Catalytic activity of zymomonas mobilis extracellular "levan-levansucrase" complex in sucrose medium.

The fructan biosynthesis by ethanol sedimented "levan-levansucrase" complex from Zymomonas mobilis fermentation broth as well as purified levansucrase was investigated. The fructooligosaccharide (FOS) producing activity of "levan-levamsucrase" sediment was investigated in 55% sucrose syrup at 45 degrees C. It was shown that FOS in the syrup were presented by 1-kestose, 6-kestose, neokestose and nystose. The increase of gluconic acid concentration was observed in the reaction mixture during the incubation suggesting about presence of glucose/fructose oxidoreductase in "levan-levansucrase" sediment. The influence of ethanol, glycerol and NaCl on levan and fructooligosaccharide formation by "levan-levansucrase" complex and purified levansucrase was studied and the changes in the ratio between different activities of levansucrase (sucrose hydrolysis, levan biosynthesis and FOS formation) were observed. Ethanol increases the FOS biosynthesis part in total activity of purified levansucrase. The technology of the production of prebiotics containing food product--fructan syrup by "levan-levansucrase " sediment as biocatalyst was developed.

The effect of osmo-induced stress on product formation by Zymomonas mobilis on sucrose.

The intensification of biosynthesis of fructooligosaccharides in the presence of high salt concentrations was observed during sucrose (10%) fermentation by Zymomonas mobilis 113S. A 0.6 M NaCl concentration led to an increase of oligosaccharide productivity by 3.5-fold. Sorbitol formation was increased in the presence of 0.16 M NaCl and was inhibited at highest salt concentrations. In a medium with high (65%, w/w) sucrose content the salts gave inhibitory effects on fructooligosaccharide production by lyophilised Z. mobilis cells. Influence of salts on gluconic acid and sorbitol formation under these conditions was studied. The ratio of oligosaccharides and gluconic acid productivity (Qolig./Qglucon.) was increased approximately 2 times at 1% KCl. Sorbitol formation was not significantly influenced in the presence of KCl (up to 2%).

Steric hindrance of growth of filamentous fungi in solid substrate fermentation of wheat straw.

Cellulolytic fungi, such as Trichoderma reesei, T. lignorum, and Chaetomium cellulolyticum reach a low packing density of mycelia when grown on straw under conditions of solid substrate fermentation. The low packing density is shown to be caused partially by the geometric limitation of the growth of mycelia in the substrate and particularly in its pores, but the exact contribution of this limitation and other limitations such as mass transfer and substrate availability cannot be easily distinguished. The combined effect of such limitations is called steric hindrance. This steric hindrance is associated with and may be the principal cause of low biomass concentration in SSF.

Solid substrate fermentation of wheat straw to fungal protein.

Steam-treated wheat straw at a 70% (w/w) moisture level was subjected to solid substrate fermentation (SSF) with Trichoderma reesei (Riga, USSR) or a mixed culture of T. reesei and Endomycopsis fibuliger (R-574) in fermentation equipment of various design: some with mixing, some with stationary layers, including a mixedlayer 1.5-m(3) pilot plant scale fermenter. The best protein productivity was obtained in stationary layer fermenters with a product containing 13% protein. The main limitations of lignocellulose SSF, such as hindrance of fungal growth, limiting accessibility and availability of substrate, and difficulty in moisture and heat control, were analyzed. The technological parameters of SSF, submerged fermentation, and alternate lignocellulose conversion processes were compared. The SSF had lower overall efficiency but higher product concentration per reaction volume than other conversion schemes.