Study On The Oil Content Of Fried Dishes And The Deterioration Of The Quality Of Reused Oil

Fats and oils are essential macronutrients for human metabolic activities,but excessive intake can easily lead to cardiovascular diseases,while their oxidative decay can produce harmful substances such as aldehydes and ketones.Chinese dishes are the most important source of the nation’s daily diet and the primary source of fat intake.Chinese dishes are often erroneously assumed as fried food,for example,the English definition of this concept is stir-frying,and the fried food is already considered as junk food by public.Thus,it is necessary to study the oil content and fat quality deterioration of dishes after cooking by comparing the stir-frying and frying procedure.Moreover,only the solid main ingredients of stir-fried dishes are consumed and the residual oil broth is usually discarded.In this way,the total fat intake is mainly determined by the oil content of the solid main ingredients.The safety of the oil content and quality of fats and oils are important factors for national dietary health.Therefore,it is necessary to carry out the research on the formation of the oil content of dishes in the stir-frying process and the corresponding quality deterioration pattern,together with the safety control of repeated use of oil.To simplify the experiment,a typical cooking material,pork tenderloin,was used as the research object.As cooking maturity is related to the oil content of the dish,samples were taken at a set cooking maturity value（M）.The main findings are as follows:（1）The effect of“Huohou”control on the oil and moisture content of pork tenderloin was explored.The results show that the oil content of pork tenderloin increases from 5.61%（oil content of fresh meat）to 11.79%with increasing maturity value at stir-frying temperatures of 100～180°C,while the moisture content shows the opposite trend,decreasing from 68.74%to 35.83%,and can be reduced by controlling the maturity of the dish.The oil and moisture content of the pork tenderloin were 6.39～7.41%and 62.21～64.72%respectively when the termination maturity value(maturity value when just ripe,M_T70°C)was 0.5 min,with the lowest oil and highest moisture content in the meat samples at 140°C,proving that different oil temperatures also affect the oil content of the dish when just ripe and that there is a minimum oil content of cooking oil temperature.This shows that the oil content of a dish is governed by the“Huohou”control and that the lowest oil content and highest moisture content are obtained at the optimum“Huohou”control(oil temperature 140°C and cooking to M_T70°C=0.5 min).（2）The changes of total oil,surface oil,structural oil and penetrated surface oil content of pork loin when heated to M_T70°C=0.5 min under different oil stir-frying temperatures were studied by Sudan red staining to explore the spatial distribution of oil content of meat samples and to investigate the mechanism of oil absorption.The results indicate that the total oil content of surface oil accounted for the largest proportion of 54.92%to 57.83%,the structural oil accounted for 40.22%to 43.18%and the penetrated surface oil accounted for 1.82%to 1.95%.The oil distribution during the stir-frying process was further analyzed by optical and body microscopy and scanning electron microscopy.The results showed that the staining oil mainly existed on the surface and crevices of the meat samples after oil stir-frying,and with the increase of oil temperature,the greater the degree of destruction of the spatial structure on the surface of the meat samples,the larger the resulting crevices,and the more the distribution of staining oil.Therefore,the oil absorption in the stir-frying process was judged by microstructure may be the surface oil adsorption caused by the surfactant effect.Compared with frying,no crust layer was formed to absorb the oil during the stir-frying process,and the oil was mainly adsorbed on the surface of the meat samples.At the same time,the stir-frying time is shorter,only equivalent to the initial stage of frying,the heating intensity is lower,Therefore,they are different food processing processes.（3）In order to explore the deterioration pattern of the quality of repeated use of fats and oils during the stir-frying process,pork tenderloin was stir-fried at 140℃,160℃,and 180℃until cooked（M=1 min）,repeated 150 times,and sampled 10 times to determine the color,acid value,peroxide value,carbonyl value,and other indexes.The results showed that the color of soybean oil deepened as the number of stir-frying times increased,and the acid value and carbonyl value showed an overall increasing trend,with the final values ranging from 0.06 to 1.42 mg/g and 5.41 to 29.18 meq/kg respectively,both within the range of the national standard;the iodine value decreased,anisidine value,and the total oxidation value showed fluctuating changes.Compared to frying,the stir-frying process 1)has a higher rate of grease renewal,2)has a lower heating intensity and 3)filters out the food residue each time,making the overall deterioration effect of the old and new mixed fats weaker after stir-frying cooking and extending the service life of the old and new mixed fats.（4）The Arrhenius equation was chosen to predict the quality deterioration of fats and oils during repeated stir-frying,and an oxidation kinetic model based on the acid price index was established for the repeated use of fats and oils,and kinetic parameters such as the rate constant and activation energy were obtained.The kinetic parameters such as rate constant and activation energy were obtained.This model was combined with the oil renewal rate using MATLAB,and a prediction model based on the oxidation kinetics was finally established to predict the change in acid value based on the oil renewal rate.The simulated acid value fitted well with the measured acid value,which proved the reasonableness of the prediction model.Under the test conditions,the prediction model was also used to calculate the limit number of times the oil could be reused without exceeding the standard at 140°C,160°C,and 180°C,520,420,and 350times respectively.The above study provides a preliminary methodology for studying the oil content of dishes under more cooking conditions and the deterioration of the quality of reused fats and oils,as well as providing scientific guidance for the rational reuse of fats and oils by catering companies.