Study On Enzymatic Extraction Of Fish Oil From Hairtail Viscera And Preventing Fish Oil Being Oxidized

Hairtail, which is one of the four marine important fish species and the most important fished specie of China's marine fisheries, has rich nutritional value and its output ranks first in all kinds of fish species. Currently, hairtail is mainly used for fish product processing. However, it produces viscera and other waste during the processing. The fish oil of viscera has not been effectively used and been of low added value. With the development of research on marine food, the functional components of fish oil have been increasingly concerned. Enzymatic extraction of fish oil has potential application because of its mild conditions, the small loss of the physiological active components and no pollution. In addition, fish oil is easily oxidized due to being rich in polyunsaturated fatty acids, and adding antioxidants to the fish oil can effectively prevent it being oxidized.With the hairtail viscera as material, this paper focused on extraction of fish oil by compound enzymatic hydrolysis method combined with extraction process, and studied effects of natural antioxidants on it. Meanwhile, hairtail crude fish oil was detected by gas chmmatography-mass spectrometry (GC-MS) to test fatty acid composition.The study can provide a theoretical basis for the comprehensive utilization of hairtail resource and the enrichment of DHA and EPA of hairtail fish oil. The main results are as follows:(1) The basic constitute of hailtail viscera was identified. The moisture content was 70.07% by using direct drying method. The crude protein was 16.35% by using Kjeldahl Nitrogen determination method. The crude fat content was 8.72% by using Soxhlet extraction method. The ash content was 4.86% by using ashing method.(2) Five kinds of enzymes including pepsin, alkaline protease, neutral protease, papain and trypsin were used for choosing two kinds of enzyme, and compound proportion of the two kinds was determined to obtain the best enzymatic extraction of fish oil. The results showed that compound enzyme with neutral protease and trypsin at the ratio of 1:1 achieved better effect of enzymatic extraction of fish oil.(3) Using compound enzyme with neutral protease and trypsin at the ratio of 1:1, through single factor and orthogonal tests, the optimum enzymatic extraction parameters were confirmed as follows: liquid-to-solid ratio 1.0:1, amount of enzyme 2.2%, enzymolysis pH value 7.5, enzymolysis temperature 50℃and enzymolysis time 160min.(4) Adopting quadratic orthogonal regression rotary combination design, the mathematical regression mode between extraction rate (Y) and extraction temperature (X₁), extraction pH value (X₂) and extraction time (X₃) was established. The regression equation was as follows:Y=78.839827 + 2.372200X₁ - 0.593078X₂ + 1.847572X₃ - 1.748833X₁² - 0.045000X₂X₁ - 2.528227X₂² + 1.075000X₃X₁ - 0.267500X₃X₂ - 2.040443X₃². According to the regression model, parameters of the extraction of fish oil were optimized.The optimum technique parameters were extraction temperature 43℃, extraction pH value 4.0 and extraction time 34 min.(5) The physical and chemical properties of hairtail crude fish oil were measured. The results showed that moisture and volatile matter content, acid value, iodine value and peroxide value of hairtail crude fish oil were 1.02%, 10.08 mg/g, 183.6 g/100g and 4.76 meq/kg, respectively. The indicators of crude fish oil met the required standards of crude fish oil except moisture and volatile matter content.(6) Fatty acid composition of hairtail crude fish oil was analyzed by using GC-MS. Sixteen kinds of fatty acids were identified in this study, and the main types of fatty acids in the fish oil were C₁₄-C₂₂ fatty acids. Saturated fatty acids accounted for 36.97%, and the highest content of saturated fatty acids was palmitic acid(24.07%). Unsaturated fatty acids totaled 63.03%. The monounsaturated fatty acids was composed of 33.32%, and the major component of monounsaturated fatty acids was oleic acid (27.16%). Polyunsaturated fatty acids was approximately 29.71% of the total, and the main components were EPA (6.57%) and DHA (18.75%).(7) Antioxidant effects of frequently used natural antioxidants on hairtail oil were investigated. The results showed that the additional levels of compound antioxidant were tea polyphenol 0.015%, VE0.005% and phytic acid 0.010%. At those levels, the peroxide value of fish oil was 11.68meq/kg which could meet Standard A of crude fish oil.