Triantafyllos Roukas

Optimization of lactic acid production from beet molasses by Lactobacillus delbrueckii NCIMB 8130

Production of lactic acid from beet molasses by Lactobacillus delbrueckii NCIMB 8130 in static and shake flask fermentation was investigated. Shake flasks proved to be a better fermentation system for this purpose. Substitution of yeast extract with other low cost protein sources did not improve lactic acid production. The maximum lactic acid concentration was achieved without treatment of molasses. A Central Composite Design was employed to determine the maximum lactic acid concentration at optimum values for the process variables (sucrose, yeast extract, CaCO3). A satisfactory fit of the model was realized. Lactic acid production was significantly affected both by sucrose–yeast extract and sucrose–CaCO3 interactions, as well as by the negative quadratic effects of these variables. Sucrose and yeast extract had a linear effect on lactic acid production while the CaCO3 had no significant linear effect. The maximum lactic acid concentration (88.0 g/l) was obtained at concentrations for sucrose, yeast extract and CaCO3 of 89.93, 45.71 and 59.95 g/l, respectively.

Pretreatment of beet molasses to increase pullulan production

Pretreatment of beet molasses with cation exchange resin, sulphuric acid, tricalcium phosphate, potassium ferrocyanide, and ethylenediaminetetraacetic acid and disodium salt (EDTA) to increase the production of pullulan was investigated. Among the above techniques used for the removal of heavy metals, sulphuric acid treatment gave better results regarding polysaccharide concentration, polysaccharide yield, and sugar utilization. Aureobasidium pullulans grown on beet molasses produced a mixture of pullulan and other polysaccharides. The pullulan content of the crude polysaccharide was 30–35%. The addition of nutrients improved the production of polysaccharide. A maximum polysaccharide concentration (32·0±1·0 g litre−1) was achieved in molasses solution (70 g litre 1 initial sugar concentration, pH 6·5–7·5) treated with sulphuric acid and supplemented with K2HPO4 0·5%, l-glutamic acid 1%, olive oil 2·5% and Tween 80 0·5%. In this case, the highest values of biomass dry weight (33·8±1·0 g litre−1), polysaccharide yield (63·5±2·5%), and sugar utilization (97·5±1·5%) were obtained at pH 6·5, 3·5, and 4·5–7·5, respectively.

Lactic acid production from deproteinized whey by mixed cultures of free and coimmobilized Lactobacillus casei and Lactococcus lactis cells using fedbatch culture

The production of lactic acid from deproteinized whey by mixed cultures of free and coimmobilized Lactobacillus casei and Lactococcus lactis cells in batch and fedbatch culture was investigated. Fedbatch culture proved to be a better fermentation system for the production of lactic acid than batch culture. The maximum lactic acid concentration (46 g l−1) in fedbatch culture was obtained with both free cells mixture and coimmobilized cells at a substrate concentration of 100 g l−1 and a feeding rate of 250 ml h−1. In repeated fedbatch culture, coimmobilized L. casei and L. lactis cells gave a higher overall lactic acid concentration compared with the free cells mixture. The coimmobilized L. casei and L. lactis cells in Ca-alginate beads retained their ability to produce lactic acid for 20 days.

Citric acid production from carob pod by solid-state fermentation

Abstract The production of citric acid from carob pod by Aspergillus niger in solid-state fermentation was investigated. The maximal citric acid concentration (176 ± 4 g kg−1 dry pod), biomass dry weight (30 ± 0.7 g kg−1 wet substrate), citric acid yield (55 ± 2%), and sugar utilization (64 ± 2.5%) were obtained at a particle size of 0.5 mm, moisture level of 65%, pH of 6.5, and temperature of 30°C. The addition of 6% (w/w) methanol into the substrate increased the concentration of citric acid from 176 to 264 g kg−1 dry pod.

Pretreatment of date syrup to increase citric acid production

Pretreatment of date syrup with sulfuric acid, tricalcium phosphate, tricalcium phosphate with hydrochloric acid, potassium ferrocyanide, and EDTA to increase the production of citric acid was investigated. Among the above techniques used for the removal of heavy metals, 2% tricalcium phosphate treatment gave better results regarding citric acid concentration (55 ± 1.5 g l−1), citric acid yield (50 ± 1.5%), and sugar utilization (73.3 ± 1%). The optimum pH for citric acid production was 6.5. The addition of 4% (ν/ν) methanol in the date syrup solution treated with 2% tricalcium phosphate increased the concentration of citric acid from 55 to 90 g l−1.

Evaluation of carob pod as a substrate for pullulan production byAureobasidium pullulans

The production of extracellular polysaccharides from carob pod extract by Aureobasidium pullulans in batch fermentation was investigated. Optimum conditions for polysaccharide productivity, polysaccharide yield, and fermentation efficiency were: initial sugar concentration of 25 g/L, initial pH 6.5, and temperature 25–30°C. A maximum polysaccharide concentration (6.5 g/L), polysaccharide productivity (2.16 g/L/d), total biomass concentration (6.3 g/L), and polysaccharide yield (30%) were obtained with inoculum at 10% (v/v), initial sugars in carob pod extract of 25 g/L, pH 6.5, and 25°C. The highest values of pullulan proportion (70% of total polysaccharides) and fermentation efficiency (89%) were assumed at initial sugar concentration of 25 g/L, pH 6.5 and 30°C. Structural characterization of purified pullulan samples by monosaccharide and methylation analyses, 13C-NMR, and pullulanase digestion combined with size-exclusion chromatography revealed the presence of mainly α-(l → 4) (68%) and α-(l → 6) (31%) glucosidic linkages; however, small amounts (<1%) of triply linked (1, 3, 4-and 1, 4, 6-Glc) glucose residues were detected. The molecularsize distribution and intrinsic viscosity of pullulan derived from culture grown at pH 4.5 (30°C) showed a higher molecular weight than its counterpart obtained at pH 6.5 (30°C).

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°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°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 of Industrial Microbiology & Biotechnology (2000) 25, 298–304.

Pullulan production by a non-pigmented strain of Aureobasidium pullulans using batch and fed-batch culture

The production of pigment-free pullulan by Aureobasidium pullulans in batch and fed-batch culture was investigated. Batch culture proved to be a better fermentation system for the production of pullulan than the fed-batch culture system. A maximum polysaccharide concentration (31.3 g l−1), polysaccharide productivity (4.5 g l−1 per day), and sugar utilization (100%) were obtained in batch culture. In fed-batch culture, feed medium composition influenced the kinetics of fermentation. For fed-batch culture, the highest values of pullulan concentration (24.5 g l−1) and pullulan productivity (3.5 g l−1 per day) were obtained in culture grown with feeding substrate containing 50 g l−1 sucrose and all nutrients. The molecular size of pullulan showed a decline as fermentation progressed for both fermentation systems. At the end of fermentation, the polysaccharide isolated from the fed-batch culture had a slightly higher molecular weight than that of batch culture. Structural characterization of pullulan samples (methylation and enzymic hydrolysis with pullulanase) revealed the presence of mainly α-(1→4) (∼66%) and α-(1→6) (∼31%) glucosidic linkages; however, a small amount (<3%) of triply linked (1,3,4-, 1,3,6-, 1,2,4- and 1,4,6-Glc p) residues were detected. The molecular homogeneity of the alcohol-precipitated polysaccharides from the fermentation broths as well as the structural features of pullulan were confirmed by 13C-NMR and pullulanase treatments followed by gel filtration chromatography of the debranched digests.

Production and characterization of pullulan from beet molasses using a nonpigmented strain of Aureobasidium pullulans in batch culture

The production of pullulan from beet molasses by a pigment-free strain of Aureobasidium pullulans on shake-flask culture was investigated. Combined pretreatment of molasses with sulfuric acid and activated carbon to remove potential fermentation inhibitors present in molasses resulted in a maximum pullulan concentration of 24 g/L, a biomass dry wt of 14 g/L, a pullulan yield of 52.5%, and a sugar utilization of 92% with optimum fermentation conditions (initial sugar concentration of 50 g/L and initial pH of 7.0). The addition of other nutrients as carbon and nitrogen supplements (olive oil, ammonium sulfate, yeast extract) did not further improve the production of the exopolysaccharides. Structural characterization of the isolated polysaccharides from the fermentation broths by 13C-nuclear magnetic resonance spectroscopy and pullulanase digestion combined with size-exclusion chromatography confirmed the identity of pullulan and the homogeneity (>93% dry basis) of the elaborated polysaccharides by the microorganism. Using multiangle laser light scattering and refractive index detectors in conjunction with high-performance size-exclusion chromatography molecular size distributions and estimates of the molecular weight (Mw=2.1−4.1×105), root mean square of the radius of gyration (Rg=30−38 nm), and polydispersity index (Mw/Mn=1.4−2.4) were obtained. The fermentation products of molasses pretreated with sulfuric acid and/or activated carbon were more homogeneous and free of contaminating proteins. In the concentration range of 2.8−10.0 (w/v), the solution’s rheologic behavior of the isolated pullulans was almost Newtonian (within 1 and 1200 s−1 at 20°C); a slight shear thinning was observed at 10.0 (w/v) for the high molecular weight samples. Overall, beet molasses pretreated with sulfuric acid and activated carbon appears as an attractive fermentation medium for the production of pullulan by A. pullulans.

Pullulan production from brewery wastes by Aureobasidium pullulans

The production of pullulan from brewery wastes by Aureobasidium pullulans in shake flask culture was investigated. The maximum pullulan concentration (6.0 g/l) was obtained after 72 h of fermentation. The external addition of nutrients into the spent grain liquor improved significantly the production of pullulan. In this case, the highest values of pullulan concentration (11.0 ± 0.5 g/l), pullulan yield (48.2 ± 1.5%), and sugar utilization (99.0 ± 0.5%) were obtained in the medium (pH 6.5–7.5) supplemented with K2HPO4 0.5%, l-glutamic acid 1%, olive oil 2.5%, and Tween 800.5%.