| dc.description.abstract | Antrodia camphorata (Chinese name, niu-chang-chih or chang-chih) is an exclusive fungus parasitic on the inner cavity of the endemic species Cinnamomum kanehirai Hayata and an important traditional Chinese medicinal fungus (Basidiomycetes) for the treatment of human diseases such as food and drug intoxication, diarrhea, abdominal pain, hypertension, itchy skin and liver cancer. Some bioactive compounds of A. camphorata including sesquiterpene lactone, steroids and triterpenoids have been isolated and characterized. Recently, polysaccharides extracted from fruiting bodies and mycelial cultures of A. camphorata have been shown to have anti-hepatitis B virus activities. In spite of these potential pharmaceutical applications, relatively rare information regarding the process aspects of producing these bioactive compounds has been published. This might be partially due to host specificity, rarity in nature and little success in artificial cultivation. Therefore, the submerged culture might be the major route of production of valuable metabolites including exopolysaccharide. Our research is attempting to promote the production of exopolysaccharides by A. camphorata in a batch culture through organic acids and pH regulation. Also, the biological activities of exopolysaccharides were examined. In order to design and optimize both laboratory scale and industrial scale processes, mathematical models were also developed to describe the pH effect.
Our results could be concluded that five out of six organic acid supplemented cultures showed negative effects on cell growth except the pyruvic acid supplemented culture, and lower number average molecular weight (Mn) of EPS were obtained in all organic acid supplemented cultures in shaker flasks. EPS production was enhanced by 31% due to the supplement of succinic acid. An optimum product yield was achieved at 3.0 g dm-3 succinic acid; however, the specific production of EPS increased monotonically as succinic acid was supplemented from 0 to 5 g/L. Enhancement of EPS yield by 28 % and a higher Mn of EPS around 310 kDa due to the supplement of succinic acid were also demonstrated in an air-lift bioreactor. Besides, a novel fermentation process resistant to EPS degradation was proposed by the organic acid supplementation.
Culture pH significantly affected antioxidant and scavenging free radical activities of methanolic extracts from mycelia and filtrates. Antioxidant activities of methanolic extracts from mycelia (MEM) and filtrates (MEF) have been successfully correlated with total polyphenol content, polysaccharide content and protein/ polysaccharide ratios. The optimal culture pH for antioxidants production by Antrodia camphorata was 5.0, and the maximum total polyphenol and polysaccharide/protein ratio in MEM were 152.2 mg/g and 33.5%, respectively. Higher amounts of antioxidants were obtained in the submerged culture at pH 5.0 as compared with that of fruiting body. Besides, the maximum polysaccharide in MEF was 55.3 mg/g. The relatively low antioxidant ability of methanolic extracts from culture medium indicated that the antioxidant abilities of MEM and MEF were mainly derived from the fermentation process. Besides, an alternative approach to produce the antioxidants of A. camphorata by submerged culture was proposed.
The effects of culture pH ranging from pH 3.0 to 6.0 on cell growth, exopolysaccharide biosynthesis and molecular weight distribution of exopolysaccharides of A. camphorata were examined both in shake flask culture and in a stirred tank fermenter. In a controlled pH stirred tank fermentation, the optimum pH for cell growth was 4.0 with a cell yield at 0.3 g/g while that for exopolysaccharide formation was 5.0 with a product yield at 5.05 mg/g. A relatively high molecular weight exopolysaccharide with a lower yield was obtained at low pH values while a relatively low molecular weight exopolysaccharide with a high yield was obtained at higher pH values. The average molecular weight of the exopolysaccharide in the flask culture was higher than that in the stirred tank fermenter. A two stage pH process that maximized product formation was demonstrated with a high product yield of 148 mg/liter with the relatively high average molecular weight of 2.18 x 105.
Fermentation kinetics of pH effects on growth and polysaccharide production of Antrodia camphorata was studied in a pH-controlled batch system. A simple model was proposed by using the logistic equation for cell growth, the Luedeking-Piret equation for polysaccharide production and a modified Luedeking-Piret equation for glucose consumption. The pH dependence of the parameters in this model was evaluated. The growth rate constants and the average molecular weight of polysaccharides were modeled with an exponential equation. The maximum biomass concentration, non-growth-associated constants for product formation and product yields were modeled with a Gaussian equation. The parameters of the modified Luedeking-Piret equation were modeled with a quadratic expression. The model developed in this study accurately described the experimental data. | en_US |