Mauro Moresi

Effect of pH and stirring rate on itaconate production by Aspergillus terreus

The production of itaconic acid from glucose-based media by Aspergillus terreus NRRL 1960 was found to be controlled by stirring rate and pH. When the phosphorous (P) level in the production medium was reduced to less than 10 mg l(-1), the fungal mycelium exhausted its primary growth and started to excrete itaconic acid, while it continued its secondary growth at the expense of ammoniacal nitrogen. The fermentation exhibited a mixed-growth-associated product formation kinetics, the non-growth associated production term (mI) being practically zero only when the pH was left free to change from 3.4 down to 1.85. On the contrary, when the pH was kept reducing up to a constant value by automatic addition of KOH 4 mol l(-1), the itaconate yield coefficient on the initial glucose supplied (Y(I/So)) and mI and were 0.53 g g(-1) and 0.028 h(-1) at pH 2.4 and 320 rev min(-1) and 0.5 g g(-1) and 0.036 h(-1) at pH 2.8 and 400 rev min(-1), respectively. Although the differences between mI and Y(I/So) were statistically insignificant at the 95% confidence level, the net difference in the corresponding yield coefficients for itaconic acid on mycelial biomass resulted in a maximum itaconate production rate of 0.41 g l(-1) h(-1) at pH 2.8 and 400 rev min(-1), thus showing that this operating condition is no doubt optimal for the process under study.

Optimization of fumaric acid production from potato flour by Rhizopus arrhizus

SummaryFumaric acid production by Rhizopus arrhizus from potato flour was studied at different initial substrate concentrations (S), C/N ratios and fermentation times (tf) in a composite design experiment. By using response surface methodology and canonical analysis, the experimental values of fumaric acid and mycelial biomass yields and productivity were fitted to the only statistically significant factors with mean percentage errors of 11, 26 and 13%, respectively. Owing to the limited statistical significance of the C/N ratio, it was possible to determine the values of S (25–50 g/l of glucose equivalent) and tf(44–100 h) associated with fumaric acid yields ranging from 60 to 75% and productivities varying from 6 to 8.4 g/l per day. Since such results were in quite good agreement with previous experiments carried out on other starchy materials, the above operating conditions might be used to minimize fumaric acid production costs as a function of the feed-stock used.

Effect of dissolved oxygen concentration on repeated production of gluconic acid by immobilised mycelia of Aspergillus niger

SummaryGluconic acid production from corn starch hydrolysates by immobilised mycelia of Aspergillus niger was studied in a laboratory-scale stirred fermentor at different concentrations of glucose (S0) and dissolved oxygen (DO) in the culture broth. Its evolution was simulated quite well by applying the same unstructured model set up in previous experiments using stirred and airlift fermentors. In particular, increasing S0 in the range 70–160 g/l, although uninfluential upon the yield coefficient, resulted in an exponential decrease in the gluconic acid formation rate constant. Nevertheless, the greater the oxygen transfer rate used in the fermentor, the smaller the inhibitor effect of the higher concentrations of glucose on gluconate productivity became. This was achieved by enriching the inlet air with pure oxygen so as to maintain the DO level above 75% saturation throughout the fermentation.

Scaling-up of a batch whey fermentation by Kluyveromyces fragilis

SummaryA whey fermentation by Kluyveromyces fragilis was scaled-up to a 1000-dm3 stirred fermentor, by varying the stirrer speed, the air-flow rate and the initial concentration of lactose. Its evolution was simulated by applying the same unstructured model (consisting of a microbial specific growth rate of pseudo-first order with respect to the COD concentration and constant biomass yield per unit COD removed) set up in previous experiments using 8- to 80-dm3 fermentors. Despite the great scale-up ratios, very different operating conditions, and geometric dissimilarity, a series of empirical regressions previously developed allowed approximate, but acceptable prediction of the stoichiometric and kinetic coefficients of the above mathematical model, thus confirming the capability of this model to provide a reliable basis for further scale-up of this fermentation process to a production scale.

Modelling of cyclic fed-batch plus batch polygalacturonase production by Aureobasidium pullulans on raw orange peel

SummaryCyclic fed-batch plus batch polygalacturonase production by Aureobasidium pullulans in slurry fermentation systems using raw orange peel as substrate was studied in a 3-dm3 stirred fermentor by setting the main operating variables (T=297°K; pH0=3.2; OP0=3% w/v; n=700 rpm) to optimal values determined previously. In this way, it was possible to stabilize enzyme excretion at 130–140 VU cm−3. The time course of this fermentation process in terms of cell growth, substrate consumption and enzyme synthesis was reconstructed with a mean standard error less than 10%, by applying an unstructured model set up in a batch run and further refined in a series of cyclic fed-batch plus batch operations. In particular, the enzyme formation rate was related to the effect of reducing sugars as inhibitors at higher concentrations and as activators at lower levels by using an exponential equation. Moreover, the consumption rate of reducing sugars was found to be linearly related to the cell growth rate, its specific date being of pseudo-first order with respect to the reducing sugar concentration.

Development and testing of a novel lab-scale direct steam-injection apparatus to hydrolyse model and saline crop slurries

In this work, a novel laboratory-scale direct steam-injection apparatus (DSIA) was developed to overcome the main drawback of the conventional batch-driven lab rigs, namely the long time needed to heat fiber slurry from room to reaction temperatures greater than 150 °C. The novel apparatus mainly consisted of three units: (i) a mechanically-stirred bioreactor where saturated steam at 5-30 bar can be injected; (ii) an automatic on-off valve to flash suddenly the reaction medium after a prefixed reaction time; (iii) a cyclone separator to recover the reacted slurry. This system was tested using 0.75 dm³ of an aqueous solution of H₂SO₄ (0.5%, v/v) enriched with 50 kg m⁻³ of either commercial particles of Avicel® and Larch xylan or 0.5 mm sieved particles of Tamarix jordanis. Each slurry was heated to about 200 °C by injecting steam at 28 bar for 90 s. The process efficiency was assessed by comparing the dissolution degree of suspended solid (Y(S)), as well as xylose (Y(X)), glucose (Y(G)), and furfural (Y(F)) yields, with those obtained in a conventional steam autoclave at 130 °C for 30 or 60 min. Treatment of T. jordanis particles in DSIA resulted in Y(S) and Y(G) values quite similar to those obtained in the steam autoclave at 130 °C for 60 min, but in a less efficient hemicellulose solubilization. A limited occurrence of pentose degradation products was observed in both equipments, suggesting that hydrolysis predominated over degradation reactions. The susceptibility of the residual solid fractions from DSIA treatment to a conventional 120 h long cellulolytic treatment using an enzyme loading of 5.4 FPU g⁻¹ was markedly higher than that of samples hydrolysed in the steam autoclave, their corresponding glucose yields being equal to 0.94 and 0.22 g per gram of initial cellulose, respectively. Thus, T. jordanis resulted to be a valuable source of sugars for bioethanol production as proved by preliminary tests in the novel lab rig developed here.

Fermenter Design for Alcoholic Beverage Production

Up to almost fifty years ago the design of the equipment used for ethanol production (be it for beer, wine, cider, perry, or potable spirit) was more an art than a science, being the result of a large number of practical observations well rooted in traditional beliefs and techniques.

Optimal Fermenter Design for White Wine Production

The overall pattern of grape must fermentation is the combined result of a large number of factors, such as must components (i.e. sugar, nutrient and growth factor concentrations, acidity and phenolic content), microflora and operating conditions (viz. temperature, oxygen level and agitation).