Exploring the lag phase and growth initiation of a yeast culture by means of an individual-based model

Abstract

Yeast ageing and inoculum size are factors that affect successive industrial fermentation, particularly in those processes that reuse the yeast cells. The aim of the work is to explore the effects of inocula size and aging on the dynamics of yeast population. However, only individual-based modelling (IbM) makes possible studies of small, well characterized, microbial inocula. Here we have made use of INDISIM-YEAST to carry out these studies.Several simulations were performed to analyze inoculum size and their different genealogical ages on the lag phase, first division time and specific growth rate. Shortest lag phase and time to the first division where obtained with largest inocula and with youngest inoculated parent cells.

Optimization ofSaccharomyces boulardiiproduction in solid-state fermentation with response surface methodology

“…It is known that temperature is one of the most critical factors influencing the industrial fermentation, including specific growth rate and biomass yield. [17,18] Figure 1(B) shows that the maximal yeast count (1.01£10 9 CFU/g) was obtained at 30 C. After that, with increasing the temperature, the yeast count decreased rapidly. Thus, 30 C was defined as the optimal temperature.…”

Analysis of the effect of inoculum characteristics on the first stages of a growing yeast population in beer fermentations by means of an individual-based model

“…For this study, we used INDISIM-YEAST as the individual-based simulator, which is based on the generic simulator INDISIM [9,[11][12][13][14]. Although the reader can refer to some previously published papers for a description of different parts of INDISIM-YEAST [11,12], a formal and brief description of this simulation model is presented below in order to make this study more self-contained and autonomous.…”

“…This is a proof of the ability of INDISIM-YEAST to distinguish differences in the evolution of a population that emerges from small inocula with different age structures. In fact, it is particularly useful in the study of small inocula during the initial steps of growth because of the large influence of the discrete and asymmetrical nature of yeast cellular division [13]. It is here that this model has an edge over top-down continuous models, which are useful when the initial population contains a large number of cells and the interest is the inspection of average behaviours exhibited by those cells.…”

“…INDISIM-YEAST constitutes the adaptation of INDISIM to the study of the specific characteristics of the yeast cell cycle, and is designed to deal with yeast populations growing in liquid media [11,12]. Recently, this simulator was used to study the influence of cell ageing and inoculum size on the lag phase and first division time of a yeast culture [13]. The aim of this contribution is to explore, by means of the simulator INDISIM-YEAST, the effects of inoculum size and cell genealogical age on the dynamics of yeast fermentation, focussing on: (1) the first stages of yeast population growth, (2) the mean biomass evolution of the population, (3) the rate of glucose uptake and ethanol production, and (4) the biomass and genealogical age distributions, in order to be able to integrate these results and to advance understanding of the composition of yeast populations and their temporal evolution in beer fermentations.…”

Fermentation and antimicrobial characteristics of Lactobacillus plantarum and Candida tropicalis from Nigerian fermented maize (akamu)

“…Furthermore, the exhaustion of utilisable carbon dioxide (Sezonov, Joseleau-Petit, & D'Ari, 2007) in the fermentation pots (18 mL in 50 mL), where cells are increasing in number, may also explain entry into the stationary phase of growth, although L. plantarum strains isolated from fermented maize porridges have been found to withstand low pH (2.5) (Kalui, Mathara, Kutima, Kiiyukia, & Wongo, 2009). The absence of lag time could be influenced by several factors such as the inoculum quantity, the environmental conditions of the original and the new growth medium, the growth stage of the microorganisms during the time of inoculation (Ginovart, Prats, Portell, & Silbert, 2011;Swinnen, Bernaerts, Dens, Geeraerd, & Van Impe, 2004) and probably the investigation period. The L. plantarum strains and the yeasts were suspended in PBS at an active growth stage and inoculated into the maize slurry environment that had enough nutrients to support their growth.…”