| With the ever-accelerating rhythm of people's life and the maturity of microwave heating technology,the microwave oven has been widely used in family and catering industry,using microwave for heating food will produce what kind of impact on food,which has always been the focus of people's attention,however there were few related studies.Oil is essential for people's daily lives,and the chemical changes of oil under microwave heating were the focus of this research,and using the chemical reaction of oil under microwave heating to develop the added value of catering waste oil and non edible oils or fats was also the concern of this paper.The study was divided into two stages,firstly,using the edible oil-peanut oil as the material,different samples were cooked repeatedly in microwave oven,then,the acid value,peroxide value,and the changes of the function groups of peanut oil were analyzed.Then,using the non-edible oil-Chinese tallow oil as the material,and heated in the microwave,thermal cracked,and then analyzed the variation of components of liquid products.Also,using tofu,pork,and potato as the raw materials and the peanut oil as the subject,simulating the microwave cooking,we heated the samples 6 times repeatedly,and found that,the acid values of the repeatedly cooked peanut oil by microwave in the three samples were lower than the untreated peanut oil,probably owing to the free fatty acids been cracked during the repetitive microwave cooking.However,the peroxide values of repeatedly cooked peanut oil by microwave in the three samples were higher than that of the untreated peanut oil,and appeared the tortuous trend,mainly due to the free fatty acids thermal decomposed to aldehydes and ketones,oxygen-containing compounds,and with the increasing times of microwave cooking,the oxygen-containing compounds were oxidized to peroxide,and the peroxide value were increased in this process,the peanut oil's peroxide valuesfor the tofu,pork,potato samples were 9.5 meq/kg,8 meq/kg,9 meq/kg,respectively,because of the different components in the samples.And with the further increase in microwave cooking times,the peroxide compounds were further cracked,leading to the reduction in peroxide values.Comparing with the original peanut oil,the FTIR analysis of the peanut oil repeatedly treated by the microwave cooking showed that,the functional groups in the peanut oils were changed,there appeared to be a double bond C=C stretching vibration peak at 1654 cm-1,indicating the presence of olefin.Hydrocarbons are harmful to humans,but for biofuels,they are the most effective ingredients.Therefore it may be useful to explore further of the variation in the liquid products by microwave heating for this purpose.Considering the expensive price of the edible oil,the non-edible oil-Chinese tallow oil was used as the raw material for the further study,which consists linoleic acid,linolenic acid,and the harmful component of decadienoic acid.Firstly,Chinese tallow oil were treated by NaOH,KOH.After saponification,it was heated by microwave,the liquid products were then analyzed by GC-MS.The results showed that the main components of the liquid products were C8-C18 olefins,cycloalkanes,cyclic olefins,dienes,aromatic hydrocarbons,a small amount of oxygen-containing compounds and some unidentified compounds.The contents of hydrocarbons in the liquid products from the microwave heating of the potassium soap of the Chinese tallow oil reached91.33%under the temperature of 550 ?.When using basic catalyst KF/CaO for the catalytic pyrolysis of the Chinese tallow oil potassium soap by microwave,different amount of KF/CaO showed different hydrocarbons contents of liquid products,the relative content of hydrocarbons reached 91.44%whenthe KF/CaO addition was 10%.With the help of the microwave absorber SiC and the alkaline catalyst,the fast microwave pyrolysis of the Chinese tallow oil was achieved,and the oxygen contents in the liquid products were relatively high.With the help of the catalyst KOH,the oxygen content can be significantly reduced.In the presence of microwave absorber-SiC,the potassium soap of Chinese tallow oil were pyrolyzed in the fast microwave pyrolysis process,as the feeding rate increased from 3 g/min to 15 g/min,the relative contents of hydrocarbons in pyrolytic products decreased from 91.53%to 86.83%,at the same time,the relative contents of oxygen-containing compounds increased from 5.25%to 9.24%.And the relative contents of aromatic hydrocarbons significantly increased,reached 40.07%under the feed rate was 3g/min,which can significantly improve the octane number and stability of liquid products. |
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