| Summary: | 碩士 === 東海大學 === 食品科學系 === 95 === Abstract
Agaricus blazei Murrill, an edible and medicinal mushroom originally grown in Brazil, was recently developed as a functional food. The metabolites of this mushroom from submerged culture were proved to have unique biological activity such as antitumor, antioxidative and immunity-stimulating capabilities. This research was aimed to study the effects of submerged-culturing conditions and different types of fermentors on the production and functional properties (molecular weight, antibacterial and antioxidative activities) of exopolysaccharide (EPS) by A. blazei.
Results showed that the optimal submerged-culturing conditions were : incubation temperature of 25℃, initial pH of 5.4, culture volumes of 50ml, corn steep liquor at 0.3% (w/v), fructose at 4% (w/v), yeast extract at 0.4% (w/v), and a C/N ratio (fructose / yeast extract) of 10. The maximal yields of EPS and mycelial biomass, 0.302 and 25.2 g/l, respectively, were reached on the 14th day of incubation from shake flask culture under the optimized culturing conditions.
A shorter incubation time for maximal EPS and mycelial production (7~10 vs. 14 days), greater EPS yield (3.20~6.96 vs. 0.302 g/l) and higher mycelial biomass (42.01~46.70 vs. 25.22 g/l) were obtained from cultures of fermentors as compared with those from shake flask culture.
Among the three types of fermentors, the agitated fermentor showed the highest specific growth rate (μ=0.476 day-1) and the lowest EPS formation rate (Qp=0.46 g/l/day). On the contrary, the air lift fermentor demonstrated the lowest specific growth rate (μ=0.365 day-1) and the highest EPS formation rate (Qp=0.77 g/l/day). As for specific EPS yield (Yp/x), EPS yield (Yp/s) and biomass yield (Yx/s), results showed an increasing tendency of air lift fermentor > air bubble fermentor > agitated fermentor.
Cultures of fermentors had higher and broader spectrum of antibacterial activies than shake flask culture. The inhibitory capability also demonstrated the same order as : air lift fermentor > air bubble fermentor > agitated fermentor. The bacterial strains susceptible to fermented cultures were : Bacillus cereus, Salmonella typhimurium, Staphylococcus aureus, Enterococcus faecalis, Enterobacter aerogenes, Escherichia coli, Proteus vulgaris, Listeria monocytogenes, Shigella dysenteriae and Pseudomonas aeruginosa. Among the ten strains, B. cereus was the most susceptible one. This finding could be applied to use the culture broth of A. blazei as a potential biopreservative.
Same major molecular weights (2.5×105 and 3.0×103 Da) and molecular weight distribution (7.4×104~2.1×106 Da) were observed for EPS from the three batch cultures of fermentors. The EPS from culture of air lift fermentor had higher content of molecular weight of 2.5×105 Da.
The antioxidative activity (DPPH scavenging effect) of the three fermented cultures was equal or higher than that of control antioxidants. Under the same concentration, the fermented culture of air lift fermentor presented the highest antioxidative activity.
As far as the EPS yield, the mycelial biomass production, the formation rates of EPS and mycelial biomass, and the antibacterial and antioxidative activities of fermented cultures were concerned, all above results showed a trend of air lift fermentor > air bubble fermentor > agitated fermentor. In conclusion, using the air lift fermentor, which has lower shearing force and better convective circulation as compared with agitated and air bubble fermentors, could produce higher yield of EPS from A. blazei with better functional properties.
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