Accumulation and Release of Metal Ions by Brewer's Yeast During Successive Fermentations

The Use of Non-Saccharomyces Yeast and Enzymes in Beer Production

The objective of this paper was to test the potential of selected non-Saccharomyces strains for beer production, by using Saccharomyces cerevisiae as a control sample. For some of variants brewing enzymes were added to wort to increase the content of fermentable sugars. The non-Saccharomyces yeasts differed in the fermentation process rate. The basic beer physiochemical parameters were assessed, including: alcohol content, extract, free amino nitrogen, sugars, acidity, colour, and the profile of volatile compounds and metal ions. The use of enzymes caused an increase in alcohol and fusel alcohols concentration in beers obtained. Total acidity, free amine nitrogen content, colour and sugar content indicated that the tested non-Saccharomyces yeast allowed obtaining beers with the proper analytical parameters.

Chemical Composition of Sour Beer Resulting from Supplementation the Fermentation Medium with Magnesium and Zinc Ions

The bioavailability of minerals, such as zinc and magnesium, has a significant impact on the fermentation process. These metal ions are known to influence the growth and metabolic activity of yeast, but there are few reports on their effects on lactic acid bacteria (LAB) metabolism during sour brewing. This study aimed to evaluate the influence of magnesium and zinc ions on the metabolism of Lactobacillus brevis WLP672 during the fermentation of brewers’ wort. We carried out lactic acid fermentations using wort with different mineral compositions: without supplementation; supplemented with magnesium at 60 mg/L and 120 mg/L; and supplemented with zinc at 0.4 mg/L and 2 mg/L. The concentration of organic acids, pH of the wort and carbohydrate use was determined during fermentation, while aroma compounds, real extract and ethanol were measured after the mixed fermentation. The addition of magnesium ions resulted in the pH of the fermenting wort decreasing more quickly, an increase in the level of L-lactic acid (after 48 h of fermentation) and increased concentrations of some volatile compounds. While zinc supplementation had a negative impact on the L. brevis strain, resulting in a decrease in the L-lactic acid content and a higher pH in the beer. We conclude that zinc supplementation is not recommended in sour beer production using L. brevis WLP672.

Effect of exogenous metal ions and mechanical stress on rice processed in thermal-solid enzymatic reaction system related to further alcoholic fermentation efficiency

Metal-rich thermal-solid enzymatic processing of rice combined with yeast fermentation was investigated. 8 Metal ions were exogenously supplied at 0.05, 0.5 and 5mmol/100g (MG) rice prior to static high pressure enzymatic cooking (HPEC) and dynamic enzymatic extrusion cooking (EEC). Treated rice and its fermentation efficiency (FE) were characterized by rapid viscosity analyzer (RVA), UV-Vis, FT-IR and atomic absorption spectrophotometer (AAS). The optimum pH range of enzyme in solid system (>4.9) was broader than in a liquid system (>5.5). Cations decreased enzymatic activity in HPEC probably due to metal-induced aggregation of rice matrix with reduced reacting area as well as strengthened structure of starch/polysaccharides modified by metals. While using the EEC with mechanical mixing/shearing, relative activity was activated to 110 and 120% by Mg²⁺ (0.05-0.5MG) and Ca²⁺ (0.05-5MG), respectively. Furthermore, the effectiveness of residual ions to promote further FE was found to follow the order: Ca²⁺>K⁺>Zn²⁺>Mg²⁺>Mn²⁺>Na⁺≈Control>Fe²⁺>Cu²⁺, individually.

Microencapsulation of Baker’s Yeast in Gellan Gum Beads Used in Repeated Cycles of Glucose Fermentation

The purpose of this work is to prepare ionically cross-linked (with CaCl2) gellan particles with immobilized yeast cells for their use in repeated fermentation cycles of glucose. The study investigates the influence of ionic cross-linker concentration on the stability and physical properties of the particles obtained before extrusion and during time in the coagulation bath (the cross-linker solution with different CaCl2 concentrations). It was found that by increasing the amount of the cross-linker the degree of cross-linking in the spherical gellan matrix increases, having a direct influence on the particle morphology and swelling degree in water. These characteristics were found to be very important for diffusion of substrate, that is, the glucose, into the yeast immobilized cells and for the biocatalytic activity of the yeast immobilized cells in gellan particles. These results highlight the potential of these bioreactors to be used in repeated fermentation cycles (minimum 10) without reducing their biocatalytic activity and maintaining their productivity at similar parameters to those obtained in the free yeast fermentation. Encapsulation of Saccharomyces cerevisiae into the gellan gum beads plays a role in the effective application of immobilized yeast for the fermentation process.

The influence of serial repitching of Saccharomyces pastorianus on its karyotype and protein profile during the fermentation of gluten-free buckwheat and quinoa wort

Gluten-free beer-like beverages from malted buckwheat and quinoa are somehow close to their commercial production, but rather high expenses are expected due to the relatively high price of grain, some technological adaptations of process and the need for external enzyme supplementation during mashing. One of the common and efficient cost reduction measures in the industrial scale is serial repitching of the yeast biomass, which has not been studied for the buckwheat and quinoa wort fermentation before. In that manner we have monitored possible changes in yeast's proteins and chromosomal DNA during eleven serial repitchings of the yeast Saccharomyces pastorianus strain TUM 34/70 for fermentation of the barley, buckwheat and quinoa wort. Karyotypes showed changes in regard to the raw materials used and many responsible candidate proteins are suggested which could cause these differences. Different relative expressions of some protein bands were also linked to the proteins involved in yeast stress response and proteins involved in fermentation performance. Results suggest that serial repitching of the strain TUM 34/70 seems suitable for the production of gluten-free beer-like beverages from buckwheat and quinoa.