Culture conditions influence biomass and alkali-insoluble cell-wall polysaccharide production in indigenous Saccharomyces cerevisiae strains

Abstract

Saccharomyces cerevisiae is an important source of yeast biomass and alkali–insoluble cell–wall polysaccharide fractions (AICWP), which may contain substantial β–glucan. In the present study, indigenous yeast isolates from diverse natural sources were screened for biomass formation and AICWP accumulation. Four S. cerevisiae strains, selected from 54 previously isolated yeasts, were evaluated for growth performance under the investigated culture conditions. Yeast isolates were obtained through selective cultivation and characterized morphologically and microscopically. High biomass–producing isolates were identified through growth–based screening, and the effects of glucose, ammonium sulfate, and inoculum size on biomass accumulation were assessed using a Plackett–Burman (PB) design and further examined by Response Surface Methodology (RSM). Under one set of selected cultivation conditions, biomass concentration reached 250.01 g/L wet weight (100.04 g/L dry weight), and the alkali–insoluble cell–wall fraction contained 7.01 g/L total carbohydrate expressed as glucose equivalents. Because the phenol–sulfuric acid assay is non–specific, this value represents total carbohydrate equivalents in the extracted alkali–insoluble fraction and does not constitute a direct measurement of purified β–glucan. Scanning electron microscopy (SEM) showed dense aggregation of yeast cells with predominantly oval–to–round morphology and generally intact surfaces, consistent with the typical morphology of S. cerevisiae . Biomass concentration declined by approximately 18% under 5% sorbitol and by 36% under 0.005% SDS; viable counts were 8.83 and 8.20 Log CFU/mL, respectively, compared with 9.07 Log CFU/mL in the control. Evaluation in a 3–L stirred–tank bioreactor with a 1–L working volume revealed that spray drying yielded a higher recovered dry powder concentration (144.75 ± 2.90 g/L) than freeze drying (125.12 ± 2.50 g/L), whereas freeze drying yielded higher viable–cell recovery after rehydration and 24 h incubation (0.2 × 10 9 vs. 0.9 × 10 8 CFU/mL). These findings provide preliminary feasibility evidence under the tested bioreactor conditions; further studies are required to evaluate oxygen transfer, hydrodynamics, reproducibility, and scalability.