| Rice bran oil is recommended as“one of three healthy oils" by the World Health Organization due to its ideal fatty acids profile and abundant ?-oryzanol(1%?3%).It has been reported that ?-oryzanol,a unique nutraceutical of rice bran oil,has multiple bioactivities.Exploring the thermal degradation mechanism of ?-oryzanol and clarifying the frying applicability of rice bran oil are very helpful for the quality control of rice bran in cooking as well as the development of rice bran oil industry and ?-oryzanol functional foods.In this project,the experiment was performed to study:1)effects of environmental conditions on stability of ?-oryzanol;and 2)thermal degradation mechanism and degradation products of ?-oryzanol;and 3)the changes of ?-oryzanol,phytosterols,fatty acids,tocopherols,malondialdehyde,conjugated diene,color,and viscosity of rice bran oil and rapeseed oil during deep-frying using potato chips;The main conclusions were as follows:(1)?-oryzanol was stable when heated at 90?120? in coconut oil.However,the thermal degradation of ?-oryzanol at 150?210? in coconut oil was accelerated,which was in accordance with the first-order kinetics model with activation energy at 104.52 kJ/mol.Results showed that light,oxygen and metal could increase the thermal degradation of ?-oryzanol(2)Thermodynamic analysis of ?-oryzanol showed that were two stages of decomposition under an air atmosphere:1)The first stage was initiated at about 300?,and the second stage started at about 420?.These two stages were exothermic reactions.?-Oryzanol was stable enough to resist breakdown when the temperature was blow 300?.On the contrary,pre-oxidation of oil could accelerate the thermal degradation of ?-oryzanol;?-oryzanol degraded more rapidly in oils with more unsaturated bounds,followed as tea oil<safflower seed oil<perilla seed oil.Therefore,?-oryzanol in our study was subject to thermo-oxidative degradation,which played a role as an antioxidant under cooking conditions.What's more,the content of sterol compounds in coconut oil decreased when heated at 180?,with little amount ferulic acid found during this process.Cleavage of ester bond in ?-oryzanol might be the degradation pathway.It was proposed that sterol compounds and ferulic acid were degradation products of ?-oryzanol in this study.(3)Potato chips were deeply-fried in rice bran oil and rapeseed oil for 16 consecutive days,respectively.At day 16,the content of ?-oryzanol and phytosterols in rice bran oil were decreased to 10.54%and 45.66%,respectively.The content of saturated fatty acids and monounsaturated fatty acids in rice bran oil had an increase tendency,while the content of polyunsaturated fatty acids decreased significantly.The content of tocopherols and the production of malondialdehyde and conjugated diene in rice bran oil were lower than those in rapeseed oil,while rice bran oil had a higher level of ?-carotene than that in rapeseed oil.Deep-frying significantly changed the color and viscosity of both edible oils,however rice bran oil could reverse these changes compared to rapeseed oil.To conclude,rice bran oil showed a superior frying applicability. |
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