L. E. Romero

Optimization of immobilization conditions for vinegar production. Siran, wood chips and polyurethane foam as carriers for Acetobacter aceti

Abstract A complete experimental design has been developed to study the properties of three different solid carriers (Siran, wood chips and polyurethane foam) in the immobilization of acetic acid bacteria. Temperature-controlled reactors of 450-ml volume were employed to compare a standard immobilization procedure consisting of consecutive discontinuous acetic acid fermentations in the presence of the carrier. On reaching the final saturation condition, the different immobilized carriers were removed and introduced into identical sterilized reactors. These were then submitted to several semi-continuous fermentation cycles with the aim of characterising and comparing their acetification properties. Immobilization and acetification data obtained in this study have been evaluated in order to determine the best carrier material on the basis of several technical criteria. Polyurethane foam was the most successful because it allows a huge number of immobilized cells in the shortest time and leads to the highest acetification rate of the three assayed carriers.

Optimum starting-up protocol of a pilot plant scale acetifier for vinegar production

In the present work, the influences of ethanol (fermentation substrate) and acetic acid (fermentation product) concentrations on the starting-up of a pilot plant acetifier are evaluated. Some effects of activation and inhibition acting on bacterial growth of acetic acid bacteria are registered as a function of the concentrations of substrate and product. As a consequence of the related studies, an optimum starting-up protocol has been proposed. In this, the volumes of wine and inoculum that must be added at the beginning of the process, together with the appropriate instant to make the additions of fresh wine, are established. This protocol is perfectly scalable to other industrial acetifiers, following the proposed stages and addition sequences.

Operation in semi-continuous with a closed pilot plant scale acetifier for vinegar production

Abstract Several semi-continuous series of acetic acid fermentations were carried out in a novel pilot plant reactor (225 l) including a gas recycling system for the recovery of volatile compounds. The behaviour of substrate and product concentrations, acetification rates, stoichometric yields and oxygen consumption were analysed. Operation with this novel reactor proved some technical advantages in order to produce high quality vinegars: stoichometric yields of 100% and minimum oxygen supply.

A kinetic model for growth of Acetobacter aceti in submerged culture

Abstract This paper proposes a kinetic model for growth, in low alcohol media, of Acetobacter aceti in submerged culture. The model combines the influence of substrate (ethanol) concentration, product (acetic acid) concentration and dissolved oxygen on the specific microorganism growth rate. Experimental data were obtained, both in the laboratory and industrially, using a variety of discontinuous fermentation apparatus with automatic control, and either open or closed gas recirculation systems. The operation conditions applied were those typical of acetic fermentation processes in the food industry. Examination of the results obtained makes it possible to determine the characteristic influence of each of the variables indicated, and to calculate the values of the different parameters of the proposed growth equation.

Application of a gas recirculation system to industrial acetic fermentation processes

This paper describes a gas recirculation system for the exhaust gases from the aerobic fermenters normally used in acetic fermentation processes. With the application of this procedure, it is possible to operate in a closed system, so preventing the large losses of fermentation yield due to evaporation which occur in open systems. In addition, this system reduces losses of volatile organoleptic compounds (ethanol, acetic acid and ethyl acetate, among others) so enabling the product to be incorporated into processes for the manufacture of high quality vinegars.

Laboratory scale equipment for the determination of kLa in bio-reactors

Abstract The study of the oxygen transfer rate (O.T.R) in reactors designed for cell cultivation and enzyme reaction is a difficult task. In this work a bio-reactor for acetic acid fermentation purposes is studied by using the static gassing out method for KLa evaluation. Results obtained prove that KLa shows linear dependence versus operation temperature.

Mathematical model for liquid-gas equilibrium in acetic acid fermentations

An experimental study was conducted to propose an adequate mathematical model for liquid-gas equilibrium in acetic acid fermentations. Three operation scales (laboratory, pilot plant, and industrial plant) were employed to obtain the sets of experimental data. The proposed model, based in the UNIFAC method for the estimation of activity coefficients of a solution consisting of several components, takes into account the effect of temperature. However, in the set of equations, it has been necessary to put in the degree of equilibrium (epsilon). This coefficient adequately reflects the physical conditions of fermentation equipment. The experimental and numerical results help to define the fundamental mechanisms for liquid-gas equilibrium in these systems and demonstrate the model validity in the three tested scales. It was also found that in an industrial setting, closed systems are those with lowest evaporation losses. Copyright 1998 John Wiley & Sons, Inc.

Study of the deactivation process of the glucose oxidase-catalase enzymatic system by means of simulation

This paper reports the simultaneous deactivation of co-immobilized glucose oxidase and catalase in calcium alginate beads. For this purpose, the study is conducted in a continuous stirred tank reactor containing the reaction medium. After a comprehensive review of the existing literature, a three-parametered irreversible deactivation general model is put forward for each enzyme.