Fundamental Study On Quality And Safety Of Youtiao Based On Its Chemical Properties And PAHs

As one kind of traditional fried food, doing research on youtiao is significant to explore the chemical properties, PAHs and its influcing factor of fried wheat products. In this research, we chose 8 youtiao samples from canteen, supermarket and monopolized restaurant in youtiao, and analyzed their moisture content, oil content, crude proteins content, ash content, peroxide value, p-anisidine value, acid value, polar compounds and other chemical properties. The oil content of all samples ranged from 7.16% to 20.3%, while moisture content ranged from 20.28% to 32.61%.P-anisidine value of most samples were higher than 100. There were 37.5% of the samples excessing the national limiatation of 5mg KOH/g for acid values. The samples with excessive polar compounds content than national limitaion of 27% occupied 37.5% of all the samples. All of these indices had great influence on the quality and safety of fried foods. Through the fatty acid analysis, the frying oils from 7 samples were proved to be soybean oil while the other one was palm oil. We used ICP-AES to measure the content of 8 metal elements and found the samples with excessive aluminium content than the national limitation of 100mg/kg took up 50% of all the samples, which were mainly from canteen and supermarket. It showed that in these places aluminum including raising agents was more likely to be used.The amino acid composition of 8 samples was similar and the main factor causing the difference might be the level and origin of wheat flour. As the first limiting amino acid in wheat flour products was lysine, the intake of proteins from different origins was important to keep balance. Volatile compounds analysis showed that, like other kinds of fried products, youtiao contained abundant aldehyde and ketone compounds. Some precursors, like pyrazines, of acryamide, and furan compounds needed to be taken more attention.By comparison and modification, we chose the pretreatment method for PAHs based on the LLE with DMF-water(9/1,v/v) and SPE of Florisil. The result of gas chromatograph showed that the purification effect of the chosen method was satisfactory and the regression coefficients for 16 kinds of PAHs were all over 99%. The PAHs content in 8 samples were measured and the total PAHs content were in the range of 27.30 ppb to 90.00 ppb. Through contaction and comparision among PAHs content and chemical properties measured above, like oil content and aluminum content, it seemed there was some relevance between PAHs content and frying process and formula.The oxidative stability of oil also had influence on the formation of PAHs. Oxidative stability of different vegetable oil during long storage in room temperature was also tested. The result showed that during storage in room temperature, peroxide value increased sustainedly while p-anisidine value didn’t change siginificantly for all the samples. Sesame oil presented the significantly better oxidative stability than other 3 samples.