Whole Cell Biocatalyst for Soyasapogenol B Production from Soybean Saponin

摘要

Soyasapogenol B (SB), aglycone of soybean saponin, is known to have hepatoprotective, antimutagenic, antivirus, and anti-inflammatory activities. This research examined the use of whole-cell biocatalyst to produce SB from soybean saponin. It was found that Aspergillus flavus, a fungus isolated from peanut pods, was capable of expressing extracellular and intracellular saponin hydrolase enzyme. However, the total enzyme activity produced using fungal whole cells (37U) in the reaction mixture was about 3 times that produced using the extracellular (12.4U) or intracellular (11.5U) enzyme. Cells with maximum hydrolytic activity for production of SB (12.2 U/g) was obtained using production medium supplemented by 2% soybean saponin, as inducer for enzyme production, adjusted at pH 9 and incubated at 30°C for 2 days. The highest yield of SB was achieved when the reaction mixture was incubated at pH 5.5 and 45°C for 48h; using 20% wet cells (corresponding to 4% cell dry weight) and soybean saponin (2%, w/v) as a substrate. Under these optimal conditions, the cells bioconversion efficiency (SB yield) increased from 5.3 to 60%. Whole cell biocatalyst has several advantages with regard to industrial applications: a consistent quality, easy to be prepared and a very low price compared with purified enzyme. Consequently, this study is significant for production of SB from soybean saponin on an industrial scale.