Experimental investigation and numerical modeling of pilot-scale fluidized-bed drying of yeast: Part B — Viability measurements and modeling

Soltani, Behdad; McClure, Dale D.; Oveissi, Farshad; Langrish, T.A.G.; Kavanagh, John M.

doi:10.1016/j.fbp.2019.11.005

Cited by 9 publications

(6 citation statements)

References 8 publications

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“…As a consequence, the energy input at the two lowest temperatures was not sufficient for drying and the over-moistened fluidized bed collapsed (30 °C) or big lumps were formed (40 °C). Besides this, the survival of the yeast cells decreases with increasing temperature (inlet and thus also process chamber and outlet) ( Figure 5 ), as expected and reported by other researchers [ 48 , 58 ] (please note that fluidized bed drying of yeast pellets and no granulation was performed).…”

Section: Resultssupporting

confidence: 87%

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Effect of Process Parameters, Protectants and Carrier Materials on the Survival of Yeast Cells during Fluidized Bed Granulation for Tableting

et al. 2023

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The administration of living microorganisms is of special interest, with regard to probiotic microorganisms providing health benefits to the patient. Effective dosage forms require the preservation of microbial viability until administration. Storage stability can be improved by drying, and the tablet is an especially attractive final solid dosage form due to its ease of administration and its good patient compliance. In this study, drying of the yeast Saccharomyces cerevisiae via fluidized bed spray granulation is investigated, as the probiotic Saccharomyces boulardii is a variety of it. Fluidized bed granulation enables faster drying than lyophilization on the one hand and lower temperatures than spray drying on the other hand, which are the two predominantly used techniques for life-sustaining drying of microorganisms. Yeast cell suspensions enriched with protective additives were sprayed onto the carrier particles of common tableting excipients, namely, dicalcium phosphate (DCP), lactose (LAC) and microcrystalline cellulose (MCC). Different protectants, such as mono-, di-, oligo- and polysaccharides, but also skimmed milk powder and one alditol, were tested; as they themselves, or chemically similar molecules, are known from other drying technologies to stabilize biological structures such as cell membranes, and thus, improve survival during dehydration. With the combined use of trehalose and skimmed milk powder, survival rates were 300 times higher than without the use of protective additives. In addition to these formulation aspects, the influence of process parameters such as inlet temperature and spray rate were considered. The granulated products were characterized regarding their particle size distribution, moisture content and the viability of the yeast cells. It has been shown that thermal stress on the microorganisms is especially critical, which can be reduced, for example, by reducing the inlet temperature or increasing the spray rate; however, formulation parameters such as cell concentration also influenced survival. The results were used to specify the influencing factors on the survival of microorganisms during fluidized bed granulation and to derive their linkages. Granules based on the three different carrier materials were tableted and the survival of the microorganisms was evaluated and linked to the tablet tensile strength achieved. Using LAC enabled the highest survival of the microorganisms throughout the considered process chain.

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Section: Resultssupporting

confidence: 87%

“…Freeze-drying of the same yeast strain has enabled survival rates up to 42.9% [ 9 ], and fluidized bed drying of Saccharomyces cerevisiae pellets (another strain), without protectants, has enabled survival rates of up to and more than 90% [ 47 , 48 ]. In contrast, only significantly lower survival rates are achieved in the present study.…”

Section: Resultsmentioning

confidence: 99%

Effect of Process Parameters, Protectants and Carrier Materials on the Survival of Yeast Cells during Fluidized Bed Granulation for Tableting

et al. 2023

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“…18 When the cell viability is high, the cellular water content is as high as 80%, and terahertz radiation is greatly absorbed by intracellular free water (Figure 1). In the process of apoptosis, the cellular water content gradually decreased, 37 and other compounds in the cells became the main components, resulting in the reduction of the absorption to terahertz radiation of cells. The detailed description of the terahertz spectrometer experimental platform (Figure 2c) is shown in Methods and Experiments.…”

Section: Resultsmentioning

confidence: 99%

Deep-Learning Terahertz Single-Cell Metabolic Viability Study

Yang,

Shi,

Wei

et al. 2023

ACS Nano

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Cell viability assessment is critical, yet existing assessments are not accurate enough. We report a cell viability evaluation method based on the metabolic ability of a single cell. Without culture medium, we measured the absorption of cells to terahertz laser beams, which could target a single cell. The cell viability was assessed with a convolution neural classification network based on cell morphology. We established a cell viability assessment model based on the THz-AS (terahertz-absorption spectrum) results as y = a = (x – b) c , where x is the terahertz absorbance and y is the cell viability, and a, b, and c are the fitting parameters of the model. Under water stress the changes in terahertz absorbance of cells corresponded one-to-one with the apoptosis process, and we propose a cell 0 viability definition as terahertz absorbance remains unchanged based on the cell metabolic mechanism. Compared with typical methods, our method is accurate, label-free, contact-free, and almost interference-free and could help visualize the cell apoptosis process for broad applications including drug screening.

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“…Such a behavior was already observed in other studies. [4,6,31] Spreutels et al [4] showed, through a model of the drying kinetics of yeast pellets, that a water content of about 0.5 is obtained when almost all the extracellular water has been removed. This suggests that this sudden drop of quality could be related to the removal of the intracellular water.…”

Section: Discussionmentioning

confidence: 99%

“…), a trend that has already been reported in several studies on the quality of yeasts in the absence of carrier. [4,6,31] On the other hand, the addition of a solid carrier leads to a continuous decrease in yeast fermentation activity from the beginning of drying. A possible explanation for this decrease is that the removal of the intracellular water takes place after most of the extracellular water has been removed in the absence of a solid carrier, whereas it takes place continuously throughout the drying process when a hygroscopic material such as wheat flour is included in the pellets.…”

Section: Discussionmentioning

confidence: 99%

Evolution of the quality of baker’s yeast pellets containing a carrier during their convective drying

et al. 2021

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The addition of a solid carrier before drying seems a promising way to improve the processability and the drying kinetics of yeast pellets. However, its influence on the quality of the yeasts during and at the end of the drying is not yet well understood and is investigated in this communication. A yeast paste was mixed with different amounts of wheat flour, a solid carrier, to obtain pellets with 69, 55, and 40 wt% moisture content. The fermentation activity of the yeasts was measured in samples taken throughout the drying process of these pellets. The experimental results highlight that the addition of a carrier does not significantly alter the quality of the yeasts before drying but has a negative impact on their final quality at the end of the drying process. Moreover, the addition of a solid carrier leads to a continuous decrease in the fermentation activity of the yeasts from the beginning of drying, in contrast to the activity of the yeasts in the absence of a carrier, which remains high during drying, as long as the moisture content of the pellets is larger than about 0.5 (d.b.).

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Experimental investigation and numerical modeling of pilot-scale fluidized-bed drying of yeast: Part B — Viability measurements and modeling

Cited by 9 publications

References 8 publications

Effect of Process Parameters, Protectants and Carrier Materials on the Survival of Yeast Cells during Fluidized Bed Granulation for Tableting

Effect of Process Parameters, Protectants and Carrier Materials on the Survival of Yeast Cells during Fluidized Bed Granulation for Tableting

Deep-Learning Terahertz Single-Cell Metabolic Viability Study

Evolution of the quality of baker’s yeast pellets containing a carrier during their convective drying

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