1.82 and 1.42 for viscosity (m.Pa.sec./25 oC), refractive index, colour, acid value, iodine value, saponification value, unsaponifiable matter (%), peroxide value and thiobarbituric acid, respectively.
B-Fatty acid composition of cottonseed and canola oils:
The major fatty acid content of oil samples under investigation, namely palmitic (C16:0), oleic (C18:1) and linoleic (C18:2). The highest percentage of palmitic acid was recorded in cottonseed oil (23.20 %). Meanwhile, canola oil contained much lower amounts of palmitic acid (5.82 %). Also, the amount of stearic acid in the investigated oils was ranged between 2.05 % and 2.15 %. Canola oil had the highest amounts of total unsaturated fatty acids (91.07 %) followed by those found in cottonseed oil (73.47 %). The data indicated that the majority of oleic acid was found in canola oil (56.54 %) compared with lower amounts in cottonseed oil (25.06 %). However, polyunsaturated fatty acids in cottonseed oil (46.85 %). Besides, canola oil contained much lower amount of linoleic acid (25.81 %). The highest value of linolenic acid (6.80 %) was found in canola oil in comparison with the lowest value (0.1 %) in cottonseed oil. The percentage of gadoleic (C20:1) and erucic (C22:1) of canola oil were 1.72 and 0.20 %, respectively, whereas, these fatty acids were not detected in cottonseed oil. Generally, canola seed oil contained large amount of unsaturated fatty acids especially oleic acid and considerable amount of linoleic and linolenic acids as compared other investigated oils. Therefore, canola oil can be used in food purpose side to side with other common plant oils.
C-Effect of frying (at 180 oC for 12 hours) on physical and chemical characteristics as well as fatty acid composition:
1-The viscosity increased gradually as frying time of the oil increased. The rate of increasing depends on the kind of vegetables used in frying as well as the type of oil.
2-The colour intensity was increased during frying but, the extent of increase was affected by the kind of vegetables used in frying, oil brand and frying time. The highest increase in colour intensity was recorded in cottonseed and canola oil samples remaining after 12 hours of frying eggplant (red 11.5 and blue 3.7 in cottonseed oil while red and blue were 11.7 and 5.0, respectively, in canola oil). In contrast, the lowest value of increase in colour intensity was obtained in cottonseed and canola oil samples remaining after 12 hours of frying potatoes: this variation could be attributed to the browning pigments from the foods which were dissolved into frying oils.
3-The decrease in refractive index of the refined and deodorized oils during intermittent heating at 180 oC was attributed to the polymerization which could have occurred during heating at high temperature. In addition, the refractive index of the studied oil samples decreased gradually with increase in frying time. The rates of increasing depend on the kind of vegetables used in frying as well as oil brand.
4-The differences in acid value (A.V.) may be due to the conditions during ripening of the seeds and conditions of harvesting and storage as well as conditions during processing. Furthermore, the change in A.V. for canola oil was the highest followed by cottonseed oil. On the basis of acid value, the eggplant slices were found to affect the acidity of oil samples more markedly than potato and squash samples.
5-The iodine value (I.V.) decreased gradually in all oil samples during heat treatment. The extent of decrease in I.V. was affected by kind of vegetable, frying time as well as the oil brand used as frying medium. The decrease of I.V. during frying could be attributed to the formation of fatty acids which differ in their degree of unsaturation or to the distribution of double bonds. In addition, the highest decrease in I.V. was observed in oil samples remaining after 12 hours of frying squash. This variation may be due to the differences in chemical composition of vegetables used in frying processes.
6-The saponification value (S.V.) increased gradually in all oil samples as heating or frying time increased. The rate of increase in S.V. was affected by frying time, kind of vegetable and oil brand used in frying process. The oil sample remaining after 12 hours of frying eggplant recorded the highest increase in S.V. In contrast, the oil sample remaining after frying squash for the same period of frying showed the lowest increase in S.V.
7-The unsaponifiable matter percentage decreased gradually in all oil samples during frying. Also, the oil samples remaining after 12 hours of frying potatoes was recorded the highest decrease in unsaponifiable matter percentage than other vegetables. In contrast, the oil samples remaining after 12 hours of frying eggplant showed the lowest decrease in the percentage of unsaponifiable matter.
8-The peroxide value (P.V.) and thiobarbituric acid (T.B.A.) are employed in this study to determine the extent of oxidation caused in the investigated oils. This variation in either P.V. or T.B.A. values may be due to the differences in chemical constituents of oil samples. Generally, the P.V. increased gradually in all oil samples (either canola or cottonseed) due to frying at 180 oC. The data clearly show a difference between the two oils. While cottonseed oil showed a rapid increase in P.V. from 9.40 to 16.20, 15.70 and 14.20 meq. peroxide/Kg after 12 hours of frying eggplant, potatoes and squash, respectively. For the canola oil, the results showed a slight increase in the P.V. value from 1.82 to 1.99, 2.10 and 1.89 meq. peroxide/Kg after 12 hours of frying eggplant, potatoes and squash, respectively. Also, the T.B.A. value increased gradually as heating or frying time increased in all samples. The oil samples remaining after 12 hours of frying eggplant showed the highest increase in T.B.A. values than oil samples of potatoes and squash. This variation might be due to the difference in glycerids structure which depends on the oil source.
9-Concerning the effect of frying on the fatty acid composition of cottonseed and canola oils, the obtained results indicated that the heating temperature during frying caused a gradual increase in C10:0, C12:0, C14:0, C16:0, C18:0, TSFA and ratio of C18:2: C18:1 with increasing frying time. In contrast, a gradual decline was observed in C16:1, C18:1, C20:1, C22:1, TMUFA, C18:2n-6, C18:3n-3, TPUFA, TUFA as well as ratio of TUFA: TSFA.
D-Effect of storage period and antioxidants on physical and chemical characteristics as well as fatty acid composition:
1-The viscosity increased gradually in all oil samples during storage. The highest increase in the viscosity was recorded in the control sample after six months of storage either in cottonseed oil (51.70 mPa.sec.) or canola oil (75.80 mPa.sec.). On the other contrary, the lowest increase in the viscosity was found in oil samples stored for three months and treated with 0.02 % of either B.H.A. or B.H.T.
2-The unsaponifiable matter of the stored oil samples a slightly decrease in the unsaponifiable matter content during storage.
3-The refractive index of oil samples was decreased gradually as storage period increased. However, the decrease in the refractive index of the studied oil samples during storage could be explained on the basis of the double bonds saturation of the fatty acids during the production of hyDROPeroxides and intermediate compounds.
4-The colour intensity was increased during storage. The extent of increase was affected by the storage period; oil brand, type and concentration of antioxidants. The increase in colour intensity of the oil samples during storage could be attributed to the formation of fatty acid polymers which accumulate as a result of triglycerides hydrolysis during storage. The increase in colour index is probably due to oxidation typically resulting in the generation of hyDROPeroxides, conjugated dienoic acids, epoxides, hydroxides and keteones. Oils and fats can also produce dimeric acids, and form polymers of higher molecular weight, causing a darker colour and a deposit of yellow or brown pigments.
5-The acid value increased gradually in all oil samples during storage. The control oil samples stored for six months had the highest increase in acid value either in cottonseed oil (0.46) or in canola oil (0.98) followed by control oil samples stored for three months. The lowest increase in acid value was found in oil samples stored for three months and treated with 0.02 % B.H.A. (0.27 and 0.55 in cottonseed and canola oil samples, respectively). The oil samples treated with the concentration 0.01 % of antioxidants showed a little higher increase in acid value than oil samples treated with 0.02 %. The slight gradual increase in the acidity could be attributed to the hydrolysis of some phosphatides and triglycerides into glycerol and free fatty acids. Although the acid value is an index of hydrolytic rancidity, it was measured as acids contribute to the development of off-flavours and off-odours in the product.
6-The P.V. and T.B.A. values were increased gradually in all oil samples during storage; the rate of increase was higher in the oil samples stored for three months. Also, the rate of increase in P.V. and T.B.A values were higher in oil samples (either cottonseed or canola) treated with 0.01 % concentration of antioxidants than those treated with 0.02 % concentration. In addition, the control oil samples stored for six months had the highest increased in P.V. and T.B.A values. The gradual increase in the P.V. value could be attributed to the accelerating effect of storage temperature in the presence of oxygen on oxidation and peroxide formation. The increase in TBA value due to increasing in absorption at 532 nm could reflect increases in shorter chain dienals and malonaldehydes which are not as pleasant in flavour.
7-The iodine value (I.V.) of all oil samples was decreased during storage. The highest decrease in iodine value was recorded in control oil samples stored for either three or six months. The rate of decrease in iodine value of the oil samples treated with 0.01 % concentration of antioxidants was higher than those oil samples treated with 0.02 % either stored for three or six months.
8-The S.V. increased gradually in all oil samples as storage period increased. The rate of increase in S.V. was affected by storage time, type of oil, type and concentration of antioxidants. The highest increase in S.V. was recorded in control oil samples stored for six months.
9-The values of fatty acids; C10, C12, C14, C16, C18, C20, TSFA and ratio of C18:2: C18:1 were increased with increasing the storage period in all oil samples. In contrast, the values of C16:1, C18:1, C20:1, C22:1, TMFA, C18: 2n-6, C18:3n-3, TPUFA, TUFA and ratio of TUFA: TSFA were decreased. The rate of changes was dependent on the oil brand, antioxidant type and concentration. The decrease in unsaturated fatty acids either polyunsaturated fatty acids (C18: 2n-6 and C18:3n-3) or monounsaturated fatty acids could be attributed to the oxidation and hence the change in the degree of unsaturation. Finally, the storage of cottonseed and canola oils for long period at room conditions causes undesirable changes in their physical and chemical properties. Furthermore, it reduced the nutritive value of the stored oils through the reduction of their unsaturated fatty acid contents.