| Recently, there has been a considerable research interest in antioxidant capacities of phytochemicals from various materials. Several epidemiological studies suggest that a high intake of food rich in natural antioxidants increases the antioxidant capacity of the plasma and reduces the risk of certain, but not all, cancers, heart diseases, and stroke. This was attributed by some researchers to antioxidants from vegetables and fruits. Lotus is a perennial aquatic crop with stout creeping yellowish white colored rhizomes. It is both an ornamental plant and a dietary staple in Eastern Asia, particularly in China, especially it has been applied in Chinese herbal prescriptions to alleviate tissue inflammation, cancer, and liver cirrhosis for a long time. In the current study, we evaluated the antioxidant activity of various extracts of lotus rhizome and investigated the effect of antioxidant capacity, as well as the substances in it.Antioxidant activity of lotus rhizome was compared with other 11 vegetables using FRAP assay, DPPH radical scavenging assay andβ-carotene bleaching assay respectively.The total phenol content of these vegetables was also determined. Results showed that amaranth, lotus and mushroom had high antioxidant activities by all three antioxidant activity assays, while eggplant showed the highest scavenging activity by the DPPH method. Bamboo shoot, cucumber and carrot showed low antioxidant activities by all three antioxidant activity assays, while onion exhibited the lowest antioxidant activity in the DPPH method. Amaranth had the highest total phenol content, while cucumber had the lowest. The correlations between the antioxidant activity and the total phenol content differed with the antioxidant activity assay method selected. FRAP values and the total phenol content showed the highest positive correlation. All three antioxidant assays had positive correlations with each other respectively.The antioxidant properties and phenol contents of lotus rhizome from four varieties, named Na ma, E lian si hao, E lian wu hao and Dong he zao ou, were also compared. Results indicated that no different exists between their phenol content of water extracts, while 80% ethanol extracts from E lian wu hao had lower phenol content than others. FRAP value and DPPH scavenging capacity of four lotus showed the same trend as their phenol content, however, 80% ethanol aqueous extracts showed significant difference (p<0.05), and E lian wu hao had lower FRAP value and DPPH scavenging capacity compared with the others. Total phenol content and antioxidant activities from peel of lotus rhizome were higher than that from flesh of lotus. Maturity also affect total phenol and antioxidant activity of lotus, our results showed old lotus exhibited higher phenol content and antioxidant activity than young one either in peel or flesh.Using 80% ethanol aqueous could extracted more phenol from lotus rhizome than water, 146mg GAE/100g fresh lotus rhizome could be harvested by 80% ethanol aqueous while only 117mg/100g fresh lotus rhizome by water. 80% ethanol aqueous extracts showed generally stronger FRAP value and DPPH radical scavenging capacity than water estracts, however, all waters extracts showed higher antioxidant acitivities than 80% ethanol aqueous extracts when tested byβ-carotene bleaching assay.Two schemes were used here to study polarities of antioxidants in lotus. Lotus rhizome was first extracted by 60% ethanol aqueous and then organic solvent was removed. The remained aqueous was extracted by solvents in turn in an order of descending polarity. Total phenol and antioxidant activity of the extracts were evaluated. Results indicated that ethyl acetate extracts had more phenols, extracts of butanol, chloroform, water respectively were followed. DPPH radical scavenging capacity of different extracts was positively correlated with their total phenol contents. Four extracts, except water significantly inhibited the fading ofβ-carotene linoleic acid emulsion, while butanol extracts showed weaker inhibition than others. Several organic solvents were also used to extract antioxidant from lotus powder directly, and antioxidant acitivties of the extracts were evaluated by DPPH assay andβ-carotene bleaching assay. Methanol showed the highest extract yield among all of solvents. Although acetone extract had the highest total phenolics content, methanol extract had the highest total phenolics recovery from lotus powder. Extract of either methanol or acetone demonstrated the highest DPPH scavenging activity at both 66.7mg/L and 133.3mg/L. All extracts exhibited higher antioxidant activity coefficient (AAC) than that of ascorbic acid, furthermore, dichloromethane and petroleum extracts had comparable AAC with BHA by theβ-carotene bleaching assay. The properties of the extracting solvents significantly affected the yield, total phenolics content and antioxidant activity of lotus rhizome extracts.Single factor trial and orthogonal intersection were used to study the best extracting conditions of total phenol and antioxidants from lotus rhizome. Single factor trials showed that the optimum conditions for extracting both total phenol and antioxidants from lotus rhizome were: 20% ethanol concentration, solvent to solid ratio 1:6, 60℃, and no more than 2 hours of extraction time. Orthogonal intersection trials revealed that solvent to solid ratio became the major affecting factor of total phenol recovery, followed by ethanol concentration, temperature and time; while ethanol was the prime affecting factor of antioxiclant recovery, followed by solvent to solid ration, time and temperature.Qualitative tests indicated that lotus rhizome contain phenol compound and ellagitannins, organic acids, reducing sugars, polysaccharides or its glycosides, saponins, volatile essence, but contain no flavonoids, alkaloid. Nutritional compositions in lotus rhizome were also evaluated in this study.Gradient elution of RP-HPLC was used to establish an assay to separate 11 phenolics. The separation parameters, such as changing rate, PH, flow rate of mobile phase and operating temperature were optimized to obtain a clear differentiation of various phenolic compounds. Results showed this assay was accurate and simple. It could be used as a method to separate natural phenolics or as an reference for optimization of test conditions in actual analysis. |
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