In this study, we investigated the inhibitory effects
of three
soybean isoflavones and two soybean phytosterols on the formation
of 3-chloropropane-1,2-diol fatty acid esters (3-MCPDE) and aldehydes
in heated soybean oil model. 0.4 mM of genistin, genistein, daidzein,
stigmasterol, and β-sitosterol significantly reduced 3-MCPDE
formation by 25.7, 51.4, 21.4, 61.6, and 55.7%, and total aldehydes
formation by 42.03, 43.94, 28.36, 54.74, and 39.23%, respectively.
Further study showed that stigmasterol reduced the content of glycidyl
esters (GEs) and glycidol, two key intermediates of 3-MCPDE, and prevented
fatty acids degradation in the oils. Moreover, the effects of continuous
frying time on the content of stigmasterol and the migration of stigmasterol
were evaluated in the fried dough sticks model system. The content
of stigmasterol in soybean oil was found to be significantly decreased
with prolonged heating time. The concentrations of stigmasterol in
fried dough sticks and the migration rates of stigmasterol from soybean
oil to fried dough sticks decreased with repeated frying sessions.
In addition, stigmasterol undergoes oxidative changes during heat
treatment, and the oxidation products including 5,6α-epoxystigmasterol,
5,6β-epoxystigmasterol, 7α-hydroxystigmasterol, 7β-hydroxystigmasterol,
stigmasterlol-3β,5α,6β-triol, and 7-ketostigmasterol
were identified in the frying oils but not in the fried dough sticks.
Overall, stigmasterol could be added to soybean oil to reduce 3-MCPDE
and aldehydes formation, and reacting with GEs/glycidol and protection
of lipid acids from oxidation may be the mechanism of action of stigmasterol.