F. Federici

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.

Direct ammonium fumarate production by Rhizopus arrhizus under phosphorous limitation

Direct ammonium fumarate production from glucose-based media with Rhizopus arrhizus NRRL 1526 was obtained using 2-kmol (NH4)2CO3 per-m3 as neutralising agent and controlling mycelial growth by phosphorous (P) limitation. As the P level in the production medium was increased from 0 to 0.3-kg of KH2PO4 per m3, the fumarate yield decreased from 0.32 to 0.13-g per-g of glucose consumed; maximum ammonium fumarate productivity (0.46-kg-m−3-h−1) was obtained when using 0.1-kg phosphate-m−3.

Pectic enzyme production by Cryptococcus albidus var. albidus on olive vegetation waters enriched with sunflower calathide meal

Abstract Because of the large volume and high organic load, olive vegetation waters represent a major pollutant which causes significant environmental problems. The waters contain, however, simple sugars, polysaccharides and pectins which make them a possible substrate for suitable micro-organisms. Cryptococcus albidus var. albidus IMAT-4735 was capable of growing on suitably treated vegetation waters, producing pectic enzyme. Enzyme production was favoured by increasing concentrations of sunflower calathide meal in the medium. On the basis of preliminary tests, the enzyme was characterized as an endopolygalacturonase with considerable potential technological interest.

Continuous production of glucoamylase by immobilized growing cells ofAureobasidium pullulans

SummaryYeast-like cells ofAureobasidium pullulans were immobilized in Ca-alginate gel beads and employed for continuous production of glucoamylase in a fluidized-bed reactor (250 ml working volume). After an activation time of 48 h, to allow the “in situ” germination of the fungal blastospores, the reactor was operated continuously for over 150 h. A steady state enzyme concentration of 1.2–1.3 U ml−1 of glucoamylase activity and an enzyme volumetric productivity of ca. 130 U ml−1 h−1 were obtained at a medium flow rate of 26 ml h−1. Enzyme activity and volumetric productivity were influenced by fermentation conditions such as inoculum size and airflow rate.

Extracellular enzyme production in species of the genus Penicillium

Fungi have long been known as enzyme producers and some species are being exploited industrially to make, e.g., amylases and cellulases (Priest, 1984). Among others, some species of the genus Penicillium have been reported to possess enzymes with high levels of activity (AbdelFattah et al., 1972; Ghosh and Thangamani, 1973; Yamasaki et al., 1977). In this short communication we report the results of a preliminary screening conducted on 40 strains, representing 24 species of Penicillium, for the production of enzymes of possible industrial interest. The strains used in this study were obtained from the culture collections of the Dipartimento di Biologia Vegetale, University of Perugia, Italy, and the Istituto Superiore di Sanita, Rome, Italy. Stock cultures were maintained at 5 C on slants

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.

Scanning electron microscopy of Ca-alginate-immobilized Aureobasidium pullulans grown under various culture conditions

The morphological development of a glucoamylase-producing strain of Aureobasidium pullulans immobilized in Ca-alginate was investigated during semicontinuous fermentations in a fluidized-bed reactor. A dense mycelium layer was developed by the fungus on the gel bead surface which gave the beads a pellet-like configuration. Varying culture conditions, such as bead, substrate and CaCl2 concentrations and aeration rate, had a consistent effect on both enzyme production and morphological development of the in situ grown cells. Optimization of the growth conditions appeared to be necessary to prevent fungal overgrowth and to enable the immobilized inoculum to continue a sustained level of glucoamylase production over a great number of transfers.