Study On The Quality Monitoring Of Repeated Usage Of Deep-frying Oil

Repeated usage of deep frying oil is a general approach in food manufactures and fast food restaurants for cost saving.To use repeated frying oil properly and control the food safety,it is important to monitor the oil qualiy during deep frying.Twelve categories of frying oils were selected in present study which includes seven single oils and five blending oils products.The single oils include soybean oil,palm oil(42degree),cottonseed oil,rapeseed oil,rice bran oil(RBO),high oleic canola oil(HOCAN),and high oleic sunflower oil(HOSUN).The components of blending oils were listed as follows:W1 was the mixture of sunflower oil,HOSUN,RBO,and corn oil.W2 and C1 were the mixture of soybean oil,HOCAN,corn oil and hydrogenated soybean oil.CA was the mixture of rapeseed oil,HOCAN,and HOSUN.CE was the mixture of rapeseed oil,sunflower oil,HOCAN,and HOSUN.Three products,French fries,chicken nuggets and fish filets,were selected for deep frying test.The Lovibond color(Red),anisidine value,peroxide value,acid value,and total polar compounds were measured every twelve hours during frying.The results showed that HOCAN,HOSUN and five blending oils exhibited much better performances during deep frying.The oil deterioration rates were much slower than other oils:the frying time lasted for 24 to 28 days when the total polar compounds content reached to 27%,and 10 to 29 days when acid value increasd to 5 KOH mg/g in French fries.While the blending oil CE presented longest frying time,which was 29days.On the contrary,soybean oil demonstrated the shortest frying time of,it was 8 days when the level of total polar compounds exceeded the limitation standard and 6 days the time acid value increasing to 5 KOH mg/g.The influence of food type on these parameters was significant as well,the frying time of oil used for French fries was longer than that of chicken and fish.The product weight per batch did not obviously influenced the frying time of the oil.However,the capacity of exhausted ventilator had significant effect on the acid value and total polar compound(TPC)of oil during deep frying.Higher capacity of exhausted ventilator could slow down the increasing of acid value and TPC.The detection method of total polar compounds using fast detector showed significant correlation with column chromatography method when its level was lower than 20%(Pearson correlation coefficient was from0.744 to 0.984,P<0.01).But the correlation coefficient was lower when the level of total polar compounds exceed 20%(Pearson correlation coefficient was from 0.553 to 0.928,P<0.01),in which palm oil and soybean oil showed better correlation between these two method(R~2=0.8517 and 0.8632,respectively),but correlation coefficient of other type of oils were lower(R~2=0.1492 to 0.7762).The results provided the data for the quality monitoring of repeated usage of deep frying oil.