Studies On The Changes Of Quality And Volatile Compounds In Fish Oil During Refining And Storage

Fish oils are the main source of polyunsaturated fatty acids(PUFAs),namely,eicosapentaenoicacid(EPA,C20:5 n-3)and docosahexaenoic acid(DHA,C22:6 n-3).These PUFAs have been demonstrated the health-promoting effects that include prevention in cardiovascular diseases,regulation of the immune function and enhancenment of the memory,so the fish oil is widely used in the health care industry and other food process industry.Traditionally,crude fish oil contains impurities and other undesirable compounds,which damage the quality and the acceptance of consumers seriously.Furthermore,PUFA in fish oils are exceptionally susceptible to be oxidized,and the breakdown of n-3 chain during oxidation process causes nutritional loss and detrimental sensory with an unacceptable rancidity and fishy odor.In the case of minimizing the loss of active substances in fish oil,how to remove the undesirable odour compounds as much as possible has always been the key points and difficulty of the study.To evaluate the effect of chemical refining on volatile compounds,fatty acid profile of crude fish oil and analyze the storage property is of great significance,which can provide a theoretical basis for the optimization of crude oil refining process,obtaining higher quality refined fish oil,extend the shelf life and improving the quality of fish oil.In this study,crude fish oil extracted from tuna and anchovies by-products including heads,viscera,skins,and skeletons was used as experimental material,the effect of crude oil refining process on its quality was analyzed.Sensory evaluation,physicochemical indexes contained acid value,peroxide value,iodine value,and saponification value,fatty acid composition,and volatile compounds were used as evaluation criteria,the effect of deodorization methods on the unpleasant odors,saturability and cis/trans configuration of fatty acids in fish oil during refining was analyzed.Finally,the changes of physicochemical indexes contained acid value,peroxide value,and anisidine value,fatty acid composition,and volatile compounds of fish oil were studied.The changes of crude fish oil and refined fish oil quality under different storage temperature were analyzed.The main research results are as follows:1.The volatile compounds and fatty acids profile of crude fish oil change in chemical refining process was analyzed.Every step of refining process can affect the volatile compounds and fatty acids profile of fish oil.After refined,the relative contents of saturated saturated fatty acids in fish oil decreased significantly,while the relative contents of PUFA increased.The SFA in the crude oil,degummed oil,deacidified oil,bleached oil,and deodorized oil accounted to 43.89%,37.02%,35.10%,34.80%,33.92%,respectively.And the PUFA accounted to 26.45%,30.64%,35.82%,36.30%,37.80%,respectively.Hexanal,nonanal,undecanal,and 2-undecanone are the key volatile components of fish oil,and the relative content of each compound changed significantly.The relative content of hexanal changed most significantly,crude oil was 2.13%,degummed oil was 1.64%,deacidified oil was 0.67%,bleached oil was 0.53%,and deodorized oil was 0.75%.Therefore,the whole refining process could effectively reduce the SFA content,and the volatile aldehydes,alcohols,ketones,hydrocarbons,and other substances with undesirable odor could be removed,the nutritional value of fish and the overall flavor could be improved significantly.2.In this study,several traditional methods including molecular distillation,steam distillation,green tea polyphenol treatment,liquid-liquid extraction,and solid-phase absorption with activated clay,zeolites or diatomite were studied and compared during fish oil refining in terms of physicochemical characteristics,sensory properties,saturability and cis/trans configuration of fatty acids,and volatile compounds.The results showed that molecular distillation was superior in reducing acidity,peroxide,and saponification value,enriching EPA and DHA,and removing unpleasant volatiles.The effect of liquid-liquid extraction on the removal of undesirable odor in fish oil was second only to molecular distillation.The vast majority of fishy odor in the.oil could be dissolved in alkaline dilute ethanol solution and separated under low temperature and short time conditions,which could effectively prevent PUFA from being oxidized.But the effect of liquid-liquid extraction on physicochemical characterization and sensory properties of fish oil was poor.Active clay adsorption was good at bleaching,which could make the fish oil bright yellow and transparent.Steam distillation,GTP treatment,and solid phase adsorption(zeolite,diatomaceous earth)had little effect on the improvement of the overall quality of fish oil.Therefore,molecular distillation method was the best deodorization method,but the bad effect of high temperature conditions on PUFA should be taken into consideration.3.Quality changes in fish oil before and after Refinement were analyzed at 35℃,25℃,15℃,5℃,respectively.The result showed that the effect of storage temperature on the quality of fish oils was significant,the stability was worse and the changes of quality in fish oils were bigger under the higher temperature,and the stability of refined fish oils were worse than crude fish oils.During the storage period,the acid value,peroxide value,and anisidine value of fish oils all increased significantly;the total content of saturated fatty acid increased,but the total content of unsaturated fatty acid and the overall degree of unsaturation were decreased;1-penten-3-ol,nonanal,hexanal,2-nonanone,2-undecanone,acetic acid,and butyric acid were the most significant volatile flavor compounds,which had the great influence on the overall flavor of fish oil.As the refining process in the removal of harmful components in the fish oil would also be part of the antioxidant material away,which caused the storage stability of refined fish oil was worse than the crude fish oil.According to the standard of fish oil industry SC/T 3502-2016,the acid value and peroxide value were used as the criterion of deterioration of fish oil.At 35 ℃,the shelf life of refined fish oil was about 20 days,and the crude fish oil was about 40 days.At 25 ℃,the shelf life of refined oil was about 40 days,and the crude oil is about 65 days.At 15 ℃,the shelf life of refined oil was about 65 days,and the crude oil was about 80 days.At 5 ℃,the shelf life of refined oil was about 115 days,while the crude fish oil did not deteriorate during 120 days of storage.Therefore,storing at 5℃ could help reduce the rate of fatty acid oxidation,and extend the storage time.