Dried yeast (Saccharomyces cerevisae) as a protein source for horses

Acclimation to a broad range of nitrate strength on a euryhaline marine microalga Tetraselmis subcordiformis for photosynthetic nitrate removal and high-quality biomass production

Industrial wastewaters usually possess a wide range of nitrate strength. Microalgae-based nitrate-rich wastewater treatment could realize nitrate recovery along with CO₂ sequestration for sustainable biomass production, but the low tolerance of the microalgal strains to high-strength nitrate restricted the treatment process. The present study comprehensively evaluated a euryhaline marine microalga Tetraselmis subcordiformis for photosynthetic nitrate removal and biomass production in synthetic wastewater with a broad range of nitrate strength (0.24-7.0 g NO₃^--N/L). This alga could acclimate to high nitrate strength up to 3.5 g NO₃^--N/L (HN) without compromising biomass production. Nitrate could be completely removed within four days when low nitrate (0.24 g NO₃^--N/L, LN) was loaded. The maximum nitrate removal rate of 331 mg N/L/day and specific nitrate removal rate of 360 mg N/day/g cell was obtained under medium nitrate condition (1.8 g NO₃^--N/L, MN). High-nitrate stress under 7.0 g NO₃^--N/L (SHN) caused an increased light energy dissipation while decreased the density of photosystem II active reaction center, which partially protect the cells from photodamage and contributed to their acclimation to SHN. The algae also enhanced amino acid/fatty acid proportions essential for maintaining intracellular redox states to cope with the stress caused by LN or SHN. HN and SHN was in favor of protein accumulation and maintenance with enhanced proportion of essential amino acids, which entitled the algal biomass to be of high quality for animal feed applied in livestock graziery and aquaculture. LN facilitated productive starch and lipid accumulation with good quality for biofuels production. The nitrate removal rate and biomass productivity exceeded most of the microalgae reported in literature under similar conditions, which highlighted Tetraselmis subcordiformis as a potent strain for flexible nitrate-rich wastewater remediation coupled with fast CO₂ bio-mitigation and high-quality biomass production for sustainable algal biorefinery.

Removal of platinum (IV) from aqueous solutions with yeast-functionalised bentonite

There is a need for cheap but, efficient methods for the removal of precious metals from wastewaters, which are normally lost during mineral processing. Moreover, the disposal of yeast waste from brewing has been a problem in many parts of the world. In this study, the removal of Pt(IV) from aqueous solutions using the readily available bentonite clay functionalised with spent yeast from brewing was investigated. The maximum adsorption capacity of Pt(IV) with 100 mg yeast-functionalised bentonite at pH 2 within 90 min was 255 μg g^-1 (98.5% efficiency) but, decreased as pH increased. The adsorption capacity of Pt(IV) was insignificantly (p > 0.05) affected by the presence of competing ions (Fe(III), Ca(II), Mg(II), K(I), Co(II)^, Ni(II), Hf(IV), Zn(II) and other platinum group metals (PGMs)). Moreover, most of these metals were significantly adsorbed along with Pt(IV). The indicative cost-benefit analysis showed that 1 kg of the yeast-functionalised bentonite can remove ∼700 g Pt(IV) in which a profit of more than USD20000 can be made. The bentonite functionalised with spent yeast from brewing has a potential to recover lost PGMs in wastewater. Since, this is a cheap process, the mining and other industries can make much profit from such recoveries.

Effects of Fermentation by Yeast and Amylolytic Lactic Acid Bacteria on Grain Sorghum Protein Content and Digestibility

Despite many advantages to its cultivation, grain sorghum is an underutilized crop because of low nutrient availability, particularly protein digestibility, due to antinutritional compounds in the grain and by moist-heat cooking. Some of these concerns can be mitigated by how the grain is processed. Fermentation is one processing method that can improve digestibility and at the same time concentrate protein in a substrate. In this experiment, grain sorghum was subjected to different treatments and fermented with baker’s yeast (Saccharomyces cerevisiae) and an amylolytic species, Lipomyces kononenkoae, to improve and increase protein content. The effects of pasteurization or sterilization of the substrate, nitrogen supplementation, amyloglucosidase addition, and coculture with Lactobacillus amylovorus were examined. After fermentation, baker’s yeast samples treated with enzyme increased in crude protein, from 9% in unfermented grain to approximately 27% after treatment. Nitrogen supplementation accelerated protein enrichment and was a significant factor at 24 hours of fermentation. Both types of yeast increased pepsin digestibility of sorghum protein compared to thermally processed control samples. The ratio of phytate to protein was reduced by both yeast species. L. kononenkoae reduced phytates in the substrate but did not enrich protein content. The lactic coculture had no significant effect on measured responses.

Nitrate concentration-shift cultivation to enhance protein content of heterotrophic microalga Chlorella vulgaris: Over-compensation strategy

Protein production from microalgae requires both high cell density during cultivation and high protein content in cells. Heterotrophic microalgae can achieve high cell density, and yet are confronted with the problem of low protein content. Based on over-compensation strategy, a new concentration-shift method was proposed to cultivate heterotrophic Chlorella vulgaris, aiming to increase protein content. With a prior starvation period, microalgae utilized more nitrate and accumulated more proteins compared to one-stage cultivation. Considering the convenience of operation, nitrate-added culture was adopted for producing heterotrophic microalgae, rather than sterile centrifugal culture. Operating parameters including nitrate concentration in N-deficient medium, N-starved time and nitrate concentration in N-rich medium were optimized, which were 0.18gl^-1, 38h and 2.45gl^-1, respectively. Under the optimized conditions, protein content in heterotrophic Chlorella reached 44.3%. Furthermore, the heterotrophic microalga was suggested to be a potential single-cell protein source according to the amino acid composition.

Application of anhydrobiosis and dehydration of yeasts for non-conventional biotechnological goals

Dehydration of yeast cells causes them to enter a state of anhydrobiosis in which their metabolism is temporarily and reversibly suspended. This unique state among organisms is currently used in the production of active dry yeasts, mainly used in baking and winemaking. In recent decades non-conventional applications of yeast dehydration have been proposed for various modern biotechnologies. This mini-review briefly summarises current information on the application of dry yeasts in traditional and innovative fields. It has been shown that dry yeast preparations can be used for the efficient protection, purification and bioremediation of the environment from heavy metals. The high sorption activity of dehydrated yeasts can be used as an interesting tool in winemaking due to their effects on quality and taste. Dry yeasts are also used in agricultural animal feed. Another interesting application of yeast dehydration is as an additional stage in new methods for the stable immobilisation of microorganisms, especially in cases when biotechnologically important strains have no affinity with the carrier. Such immobilisation methods also provide a new approach for the successful conservation of yeast strains that are very sensitive to dehydration. In addition, the application of dehydration procedures opens up new possibilities for the use of yeast as a model system. Separate sections of this review also discuss possible uses of dry yeasts in biocontrol, bioprotection and biotransformations, in analytical methods as well as in some other areas.

Chemical composition and biological value of proteins of the yeast Yarrowia lipolytica growing on industrial glycerol

Michalik, B., Biel, W., Lubowicki, R. and Jacyno, E. 2014. Chemical composition and biological value of proteins of the yeast Yarrowia lipolytica growing on industrial glycerol. Can. J. Anim. Sci. 94: 99–104. The aim of this study was to evaluate the chemical composition and biological value of proteins from the yeast, Yarrowia lipolytica, after cultivation on glycerol, a waste product obtained in the production of biofuel from rapeseed. In the tested material we determined moisture, crude protein, ether extract, nitrogen-free extract (NFE), ash, calcium, phosphorus, cadmium, mercury, arsenic, amino acids and fatty acids. The biological value of Y. lipolytica and Saccharomyces cerevisiae proteins was determined with laboratory rats by two methods: the growth method (protein efficiency ratio standardized for casein, PERstand; net protein retention, NPR) and the Thomas–Mitchell method (biological value, BV; true digestibility, TD). The protein content of Y. lipolytica [467 g kg−1 dry matter (DM)] was similar to that of S. cerevisiae (479 g kg−1 DM). Of particular interest was the almost 30-times higher crude fat content in Y. lipolytica (200 g kg−1 DM) than in S. cerevisiae (6.7 g kg−1 DM). Yarrowica lipolytica cells accumulated substantial amount of fat in which more than 90% of fatty acids were unsaturated fatty acids with a considerable share of polyunsaturated fatty acids (34%). The low share of sulfur amino acid of Y. lipolytica (2.05 g 16g−1 N) and S. cerevisiae (2.32 g 16g−1 N) limited the nutritional value of the protein of the studied yeast. The biological value of proteins as assessed by the growth method (PER, NPR) did not differ between the two yeast species. Finally, Y. lipolytica was a rich source of highly digestible ether extract (over 57%).