Yeast vitality determination based on intracellular NAD(P)H fluorescence measurement during aerobic-anaerobic transition

Abstract

This work presents a yeast-cell vitality-assessment method based on on-line intracellular fluorescence measurement. The intracellular NAD(P)H fluorescence of a cell suspension is recorded during transition from aerobic to anaerobic conditions and the output signal is evaluated as a measure of yeast vitality (quality). This fluorescence method showed a highly satisfactory correlation with even low dead cell numbers where the acidification power test could not be applied. Abbreviations NAD(P)nicotinamide adenine dinucleotide (phosphate) FI fluorescence intensity NAD(P)H reduced form of nicotinamide adenine dinucleotide (phosphate)FI rel relative increase of NAD(P)H fluorescence AP acidification power μ max maximum specific growth rateThe high quality of microbial catalyst, expressed as "vitality", strongly influences the course of several processes in food industry, such as beer and wine fermentation, dough leavening or cheese making. The term vitality describes a group of characteristics and capabilities of microbial cells related to their metabolic activity and stress resistance (Sigler et al. 2006). Several quantitative methods have been developed to evaluate the vitality of cells including measurements based on intracellular content of different components (Majara et al. 1996;Hutter 2002) or manifestation of metabolic activity (Peddie et al. 1991;Imai et al. 1994) or gravimetric analysis of the course of fermentation (Košin et al. 2008). In fact, none of these methods has found widespread application in industrial biotechnologies.One of the areas where an expeditious and reliable method of yeast vitality estimation would be appreciated is brewing industry. The brewing yeast vitality is an important factor determining the fermentation performance and the formation of sensorially active metabolic by-products (Guido et al. 2004;Brányik et al. 2005). Nevertheless, the methods of yeast vitality estimation developed so far have not met the requirements for routine applicability (Mochaba et al. 1998;Košin et al. 2007).Sensors using intracellular fluorophores (NAD(P)H) have been developed for different application in biotechnology and particularly for bioprocess monitoring (Marose et al. 1998;Podrazký and Kuncová 2005). However, the number of practical applications of fluorometry in biotechnologies has been very limited due to the many factors that affect culture fluorescence (Li et al. 1990).This paper presents a novel application of NAD(P)H-dependent fluorescence monitoring for determination of yeast vitality. The method is based on the monitoring of intensity of NAD(P)H fluorescence during a forced transition from aerobic to anaerobic conditions (AA transition). The relative fluorescence increase (FI rel ) change and its rate (dFI/dt) during AA transition was evaluated as a measure of yeast vitality and it was compared with acidification power (AP) test, specific growth rate (μ) measurement and dead cell count. MATERIALS AND METHODSYeast strain. The industrial bottom-fermenting brewing yeast strain Saccharomyces cer...

The Impact of Xanthohumol on a Brewing Yeast's Viability, Vitality and Metabolite Formation

“…The yeast's vitality was also measured by a recent methodology developed by Kuřec et al 12 . This method is based on an on-line intracellular fluorescence measurement.…”

“…Yeast viability is an expression used to describe the ability of cells to grow, reproduce and interact with their immediate environment 8 . The term vitality describes a group of characteristics and capabilities of microbial cells related to their metabolic activity and stress resistance 12 . The vitality tests are generally used to identify gradual variations in a yeast's physiological condition, as opposed to viability tests that only measure the live/dead status of a cell and do not provide any indication about the activity level of the live cells 31 .…”

“…There are a large number of methods proposed for assessing yeast vitality. These are essentially based on the intracellular content of different components, metabolic activity or a gravimetric analysis on the course of fermentation 7,12 . Details of these and other methods can be found in several reviews 9,10,13 .…”

“…Details of these and other methods can be found in several reviews 9,10,13 . However, none of these methods has found widespread application in industrial biotechnologies 12 .…”