Production and characterization of cellular and released polysaccharides by Papiliotrema laurentii strains bioreactor-cultivated on Mizithra secondary cheese whey

• SCW effectively supports large-scale growth of P . laurentii and high exopolysaccharide production. • Yeast dry biomass is rich in β -glucans, while EPS are rich in galacto- xylo -mannans. • Cellular polysaccharides of P. laurentii NRRL YB-3594 possess high antioxidant capacity. • cPS of both strains and EPS of P . laurentii Y-2536 presented cytotoxicity against cancer cells. • Heat-treated EPS of Y-2536 and untreated EPS of YB-3594 did not present cytotoxicity. Polysaccharides produced by Papiliotrema laurentii strains are of great interest due to their functional properties and potential applications in the food, feed, pharmaceutical, and cosmetic industries. Microbial bioconversion of agro-industrial by-products into high value-added compounds, such as polysaccharides, is of major importance within the framework of the circular economy, as it significantly reduces bioprocessing costs. The present study aimed to produce cellular (cPS) and released extracellular (EPS) polysaccharides through the biotechnological valorization of secondary cheese whey (SCW), a major by-product of cheese manufacturing. The non-extensively studied strain P . laurentii NRRL Y-2536, cultivated on pretreated SCW, produced biomass (14.8 g/L) rich in intracellular polysaccharides (>46 %, w/w), as well as released EPS (22.7 g/L – 504 mg/L/h). cPS were extracted using high-pressure homogenization and deproteinized in the presence of n-butanol–chloroform solvents. Both cPS and EPS were analyzed via FTIR, HPLC, and FRAP assay to assess their structure, composition, and antioxidant capacity. The effects of cPS and EPS on the viability of two human cancer cell lines, Caco-2 and HT29-MTX, were evaluated. The cPS of P . laurentii NRRL Y-2536 and P . laurentii NRRL YB-3594 were rich in β -glucans (>62 % of total cPS), while the EPS were composed of galacto- xylo -mannans. Notably, the cPS from P . laurentii YB-3594 exhibited the highest antioxidant activity. Both cPS isolates, along with the EPS from P . laurentii Y-2536, presented cytotoxic activity at the highest concentrations tested, suggesting their potential application as anticancer agents. In contrast, the heat-treated EPS from P . laurentii Y-2536 and the untreated EPS from P . laurentii YB-3594, which were non-cytotoxic, could be further explored as functional ingredients for food, feed, cosmetic, or biomedicine applications.