| The temperature of edible vegetable oil will rise in the heating process,which leads to the changes in the sensory,acid value,peroxide value,carbonyl value and the ratio of different kinds of fatty acids in plant oil,thus causing the decline of the quality of plant oil.By studying the changing rules of these indexes,we analyzed and clarified the effects of temperature,time,heating mode and kinds of oils on changes of quality and index of vegetable oil in the heating process.In this study,soybean oil,olive oil and edible blend oil were chosen to be heated separately without contact with food and soybean oil was chosen to be heated in contact with pork,potato and dough respectively.According to the design theory of orthogonal experiment,the color change,acid value,peroxide value and carbonyl value of vegetable oil were observed and measured in order to study the effects of heating temperature,heating time,heating way and variety of oil on the quality of edible vegetable oil.Gas chromatography(GC)was used to analyze and test the components and contents of fatty acids in soybean oil after heat treatment.In addition,the infrared spectra(FTIR)of the heat treated oil samples were analyzed to study the change of fatty acid composition.The results show that:In terms of sensory color,the color changes of olive oil is easier than soybean oil and blend oil.The aspect of acid value:three kinds of oil have no obvious change under the condition of heating themselves,but after three kinds of food substrates were introduced,the acid value of soybean oil was changed from 0.5mg/g to 1.50mg/g at 300 C,4h.The aspect of peroxide value:The peroxide value rises sharply at 210?.The change rate of olive oil is the fastest,from 0.4596g/100g to 1.7126g/100g.The second is edible blend oil,from 0.131 1g/1000g to 1.4160g/100g and the change of soybean oil is the smallest.When the temperature reaches 300?,the peroxide value increases first and then decreases.After introducing food matrix,the peroxide value of the whole process has been increasing.The carbonyl value of carbonyl:The value of the three kinds of oil is proportional to the heating temperature and time,rising from 13.0meq/kg to about 100meq/kg.The types of oil and the food matrix have little effect on it.Above all,heating temperature and heating time are the most important factors which affecting the above indicators.The heating way is secondary,such as the food matrix introduced.The kinds of edible vegetable oil were the least.In terms of composition and content of fatty acids,the contents of the main saturated fatty acids:palmitic acid C16:0 and stearic acid C18:0 increased with the heating time.Saturated fatty acids rise from 15.3%to about 18.5%.In contrary to saturated fatty acids,the content of unsaturated fatty acids,oleic acid C18:1,linoleic acid C18:2,linolenic acid C18:3 and erucic acid C22:1 decreased with the prolongation of heating time.The unsaturated fatty acids are reduced from 88%to 65.4%.The total fatty acid content gradually decreased with the heating time increasing,from 99%to 85%.In addition,the change rate of fatty acid content is directly proportional to heating temperature and heating time.It also has a certain relationship with the types of fatty acids.In addition,the aspect of the infrared spectrum(FTIR)analysis of the heat-treated oil samples showed that the infrared spectrum characteristics of edible vegetable oil were basically the same after heat treatment,indicating that the main groups of edible vegetable oil did not change significantly.But with the increase of temperature and time,a distinct wide peak appears in the range of 3600cm-1-3400cm-1 wave numbers,especially when the temperature reached 300?heating time 4 h.That shows the by-products increased and the edible vegetable oil has serious quality deterioration. |
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