Tohru Kouda

Effect of lactate on bacterial cellulose production from fructose in continuous culture

Abstract Bacterial cellulose (BC) was produced from fructose by Acetobacter xylinum subsp. sucrofermentans BPR3001A was performed in continuous culture and the effect of lactate on the production was investigated. In continuous culture with feeding of CSL-Fru medium containing 30 g· l −1 fructose at a dilution rate of 0.07 h −1 , a higher production rate (0.62 g· l −1 ·h −1 ) was obtained than that (0.40 g· l −1 ·h −1 ) in a batch culture using CSL-Fru medium with 70 g· l −1 initial fructose. However, when the dilution rate or fructose concentration in the feed medium were increased, the total yield of BC declined because the residual fructose concentration in the drawn broth increased. Supplementing 12.5 g· l −1 lactate to the feed medium increased the cell concentration and fructose consumption at a steady state, resulting in a production rate of 0.90 g· l −1 ·h −1 and a BC yield of 36% at a dilution rate of 0.1 h −1 . The ATP content of viable cells was maintained at a higher level by feeding a lactate-supplemented medium rather than the unsupplemented CSL-Fru medium. In a batch culture using lactate as the main carbon source, 77% of the lactate consumed was oxidized to CO 2 and only 6.9% was converted to BC. These findings indicated that lactate functioned as an energy source, not as a substrate for BC biosynthesis. Increased intracellular ATP resulting from lactate oxidation may have improved the fructose consumption and BC production in the continuous culture.

Effect of agitator configuration on bacterial cellulose productivity in aerated and agitated culture

Abstract To improve the bacterial cellulose (BC) productivity in aerated and agitated culture, the agitator configuration was improved. Agitators were selected by measuring mixing delay time and K L a of a 1% BC suspension and cultivating Acetobacter xylinum subsp. sucrofermentans BPR3001A. We concluded that (i) the impellers such as Maxblend and gate with turbine were suitable for BC fermentation because they mixed culture broth well and had large K L a , (ii) the production rate and yield of BC were dependent on K L a and the oxygen consumption rate, and (iii) the static gassing-out method to measure K L a was useful for characterization of the agitation conditions and the agitator configuration.

Effects of oxygen and carbon dioxide pressures on bacterial cellulose production by Acetobacter in aerated and agitated culture

Abstract With the aim of improving bacterial cellulose (BC) production in an aerated and agitated culture, the effects of the oxygen and carbon dioxide pressures were investigated. The BC production rate was dependent on the oxygen transfer rate, which declined as the broth viscosity increased, accompanied by BC accumulation. Increasing the partial pressure of oxygen by sparging with oxygen-enriched air and/or raising the operating pressure improved the oxygen supply, while the agitation power required was lowered. Although the BC production rate was not affected by higher oxygen pressure, it was reduced as the operating pressure was raised. The reduction in the production rate was considered to be due to the high carbon dioxide pressure, because carbon dioxide-enriched air also reduced the BC production rate, while the reduction was canceled out by increasing the air flow rate.

Characterization of non-newtonian behavior during mixing of bacterial cellulose in a bioreactor

The mixing properties of bacterial cellulose (BC) in an aerated and agitated vessel are described. To characterize the mixing of BC culture broth, which can affect the productivity of BC, non-Newtonian behavior during mixing of a 1% BC suspension was studied using an image processor capable of detecting decoloration of a pH indicator and was compared with that of a 2% carboxy methyl cellulose (CMC) solution. CMC solution was mixed homogeneously within the measured range of agitation speed, but the BC suspension was not mixed homogeneously at agitation speeds lower than 15 rps because mixing was delayed in some areas of the vessel. A possible reason for the inhomogeneity of the BC suspension at low agitation speeds is the non-Newtonian behavior which increases viscosity at low shear rates.

Regular paperEffect of ethanol on bacterial cellulose production from fructose in continuous culture

Effect of ethanol on bacterial cellulose (BC) production from fructose by Acetobacter xylinum subsp. sucrofermentans BPR3001A was investigated in continuous culture. Supplementation of 10 g·l−1 ethanol to the feed medium containing 30 g·l−1 fructose as the main carbon source enhanced the ATP content of viable cells, cell concentration, and fructose consumption rate, establishing a 72-h steady state with 0.95 g·l−1·h−1 of BC production rate and 46% of BC yield in continuous culture with a dilution rate of 0.07 h−1. However, an increase in concentration of ethanol to more than 15 g·l−1 decreased BC production rate due to the inhibition of cell growth by the generated acetate. Results from batch culture experiment using ethanol as the main carbon source suggested that ethanol functioned as an energy source for ATP generation, and not as a substrate for BC biosynthesis. On the other hand, fructose hexokinase (FHK) activity was increased and activities of glucose 6-phosphate dehydrogenases (G6PDs) were inhibited by ATP, suggesting that the improved BC production from fructose by ethanol supplementation was a result of increased fructose dissimilation and abundant flow of glucose 6-phosphate (G6P), a precursor of BC, into the BC biosynthetic pathway due to the inhibition of G6PDs by increased levels of ATP.

Influence of broth exchange ratio on bacterial cellulose production by repeated-batch culture

Abstract The influence of broth exchange ratio on bacterial cellulose (BC) production by repeated-batch culture using Acetobactor xylinum subsp. sucrofermentans BPR3001A was investigated. When repeated-batch cultures were conducted at various broth exchange ratios ( α ), the highest BC production rate (0.43 g l −1 h −1 ) and BC yield (28%) were obtained at α of 0.9. With a larger α than 0.9, the ATP content was lower than that at α of 0.9 and the culture time was prolonged, resulting in a lower BC production rate. On the other hand, with a smaller α than 0.9 the dissolved oxygen could not be maintained at 10% of air saturation and CO 2 evolution from fructose increased, resulting in a lower BC yield, whereas the ATP content maintained higher level than that at α of 0.9. When six cycles of repeated-batch culture were conducted with α of 0.9, at least four cycles of repeated-batch culture were possible with a BC production rate of 0.42 g l −1 h −1 and a BC yield of 28% on average, and BC productivity was 2.5 times higher than that in single batch culture.

Effect of a kokumi peptide, γ-glutamyl-valyl-glycine, on the sensory characteristics of chicken consommé

BackgroundRecent studies have demonstrated that kokumi substances such as glutathione are perceived through the calcium-sensing receptor (CaSR). Screening by a CaSR assay and sensory evaluation have shown that γ-glutamyl-valyl-glycine (γ-Glu-Val-Gly) is a potent kokumi peptide. In the present study, the sensory characteristics of chicken consommé with added γ-Glu-Val-Gly were investigated using descriptive analysis.ResultsChicken consommé containing γ-Glu-Val-Gly had significantly stronger “umami” and “mouthfulness” (mouth-filling sensation) characteristics than the control sample at a 99% confidence level and significantly stronger “mouth-coating” characteristic than controls at a 95% confidence level.ConclusionsThese data suggest that a kokumi peptide, γ-Glu-Val-Gly, can enhance umami, mouthfulness, and mouth coating, implying that the application of this peptide could contribute to improving the flavor of chicken consommé.

Flavour improvement of reduced-fat peanut butter by addition of a kokumi peptide, γ-glutamyl-valyl-glycine

BackgroundRecent studies have demonstrated that kokumi substances, which enhance basic tastes and modify mouthfulness and continuity although they have no taste themselves, are perceived through the calcium-sensing receptor (CaSR). Screening by a CaSR assay and sensory evaluation have shown that γ-glutamyl-valyl-glycine (γ-Glu-Val-Gly) is a potent kokumi peptide. In our previous study, it was reported that the addition of γ-Glu-Val-Gly to chicken consommé significantly enhanced mouthfulness, continuity and thickness. In this study, the effect of γ-Glu-Val-Gly on reduced-fat peanut butter was investigated.ResultsPrior to the evaluation of the effect of γ-Glu-Val-Gly, a comparison test was conducted between full-fat model peanut butter and reduced-fat peanut butter. The sensory attributes in which the score of the full-fat model was significantly higher than that of the reduced-fat sample were used for the evaluation of the effect of γ-Glu-Val-Gly. The addition of γ-Glu-Val-Gly significantly enhanced thick flavour, aftertaste, and oiliness in the reduced-fat peanut butter.ConclusionsA kokumi peptide, γ-Glu-Val-Gly, can enhance thick flavour, aftertaste and oiliness in reduced-fat peanut butter. This suggests that addition of γ-Glu-Val-Gly can improve the flavour of low-fat foods.