Study On Preparation Of Special Oil For Quick-frozen Food Based On Enzymatic Interesterification And Its Properties

Quick-frozen special oil is one of necessary materials for quick-frozen food production, and it plays a key role on the quality of quick-frozen food. Presently, the most used oil and fat for quick-frozen food production is general-purpose margarine, which can not meet the special requirement for quick-frozen special oil. With the rapid development of quick-frozen food industry, it’s necessary to exploit new special oils with excellent qualities for quickfrozen food. Enzymatic interesterification is an important oil-fat modification method with many advantages, such as mild reaction conditions, high catalytic efficiency, less by-products and environmental friend. However, there is few reports about the application of enzymatic interesterification in preparing special oils for quick-frozen food, and to our knowledge, the expansion of the above reaction in a reactor is not reported yet. Hence, in this study, the enzymatic interesterification of palm stearin(PS) and soybean oil(SO) with different ratios was first performed in the flask, and then the change of triacylglycerol composition before and after reaction as well as its influence on the melting point, the solid fat content(SFC) and crystal form of oil were analyzed. Thus the substrate ratio which can serve as base oil for preparation of special oil for quick-frozen food was determined. After that, the scale-up of the enzymatic interesterification was performed in a fluidized bed reactor which was appropriately designed for the reaction. Finally, the resulting interesterified oil was applied to the production of special oil for quick-frozen food and its properties were evalutated by using it for preparation of quick-frozen food. The major research work in this thesis are as follows:1. Palm stearin and soybean oil with different ratios(PS:SO = 9:1、8:2、7:3、6:4、5:5,w/w)were catalyzed by immobilized lipase Lipozyme TL IM to the slip melting point of which kept stable in the flask. The results showed that after interesterification, the content of PPP and LLL decreased while the content of PLL, PLO and PPL increased for all blends, but the content of POP decreased except for PS:SO 9:1. For the type of triacylglycer, the content of S3 and U3 reduced obviously, but the content of SU2 and S2 U increased with different degrees. The SFC of all blends declined apparently while the plastic range enlarged. The slip melting point and crystal form of the five blends changed differently after interesterification. Albeit the slip melting points all decreased, for PS:SO 7:3, 6:4 and 5:5, their values were lower than 45 oC, while for PS:SO 9:1 and 8:2, their values were greater than 45 oC. Similarly, for PS:SO 7:3, 6:4 and 5:5, the contents of β′ crystal increased from 55.59%, 50.74% and 54.90% before reaction to 74.60%, 90.57% and 85.75% after interesterification, while the contents of β′ crystal declined for PS:SO 9:1 and 8:2.2. The ideal slip melting point and crystal form of special oil for quick-frozen food are 45 oC and β′ crystal, respectively. Based on the above results of batch enzymatic reaction, the PS:SO 7:3, 6:4, 5:5 were chosen for further scale-up in the fluidized bed reactor. It was found that the flow rates which could result in 45 oC blends after enzymatic interesterification for the above three substrate ratios were 2.24, 1.57 and 0.40 m L/min. After reaction, the most aboundant triacylglycer types were SU2 and S2 U, the SFCs of all blends declined as well as their plastic range expanded at 20 ~ 35 oC. Melting thermograms indicated that the endothermic peak areas of high and low slip melting point decreased, and the whole endothermic peaks got closed to the centre from both sides. The endothermic peak areas of the highest slip melting points were near to 45 oC in all the interesterified oils, which were in accordance with the results of slip melting points, while the endothermic peaks of middle melting points increased in all blends. Except for PS:SO 5:5, the variation trend of exothermic curves of the other two blends was similar to that of endothermic curves. In the interesterified blends, the content of β′ crystal enhanced while the content of β crystal declined, especially the amount of β′ crystal in the PS:SO 6:4 after reaction was almost 100%. Besides, the crystal structure of the blends changed from bulky spherical crystal before reaction to more compact and fine needle crystal after interesterification.3. The based oil of 45 oC after interesterification in the fluidized bed reactor was emulsified to prepare special oil for quick-frozen food. It was found that the best emulsification stability of quick-frozen special oil was obtained when the concentrations of propylene glycol, sorbitan fatty acid ester and soya bean lecithin were 0.3%, 0.5% and 0.3% respectively, and the ratio of oil to water was 85:14(w/w). Three types of quick-frozen special oils, named as PS:SO 7:3, 6:4 and 5:5, were prepared with the above three interesterified blends as base oils under the best emulsifying conditions, and then they were applied to make quick-frozen dumplings. The resulting quick-frozen dumplings were recognized as the types of 7:3, 6:4 and 5:5. The properties of quick-frozen dumplings, like frost crack rate, water loss rate, cooking loss rate and light transmittance, and so on, were measured after 4-times repeated freeze-thaw cycles. The results showed that the qualities of quick-frozen dumplings prepared with oils were better than that of the negative control without oil. Compared to the quick-frozen dumplings prepared with commercially available oil(positive control), there was no obvious improvement in the quality of type 5:5 quick-frozen dumplings. However, for the types of 6:4 and 7:3 quick-frozen dumplings, their frost crack rates, water loss rates, water absorption rates after cooking and cooking loss rates after 4-times repeated freeze-thaw cycles decreased from 33.3%, 7.5%, 19.8% and 1.7% for the positive control to 12.5%, 5.7%, 17.8%, 1.4% and 15.0%, 6.0%, 16.3% and 1.4%, respectively. While their light transmittances increased from 54.8% for the positive control to 70% and 68%, respectively. Additionally, the sensory evaluation results also showed that the composite scores for the types of 6:4 and 7:3 quick-frozen dumplings were higher than those of other three dumplings. Hence, the enzymatically interesterified oils of PS:SO 6:4 and 7:3 is potential for production of high quality special oils for quick-frozen food.This study provides the theoretical and practical basis for preparing high quality quickfrozen special oils based on enzymatic interesterification, which is of great significance in promoting the development of quick-frozen food in china.