| Tuna oil is rich in omega-3 unsaturated fatty acids with high ratio of eicosapentaenoic acid(EPA)and docosahexaenoic acid(DHA)which have many benefits to the human health,such as preventing cardiovascular disease,enhancing immunity,brain-protecting and protecting the retina.However,fish oil is insoluble in water and could produce multi-stage oxidation products when it exposed to light,heat and oxygen and other aggressive agents,which leads to unpleasant astringency.All the defects metioned above have greatly limited its wide application in the field of food industry.The microencapsulation of oil is a technique of enclosing oil in a micron-sized spherical microcapsule by using a certain wall material,and the obtained microcapsule product can effectively prevent oxidation of oil,and is convenient for transportation and metering,thereby making it more suitable for industrial production.As a microcapsule wall material,chitosan can make full use of its good film forming property,biocompatibility and degradability,and expand the application range of fish oil.In this paper,refined tuna oil was used as raw materials,the low-molecular-weight chitosan was used as wall material,the tuna oil microcapsules were prepared by spray drying and freeze drying methods respectively.The effects of microcapsule preparation on tuna oil quality were analyzed.The preparation process of freeze-drying method was optimized by orthogonal test,and microcapsules were prepared under the optimal conditions.The storage accelerated test was used to compare the changes of peroxide value,fatty acid composition and volatile components during the storage of tuna oil and tuna oil microcapsules.This study can provide theoretical guidance and technical support for the application of chitosan and the comprehensive utilization of deep sea fish processing by-products.The main research results are as follows:(1)Refined ethyl ester tuna oil is obtained from tuna crude oil,after degumming,deacidification,decolorization and deodorization as well as ethyl acetate and urea embedding process.The quality of refined fish oil was in line with the standards of the second-grade refined fish oil.The unsaturated fatty acid content was 92.46%,and the polyunsaturated fatty acid accounted for 64.45%(DHA and EPA contents were 48.42%and 8.59%respectively).The results of GC-MS analysis showed that the volatile components of refined tuna oil were mainly esters,27 kinds in total,accounting for 79.72%.Furthermore,small amounts of(E,E)-2,4-heptadienal,n-hexanal,2-nonanone,and the like related to fishy smell were also detected.(2)Tuna oil microcapsules were prepared by spray drying and freeze drying.The spray-dried fish oil microcapsules were light yellow powder with uniform particles and slightly fishy smell.Except for the slightly higher peroxide value,the other indicators are in line with industry standards,and the encapsulation efficiency is 77.26%.A total of 14 fatty acids were detected by GC.The relative content of saturated fatty acids was 7.54%.The content of monounsaturated fatty acids was 39.77%,which was higher than that of refined fish oil.And the relative content of polyunsaturated fatty acids was lower,accounted for 52.71%.After spray drying,the volatile components in fish oil microcapsules were mainly esters,but a large amount of materials associated with fishy smell such as 2-nonanone and(E,E)-2,4-heptadienal are detected at the same time,which were probably formed by unsaturated fatty acids oxidative degradation under high temperature.The fish oil microcapsules made by freeze drying method conformed to the industry standard.The entirety was loose and blocky after freeze-drying,then turned to light yellow powder after grinding,these samples had no obvious odor.The encapsulation efficiency was lower than that of spray-dried fish oil microcapsules,which was 63.86%.A total of 16 fatty acids were detected by GC,the content of saturated fatty acids was only 4.77%.The content of monounsaturated fatty acids and polyunsaturated fatty acids were similar to that of refined tuna oil,which were 33.23%and 62.11%respectively.No typical fishy substances was detected in the freeze-dried product,demonstrating that the freeze-drying process effectively masked the bad flavor of tuna oil.(3)The obtained two kinds of microcapsules had similar quality,considering the excellent performance of freeze-dried product in masking bad flavors,the freeze-drying method was chosen as optimal preparation method.The embedding rate was used as the evaluation index to optimize the preparation process.Box-Behnken center-united experimental design was carried out based on single-factor experiments.The optimal parameters of microcapsules preparation process were 2.15%of wall material concentration,1.9:1 of wall-core ratio,0.83%of emulsifier content.Under the optimal conditions,the theoretical value of encapsulation efficiency was 67.82%,while the actual average value was 66.87%.,the responsive surface optimization results were reliable.(4)The quality changes of tuna oil and two kinds of tuna oil microcapsules at 60 ℃ were studied by using the accelerated storage test.The peroxide value of fish oil increased significantly with time during storage,DHA and EPA retention rate decreased,the contents of 2-nonanone,(E,E)-2,4-heptadienal,1-penten-3-ol and n-hexanal in the volatile components increased with time,which proved that fish oil produced a large amount of oxidation products during storage,giving off an unpleasant flavor such as fishy smell,and degading the oil quality.The growth rate of the peroxide value of the two kinds of fish oil microcapsules was significantly lower than that of the fish oil.The change in retention of DHA and EPA is similar to that of refined fish oil,but the difference in volatile composition between the two is quite different.The relative contents of 1-octene-3-ol and ethyl oleate in spray-dried fish oil microcapsules tended to be stable.The relative percentages of other key volatile substances showed a downward trend.(E,E)-2,4-heptadienal,n-hexanal and 1-penten-3-ol that related to fishy smell all fell to a lower level,significantly lower than the tuna oil of the same period,indicating that microcapsules prevent fish oil from further oxidation,did have a masking effect on the bad flavor.However,the freeze-dried fish oil microcapsules did not detect any typical fishy substances.It detected oleic acid,ethyl oleate,ethyl oleate and other substances related to fatty acid oxidation,which was significantly lower than the refined tuna oil and dried tuna oil microcapsules in the same period,indicating that the freeze-drying treatment has good protection effect on tuna oil. |
