| Recently, plant polyphenols and their antioxidant capacitieshave attracted widespread attentions in the researchfield of natural active products.Lotus(Nelumbo nucifera G.) root, which is a nutritionalvegetable with health protection function, can be eaten as fresh or after been cooked.Compared with other common vegetables, lotus root showed a stronger antioxidant activity, itcould be related to the higher content of polyphenols.At present, the low processing level of lotus root showed the mainproblems including most products in the market are similar and the node and peel as the main by-productshave not been well used. It did not exhibit the characteristic and advantage of this vegetable. To explore the antioxidant properties oflotus root and further promote its deep processing, the contents, compositions and antioxidant activities of polyhenols from different parts of lotus root were comparatively analyzed, and the main research methods and results are as follows:1. Comparison on the contents, compositions and antioxidant activities of polyphenols from different parts of lotus root.‘E Lian’ series of lotus root including No. 5, No. 6, No. 7 and No. 8 were used as raw materials. The total contents of polyphenols and flavonoids and their compositions in the different parts of lotus root were respectively measured. Further, the scavenging abilities of polyphenol extracts from the different parts on DPPH and ABTS radicals were analyzed. The results showed that polyphenols and flavonoids fromthe different parts of four lotus rootsmostly exist as fresh, and their contents could be all ordered as node > peel >edible part. The polyphenol compounds in lotus root were mainly composed of gallic acid, caffeic acid, vanillic acid, rutin, epicatechin, chlorogenic acid and resveratrol. The polyphenol composition and content among different parts of lotus root were significantly different, as well as those among different varieties in the same part. Compared with free polyphenols,bound polyphenols had a stronger DPPH radical scavenging ability, while a weaker ABST radical scavengingability. Moreover, the edible parts of lotus root showed the strongest DPPH radical scavenging ability, and the node showedthe strongest ABST radical scavenging ability.Based on the comparison on polyphenol content and radical scavenging ability, ‘E Lian’ No. 7 was found to be the advantage variety of lotus root for the development of natural antioxidant, especially its node and peel had excellent potentials.2. Homogeneous-extractiontechnology optimization oflotus root polyphenols and their antioxidant effects on oil.Polyphenol extraction yield and DPPH free radical scavenging rate were respectively used as evaluation index. Volume ratio of hydrochloric acid to methanol, homogenization time and speed were selected to establish regression mathematical models based on single factor experiments.Two optimized extractiontechnologies were then obtained, and the corresponding extracts were compared on polyphenol content and DPPH free radical scavenging rate to define one for the extractions of polyphenols from different parts of ‘E Lian’ No. 7 lotus root. The inverse microemulsionsof polyphenol extracts were respectively prepared and evaluated on antioxidant activity in oil by Schaal oven method. The optimized extraction conditions were as follows: volume ratio of hydrochloric acid to methanol was 22:78(m L/m L), homogenization time was 6.8 min and homogenization speed was 10500 r/min. Under these conditions, polyphenol extraction yield was165.85 mg GAE/100 g FW and the IC50 value of DPPH free radical scavenging of polyphenol extract was 4.75 μg GAE/m L. The effects of experimental factors on polyphenol extraction yield and DPPH free radical scavenging rate could be both ordered as: hydrochloric acid to methanol > homogenization time > homogenization speed. In the concentration range of 10-30 μg/m L,the inverse microemulsions of polyphenols from different part of lotus root all showed good antioxidant effects on oil, and their effectswere better than that of VE. The inverse microemulsionscontaining polyphenols from different parts with various addition ratios(total polyphenol concentration was 10μg/m L) showed significant differences on antioxidant activity. Polyphenols from node and peel showed the obvious synergistic effect on antioxidant activity when mixed at the concentration ratio of 1:1, and could effectively inhibit oil oxidation.The contents, compositions and biological activities ofpolyphenols from different parts of plantusually show significant differences, andaccordingly have different pathways and methods for development. This study aims to provide theoretical basis for the comprehensive utilization and deep processing of lotus root. The differences of polyphenols from different part of lotus root on content, composition and radical scavenging activity have been explored. In addition, the technology system, which is related to the development of natural antioxidants in oil and contains the extraction, preparation and application of lotus root polyphenols, has been established. The study can be referred to the relative works on the innovative evaluation and utilization of lotus root. |
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