Effect of blueberries addition during beer maturation on yeast metabolism

In recent years, there has been a significant interest in beverages with increased biological value, such as beer with blueberries. In this study, blueberries were added at the beginning of maturation of lager beer with an initial extract of 12, 14 and 16ºP. The effect of blueberries addition on yeast metabolism was investigated as concentration of ethanol, higher alcohols, esters, aldehydes, and vicinal diketones in the final beer were measured and compared to control samples without blueberries. The results showed that blueberries affected positively ethanol formation only when wort with initial extract of 12°P was used and had no significant effect when wort with higher extract was used. In regard to secondary metabolites, blueberries addition led to a decrease in higher alcohols concentration and an increase in esters amounts. All the carbonyl compounds (aldehydes and vicinal diketones) were higher in beer with blueberries.

Effects of Obligate Heterofermentative Lactic Acid Bacteria Alone or in Combination on the Conservation of Sugarcane Silage

Our objective was to determine the effects of two strains of obligate heterofermentative bacteria, alone or in combination, on the fermentation profile, gas production kinetics, chemical composition, and aerobic stability of sugarcane silage. A plot of sugarcane was manually harvested, mechanically chopped and treated with: distilled water (5 mL kg–1; Control), Lentilactobacillus hilgardii CNCM I-4785 [3 × 105 colony-forming units (cfu) g–1; LH], Lentilactobacillus buchneri NCIMB 40788 (3 × 105 cfu g–1; LB), and LH+LB (1.5 × 105 cfu g–1 of each strain). Treated forages were packed into 1.96-L gas-tight silos (0.40 porosity) and stored at 25 ± 1.5°C for 70 days (4 replicates per treatment). All heterolactic inoculants were effective to increase acetic acid concentration and inhibit yeast metabolism, as treated silages had lower formation of ethanol, ethyl esters and gas during fermentation. Lower fungal development spared soluble carbohydrates, consequently resulting in silages with higher in vitro digestibility. Nevertheless, L. buchneri was the most effective strain to extend the aerobic stability of sugarcane silage (based on both temperature and pH rise). The use of L. buchneri alone or in combination with L. hilgardii, applied at 3 × 105 cfu g–1, is a feasible strategy to inhibit yeast metabolism and increase the nutritional quality of sugarcane silage.

Impact of the Whole Genome Duplication Event on PYK Activity and Effects of a PYK1 Mutation on Metabolism in S. cerevisiae

Background: Evolution of aerobic fermentation (crabtree effect) in yeast is associated with the whole genome duplication (WGD) event, suggesting that duplication of certain genes may have altered yeast metabolism. The pyruvate kinase (PYK) gene is associated with alterations in cell metabolism, and duplicated during the WGD, generating PYK1 and PYK2. Thus, the impact of WGD on PYK activity and role of PYK in yeast metabolism were explored.Methods: PYK activity in the presence or absence of fructose-1,6-bisphosphate (FBP) was compared between pre- and post-WGD yeast. Glucose consumption, ethanol production, and oxygen consumption were measured in wildtype yeast and yeast with a T403E point mutation, which alters FBP binding affinity.Results: FBP stimulated increased PYK activity in pre-WGD yeast and in the PYK1 isoforms of post-WGD yeast, but not in the PYK2 isoforms of post-WGD yeast. Compared to wildtype, T403E mutant yeast displayed reduced glucose consumption, reduced ethanol production, and increased mitochondrial metabolism.Conclusion: The WGD event impacted the sensitivity of PYK activity to FBP. Mutations in the FBP binding domain of PYK induce metabolic shifts that favor respiration and suppress fermentation.

BIOCONVERSION OF PLANT RAW MATERIALS INTO ETHANOL AND FEED PRODUCTS IN A CLOSED CYCLE

In the process of bioconversion of grain raw materials into ethyl alcohol and protein feedstuffs, liquid effluents are formed. There is a possibility of effluent using in the treatment process in a closed cycle. The article presents the results of studies on the use of stillage filtrate and acidic condensate and their effect on yeast metabolism.

Engineering of critical enzymes and pathways for improved triterpenoid biosynthesis in yeast

Triterpenoids represent a diverse group of phytochemicals, widely distributed in the plant kingdom with many biological activities. Recently, the heterologous production of triterpenoids in Saccharomyces cerevisiae has been successfully implemented by introducing various triterpenoids biosynthetic pathways. By engineering related enzymes as well as yeast metabolism, the yield of various triterpenoids is significantly improved from milligram-scale per liter to gram-scale level per liter. This achievement demonstrates that engineering of critical enzymes is considered as a potential strategy to overcome the main hurdles of translation of these potent natural products into industry. Here, we review strategies for designing enzymes to improve the yield of triterpenoids in S. cerevisiae, which is mainly separated into three aspects: 1. elevating the supply of the precursor—2,3-oxidosqualene, 2. optimizing triterpenoid-involved reactions, 3. lowering the competition of the native sterol pathway. And then we provide challenges and prospects on further enhancing the triterpenoid production in S. cerevisiae.