Production of lactic acid from renewable materials by Rhizopus fungi

The Mycota highlights developments in both basic and applied research and presents an overview of fungal systematics and cell structure. Foremost authorities in research mycology have been assembled to edit and contribute to the eight volumes. Topics include: Sexual and Parasexual Genetics.- Mitochondrial Genetics.- Viruses, Plasmids and Transposons.- Transformation and Gene Expression.

Genetics and biotechnology

The production of L(+)-lactic acid using alginate immobilizedRhizopus oryzae in tapered-column fluidized-bed batch reactor was tested and simulated using the kinetic data taken independently in shake-flask cultures. The data show saturation kinetics with substrate and product inhibitions in linear form. Analysis of the kinetic data gave kinetic constants:V
 m, 11.04 g lactic acid/(L-bead. h);K
 m, 20.9 g glucose/L; andK
 i, 365 g glucose/L for lactic acid production. The product inhibition constant,K
 p, was found to be 316 g lactic acid/L. The simulation results showed a good agreement with the experimental results when the initial lag phase was taken into account in the simulation model. Without the adjustment for the initial lag period, the kinetic model showed higher conversion. Starting with a glucose concentration of 150 g/L, it was possible to produce 73 g/L of L(+)-lactic acid in 44.5 h. The lactic acid yield was 64.8% by weight based on the amount of glucose consumed.

Production of L(+)-lactic acid using immobilized rhizopus oryzae reactor performance based on kinetic model and simulation

The influence of basic physiological factors on the quality of inocula and L(+)-lactic acid production by Rhizopus arrhizus CCM 8109 were studied. The most effective preparation of the spores (5 x 10 7 spores/ml) and subsequent good lactate production was achieved on the agar medium with soil extract and malt agar. The optimum initial amount of active spores for inoculation was 10 3 -10 4 spores/ml. The preparation of inoculum required intensive stirring with lower aeration and pH maintained in the range from 4.8 to 6.0 by the addition of CaCO 3 . The maximum yield of lactic acid production was achieved by using 5% (v /v) of 24-h-old inoculum. The intensity of lactic acid production in the inoculum was proportional to its production in the subsequent steps of fermentation and can be used as a fast control of the physiological state of the producers.

Physiological restriction of the L‐lactic acid production by Rhizopus arrhizus

Two filamentous fungi, Trichoderma harzianum and Trichoderma viride, were compared for their ability to synthesize lipids on different carbon and nitrogen sources. Three culture media were selected for each strain after preliminary screening. All the test media were nitrogen-deficient (C/N = 60) so as to stimulate lipid accumulation. For both microorganisms the glucose-ammonium sulphate medium was the most conducive to lipid production: a lipid accumulation of 17% (w/w) of biomass dry weight was obtained for T. harzianum and of 32% (w/w) of biomass dry weight for T. viride. In sucrose-sodium nitrate medium T. harzianum was able to accumulate almost 25% (w/w) of its biomass in lipid form. However the small quantity of biomass produced (2 g dry weight/l) limited the quantity of lipid obtained. Neutral lipids, free fatty acids and phospholipids were monitored during 8 days of cultivation of the two fungi.

Lipid accumulation in Trichoderma species

The formation of 10 g polyols/L (glycerol, arabitol, xylitol) during L-lactic acid synthesis byRhizopus arrhizus was observed. Consumption of polyols after glucose exhaustion was discovered resulting in a subsequent rise in the lipid content of the mycelium. Lactate utilization was not detected.

L. Krištofiková

Papers

The formation of polyols and fatty acids during l-lactic acid fermentation by rhizopus arrhizus