Study On Microbial Degradation Of Tara Tannin To Gallic Acid

Tara tannin belongs to gallotannins. Its hydrolysate, gallic acid, possesses high chemical and biologic activities, which has been widely applied. As a complement of gallnut, tara is more and more continually used to obtain gallic acid by microbial degradation.As a typical rumen bacterium, the study on degradation of tara tannin by Escherichia coli could not only provide new approach to finer and value-added utilization of tara tannin but also could be helpful to indicate the nutrient or anti-nutrient characteristics of vegetable tannins. After a step-wise domestication, a strain which could tolerate 8g/L tara tannin extract and even degrade tara tannin to gallic acid was gained. Maximum gallic acid yield ( 83.8%) was obtained after Escherichia coli was cultivated aerobicly in 100mL liquid culture medium with 7g/L tara tannin extract and 1g/L complementary urea on snaker (120 rpm) at initial pH 6.0 and 28℃for 28h, while maximum tannin reduction rate (43.6%) was obtained after 5g/L glucose was supplied instead of urea in the same degrading conditions above.Nowadays, studies on degradation of vegetable tannins by fungi have been reported frequently. However, it seems that fewer studies referring to biodegradation of tara tannin have been carried out. A strain which utilized tara tannin extract as its sole carbon and nitrogen source was isolated from tara pods and identified as Aspergillus niger. After a step-wise domestication, Aspergillus niger could tolerate 100g/L tara tannin which is 97.5% higher than Escherichia coli do ( 2.5g/L tara tannin). Maximum gallic acid yield ( 85.31%) was obtained in the 100 mL...