桑叶发酵前后总黄酮、总酚酸含量变化及抗氧化活性研究

Antioxidant activities and determination of total flavonoids and total phenolics in the fermentation and non- fermentation products in Mulberry leaf

目的:比较桑叶70%乙醇提取物液体发酵前后的抗氧化活性,并考察发酵前后总黄酮、总酚酸含量的变化。方法:利用冠突散囊菌在桑叶70%乙醇提取物的液体培养基中发酵培养,将得到的发酵液和未发酵的桑叶70%乙醇提取物以抗坏血酸和EDTA为阳性对照,针对指定指标(DPPH、ABTS、FRAP、OH·、螯合能力)进行体外抗氧化活性试验;并对发酵前后总黄酮、总酚酸含量进行测定。结果:未发酵桑叶70%乙醇提取物的抗氧化活性整体优于液体发酵后的抗氧化活性。其中未发酵桑叶70%乙醇提取物对DPPH、ABTS、螯合能力的IC50值分别为:4.69mg·ml-1、2.03mg·ml-1、20.89mg·ml-1,而液体发酵后的桑叶70%乙醇提取物三者的IC50值分别为:12.42mg·ml-1、2.65mg·ml-1、14.81mg·ml-1;同时含量测定结果显示,发酵后桑叶中总多酚含量较发酵前明显下降,而发酵后桑叶中总黄酮含量却明显高于发酵前总黄酮含量。其中发酵前桑叶中总黄酮、总酚酸含量分别为4.39mg·ml-1、3.95mg·ml-1,而发酵后桑叶中总黄酮含量高达8.53mg·g-1,总酚酸却下降为1.24mg·g-1。结论:桑叶70%乙醇提取物液体发酵前后体外均具有一定的抗氧化活性,但发酵前抗氧化作用较明显。此外通过微生物转化,显著性提高桑叶中总黄酮含量的同时,却降低了桑叶中总酚酸含量,因此可以推测,桑叶中起到抗氧化作用的主要成分并非是黄酮类化合物,而是非黄酮类的多酚类成分。

Objective To investigate in vitro antioxidant activities of 70% ethanol extract from mulberry leaves between liquid fer- mentation and non - fermentation, as well as determine the total phenolics and flavonoid contents in them. Methods The activated eu- rotium cristatum were inoculated into the liquid medium that it was 70% ethanol extract from mulberry leaves and evaluated the antioxi- dant activities of its total extract （70% ethanol）. With ascorbic acid and EDTA as positive controls, several in vitro experiments were conducted including DPPH assay, ABTS assay, OH radicals assay, ferric - reducing power （FRAP） assay and ion - chelating as- say. At the same time, the contents of the total phenolics and flavonoid were determined before and after fermentation. Results The 70% ethanol extract of non - fermented mulberry leaves showed stronger antioxidant activities than the fermented one. For example, the total extract of the non - fermented had capacities of scavenging DPPH , ABTS＋ radicals and ion - chelating with IC50 values of 4. 69, 2. 03, 20. 89mg · m1^-1, respectively. Compared with the non -fermented, the fermented one had the three abilities with IC50 values of 12.42, 2. 65, 14. 81mg · ml^-1 , respectively. In the extract from the fermented mulberry leaves, the total phenolic content was significantly lower than the non -fermented one, while the total flavonoids content was increased more than 2 -fold. Such as the total flavonoids and the phenolic contents of the non - fermented one were 4. 39 and 3.95mg · ml^ -1, respectively , which the fermen- ted one were 8.53 and 1.24mg · g^-l Conclusion The 70% ethanol extracts, whether fermented or non - fermented, show antioxi- dant activities . However, the antioxidant activity of the non - fermented mulberry leaves is stronger than the fermented one. Base on the increase of the total flavonoid and the decline of the total phenolics, we conclude that the principal active components are the phe- nolics, but not flavonoids.