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Summary: Deep‐frying oil featuring total polar compound (TPC) has been found to be unhealthy. However, little information is available regarding the impact of TPC on the lipid digestion behaviour. In this study, three typical edible oils (palm oil, PO; high oleic acid peanut oil, HOA; and high linoleic acid sunflower oil, HLA) were selected to investigate the effect of deep‐frying on the lipid digestion. Digestion behaviour was monitored by pH‐Stat method in vitro. Digestibility rate analysis showed that free fatty acids release rate of all TPC groups was the slowest among corresponding fresh oils and deep‐frying oils, indicating deep‐frying decreased lipid digestion rate. Lipid droplet analysis uncovered that deep‐frying could increase lipid particle size. Correlation analysis showed the polymers in TPC are negatively correlated with digestion rate and particle size, suggesting the digestion behaviour of deep‐frying oil is related to TPC constitution. In conclusion, this study highlights that deep‐frying weaken the lipid digestion capacity, and the multiplicity of TPC distribution which vary in terms of FAs type contribute to differences of digestion behaviour in deep‐frying oils. [ABSTRACT FROM AUTHOR]

• Epoxy group weakened the digestion capacity of triglyceride. • Epoxy group increased the mean particle diameter of triglyceride. • Epoxy group decreased binding capacity of triglycerides to salt ions in digestive juice. • Epoxy group enhanced the flexibility of lipase. The digestion behavior of epoxy triglyceride, the main cytotoxic product of deep-frying oil, remains unknown, which may affect its biosafety. In this study, epoxy triglyceride (EGT) and triglyceride (GT) were used to reveal the effect of epoxy group on digestion. Digestibility rate analysis showed that the free fatty acids release rate of EGT was slower. To clarify this phenomenon, binding ability with salt ions in digestive juice and particle size were also been studied. Cluster size analysis indicated that epoxy group increased triglyceride particle size, resulting in smaller contact area between EGT and lipase. Interface behaviors displayed EGT decreased binding ability with salt ions in digestive juice. Spectroscopic analysis showed EGT caused the red shift of lipase peak, indicating that epoxy group changed lipase structure. Molecular dynamics simulation suggested EGT leads to loosen lipase structure. In conclusion, this study highlights that epoxy group could weaken the triglyceride digestion. [ABSTRACT FROM AUTHOR]