Effects Of Different Frying Processes On The Quality Of Pork Products

Fried food is popular with people for their golden color,crisp taste and unique flavor.However,it is also a food with high fat content,and high-temperature frying tends to lead to deterioration of oil and loss of nutrients.Therefore,people have been working on improving the quality of fried food.Earlier research of improving the quality of fried food and inhibit lipid oxidation was focused on the pretreatment of food and changed of frying conditions,such as frying time,temperature and kinds of oil.With the increasing demand for the quality of fried foods,especially the demand for low-fat,low-calorie fried foods,some new frying processes were established by people.Research found that vacuum frying and microwave-assisted vacuum frying can effectively reduce the fat content of food,lower breaking force of fried foods compared with conventional frying.However,researches were mainly about fruit and vegetables food,which contributes to the lack of research of the chemistry changes of meat products during frying,such as lipid oxidation and protein oxidation.Therefore,this paper mainly takes pork as object of study,the effects of three kinds of frying processing techniques,including conventional frying,microwave frying and microwave-assisted vacuum frying,on the physical characteristics(color,texture)and chemical properties(moisture content,fat content,protein carbonyls,TBARS and volatile compounds)of pork were analyzed.Firstly,effects of different frying temperature(150,165 and 180?)and time(110,200,290,380,470 s;90,150,210,270,330 s;70,110,150,180,210 s)of conventional frying on the quality of pork nuggets(3×3×1 cm)were evaluated.Changes of pork nuggets' quality were analyzed by the indexes including color,hardness,moisture content,fat content,protein carbonyls thiobarbituric reactive substances(TBARS)value and volatile aldehydes.The experimental results showed that decrease of moisture content fried at 150,165 and 180 ? for 470,330 and 230 s were 56.25%,52.82%,48.92%(p<0.05),the moisture loss was lower at high temperature in short time.Changes of fat content was not significantly when the frying temperature was 150 and 165 ?,but it increased significantly when the pork nuggets were fried at 180 ?(p<0.05).Hardness increased significantly(p<0.05)during frying process and reached a maximum value of 37.59 kg when frying at 150 ? for 470 s.Higher cooking temperature–time combinations increased protein carbonyls,it was 2.17 nmol/mg protein of pork nuggets fried at 180 ? for 150 s.TBARS values and hexanal increased significantly after frying.TBARS values of pork nuggets fried at 180 ? for 150 s were 0.71 mg MDA/kg.A highly significant correlation coefficients of fried pork nuggets treated with 150 ?(r=0.962)and 180 ?(r=0.997)were observed between TBARS values and hexanal content.Frying at 180? for 150 s was the best condition for pork nuggets with golden color,good texture and low protein and lipid oxidation.Secondly,the effects of conventional frying and microwave frying on the quality of pork nuggets were compared and changes of pork nuggets' quality after fried at different microwave power(2400,3000,3600 W)and different time(100,145,190,235,280 s)were analyzed by the indexes such as color,hardness,moisture content,fat content,TBARS,protein carbonyls and volatile aldehydes.Results indicated that the type of frying and frying time had significant effect on the quality.Microwave promoted the occurrence of pigment,increased the hardness of pork nuggets,more water loss and oil uptake.The brightness L* has a maximum value of 71.34 after the pork nuggets fried for 100 s under conventional conditions,L* decreased whereas a* increased with the increase of microwave power level,b* didn't change significantly.When the frying time less than 190 s,the higher microwave power,the more serious water loss.Fat content had the lowest level when the pork nuggets fried for 280 s at the microwave power of 3600 W.The TBARS value and protein carbonyl content of microwave frying were significantly lower than those of conventional frying(p<0.05)and decreased with the increase of microwave power.Microwave promoted the oxidation of fat to produce volatile aldehydes.Furthermore,the paper also investigated the effects of microwave-assisted vacuum frying on the color,moisture content,fat content,hardness,TBARS,protein carbonyls of pork nuggets under different temperature(110?125?140 ?),time(2?3?4?5?6 min),vacuum degree(0.05?0.07?0.09 MPa)and microwave power(2400?3000?3600 W)and optimized the frying condition by response surface methodology.The results showed that the low temperature of 110 °C was not conducive to the process of Maillard and caramelization reaction,and the pork nuggets did not turn into golden at 110 °C.The higher vacuum degree,the higher hardness.Hardness is not significantly affected by microwave power when the frying time is less than 5 min.The reduction of vacuum degree is beneficial to reduce moisture loss and moisture content had the larger level of 44.86% when the vacuum degree was 0.05 MPa after fried 6min.the fat content was lower at high microwave power;hardness was significantly affected by the degree of vacuum(p<0.05).TBARS decreased with temperature,vacuum degree,and microwave power.When the vacuum degree was 0.05 and 0.09 MPa,the content of protein carbonyls was lower which contributed to the reduction of the protein oxidation.Frying temperature,time and vacuum degree were recognized as main factors that affect fat content,hardness and TBARS of pork nuggets.From the results of response surface analysis,it was found that the optimum conditions for the microwave-assisted vacuum frying of pork nuggets were frying at 123-125 ? for 5-5.30 min at the vacuum degree of 0.05-0.06 MPa and microwave power of 3600 W.Effects of conventional frying,microwave frying and microwave-assisted vacuum frying on the quality of pork nuggets were researched systematically in this paper.The results have important theoretical values and guiding significance to enhance the quality of the fried meat produces.