| Tilapia,also known as African crucian carp or basso fish,is an adaptable,omnivorous fish which can survive in both freshwater and seawater.In Guangzhou and the Hainan province of China tilapia farming occurs on a large scale and accounts for about one-third of the country's total.It is a typical export-dependent product,sold mainly as frozen tilapia fillets with the remaining parts of the fish(head,skin,fish tail,fish scales,fish bones,internal organs)going to waste.Tilapia fish oil is rich in unsaturated fatty acids.Unsaturated fatty acids have important implications for the development,cognition and vision of infants.Although,in the last few years,more and more babies are unable to receive breastmilk for various reasons.Breastmilk is a valuable source of these unsaturated fatty acids and therefore,finding healthy and beneficial human milk fat substitutes(HMFS)has become a hot research topic and tilapia fish oil may provide a novel substitute.In this study the extraction process of tilapia fish oil and its resulting nutritional values were investigated in order to compare the effects of different extraction processes on the nutritional value of the tilapia fish oil.In addition,other raw materials found in HMFS such as soybean oil,coconut oil,corn oil,sunflower oil and fish oil were studied.The storage stability of HMFS was analyzed by synchronous fluorescence and the chemical reagent method.The microencapsulation technology of HMFS was optimized by response surface methodology.The microcapsule samples were analyzed for their quality and the influence of microcapsule process on HMFS.The chief conclusions of this academic paper are as follows:(1)Freeze-dried tilapia contains crude fat(36.69%),protein(49.95%),ash(12.04%)and water(1.21%).(2)The optimal conditions for different extraction methods were studied using freeze-dried tilapia whole fish as the raw material.The results showed that the optimal conditions of dilute alkali hydrolysis were as follows:the ratio of material to liquid was 1:3 at pH 7.5.The optimal extraction conditions were as follows:the ratio of material to liquid was 1:3,with 0.6%enzyme at pH9,with a hydrolysis temperature of 60? and a hydrolysis time of 2.5h.The highest extraction rate was(28.91 ± 0.18)%.The optimal conditions for microwave assisted extraction were as follows:the optimum extraction solvent was n-hexane.1:10,the microwave time was 10 min and the microwave power was 100 W.The highest extraction rate of fish oil using this method was(29.17 ± 0.13)%.The extraction rate of fish oil from alkaline hydrolysis are the highest.(3)The extraction of whole fish oil from tilapia was studied using three optimal techniques.The effect of the method of extraction on the quality of the fish oil was compared.The results showed that the acid value(AV),peroxide value(POV)and iodine value(IV)of fish oil extracted by dilute alkaline hydrolysis were the lowest at 0.77 mg KOH/g oil,3.76 mmol/kg oil and 130.01 g/100g oil,respectively.The major fatty acid components of tilapia fish oil were palmitic acid(22.78?23.16%),oleic acid(25.73?26.19%)and linoleic acid(15.69?15.98%).The concentration of docosahexaenoic acid(DHA)and eicosapentaenoic acid(EPA)in fish oil extracted by dilute alkaline hydrolysis was significantly higher than in the other two methods.Thermodynamic analysis showed that the crystal structures of the fish oils extracted by the three methods were obviously different,but the IR spectra showed that they had the same characteristic functional groups.Therefore,different extraction methods have a significant impact on the physical and chemical properties of fish oil without affecting their spectral properties.In summary,the fish oil extracted by dilute alkali hydrolysis method was superior.(4)The fatty acid composition of five raw materials from HMFS was analyzed.The results showed that soybean oil,corn oil and sunflower oil mainly consisted of palmitic acid,oleic acid,linoleic acid and stearic acid.Coconut oil was mainly composed of lauric acid and myristic acid.Fish oil fatty acid composition was more complex,but it consisted mainly of linoleic acid,9cC16:1,arachidonic acid,DHA,palmitic acid and oleic acid.The SFA,MUFA and PUFA content of soybean oil,corn oil and sunflower oil was similar while coconut oil contained the highest SFA(93.75 ± 0.06)%,with fish oil containing the highest level of UFA.(5)Molecular fluorescence and chemical reagents were used to monitor the oxidation process of HMFS.The results showed that with the prolongation of oxidation time,the fluorescence intensity gradually weakened and the value of oxidation index increased.Correlation and regression analysis showed that in six kinds of human milk there was a negative correlation between the change of the fluorescence intensity and the fluorescence intensity of the lipid substitute formulation.The fluorescence intensity showed a binary linear correlation with both the peroxide value and the total oxidation value.The correlation coefficient was linear with the anisidine value.(6)Optimization of the HMFS microcapsulation process through response surface experiments.The results showed that the optimal conditions were as follows:0.96%soybean lecithin,desalted whey powder:maltodextrin = 2.04:1,17.37%human milk fat substitute,with a homogenization pressure of 30.46 MPa.Under these conditions,the highest MEY was(82.33±1.05)%,and the highest MEE was(84.72±0.69)%.The physicochemical indexes conformed to the national standards.In vitro digestion experiments showed that the microcapsule samples were digested completely within 2h and,the release rate of free fatty acids was 64%.(7)When comparing HMFS to microencapsulated HMFS powders,the storage stability of microencapsulated lipids was obviously better than that of untreated HMFS.In addition,infrared spectroscopy analysis showed that the structure of HMFS was not damaged by the microcapsule process.SEM analysis showed that the microcapsules were uniform and spherical,and had a smooth surface with no cracks or holes.Therefore,the microcapsule process protected the raw materials and increased the shelf life of the product by preventing oxidation.Microcapsule technology may provide an improved method in the fabrication of HMFS. |
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