Biomedical subjects

T Roukas

Publications and source records attributed to T Roukas.

8 recordsLinked to original sources

PubMed2006

Role of hydrolytic enzymes and oxidative stress in autolysis and morphology of Blakeslea trispora during beta-carotene production in submerged fermentation.

The role of hydrolytic enzymes (proteases and chitinase) and oxidative stress in the autolysis and morphology of Blakeslea trispora during beta-carotene production from a chemically defined medium in shake flask culture was investigated. The process of cellular autolysis was studied by measuring the changes in biomass dry weight, pH, concentration of beta-carotene, specific activity of the hydrolytic enzymes and micromorphology of the fungus using a computerized image analysis system. In addition, the phenomenon of autolysis was associated with high concentrations of reactive oxygen species (ROS). The accumulation of ROS produced during fermentation causes oxidative stress in B. trispora. Oxidative stress was examined in terms of the activities of two key defensive enzymes: catalase (CAT) and superoxide dismutase (SOD). The profile of the specific activities of the above enzymes appeared to correlate with the oxidative stress of the fungus. The high activities of CAT and SOD showed that B. trispora is found under oxidative stress during beta-carotene production. The culture began to show signs of autolysis nearly in the growth phase and autolysis increased significantly during the production phase. The morphological differentiation of the fungus was a result of the degradation of the cell membrane by hydrolytic enzymes and oxidative stress. Increased beta-carotene production is correlated with intense autolysis of clumps, which has as a consequence the increase of the freely dispersed mycelia.

Biotechnology↗

PubMed2001

An improved method for extraction of beta-carotene from Blakeslea trispora.

An improved method for the extraction of beta-carotene from Blakeslea trispora is described. The fermentation broth was steamed at 121 degrees C for 15 min, and the liquid was centrifuged at 5000 g for 20 min. beta-Carotene was removed from the biomass by extraction with absolute ethanol at a ratio of 1:100 at 30 degrees C for 2 h in a rotary shaker incubator at 300 rpm. The carotenoid pigment was completely removed from the cells after three repeated extractions. The removal of beta-carotene from B. trispora was higher during the first stage (75%) whereas in the other stages it was very slow.

Bioreactors↗

PubMed2000

Citric and gluconic acid production from fig by Aspergillus niger using solid-state fermentation.

The production of citric and gluconic acids from fig by Aspergillus niger ATCC 10577 in solid-state fermentation was investigated. The maximal citric and gluconic acids concentration (64 and 490 g/kg dry figs, respectively), citric acid yield (8%), and gluconic acid yield (63%) were obtained at a moisture level of 75%, initial pH 7.0, temperature 30 degrees C, and fermentation time in 15 days. However, the highest biomass dry weight (40 g/kg wet substrate) and sugar utilization (90%) were obtained in cultures grown at 35 degrees C. The addition of 6% (w/w) methanol into substrate increased the concentration of citric and gluconic acid from 64 and 490 to 96 and 685 g/kg dry fig, respectively.

Journal Article↗

PubMed1999

Pullulan production from deproteinized whey by Aureobasidium pullulans.

The production of pullulan from deproteinized whey by Aureobasidium pullulans P56 was investigated using an adaptation technique and a mixed culture system. The adaptation of A. pullulans and the mixed cultures of A. pullulans and/or Lactobacillus brevisX20, Debaryomyces hansenii 194 and Aspergillus niger did not increase the production of polysaccharide. Enzymic hydrolysis of lactose in deproteinized whey gave a higher polysaccharide concentration and polysaccharide yield than acidic hydrolysed lactose. Maximum polysaccharide concentration (11.0 +/- 0.5 g L-1), biomass dry weight (10.5 +/- 0.4 g L-1), polysaccharide yield (47.2 +/- 1.8%) and sugar utilization (93.2 +/- 2.8%) were achieved using enzyme-hydrolysed whey (pH 6.5) containing 25 g L-1 lactose and supplemented with K2HPO4 0.5%, L-glutamic acid 1%, olive oil 2.5%, and Tween 80 0.5%. In this case the pullulan content of the crude polysaccharide was 40%.

Journal Article↗

PubMed1999

Effect of the shear rate on pullulan production from beet molasses by Aureobasidium pullulans in an airlift reactor.

The effect of the shear rate on pullulan production from beet molasses by Aureobasidium pullulans P56 in an airlift reactor was investigated. A maximum polysaccharide concentration (18.5 g/L), biomass dry weight (14.0 g/L), polysaccharide yield (38.5%), and sugar utilization (96%) was achieved at a shear rate of 42 s(-1). A. pullulans grown on beet molasses produced a mixture of pullulan and other polysaccharides. The highest value of pullulan proportion (30% of total polysaccharide) was obtained at a low shear rate (42 s(-1)). The apparent viscosity of the fermentation broth increased as the shear rate increased up to 42 s(-1) and then decreased. On the other hand, the dissolved oxygen concentration and the volumetric mass transfer coefficient increased with the increase of the shear rate from 21 to 84 s(-1). The external addition of L-glutamic acid, olive oil, and Tween-80 improved significantly the production of crude polysaccharide (27.0 g/L), but the pullulan content of the polysaccharide was low (20%).

Journal Article↗

PubMed1998

Carob pod: a new substrate for citric acid production by Aspergillus niger.

The production of citric acid from carob pod extract by A. niger in surface fermentation was investigated. A maximum citric acid concentration (85.5 g/L), citric acid productivity (4.07 g/L/d), specific citric acid production rate (0.18 g/g/d), and specific sugar uptake rate (0.358 g/g/d) was achieved at an initial sugar concentration of 200 g/L, pH of 6.5, and a temperature of 30 degrees C. Other kinetic parameters, namely, citric acid yield, biomass yield, specific biomass production rate, and fermentation efficiency were maximum at pH 6.5, temperature 30 degrees C, and initial sugar concentration 100 g/L. The external addition of methanol into the carob pod extract at a concentration up to 4% (v/v) improved the production of citric acid.

Aspergillus niger↗

PubMed1996

Continuous ethanol production from nonsterilized carob pod extract by immobilized Saccharomyces cerevisiae on mineral kissiris using a two-reactor system.

The continuous production of ethanol from nonsterilized carob pod extract by immobilized Saccharomyces cerevisiae on mineral kissiris using one- and two-reactor systems has been investigated. A maximum ethanol productivity of 9.6 g/L/h was obtained at an initial sugar concentration of 200 g/L and D = 0.4 h-1 with 68% of theoretical yield and 34% of sugar utilization using the one-reactor system. At S0 = 200 g/L, D = 0.05 h-1, 83% of theoretical yield, and 64% of sugar utilization, an ethanol productivity of 2.6 g/L/h was achieved. In the two-reactor system, a maximum ethanol productivity of 11.4 g/L/h was obtained at S0 = 200 g/L and D = 0.4 h-1 with 68.5% of theoretical yield and 41.5% of sugar utilization. The two-reactor system was operated at a constant dilution rate of 0.3 h-1 for 60 d without loss of the original immobilized yeast activity. In this case, the average ethanol productivity, ethanol yield (% of theoretical), and sugar utilization were 10.7 g/L/h, 71.5%, and 48%, respectively.

Biotechnology↗

PubMed1994

Kinetics of ethanol production from carob pods extract by immobilized Saccharomyces cerevisiae cells.

Kinetics of ethanol production from carob pods extract by immobilized S. cerevisiae cells in static and shake flask fermentation have been investigated. Shake flask fermentation proved to be a better fermentation system for the production of ethanol than static fermentation. The optimum values of ethanol concentration, ethanol productivity, ethanol yield, and fermentation efficiency were obtained at pH range 3.5-6.5 and temperature between 30-35 degrees C. A maximum ethanol concentration (65 g/L), ethanol productivity (8.3 g/Lh), ethanol yield (0.44 g/g), and fermentation efficiency (95%) was achieved at an initial sugar concentration of 200, 150, 100, and 200 g/L, respectively. The highest values of specific ethanol production rate and specific sugar uptake rate were obtained at pH 6.5, temperature 40 degrees C, and initial sugar concentration of 100 g/L. Other kinetic parameters, biomass concentration, biomass yield, and specific biomass production rate were maximum at pH 5.5, temperature 30 degrees C, and initial sugar concentration 150 g/L. Under the same fermentation conditions non-sterilized carob pod extract gave higher ethanol concentration than sterilized medium. In repeated batch fermentations, the immobilized S. cerevisiae cells in Ca-alginate beads retained their ability to produce ethanol for 5 d.

Culture Media↗