Rosemary extract is commonly added to food oils to mitigate degradation by thermal- and auto-oxidation during frying of snacks and to prolong shelf-life of both oils and snacks. The main compounds in rosemary extract, carnosol and carnosic acid, are thought to act as traditional free radical quenchers, but their decomposition pathways have not been elucidated, and potential antioxidant activity of decomposition products has not been evaluated. To provide critical missing information, this research addressed the following goals: confirm ability of key compounds to inhibit oxidation and increase oil stability, (2) create analytical method for rosemary extract components, (3) identify key carnosol and carnosic acid breakdown compounds in a model oil system, (4) confirm whether effects of rosemary change when a model food is introduced to the model oil system, (5) identify and characterize rosemary degradation products, and confirm their impact on shelf-life.Reverse phase HPLC-UV protocols using an Aqueous C-18 column and solvent gradients were developed to separate rosemary primary antioxidants and their degradation compounds. Novel LCMS with multimode APCI-ESI analyses quantified and identified carnosol, carnosic acid, and their breakdown products during and after frying. Analysis of a model oil treated with carnosol and carnosic acid and heated under simulated frying conditions revealed that carnosol and carnosic acid decomposed over time and formed three key compounds not previously reported: rosmanol, miltirone, and dehydromiltirone. Rosmanol, carnosol and dehydromiltirone were also present in potato slices post-frying. Oxidation stability index screening confirmed all three degradation compounds slow initiation of oxidation in commodity oils and model oil systems to varying degrees. Oxidative stability of oil with rosmanol was statistically greater than with miltirone, dehydromiltirone, and carnosol, confirming that rosmanol is the main decomposition product of rosemary extract contributing to improved oxidative stability of oil and fried foods during and post frying at 180OC. Results showed that by adjusting the initial extract concentrations, frying time, and temperature, it is possible to predict both the levels and types of antioxidants formed, which in turn support longer shelf life, as evidence by lower volatile marker levels during accelerated shelf-life testing.
Eleftherios E. Moros (Thu,) studied this question.