Study On Approach And Mechanism Of Biodegradation Of Valonia Tannin

Three strains, which could effectively degrade valonia tannins, were isolated and selected, and identified as Aspergillus niger, Endomyces and Candida utilis. Then, degradation ability of the strains on valonia tannins and factors influencing the biodegradation were comprehensively investigated.It was found that degradation rate of valonia tannin and yield of ellagic acid was limited when single-strain cultivation was employed. Using model compound, Propyl gallate (PG), the reasons for the lower biodegradation and the factors influencing activity of the degrading enzymes were evaluated.Furthermore, it was found that Aspergillus niger have higher activity of tannase than Endomyces and Candida utilis when using PG as substrate. And it was determined that hydrolysis function of Aspergillus niger on ester bond of tannin could be remarkably inhibited by additional carbon sources, glucose in particular, whilst that of Endomyces and Candida utilis was activatedIn addition, it was verified that no polyphenol oxidase (PPO) from Aspergillus niger could be determined, but activity of PPO derived from Endomyces and Candida utilis was obviously observed by using catechol as substrates. Meantime, it was approved that PPO could oxide pyrogallol and catechol, but not phloroglucinol.Based on the researches, a biodegradation system of valonia tannin byco-cultivation was established. The optimum combination and condition of co-cultivation were also obtained by the orthogonal experiment. It was showed that yield of ellagic acid would be remarkably increased when co-cultivation of strains Aspergillus niger and Candida utilis were employed. High ellagic acid yield (28.7%) was achieved in inorganic salt culture medium (pH 4.5) containing 25 g/L valonia tannin, 20g/L sucrose and 2g/L sodium nitrate, incubated for 8d at 28C in a rotary shaker (140r/min). The results showed that at least two kinds of enzymes, tannase and PPO, were involved in degradation of tannins.The approach established in this thesis and the data obtained in experiments are of theoretical importance and practical significance in both finer and value-added utilization of vegetable tannins and removal of tannin pollution in industries.