Assoc. Prof. V.Yu. Ovsyannikov, graduate student A.A. Avilov

Voronezh State University of Engineering Technologies, Russia

Study of main regularities of reproduction of bakery yeast

The study of the physiology and biochemistry of yeast in the interests of their industrial use is fraught with great possibilities. It is thanks to the use of the biological potential of yeast that the achievements of the last decade in the field of the construction of yeast-producing devices and aeration systems were realized, which enabled a sharp increase in the concentration of processed molasses, increased biomass accumulation and the removal of products from production equipment.

In the present work, the patterns of reproduction of baker's yeast and their relationship to the accumulation and release of biomass have been studied.

The yeast multiplication was studied in three main stages: anaerobic, weak aerobic and aerobic cultivation. The cultivation cycle began with an anaerobic or slightly anaerobic stage. The initial sequence was followed by three successive stages of aerobic yeast growth. The initial stage was carried out in a high medium layer without mixing (partial anaerobiosis) or with a weak periodic or continuous aeration of the medium. The duration of the stage is 12 hours. Cultivation in aerobic stages was conducted under the same conditions on a laboratory installation by an air-supply method using a 10-hour regimen.

The nutrient medium in all experiments was molasses wort, clarified by the acid-hot method for the initial stage and by the acid-cold method for all aerobic stages. Ammonium sulfate and diammonium phosphate were used as sources of nitrogen and phosphorus, the pH during the growing process was regulated with ammonia. The culture temperature was 30 ° C.

Studies were carried out with the yeast of the Saccharomyces cerevisiae race used in industry. The seeding material for the first stage was yeast from malt wort after 24 hours of cultivation at 30 °C. The aerobic stages were inoculated with washed and pressed yeast of the previous stage in an amount of 25% by weight of molasses. Thus, the yeast of each stage served as seeding material for the subsequent stage.

At all stages of cultivation, samples were regularly taken to determine the accumulation of biomass, counting the total number and number of budding cells. The final yield of biomass at each stage was expressed as a percentage of the molasses consumed. Based on the accumulation of biomass, for each stage, the average specific growth rate μ, g./h, the number of generations n, pcs, and the mean duration of generation q, h, were calculated for the following formulas:

; (1)

; (2)

, (3)

where m₀ - amount of seed yeast, gr. (25 % dry matter); m₁- amount of yeast at the end of the stage, gr.; t₁ – t₂ – duration of the stage, h.

In Fig. 1 shows the dynamics of accumulation and release of biomass in four consecutive stages of cultivation, where the initial was the anaerobic stage. The obtained data indicate that the accumulation and yield of biomass in conditions of partial anaerobiosis are low. These indicators increase sharply in the first aerobic stage and continue to increase in the second, but in the third stage, the accumulation and yield are reduced. Accumulation and yield of biomass decrease with long-stored molasses and yeast (curve 1), they increase when fresh molasses and a newly isolated yeast strain (curve 2) are used. After the transition to a continuous supply of carbohydrate nutrition in comparison with the batch feed in the first two cases, the biomass accumulation and yield increased again (curve 3), however, the established dynamics of their growth at different stages persisted. In an optimal variant, the yield by stages (average data from six experiments) was 9, 74, 85 and 80%, respectively.

Fig. 1. Change in the accumulation and yield of biomass in yeast growing:

–––– exit, %; – – – accumulation of biomass, gr.

The accumulation and yield of biomass in the aerobic stages varied in accordance with the growth rate of yeast (Fig. 2). Simultaneously, the number of generations changed, in inverse relationship - the generation time.

Thus, the intensity of yeast multiplication is different in three consecutive stages of aerobic growth, which are the same in terms of nutrition and aeration. After the stage providing the maximum accumulation and yield of biomass, the further multiplication of yeast proceeds less intensively.

Fig. 2. Change in the average specific growth rate, generation number and generation time of yeast in successive aerobic stages:

1 - using long stored molasses and yeast strain; 2 - fresh molasses and a newly excreted strain of yeast; 3 - the same in conditions of continuous supply of carbohydrate nutrition;

––––– biomass growth module; – – – number of generations; – · – · – duration of generation

n yeast, there is a period of decline in biosynthetic abilities, leading to a decrease in the accumulation and release of biomass. It follows from Fig. 1 and 2, this pattern clearly manifests itself at different levels of the biosynthetic capacity of yeast. The reason for this phenomenon is a change in the metabolism of yeast at these stages of development.

It should be noted that, despite the absence of clear indications in the scientific literature of this pattern, industrial technology is empirically constructed on this principle, according to which the maximum multiplication and yield of yeast is reached only in the last, commodity stage.