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

Abstract

Cyclic fed-batch plus batch polygalacturonase production by Aureobasidium pullulans in slurry fermentation systems using raw orange peel as substrate was studied in a 3-dm 3~ stirred fermentor by setting the main operating variables ( T = 297 ° K; pHo = 3.2; OPo=3% w / v ; n = 7 0 0 r p m ) 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 fedbatch 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 rate being of pseudo-first order with respect to the reducing sugar concentration.orange peel to a previous set of operating conditions by submitting the main controlling parameters of this process to analysis according to the step-wise variation method. Whereas the overall cell growth appeared to be practically insensitive to any of the step changes of the control variables examined, polygalacturonase production was more sensitive to the initial pH value (pHo) and stirrer speed (n) than to fermentation temperature (7) and initial concentration of orange peel (OPo). In particular, the enzymatic activity was found to reach a maximum value of 110 VU cm-3 when T was varied in the range 291-300 ° K, and OP0, pHo and n were set to 2.5-3.0% w/v, 3.2 and 700 rpm, respectively (Petruccioli et al. 1990).The main aim of this work was to improve the prediction capability of an unstructured kinetic model previously developed by Petruccioli et al. (1990) to simulate experimental cell growth, enzyme production and substrate consumption in a laboratory-scale stirred fermentor under conventional batch a n d / o r cyclic fedbatch plus batch operations, and therefore provide a basis for further scale-up of the process.

An error estimation of Michaelis-Menten (Monod)-type kinetics

“…In recently published papers (Aynsley et al 1990;Coppela and Dhurjati 1990;Dussap et al 1991;Moresi et al 1991;Nielsen et al 1991;Park et al 1991;Straight and Ramkrishna 1991) modelling of these above-mentioned problems use Michaelis-Menten-or Monod-type Correspondence to: L. Szigeti expressions for conversion rates, uptake rates, and specific rates. Before the application of these well-known hyperbolas, we think it is worth examining the errors that can be caused by this simplification.…”

Δυναμική Αύξησης Ελεύθερα Διαβιούντων Αζωτοδεσμευτικών Πληθυσμών Σε Συνθήκες Ανταγωνισμού Και Θήρευσης

“…όπου, ο όρος Q περιγράφεται από την εξίσωση: al., 1987;Moresi et al, 1991 Ισοζύγιο πηγών άνθρακα και ενέργειας:…”