Measuring and modelling the glucose-fermenting activity of Lactobacillus plantarum

Abstract

The pH decraese in a phosphate buffer due to fermentation of glucose to lactic acid by non-growing Lactobacillus plantarum cells has been studied. The method used offers a quick and reproducible way of measuring the glucose-fermenting activity of L. plantarum. The maximum observed velocity of pH decrease is linear with the biomass concentration and is defined as the activity of the cell suspension. With L. plantarum, recalculation of this arbitrary unit (ApH.min -1 per gram dry weight) to a conceivable unit of lactic acid production rate (mol.min -1 per gram dry weight) is possible. This recalculation is based on the titration theory of a weak base with a weak acid. The same theory together with the lactic acid production kinetics of L. plantarum is applied to model the entire pH-time Curve.

Characterisation of lactic starters based on acidification and reduction activities

“…There are several methods available, such as pH or impedance measurements, to study the kinetics of acidification by lactic starters [3,7,8,19,22,26]. The method of Spinnler and Corrieu [26] involves the calculation of characteristic kinetic parameters from the measurement of pH decrease [1,2,11,23,28].…”

A kinetic method for calculating the viability of lactic starter cultures

“…In a similar manner the pH decrease in phosphate buffer due to fermentation of glucose to lactic acid has been used to measure 649 the glucose-fermenting activity of L. plantarum (Lievense et al 1990). …”

“…The maximum velocity of pH decrease, in A p H / min, observed in phosphate buffer with glucose, was defined by Lievense et al (1990) as the activity of the cell suspension. In the viability tests with inocula of different ages the drop in pH was measured during growth.…”

“…Thus, this method should be relevant for any microbe dependent industry, for example the production of starter cultures for food products, silage or probiotics. The main advantages of the method are that: (1) it allows estimation of the viability of starter cultures under conditions of an industrially relevant environment and not as an instantaneous environment staining answer; (2) it avoids the long time of determination, large serial dilutions and eventual under-counting of plate-counting methods; (3) it only requires standard laboratory equipment and small samples, thus making it a very economical method; (4) it only needs the establishment of the intrinsic kinetic parameters, Xm~x and #m~x; (5) if or when required it can be complemented with studies of the fermentative activity of microorganisms by measuring the pH variation of the reinoculated medium as suggested by Lievense et al (1990).…”

Knowledge based diagnosis of inoculum properties and sterilization time in lactic acid fermentation

“…Too small of an inoculum can result in an excessively long lag phase, while a large iuoculum can result in a rapid cell growth with a decreased product concentration. Lievense et al (1990) observed with L. plantarum that during fermentation lactic acid production increases linearly with an increase in cell quantity of up to 4 g (dry weight) per liter, and defined the activity of the cell suspension as A pH min-lg-l.…”