Study On Preparation Of Fast-frozen Special Fat By Enzymatic Interesterification And Its Microstructure And Macroscopic Properties

The fast-frozen special fat as an essential plastic fat is widely applied in the preparation of traditional Chinese fast-frozen foods.At present,the most fast-frozen special fats used in fast-frozen food are all-purpose plastic fats,like margarines and shortenings,which are mostly prepared by using refined animal and/or vegetable fats and oils,hydrogenated vegetable oil,or the physical blends of them as base oil.The trans-fatty acids would be inevitably generated in the partial hydrogenation of vegetable oils and the intake of which would increase the risk of cardiovascular diseases.Moreover,these base oils with high melting points are rich in abundant saturated fatty acids,and the granular crystal in the refined animal fat-formulated margarines and shortenings impairs the properties of fat products in the application.It was found that the fast-frozen special fat obtained by enzymatic interesterification could provide desirable properties for food products.However,it is still lack of fundermental studies in the molecular level which can provide theoretical guidance for the development of the special fat.Therefore,in this paper,the base oil and the corresponding special fat with varied triacylglycerol composition were firstly prepared by enzymatic interesterification,and then followed by studying the molecular composition,physical properties and crystallization behavior of the base oil and the corresponding special fat to clarify the relationship between triacylglycerol and crystallization behavior and build the mathematical models which describe the correlations among the molecular diversity,microstructure and physical properties of fast-frozen special fat.Furthermore,the storage stability,the digestion metabolism of the enzymatic interesterified blend-based fast-frozen special fat(IBSF)and the effect of IBSF on the physical properties and microstructure of frozen dough were further studied.The main contents and results of the paper were as follows:(1)The relationship between triacylglycerol(TAG)and crystallization characteristics in enzymatic interesterified blendsA series of interesterified blends(PS:SO,PS:RO,PS:CO,7:3,6:4,w/w)with 41-45°C slip melting point(SMP)were firstly prepared in the self-designed fluidized bed reactor by changing the enzymatic interesterification conditions(lipase type,oil/fat type and proportion,flow rate).The solid fat content(SFC)of the interesterified blends was 55%-4%at 0-45°C and the crystal form was mainly??form.The statistical analysis showed that the interesterified blends were more likely to form??crystal with the increase of SUU-type TAG content and the decrease of SSS-type TAG content.In addition,the decrease of ECN 42-and ECN 48-type TAGs and the increase of ECN 50-type TAGs also significantly enhanced the formation of??crystal.Furthermore,the sn-1,3-specific Lipozyme TL IM-catalyzed interesterified blends were favorable for the formation of??crystal.(2)The preparation of enzymatic interesterified blend-based fast-frozen special fats(IBSFs)and physical properties and crystallization characters studing of IBSFThe IBSFs with 41-45°C SMP were prepared by using the abovementioned interesterified blends as the base oil.Then the physical properties including the SFC,hardness and elasticity,and the crystallization properties such as thermal properties,crystal polymorphisms and crystal microstructure were measured.Therefore,the specific characteristics of IBSFs obtained by the research results had the following properties:SFC values,45%-6%(0-45°C);hardness,20 g-50 g(25°C);elasticity,10~4-10~5 Pa(25°C),the crystal??/?,6/4-7/3;Db,1.91-1.98;small-sized spherical or short needle-shaped crystals uniformly and densely distributed in the crystalline network.Furthermore,the artificial neural network model(ANN)of IBSF under the condition of diversity of triglyceride composition(6-27-3)was obtained by optimizing training,taking the parameters of TAGs composition and microstructural crystalline network as the input data,the parameters of physical properties as the output data.The mean square error between the input value and the target value of the ANN model was0.005.The mathematical model could be used to correlate and predict the correlations among the molecular diversity,microstructure and physical properties of IBSFs.(3)Storage stability of enzymatic interesterified blend-based fast-frozen special fatsBased on the front results,the two kinds of IBSFs(A:IBSF-SO,B:IBSF-RO)with 41°C and 45°C SMP were chosen,and their oxidative stability,crystallization characteristics and physical properties during constant temperature(-20°C,4°C,25°C)and fluctuating temperature(-20°C 12 h~25°C 12 h,4°C 12 h~25°C 12 h)storage for 4 weeks,respectively,were investigated in this study.The results showed that both two kinds of IBSFs still had good oxidative stability after 4 weeks of storage,and the peroxide values of both IBSFs were less than 10.0 mmol/kg.The physical properties including the SFC,hardness and viscoelasticity results had similar changes during the storage.However,the change trend of three physical properties exhibited a non-linear relationship.XRD results showed that part??form gradually transformed into the?form in the IBSFs during the storage.The rate of crystal transformation in IBSF-B was slower than that in IBSF-A and higher??/??existed in IBSF-B.On the whole,according to the results of crystal transformation,crystal size and crystal distribution in the crystallize network of IBSFs during the storage,the integrity of crystalline microstructure showed the following order:constant temperature>fluctuating temperature,4°C>-20°C>25°C,IBSF>>PBSF,IBSF-B>IBSF-A.(4)Study on digestion metabolism of interesterified blend-based fast-frozen special fatsThe SD mouse was used as the animal model,and IBSF and PBSF were selected as the experimental group and the control group,respectively.The effects of diet made by IBSFs on growth performance,serum metabolic index and liver histomorphology of mice were studied.It was found that diet made by IBSFs group was easier to digest and absorb than that by PBSFs group.The intake of IBSF fat reduced the incidence of hyperlipidemia and hyperglycemia symptoms to a certain extent.In addition,Results showed that the proportion of metabolic probiotics in IBSF group increased and the proportion of dominant bacteria such as Firmicutes and Bacteroidetes which were related to obesity was changed.The results of liver index and liver tissue staining showed that IBSF group had little effect on the liver metabolism.On the whole the IBSFs in the study can be regarded as a potential high-quality fast-frozenspecial fat.(5)Effect of interesterified blend-based fast-frozen special fat(IBSF)on the properties of frozen doughCompared with the blank without fat,the addition of IBSF had significant influence on the physical properties and microstructure of frozen dough.The temperature and enthalpy of gelatinization increased and the degree of retrogradation reduced when IBSF was added into the frozen dough.The frozen dough added with IBSF possessed better texture and rheological property as illustrated by the enhanced extensibility,decreased hardness,increased cohesiveness and resilience,and improved flexibility.It was also showed that the freezable water content and the mobility of free water decreased when IBSF was added,suggesting that addition of IBSF into the frozen dough was helpful to reduce the cracking rate.Additionally,compared with the corresponding PBSF and C-SF,IBSF not only exhibited favorable influence on the quality of frozen dough,but didn't have trans-fatty acid.On the whole,among them,the high SMP-IBSF(45°C)had more useful in the texture improvement of the frozen dough,while the low SMP-IBSF(41°C)is more helpful in the inhibiting of the product cracking.These results indicate that IBSF is a kind of high quality special fat for prefrozen fast food preparation by improving the texture characteristics and inhibiting water migration.