Study On Preparation Of Special Oil For Quick-frozen Food By Enzymatic Interesterification

Special oil for the quick-frozen food is one of the necessary materials in the industryproduction of quick-frozen food, which determined the quality of the products. However, thespecial oil for the quick-frozen food has many problems at present, for examples, the hardnessof the special oil is too high to consume and the quality of the special oil will deteriorateduring the storage.As soon as necessary, the structure of special oil has to be modified forbetter quality.Enzymatic interesterification has gained more preference over chemicalinteresterification, which can be conducted in milder reaction conditions and has fewerby-products, less post-treatment and less pollution to the environment. The study forimproving the quality of special oil has not been reported until now.Consequently,the subjectwill modify the oil-fat by enzymatic interesterification.In order to reveal the relationshipbetween microscopic structure and the macroscopic physical properties of the oil,theproperties of the oil will be studied indepth,which contains the TAG distributions, solid fatcontent profiles, thermal properties, polymorphism and crystal microstructure.Based on these,the intersterified oil will be applied into the production practise and make good quality ofspecial oil for quick-frozen food.In this research, the interesterification of palm stearin and soybean oil (70:30, wt,%) isinvestigated.The main factors of the reaction are studied and the response surface experimentsare analyzed. The optimum conditions of interesterification are: temperature,63℃; enzymeload,10%; reaction time,5hours.Physical and chemical properties of the blends before and after interesterification arecompared, including the TAG distributions, solid fat content profiles, thermal properties,polymorphism and crystal microstructure. The main triacylglycerols (TAGS) of interesterifiedblend were POP(22.27%) compared with the physical blends being PPP(27.61%), indicatingthe increase of amounts of both SUU and SUS TAGS whilst the decrease of quantity of UUUand SSS TAGs. Meanwhile, the interesterified lipid had lower SFC than the physical blends,and the melting thermogram analyzed by DSC demonstrated a lower melting product being formed after interesterification. Isothermal crystallization curves were described according tothe change of solid fat content with time under different temperatures. The resultdemonstrated that supercooling had a significant effect on nucleation and growth mechanism.The X-ray diffraction (XRD) analysis showed that the content of β′forms in the interesterifiedblend enhanced from75.75%to87.29%, also, the box-counting fractal dimension, Db value,increased from1.77to1.89, suggesting that a more compact fine and close crystal networkwas formed for the interesterified lipid. These improved properties showed that theinteresterified blend could be used as special oil for quick-frozen food.The compatibility of mixtures of palm stearin, soybean oil and interesterified oil werestudied by iso-line diagrams of temperature. The results showed that the ternary mixtures ofpalm stearin，soybean oil, interesterified oil has a good compatibilityIn production process of the special oil,5formulas are designed. The5formulas areapplied to the quick-frozen rice dumplings.Frost crack rate and sensory evaluation of thequick-frozen rice dumplings are determined.The best formula is interesterification oil:soybean oil: palm stearin=84:13:3(wt%),under this optimum conditions, the frost crack rateof the quick-frozen rice dumplings is only5%,which is better than the commercial specialoil(30%). All above demonstrate that this formula is most suitable for making special oil forquick–frozen food.This study provides the basis of theory and practice for improving the quality of specialoil and is of great significance in promoting the development of quick-frozen food in china.