Research On Rapid Identification Methods Of Dynamics Characteristic And Quality For Fried Transgenic Soybean Oil

ABSTRACT Several chemical changes occurred during the edible oil fried at thehigh-temperature. The changes included thermal decomposition, thermalpolymerization, thermal oxidation polymerization, hydrolysis, condensation,oxidization and so on. A number of volatile aldehydes, ketones, lactones and othersubstances harmful to human health were produced. The colour, flavour, viscosity,acid value, peroxide value and carbonyl value of the edible oil were changed too. As aresult, it had important realistic meanings to find the new parameters of edible qualityfor frying oil and to achieve rapid detection on the spot.The edible soybean oil from different areas were researched in this paper.Carbonyl value promulgated by the nation was taken as reference standard. Thedynamics characteristics and change rate of pH value, conductivity, viscosity, acidvalue and peroxide value were analyzed as carbonyl value exceeded the nationalstandard during batch deep-frying and heating. At the same time, the sensoryphenomenons of frying oil were described.With the increase of frying time, the soybean oil from the lemon yellow colorgradually deepened to black, transparency had been reduced, and finally became aserious turbidity, odors from strong sweet-smelling to strong rancid-smelling, smokealso became serious gradually and even seriously irritated the eyes to tears, there wasfoam after frying5h, rancid-smelling was very strong and the soybean oil was filledwith foam after frying9h. Then fried bread stick tasted horrible.During the process of frying and heating, with the increase of frying time, thecarbonyl value increased obviously and was the significant linear relationship, pHvalue decreased gradually, conductivity increased in the frying process, butconductivity didn’t change in the heating process, viscosity also increased obviouslyand was the significant linear relationship, acid value increased on the whole, but thechanges was ups and downs and was not a linear relationship, peroxide value wasirregular. After batch deep-frying and heating12h, carbonyl value had exceeded thenational standard, acid value and peroxide value hadn’t exceeded the nationalstandard, but acid value increased obviously after frying8h and peroxide value exceeded the national standard easily after frying12h, pH value was4.16, H~+activitywas100times and conductivity was5times and to the fresh soybean oil, and themean value of viscosity was85.39mpa·s, soybean oil couldn’t be used as food at themoment. It suggested pH4.20was considered as a new expression parameter thatcould be used to identify the edible quality of fried soybean oil.There were obvious correlativity between carbonyl value, H~+activity, viscosity,acid value, peroxide value and the frying time. The relationship between conductivityand the frying time, carbonyl value was significant generally. There were obviouscorrelativity between H~+activity, viscosity and carbonyl value. The relationshipbetween acid value, peroxide value and carbonyl value was significant relatively.There weren’t correlativity between viscosity, acid value, peroxide value andconductivity.