| Fish oil is beneficial to our health because of its enrichment in n-3 polyunsaturated fatty acids, which has been the focus of research both in China and abroad over the years. As one of the deep sea fish oil products, tuna oil has deep color and large viscosity compared with other varieties of fish oil because of its characteristics of red meat fish, which make it become the widespread problem of domestic industry about degumming and decoloring in the process of refining. As is known to all, the higher the content of effective component in fish oil, the better of its healthy effects. So there are many reports about enrichment of fish oil. However, now most fish oil enterprises prepare fish oil products relying on urea inclusion joint multistage molecular distillation method. There is no breakthroug in decades. Therefore, it is very important for fish oil industry reform and upgrading in the future to explore more method. In addition, the study of fish oil quality during storage usually determine physical and chemical indicators, or active ingredients, which is complex and laborious. There must be some kind of relationship to smell and corruption considering the "clams taste" when fish oil go bad. Then I started to seek the relationship between smell and physical and chemical indicators. And further understanding oxidation mechanism of fish oil during storage and establishing the theoretical foundation for further study combined with GC-MS.In order to solve the refining problem, this paper studied the degumming process firstly, determined that parameters were citric acid/acetic acid ratio of 1.75:1(v/v), degumming temperature of 50 ?, dosage of 1.5%(the oil weight), 25 min, the degumming rate was 3.90% and the product had good transparency and light fishy smell. Then deacidification and decoloring process were studied that alkali refining with salt water and decoloring with activated clay and activated carbon, determined that parameters were as follows: 1.5 times of theoretical amount of alkali dosage, 20% NaOH, stirred at 85 ? for 20 min, 5000 r/min and after that added 10%(dosage) 90 ? 5% hot water, then added 0.5% activated carbon and 0.5% activated clay(relative to the heavy oil), 105 ? for 25 min, got decoloed oil by vacuum filtration. Under this optimized conditions, the fish oil was orange yellow and light fishy smell, acid value was 0.44 mgKOH/g, iodine value was 193.8 gl / 100 g, peroxide value was 4.52 mmol/kg, saponification substance was 0.32%, which complied with top standard of SC/T 3502-2000.Secondly, using low temperature crystallization method to enrich tuna oil. Choosing methanol and ethanol as suitable solvent, the optimum parameters for enrichment of fish oil by the method of low temperature crystallization were methanol/ethanol ratio of 9.1:1(v/v), the crystallization temperature of 34.59 ?, the crystallization time of 6.49 h, solvent/sample ratio of 6.72:1(m/m). through analysis of Box-Behnken program of design expert 7.0 software. Considering the actual operation, modified parameters as the following: methanol/ethanol ratio of 9.1:1(v/v), the crystallization temperature of 34.6 ?, the crystallization time of 6.5 h, solvent/sample ratio of 6.7:1(m/m). Repeating test for three times under this conditions, and the content of(EPA + DHA) in product was 89.20% and yield was 65.32%. The regression model had a good fit degree and good directional sense to practice.In addition, Change of smell of tuna crude fish oil and ethyl ester type fish oil during storage were studied through electronic nose. It can be distinguished by principal component analysis(PCA) and linear discriminant analysis(LDA) that samples with different storage time. Nitrogen oxides were the main volatile components of fish oil during storage. Using PLS partial least squares(PLS) to predict acid value and peroxide value of crude fish oil. Linear simulation equations were obtained that Y=1.02986X-0.48431, R2=0.9415 and Y=0.96907+0.26401 X, R2=0.9846, respectively. It had been verified for five times that average relative deviations were 10.60% and 12.04% respectively. In the same way, using PLS method to predict acid value and peroxide value of ethyl ester type fish, linear simulation equation was obtained that Y=0.99048+0.0093 X, R2=0.9755, Y=0.0204X-0.07918, R2=0.9959, three validation tests showed that prediction error were 7.00% and 5.48% respectively. From the above we knew that smell of fish oil in the process of storage was associated with the change of the acid value, peroxide value. To some extent, we can use the change of smell to analyse the change of its quality.Finally, volatile substances of fish oil were analysed by GC-MS. The results showed that volatile substances of crude fish oil included 7 kinds of ketones, 20 kinds of aldehydes, 17 kinds of alcohols, 8 kinds of alkanes, 7 kinds of olefins, 8 kinds of acids, 3 kinds of esters and some heterocyclic compounds, nitrogen compounds and so on. Volatile substances of ethyl ester type fish oil included 2 kinds of ketones, 15 kinds of aldehydes, 5 kinds of alcohols, 2 kinds of alkanes, 2 kinds of olefins, 2 kinds of acids, 18 kinds of esters, some aromatic hydrocarbons and so on. |
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