Formation Of Polycyclic Aromatic Hydrocarbon In Processing Of Sesame Oil

Sesame oil is deeply loved by people with its fragrance. But before prodoction, process requires sesame seeds need to be roasted at high temperature, which may easily lead benzo(a)pyrene(B[a]P) and other polycyclic aromatic hydrocarbons(PAHs) exceeding the standard. Firstly the determination of 16 kinds of polycyclic aromatic hydrocarbons(PAH16) which was limited by United States environmental protection agency(EPA) in sesame oil was established and optimized; to understand the contamination of sesame oil by PAHs, commercial sesame oil was investigated;and then single- factor and orthogonal experiment was designed to optimize the sesame roast process; four different sesame oil processes was simulated to analysis the differences of PAHs in different processes; ingredients of sesame was heated to analysis PAHs content in substrate and gas; sesame pyrolysis tar component was analysised to initially explored the formation of PAHs in sesame oil.(1)A determination for PAH16 in sesame with oil gas chromatography-tandem mass spectrometry was developed. The quantification limit is 0.04-0.55 μg/kg, and the detection limit is 0.01-0.18 μg/kg. Recoveries rang from 76.33 μg/kg-115.26 μg/kg; RSD≤7.67%. The method is simple, qualitative, accurate, able to meet the testing requirement for PAH16. The contents of B[a]P in 23 kinds of sesame oil samples are all below the national standard(less than 10 μg/kg); but 8 of them exceed the EU standards, accounting for 34.78 %, 10 of them exceed the EU standards for B[a]P, benzo[a]anthracene, benzo[b]fluoranthene, chrysene(PAH4), accounting for 43.48 %. PAH16 pollution situation in sesame oil is as follows: water extraction sesame oil> hot-pressed sesame oil> cold-pressed sesame oil.(2)Single factor and orthogonal sesame roasting experiment is designed to study the impact on PAH16 content. With the extension of the roasting time and roasting temperature, the sesame seed PAHs content rise. Roasted roast temperature and time hace strong impact on PAHs content; the amount of water has almost no effect on it.(3) Cold-pressed sesame oil B[a]P, PAH4, PAH16 content are much lower than other processes during the entire process and far below the EU Limited. B[a]P and PAH4 in hot-pressed sesame oil and water extraction sesame oil significantly rise after roasted, and reached the highest level in crude oil; although the B[a]P, PAH4, PAH16 content have decreased after refining, but still exceed EU standards. During extraction sesame oil processes, the crude oil B[a]P and PAH4 content is respective 20.07 μg/kg and 65.27 μg/kg; after conventional refining, B[a]P and PAH4 content decreased to 9.97 μg/kg and 35.24 μg/kg respectively, still far exceeding the EU standards.(4) Sesame skin, semen sesame, deflated sesame and sesame seeds, respectively was heated at 260 ℃ for 30 min. Deflated sesame B[a]P, PAH4, PAH16 content are the highest in heated substrate. PAHs are detected in the flue gas which sesame skin, semen sesame, deflated sesame, sesame seed produce after heated. Sesame skin gas B[a]P, LPAHs, PAH4, PAH16 levels are highest, while semen sesame gas B[a]P, LPAHs, PAH4, PAH16 levels were lowest.(5) Separate heating, skin PAHs content are the highest, and skins, oil, protein mix produce much more PAHs than other groups. Sesame seeds tar component is more complex consising not only single benzene ring substance, but also two double benzene ring substances. Naphthalene and methyl naphthalene are detected in sesame skin tar. Combining these results, we conjecture that the phenyl radical bind with other unsaturated or small radical forming a benzene ring material with unsaturated branch; some of these materials combine with each other, and some internally cyclize; ultimately PAHs are formed. Two kinds of PAHs formation pathway are gived:(1) phenyl radical and acetylene form ethynyl benzene, and adjacent position which is influenced by alkynyl group gets unstable. After bond with second acetylene, naphthalene was formed rapidly.(2)Two ethylene benzenes combined with each other forming a fourth ring compound with two double bonds. Because of its instability, fluoranthene is forming rapidly by dehydrogenation.