Research On Determining Methods For Trans-4-Hydroxy-2-Alkenals In Oils And Aluminum In Youtiao

Trans-4-hydroxy-2-alkenals(4-HAEs)were secondary oxidation products of oil and tend to form covalent adducts with proteins,phospholipids and DNA leading to biotoxicity.Alum is commonly used in youtiao as rausing agent and chronic exposure to aluminum(Al)can have toxic effects on a number of diseases.Therefore,researches on 4-HAEs in edible oil and how to achieving rapid detection of aluminum content of fried dough sticks are of great significance.Firstly,this paper was to establish a solid phase extraction-high performance liquid chromatography(SPE-HPLC)method to determine the trans-4-hydroxy-2-hexenal(4-HHE)and trans-4-hydroxy-2-nonenal(4-HNE)contents in edible oil,realizing the extraction and purification of oil samples and detection 4-HHE and 4-HNE at the same time.Good linearity was observed in the range of 0.1–0.5 ?g/mL and 0.5–10 ?g/mL for 4-HHE and 4-HNE,respectively.The supposed method had the advantages of effectiveness,high precision,simple operation and good repeatability.The change trends of 4-HHE and 4-HNE in soybean oil heating 40 h were studied using SPE-HPLC method.The contents of 4-HHE and 4-HNE increased initially and declined slightly later and content ranges were 0–0.32 ?g/g and 0–6.97 ?g/g,respectively.At the same time,this paper determined the 4-HHE and 4-HNE content(0–0.36 and 0–7.45 ?g/kg,respectively)of representative market samples and the results showed that the 4-HAEs content range of market samples was large.Secondly,we determined the concentrations of 4-HAEs in soybean and rapeseed oils during refining in this study.The results showed that the concentration ranges of 4-HHE and 4-HNE in soybean oil were 5.65–16.27 ?g/kg and 260.01–644.19 ?g/kg,respectively.In rapeseed oil they decreased from 0–21.46 ?g/kg and 37.35–5246.44 ?g/kg,respectively.In general,bleaching contributed the most to the decrease in 4-HAEs.Refining process reduced the levels of primary oxidation products,secondary oxidation products as well as the content of polar compounds effectively.These results provide valuable theoretical and practical reference for oil refining.Finally,in order to solve the issues with time-consuming and complicated aluminum element determination,this paper developed a simple and environment-friendly WDXRF method for the determination of aluminum content in youtiao.The WDXRF method has good specificity,high recovery(94.35–97.30%)and good linearity(0–1000 mg/kg).There were no significantly different between the results of WDXRF and ICP-OES(P < 0.05),which further verify the feasibility of WDXRF method.