Effect And Assessment Of Polar Compounds Extracted From Deep-fried Palm Oil On HepG2 Cells

Oils and fats are exposed to atmospheric oxygen and moisture from food in the process of frying at high temperature,resulting in oxidation,hydrolysis and polymerization,and generating products whose polarity are bigger than triacylglycerols,namely polar components(PCs).PCs include dimeric triacylglycerols,oligomeric triacylglycerols,oxidized triacylglycerols,diacylglycerols and free fatty acids,etc.At present,studies about frying oils focus on the physicochemical indexes,oxidation mechanism and in vivo evaluation,but effects of PCs on nutritional health remain largely unknown.Therefore,the changes of physical and chemical properties,fatty acid composition and oxidation stability of frying palm oil were investigated,meanwhile,effects of PCs extracted from 50 h deep-fried palm oil on HepG2 cell were studied,in order to provide the theory basis for effects of frying oil on human health at the cellular level.First of all,as the most widely used frying oil in domestic and foreign markets,palm oil was investigated by considering different physicochemical properties during frying process from 0 h to 50 h.Results showed that AV,POV,CGV,p-AV and the content of PCs of frying palm oil increased gradually with the increase of frying time,while IV and OSI decreased continuously.And it proved that PCs content,IV,CGV were more significantly related to frying time.Results of fatty acid composition showed that the content of linoleic acid and linolenic acid in frying oil samples decreased significantly with the prolonged frying time,while the amounts of total TFAs and percentage of saturated fatty acids increased continuously.The results of ~1H-NMR indicated that the content of carbon-carbon double bond,especially?-fatty acid,declined clearly as well as secondary oxidation products and hydrolysates were found in PCs when compared with fresh palm oil.Secondly,the properties of emulsions prepared by tween-80,lecithin and sodium caseinate with PCs were analyzed in order to make PCs more easily dissolved in medium.Results showed that the sizes of emulsion decreased with the increase of emulsifier concentration,while the absolute value of Zeta potential and stability rose gradually.Meanwhile,the stability of emulsion containing sodium caseinate was worst.Results of Turbiscan showed that the main reason for resulting in the instability of these three emulsions was particles migration but not flocculation or agglomeration.Finally,the effects of PCs on HepG2 cells were studied.Cell viability,lipid accumulation,oxidative stress,cell cycle and apoptosis were detected after treating with different concentrations of PCs for 12 h,24 h,and 48 h,respectively.Results of MTT assay showed that the viability of HepG2 cells decreased with the increase of the concentration and treating time of PCs,indicating that PCs could inhibit the growth of HepG2 cells.Results of oil red O test and the TG content of cells showed that PCs could promote the accumulation of lipid droplets.Meanwhile,three antioxidant enzymes activity of HepG2 cells treated with PCs presented a dose-and time-dependent decrease,making it clear that PCs could depress cell anti-oxidative capacity.The reduction of MDA and increase of ROS level indicated that PCs stimulated cells through oxidative damage.In addition,PCs could disrupt cell membrane,induce apoptosis and inhibit cells in G0/G1 phase.