Journal of Fermentation Technology最新文献

A new fermentation system employing gradual increases in the NaCl concentration of the culture medium was developed for the rapid production of Pediococcus halophilus NaCl-tolerant cells. A fermentation system with cross-flow filtration using a micro-filtration module allowed the continuous removal of inhibitory metabolites and complete recycling of the cells to the fermentor. By increasing the NaCl concentrations stepwise or linearly in the feeding media, cells of 8.48 or 9.86 g-dry weight per liter were obtained. The productivities of NaCl-tolerant cells per unit time in a cultivation with a stepwise or linear increase in NaCl concentration in the feeding media were 46 or 56-fold as high, repectively, as that in conventional batch cultivation.

The ploidies and sporulation abilities of six brewer's yeasts were examined. One (YB11-1) out of the six was triploid and sporulating, another (IFO2031) was haploid, and the others (IFO1167, IFO2003, S341 and YB3-7) were diploid and non-sporulating. The five non-sporulating strains did not have the premeiotic DNA synthesis. Their non-sporulating phenotypes were genetically analyzed by examining the sporulation abilities of hybrids between brewer's yeasts and standard genetic strains of Saccharomyces cerevisiae. All non-sporulating brewer's yeasts complemented 32 sporulation-deficient mutations (spoT–spoT23, spo1–spo5, spo7, spo8, spo10, and spo11). Hybrids between brewer's yeasts and haploid or diploid strains homozygous for the mating-type locus had poor or no sporualtion. On the contrary, hybrids between brewer's yeasts and diploid strains heterozygous for the mating-type locus sporulated at a high frequency. These results indicated that the non-sporulating phenotype of brewer's yeasts was caused by a deficiency of the mating-type genes rather than by mutations of sporulation genes. The Southern hybridization probed with the MATa gene showed polymorphisms in mating-type genes of brewer's yeasts.

Bacillus stearothermophilus MK232, which produced a highly thermostable neutral protease, was isolated from a natural environment. By several steps of mutagenesis, a hyper-producing mutant strain, YG185, was obtained. The enzyme productivity was twice as much as that of the original strain. This extracellular neutral protease was purified and crystallized. The molecular weight of the enzyme was 34,000 by SDS-polyacrylamide gel electrophoresis and gel filtration. The optimum pH and temperature for the enzyme activity were 7.5 and 70°C, respectively, and the enzyme was stable at pH 5–10 and below 70°C. The thermostability and specific activity of the new protease are around 10% and 40% higher than those of thermolysin (the neutral protease from Bacillus thermoproteolyticus), respectively. The enzyme was inactivated by EDTA, but not by phenylmethylsulfonyl fluoride. These results indicate that the enzyme is a highly thermostable neutral-(metallo)protease.

The anaerobic growth of a respiration-deficient mutant of Saccharomyces cerevisiae on solid medium was estimated by the CO₂ evolution rate (CER). The cell growth and ethanol production were calculated by a growth-model associated with CER. The estimated cell growth agreed with the observed data. The calculation and the observed CER suggested that the maximum ethanol production and maximum cell groth are restricted by the initial moisture content of the solid medium.

A gene enhancing glyoxalase I activity of a yeast, Saccharomyces cerevisiae, was cloned on a vector plasmid YEp13 as a 3-kb chromosomal DNA fragment. The glyoxalase I activity in yeast cells with the gene increased approximately 5-fold compared with that of the control cells with or without YEp13. The yeast cells with the gene also showed an elevated resistance to cytotoxic methylglyoxal and had an increased cell size. The results suggested that the glyoxalase I might be involved in both the detoxification of methylglyoxal and in the regulation of yeast cell size.

We studied the effect of the initial substrate concentration over the range of 100–250 g·l⁻¹ on the fermentation kinetics in batch cultures of Zymomonas mobilis NRRL B-4286 on glucose, fructose, and sucrose, using an adapted initial inoculum. With increasing concentrations of substrate, parameters related to growth were more rapidly and strongly affected than those related to ethanol production. This strain produced 94.0 g·l⁻¹, 76.9 g·l⁻¹, and 66.5 g·l⁻¹ of ethanol at glucose, fructose, and sucrose concentrations of 200 g·l⁻¹, respectively, more than the amount produced by the efficient strain ZM4 (NRRL B-14023).

The effects of culture conditions on l-arginine production by continuous culture were studied using a stable l-arginine hyperproducing strain of Corynebacterium aceto-acidophilum, SC-190. Strain SC-190 demonstrated a volumetric productivity of 35 g l⁻¹·h⁻¹ at a dilution rate of 0.083h⁻¹ and feeding sugar concentration of 8%, and a product yield of 29.2% at a dilution rate 0.021h⁻¹ and feeding sugar concentration of 15%. The corresponding values for fed-batch culture are 0.85 g·l⁻¹·h⁻¹ and 26%. However, the product yield decreased with an increase in the volumetric productivity. To achieve stable l-arginine production, aeration and agitation conditions sufficient to maintain an optimal level of redox potential (>−100 mV) were necessary. The addition of phosphate to the feeding medium led to a decrease in l-arginine production. It was confirmed in the steady state that growth and l-arginine formation were inhibited by a high concentration of l-arginine.

A method for the measurement of free proline in grapes and wines containing other amino acids is presented. The method included the removal of phenols and tryptophan by the pre-treatment of samples with activated carbon, the oxidation of proline to the corresponding primary amine with sodium hypochlorite, destruction of other amino acids by oxidation at pH 5.3 using a combination of hydrogen peroxide, ferric chloride, and sodium hypochlorite, and the formation of afluorescent product from the oxidized proline with o-phthalaldehyde in the presence of 2-mercaptoethanol and Brij 35 at pH 5.3. The proline in grapes and wines measured by this method agreed well with the values obtained by the method using an automatic amino acid analyzer with ninhydrin.