Effect of sucrose on nisin production in batch and fed‐batch culture by Lactococcus lactis

The effects of sucrose on cell growth and nisin production by Lactococcus lactis were investigated in batch and pH feed‐back controlled fed‐batch cultures. In batch cultures, nisin titer reached its maximum, 2658 IU cm^?3, at the initial sucrose concentration of 30 g dm^?3. With sucrose concentrations higher than 30 g dm^?3, nisin production decreased while the biomass was not influenced significantly. By using the pH feed‐back controlled method, residual sucrose concentration could be controlled well in fed‐batch cultures and three conditions (sucrose maintained at 2, 16, 20 g dm^?3, respectively) were evaluated. Maintaining a low sucrose concentration at 2 g dm^?3 during feeding favored nisin biosynthesis, and the maximum nisin titer obtained was 4961 IU cm^?3 compared with 3370 IU cm^?3 (16 g sucrose dm^?3)and 3498 IU cm^?3 (20 g sucrose dm^?3), respectively. Copyright © 2005 Society of Chemical Industry     

Batch production of L(+) lactic acid from whey by Lactobacillus casei (NRRL B‐441)

The effects of temperature, pH, and medium composition on lactic acid production by Lactobacillus casei were investigated. The highest lactic acid productivity values were obtained at 37 °C and pH 5.5. The productivity was 1.87 g dm^?3 h^?1 at 37 °C in shake flasks. In the fermenter, a productivity of 3.97 g dm^?3 h^?1 was obtained at pH 5.5. The most appropriate yeast extract concentration was 5.0 g dm^?3. Whey yielded a higher productivity value than the analytical lactose and glucose. Initial whey lactose concentration did not affect lactic acid productivity. MnSO₄ ·H₂O was necessary for lactic acid production by L casei from whey. Product yields were approximately 0.93 g lactic acid g lactose^?1. Copyright © 2004 Society of Chemical Industry     

Studies on the structural features of sodium alginate entrapped Kluyveromyces marxianus NCYC179 cells used for alcohol production from whey permeate

Alginate-entrapped living Kluyveromyces marxianus NCYC179 cells were successfully used in alcohol production from whey permeate. Using 10% whey lactose as substrate, an alcohol production efficiency of 81.5–84.9% and 84.0–88.2% with cell viability maintenance between 82.8–84.3% and 81.0–84.3% of the immobilised cells during the monitoring periods, in batch (six repeat runs) and continuous (23 days of experimenting time) systems, respectively. The immobilised samples remained stable during the course of fermentation with no leakage of K. marxianus cells into the surrounding medium in the case of the batch system. However, slight leakage after 10 days of continuous run in the continuous process was recorded. The scanning electron microscopic studies of the beads containing entrapped yeast cells and sections or crushed samples of the beads carried out at the start and termination of fermentation in both the processes (batch and continuous) revealed that the immobilisation procedure does not influence any morphological change in the entrapped cells during the prolonged periods of fermentation. Moreover, the gel matrix structure was also found to be unaffected by the fermentation conditions employed during the course of present studies.     

Mathematical model for lactic acid production from lactose in batch culture: Model development and simulation

The models available to describe lactic acid production do not seem to fit the experimental data very well, especially at the end of batch cultures. From a careful analysis of batch data, an unstructured model of the process has been derived, in which the specific growth rate variations and lactic acid concentration with time have been described by complemented logistic functions. Also, an additional term has been introduced into the Luedeking–Piret expression, taking into account the reduction in rate of lactic acid production observed at very low growth rate.     

Optimization of pullulan production from synthetic medium by Aureobasidium pullulans in a stirred tank reactor by response surface methodology

The production of pullulan from synthetic medium by Aureobasidium pullulans P56 in a stirred tank fermenter was investigated. The kinetics of polysaccharide, pullulan and biomass production was determined. Response surface methodology was used to investigate the effects of three factors (initial sugar concentration, aeration rate and agitation speed) on the concentration of pullulan in batch cultures of A pullulans. In the experiments, the range of values used for the three variables described were; 30–70 g dm^?3 initial sugar concentration, 200–600 rpm agitation speed and 1.0–3.0 vvm aeration rate. No previous work has used statistical analysis in determining the interactions among these variables in pullulan production. Results of the statistical analysis showed that the fit of the model was good in all cases. Aeration rate, agitation speed and sugar concentration had a strong linear effect on pullulan concentration. Moreover, pullulan concentration was significantly influenced by the negative quadratic effects of the given variables and by their positive or negative interactions with the exception that the interaction between agitation speed and aeration rate was insignificant (P > 0.05). Maximum pullulan concentration of 17.2 g dm^?3 was obtained at the optimum levels of process variables (initial sugar concentration 51.4 g dm^?3, aeration rate 2.36 vvm, agitation speed 345.3 rpm). These values were obtained by fitting of the experimental data to the model equation. Scanning electron microscope (SEM) photographs of polysaccharide particles containing different concentrations of pullulan were also taken to observe the morphological differences of the samples. Copyright © 2005 Society of Chemical Industry     

Optimization of lactic acid production from whey by L casei NRRL B‐441 immobilized in chitosan stabilized Ca‐alginate beads

The production of lactic acid from whey by Lactobacillus casei NRRL B‐441 immobilized in chitosan‐stabilized Ca‐alginate beads was investigated. Higher lactic acid production and lower cell leakage were observed with alginate–chitosan beads compared with Ca‐alginate beads. The highest lactic acid concentration (131.2 g dm^?3) was obtained with cells entrapped in 1.3–1.7 mm alginate–chitosan beads prepared from 2% (w/v) Na‐alginate. The gel beads produced lactic acid for five consecutive batch fermentations without marked activity loss and deformation. Response surface methodology was used to investigate the effects of three fermentation parameters (initial sugar, yeast extract and calcium carbonate concentrations) on the concentration of lactic acid. Results of the statistical analysis showed that the fit of the model was good in all cases. Initial sugar, yeast extract and calcium carbonate concentrations had a strong linear effect on lactic acid production. The maximum lactic acid concentration of 136.3 g dm^?3 was obtained at the optimum concentrations of process variables (initial sugar 147.35 g dm^?3, yeast extract 28.81 g dm^?3, CaCO₃ 97.55 g dm^?3). These values were obtained by fitting of the experimental data to the model equation. The response surface methodology was found to be useful in optimizing and determining the interactions among process variables in lactic acid production using alginate–chitosan‐immobilized cells. Copyright © 2005 Society of Chemical Industry     

Stimulations of strontium-doped calcium polyphosphate for bone tissue engineering to protein secretion and mRNA expression of the angiogenic growth factors from endothelial cells in vitro

The vascularization of tissue-engineered bone is the key problem needed solving before application of tissue-engineered bone in clinical practice. Meanwhile, endothelial cells are the major and important source of seed cells in bone tissue engineering, and significant on promoting vascularization in tissue-engineered bone. Vascularization (namely angiogenesis) is a process mainly controlled by several angiogenic growth factors (VEGF, bFGF and MMP-2) which can be secreted by endothelial cells. Therefore, the research on the stimulations of SCPP to the secretion of the angiogenic growth factors from endothelial cells is very important. This study was performed to determine the ability of strontium-doped calcium polyphosphate (SCPP) to induce angiogenesis by detecting the protein secretion levels and mRNA expression of VEGF, bFGF and MMP-2 from cultured endothelial cells. As a control, we also researched the effect of HA on the mRNA expressions and protein secretion of angiogenic growth factors from cultured endothelial cells. We cultured endothelial cells with SCPP scaffolds containing various concentration of strontium and HA. The results obtained in the MTT and SEM tests indicated that endothelial cells on SCPP scaffold exhibited higher proliferation rate and were easy to get a good spread than them on CPP, the best state of growth and proliferation of cells could be observed on 8%SCPP. The results of ELISA demonstrated that the protein levels of VEGF, bFGF and MMP-2 from cultured endothelial cells increased with the increasing Sr doped in calcium polyphosphate in SCPP groups, the peaks appeared on 8%SCPP. All SCPP groups showed a better ability to stimulate the protein secretion of VEGF, bFGF and MMP-2 from endothelial cells relative to CPP group and HA group. The results of RT-PCR suggested that the 8%SCPP group exhibited a significantly higher mRNA expression of VEGF, bFGF and MMP-2 relative to CPP group and HA group. In conclusion, the results of this study demonstrated that 8%SCPP had obvious promotion for secretion and mRNA expression of angiogenic growth factors from cultured endothelial cells.