Phenolic Compounds and Antioxidant Activity of Oat Bran by Various Extraction Methods
Recent studies have suggested that the health promoting capabilities of oats are due to its antioxidants (tocopherols, tocotrienols, and sterols) found within the bran along with phenolic compounds, such as avenanthramides, p-hydroxybenoic acid and vanillic acid. Long-chain fatty acid oxidation is directly responsible for most off-flavors in food. Since oat bran is a good source of antioxidants, a concentrated extract could be used as a natural preservative, for foods rich in unsaturated long-chain fatty acids. Three methods, traditional solvent (TSE), microwave-assisted solvent (MAS), and supercritical fluid treatment (SFT), were used to obtain the extracts. One extraction temperature in TSE, 60°C, and two extraction temperatures in MAS, 60°C and 100°C, were tested. The DPPH (2, 2'-diphenyl-1-picrylhydrazyl) method demonstrated that the MAS-100°C was the most efficient extraction in the group, thereby serving as MAS sample against the TSE and supercritical-treated samples. For the treated samples, oat bran was exposed to supercritical CO2 before extraction. Three different temperatures of CO2 were tested, 25°C, 50°C, and 75°C. The treated samples then underwent MAS-100°C to gather extracts for analysis. The experimental results for the DPPH test favored the SFT-75°C treatment at a 40?l concentration. Therefore, SFT-75°C served as the treated sample in the final three experiments. Antioxidant activity was further tested using two other methods: cholesterol oxidation and the DHA model. The total phenolic content was determined using Folin-Ciocalteau Method. The SFT-75°C treatment showed statistically higher results for antioxidant activity in both the cholesterol oxidation and DHA oxidation experiments over the TSE-60°C or MAS-100°C. In terms of total phenolics, the SFT-75°C treatment showed statistically higher results than TSE or MAS-100°C in terms of catechin equivalency, but no statistical difference was seen among the treatments when compared on the basis of total phenolics per gram of original oat bran sample. However, extraction techniques can be evaluated based on extract yield, which this research demonstrated would be SFE-75°C. In conclusion, the SFT-75°C treatment was the optimal extraction based on antioxidant activity, catechin equivalency for total phenolics, and sample yield. This information could be used in the future development of food products as a natural antioxidant source.
Advisor:Daryl McKee; Kerry Dooley; Witoon Prinyawiwatkul; Zhimin Xu
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:11/16/2006