| Phenolic compounds are well known for their antioxidant activities. In this dissertation, the effects of phenolic plant extracts on o-3 fatty acids oxidation and citral degradation were evaluated. The first study is to evaluate the effect of phenolic plant extracts on o-3 fatty acids oxidation based on the aldehyde formation. o-3 fatty acids are well-known for their health promoting benefits. However, they are highly susceptible to rapid oxidation hence there has been a great amount of effort to stabilize these oils. We developed a rapid method utilizing SPME-GC with on-fiber derivatization to monitor propanal, a major end product from o-3 fatty acids oxidation. Seal blubber oil was used as the source of o-3 fatty acids in our study. Acetaldehyde, propanal, acrolein, and malonaldehyde were identified in aged seal oil. Among these aldehydes, acrolein and malonaldehyde are known as reactive electrophiles that react with DNA and protein and are considered toxins and mutagens. The addition of plant extracts reduced the acetaldehyde and propanal concentration in sample headspace; more importantly, plant extracts significantly reduced the bioactive aldehydes, acrolein and malondialdehyde in the headspace of seal oil. It was further observed that in the pH 7.4 phosphate buffer system, EGCG from green tea extract reduced the acrolein in sample headspace by 90% after 3 hours incubation at 37°C. Further research on the reaction between phenolic compounds and reactive carbonyl species such as acrolein and malonaldehyde is highly recommended.; In the second study, the effects of phenolic plant extracts on citral degradation were evaluated. Citral is a monoterpene aldehyde, which has a strong, pleasant, lemon-like aroma; however, it is known to be unstable under acidic conditions limiting its application in the beverage and fragrance industry. In this study, black tea, pomegranate seed and grape seed extracts were used to stabilize citral under acidic condition (pH=3). Samples were stored at 37°C water bath for one week, the degradation of citral and the formation of alpha,p-dimethylstyrene, p-cymene-8-ol, and p-methylacetophenone were monitored by HPLC daily. GC-MS analysis was also conducted to identify the degradation products from citral. The addition of phenolic extracts could not stop citral degradation, however, the formation of off odor compounds, p-methylacetophenone and p-cresol was inhibited. |
