| Oat is considered to be the best food which has all sorts of nutrition and the good material for functional factor extraction. Antioxidant activity is prominent among the various physiological functions. Germination is one of the most harmless and low-cost processes with good prospect for improving the nutritional value of plant seeds. But currently, the study on the antioxidants in germinated oats was limited. In this study, oat seeds were steeped and germinated to enhance the total phenol content. Then, the phenol composition and antioxidant activity of oat extracts were studied and the structures of avenanthramides were characterized. The important results were obtained as follows:1. Extraction of oat phenols and changes of total phenol content during oat germinationThe extraction technology of oat phenols from ungerminated oat seeds was optimizated. The results indicated that the optimum conditions of solvent extraction were: ethanol concentration 80%, solid-liquid ratio 1:20, bath temperature 50℃, extraction time 2 h. Under these conditions, the extraction ratio reached 0.817 mg/g. The optimum conditions of enzymatic hydrolyzing were:papain addition 5.07 mg/g, a-amylase addition 0.88 mL/g, temperature 72.99℃, time 1.23 h. Under these conditions, the extraction ratio reached 2.169 mg/g which is much higher than solvent extraction. When the oat seeds were steeped in water, the level of total phenol decreased. Then, the total phenol content increased with germination time and the increase became slowly after 6-day. The total phenol contents in buds and roots were more than that in oat grains.2. Phenol composition of germinated oat extracts and structure characterization of avenanthramidesThe optimum purification technology was as follows:maeroporous resin was chosen AB-8 using 70% ethanol as elution solvent. pH value was adjusted to 2 using ethyl acetate as extraction solvent. The phenol composition of extracts from ungerminated oat seeds,6-day germinated oat grains, buds and roots were studied by such means as UV, IR and HPLC. The results showed that there were several kinds of phenolic acid in ungerminated oat seeds. The kind and content of phenolic acid in 6-day germinated oat grains were both reduced, but new kinds appeared in buds and roots. Avenanthramides 2c, 2p,2f, t2, t3 and unknow components w6～w12 were identificated by HPLC/Q-TOF-MS. A group of avenanthramides such as 2c,2p,2f, t2, t3 were both in ungerminated oat seeds and 6-day germinated oat grains. Avenanthramides t2 and t3 increased drastically during oat germination, so did the possible phenols w10 and w11 which existed in germinated oat grains and roots. The components w6, w7, w8, w9 from germinated oat buds were needed to futher investigate their chemical structures.3. Comparison of the antioxidant activity of germinated oat extractsThe antioxidant activity of different extracts were evaluated by reducing power and scavenging effects on DPPH, NO2-, O2-·,·OH, H2O2. The results indicated that oat phenols exerted strong antioxidant activity in various in vitro antioxidant assays. The antioxidant activity and scavenging effect on NO2 were increased to a certain extent during oat germination. Different extracts exerted different antioxidant activity which were closely related to the kind and polarity of phenols from different parts. The 6-day germinated oat grains and roots exerted higher antioxidant activity than 6-day germinated oat buds. So, we speculated that the possible phenols w10 and wll had stronger antioxidant activity than the components which existed in buds.4. Phenol composition and antioxidant activity of enzymatic hydrolyzatesThe extracts of ungerminated oat seeds and 6-day germinated oat grains were purified by the same technology as solvent extracts. The results showed that the yield of enzymatic hydrolyzates were much higher than solvent extracts, whereas the purity and antioxidant activity decreased. Furthermore, the phenol composition of enzymatic hydrolyzates changed a lot in comparison with the solvent extracts. |
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