Study On Frying Quality And Storage Performance Of Chinese Fried Dough Cake Treated With Edible Coating

With the economic development,social progress and the improvement of national living standards,food safety and nutrition has been increasingly emphasized.Frying is one of the traditional cooking methods in China,however,fried food has large content of oil and high energy density,furthermore,a variety of chemical accompanying contaminants formed during the frying process,which would endanger the health of consumers.Therefore,the reduction of oil and chemical accompanying contaminants in fried food has attracted the attention of the domestic and foreign scholars.There have been reported that coating could prevent oil absorption and moisture migration in fried food,and then reduce the oil content and improve the quality of fried food.However,the effect of coating on the frying quality and storage performance of traditional fried cereal products in China has not been reported.Hence,in this study,the effect of two different coating materials on the frying quality and storage performance of Chinese fried dough cake(CFDC)was investigated.The objective of the present study was to provide the theory basis and technical reference of processing “double-low and one-high” Chinese fried dough cake with low fat,low hazard and high quality.The details were listed as following:(1)The effect of coating on the frying quality of CFDC and oil permenation:The effects of methylcellulose(MC)and soybean isolate protein(SPI)on the quality and oil content of frying CFDC and the mechanism of coating on reducing oil content of frying CFDC were studied.The results showed that MC and SPI had significantly(P<0.05)reduced the oil content of frying CFDC.When the concentration of MC reached 1%,the oil inhibition effect was 53.77%,and the surface oil and internal oil content had decreased by 58.66% and 45.43%,and when the concentration of SPI reached 8%,the oil inhibition effect was 41.65%,and the surface oil and internal oil content had decreased by 55.81% and 17.50% respectively.The oil inhibition effect of MC coating was better than that of SPI,which was attributed by the difference of film forming property and thermal gel ability of different materials.The microstructure analysis showed that the coating could make the surface of frying CFDC smooth,reduce holes in the surface of CFDC and oil permeation depth,and control the oil permeation and migration.Meanwhile,with the range of experimental use,MC and SPI coating had no significant effect on the texture of CFDC;MC coating slightly reduced the specific volume of CFDC,but the difference was not significant,while SPI had no significant effect on the specific volume of CFDC;Furthermore,MC coating increased brightness value of product.The color of CFDC samples treated with SPI coating were darkened,which may affect its acceptability.(2)The effect of coating on typical accompanying contaminants in frying CFDC:The effect of methylcellulose(MC)and soybean isolate protein(SPI)on the physicochemical indexes,malondialdehyde(MDA),4-hydroxy-2-hexenal(HHE),4-hydroxy-2-nonnal(HNE),glycidyl esters(GEs),acrylamide(AA)and trans fatty acid(TFA)of CFDC were studied,and then analyze the influence mechanism of the generation of hazards.The results showed that MC and SPI had significantly(P<0.05)reduced the content of AV,PV,p-AV and TOTOX.The effect of MC coating was better than that of SPI.Moreover,MC coating had significantly(P<0.05)reduced the content of MDA,GEs and AA,and had no significant effect on the content of HHE and HNE,the reason is that coating can reduce the degree of lipid oxidation and improve its antioxidant performance,thus reducing the content of MDA and GEs.Meanwhile MC coating can can form a barrier to interfere with the molecule interaction between reducing sugar and asparagine,thus reducing the content of AA.SPI coating had significantly(P<0.05)reduced the content of MDA and AA,decreased the content of HNE to a lesser extent,on the one hand,SPI coating can reduce lipid oxidation degree so as to reduce the MDA content,SPI can also react with HNE to reduce the HNE content;On the other hand,some certain amino acids in SPI can compete with asparagine by consuming reducing sugars,or some amino peptides in it can directly bind to AA to reduce the content of AA.But SPI could increase the content of GEs.(3)The effect of coating on the storage performance of CFDC:The CFDC was reposited in temperature 25℃,50% humidity storage conditions for 7 days,changes of sensory properties,physicochemical indexes and chemical accompanying contaminants of control CFDC samples and CFDC samples treated with 1% MC coating during the one week storage.The results were as follows: during storage,the water content decreased,L value decreased gradually and a value and b value increased continuously,coating treatment could delay the changes of sensory properties,this is because coating can inhibit the movement of water and delay the loss of water in CFDC.At the same time,the coating can delay the lipid oxidation to delay the color change of CFDC during storage.During the storage,the hardness of coating group showed an increasing trend,while the control group first decreased and then increased,which was related to the migration of water and the aging of starch during storage.Although the contents of AV,PV,p-AV and TOTOX increased during storage,compared with the control group,the coating treatment can delay the change of these physical and chemical indicators,because the coating can form a protective layer on the surface of the CFDC,prevent the CFDC from coming into contact with moisture and oxygen in the air,thereby reducing the occurrence of lipid oxidation during storage and inhibiting the oxidation rate.During storage,MDA showed an upward trend with the prolonged storage time,and the AA content increased slowly.Similarly,the coating treatment could also delay the increase rate of the two chemical hazards because the coating film can form a barrier to delay the oxidative deterioration of the oil,or hinder the contact between the reaction substrates;But the contents of HHE,HNE,GEs and TFA do not change substantially with the storage time,mainly due to the lower temperature during storage causes less influence on its formation.