Brewer's Yeast Research Articles

Never Change a Brewing Yeast? Why Not, There Are Plenty to Choose From.

Fermented foods and particularly beer have accompanied the development of human civilization for thousands of years. Saccharomyces cerevisiae, the dominant yeast in the production of alcoholic beverages, probably co-evolved with human activity. Considering that alcoholic fermentations emerged worldwide, the number of strains used in beer production nowadays is surprisingly low. Thus, the genetic diversity is often limited. This is among others related to the switch from a household brewing style to a more artisan brewing regime during the sixteenth century and latterly the development of single yeast isolation techniques at the Carlsberg Research Laboratory in 1883, resulting in process optimizations in the brewing industry. However, due to fierce competition within the beer market and the increasing demand for novel beer styles, diversification is becoming increasingly important. Moreover, the emergence of craft brewing has influenced big breweries to rediscover yeast as a significant contributor to a beer’s aroma profile and realize that there is still room for innovation in the fermentation process. Here, we aim at giving a brief overview on how currently used S. cerevisiae brewing yeasts emerged and comment on the rationale behind replacing them with novel strains. We will present potential sources of yeasts that have not only been used in beer brewing before, including natural sources and sources linked to human activity but also an overlooked source, such as yeast culture collections. We will briefly comment on common yeast isolation techniques and finally touch on additional challenges for the brewing industry in replacing their current brewer’s yeasts.

Angiotensin-converting enzyme inhibitory and antibacterial activities of low molecular weight peptides derived from spent brewer’s yeast

According to the World Health Organization (WHO), hypertension is one of the most common chronic diseases. Cardiovascular disease causes 17.5 million deaths each year, in which hypertension is a direct cause to the death of up to 40%. This hypertension is caused by angiotensin-converting enzyme (ACE). ACE inhibitors consider as an effective therapy in hypertension treatment.Many ACE inhibitors are synthesized by chemical pathways to control high blood pressure, however, these drugs often cause side effects. Therefore, in the last two decades, many authors have been interested in studying and producing a variety of ACE inhibitory peptides, which are naturally derived (plants, animals, and microorganisms) that help reduces blood pressure and less cause side effects. On the other hand, biologically active peptides that are resistant to pathogenic bacteria are also of special interest. In this study, we refer to the limited hydrolysis of spent brewer's yeast by proteases to collect peptides with a molecular size of ≤ 10, 5 and 3 kDa. Peptide fraction with molecular size ≤ 10 kDa have ACE inhibitory activity. The results showed that smaller peptide fractions had higher ACE inhibitory activity. At concentration of 30 µg/mL, inhibitory activitiy of peptides with molecular sizes ≤ 10, 5, 3 kDa was 16.3, 27.7 and 32.7%, respectively, and the best IC50 was 48,85 µg/ml. The lowest peptide concentration for completely inhibition bacteria after 24 h of incubation was 30 mg/mL (V. cholerae), 35 mg/mL (E. coli) and 50 mg/mL (S. typhi).

Applications of Wild Isolates of Saccharomyces Yeast for Industrial Fermentation: The Gut of Social Insects as Niche for Yeast Hybrids' Production.

In the industry of fermented food and beverages, yeast cultures are often selected and standardized in order to ensure a better control of fermentation and a more stable product over time. Several studies have shown that the organoleptic characteristics of fermented products reflect geographic variations of the microbial community composition. Despite investigations of the worldwide distribution and genetic diversity of Saccharomyces cerevisiae, it is still unclear how and to what extent human intervention has shaped the brewer’s yeast population structure. The genotypic and phenotypic characterization of environmental yeast populations and their potential application in the fermentative processes can significantly enrich the industrial fermentation products. Social insects have proven to be closely associated to the yeasts ecology. The relationships between yeasts and insects represent a fundamental aspect for understanding the ecological and evolutionary forces shaping their adaptation to different niches. Studies on phylogenetic relationships of S. cerevisiae populations showed genetic differences among strains isolated from gut and non-gut environments (i.e., natural sources and fermentation). Recent evidences showed that insect’s gut is a reservoir and an evolutionary niche for Saccharomyces, contributing to its survival and evolution, favoring its dispersion, mating and improving the inter-specific hybrids production during hibernation. Here, we discuss the potential use of social insects for production of a wide range of hybrid yeasts from environmental Saccharomyces isolates suitable for industrial and biotechnological applications.

Spent brewer’s yeast proteins and cell debris as innovative emulsifiers and carrier materials for edible oil microencapsulation

Spent brewer's yeast is a by-product rich in proteins, polysaccharides, and fibres. In addition to being nutritive, this material is available in large amounts and can be considered a cheap and sustainable alternative as a carrier material for microencapsulation. The objective of this work was to use the protein hydrolysate of spent brewer's yeast as an emulsifying agent and carrier material for the microencapsulation of sunflower oil by spray drying. A Central Composite Rotational Design (CCRD) was used to determine emulsion's optimal conditions: protein concentration (1.5–6.0%), oil concentration (10–25%) and pH (5.5–7.5) regarding Turbiscan Stability Index (TSI), droplet size and zeta-potential. The validated optimised emulsion containing 4.4% protein and 17.5% oil was produced at a pH value of 6.5. This formulation had a mean droplet diameter of 6.6 ± 0.3 μm, a ζ- potential of −29.0 ± 1.7 mV and a TSI (24 h) of 0.9 ± 0.2%. This emulsion was spray-dried with and without maltodextrin (M20) at 150 and 180 °C. The highest encapsulation efficiency was 55%, achieved at 180 °C with M20, 87% higher than dry powder at the same temperature, but without M20. The water activity of powders without M20 were 58% and 14% lower (0.20 and 0.17) than powders with M20 dried at 150 and 180 °C, (0.13 and 0.15) respectively. The mean particle size was close to 50 μm. The powder without M20, dried at 150 °C, showed the highest stability against oxidation (45 °C for 4 weeks), with a peroxide index of 311 meq of peroxide per kg of oil. Powder properties were evaluated by SEM and FT-IR. Kinetically stable emulsions and particles were produced from spent brewer's yeast ingredients, which were able to act as both carrier materials and emulsifiers, providing a more noble use for an important brewing residue.

Evaluation of genetic diversity and development of core collections of industrial brewing yeast using ISSR markers.

Germplasm of industrial brewing yeast of the worldwide have a richer diversity, and various successes in improving the performance of brewing yeasts. However, they are limited in that they have relatively low odds of combining desirable traits in a correct manner. To improve germplasm resource preservation, management, and utilization efficiency. In this study, the genetic diversity of 35 industrial brewing yeasts were analyzed based upon inter simple sequence repeat (ISSR) markers, in which 151 out of 167 SSR loci (90.42%) were polymorphic between two or more strains. Three preliminary core collections were established using ISSR data, and based on three different strategies as follows: an advanced maximization (M) strategy, an allele preferred sampling (A) strategy, and a random sampling (R) strategy. Comparison of genetic parameters, including polymorphic information content, Nei's genetic diversity (H), effective allele number, observed allele number, Shannon's index (I), and principal coordinate analyses, confirmed that all the core collections accurately recapitulated the diversity of the initial germplasm. Considering the loci retention ratio and trait coverage efficiency, Core1 was considered the best core collection.

Species richness maintains mutualisms

Ecology Mutualistic communities of species that benefit each other are ubiquitous in ecosystems and are important for ecosystem functioning. However, the relationship between the persistence of mutualisms and species richness has remained unclear. Vidal et al. used a synthetic mutualism in brewer's yeast to experimentally test whether species richness buffers mutualistic communities against exploitation by species that do not provide benefits in return. They showed that richer mutualist communities survive exploitation more often than pairwise mutualisms and that higher species richness and functional redundancy allow mutualist communities to persist in the presence of exploiters. These results provide experimental support for the hypothesis that species richness is necessary for the function and maintenance of mutualistic communities. Science , this issue p. [346][1] [1]: /lookup/doi/10.1126/science.abb6703

Use of probiotic strains to produce beers by axenic or semi-separated co-culture system

This study evaluated the production of beers to serve as matrices for probiotic delivery and designed suitable fermentation systems. Two types of beers (wheat and sour) were produced by fermentation in an axenic (Saccharomyces cerevisiae var boulardii 17) or semi-separated co-culture system (Lacticaseibacillus paracasei DTA-81 and Saccharomyces cerevisiae S-04). Firstly, trial was carried out to investigate microbial interactions between L. paracasei DTA-81 and Saccharomyces (n = 4) and to determine the best cultivation system to produce sour beer. S. boulardii17 potential to ferment the beer wort was similar to those observed for other brewer yeasts, enabling potentially probiotic wheat beer production. L. paracaseiDTA-81 was able to ferment the beer wort to produce potentially probiotic sour beer. However, the cultivation system should be carefully designed to protect the lacticaseibacilli from stressful metabolites produced during yeast fermentation, especially alcohol. Thus, data obtained herein showed that the co-culture system should be avoided for potentially probiotic sour beer production, in order to prevent competitive interaction between lacticaseibacilli and yeast. Otherwise, the semi-separated co-culture system resulted in a symbiotic commensal interaction, without interfering on L. paracasei DTA-81 growth and survivability. Therefore, wheat and sour beers can be highlighted as useful matrices to deliver probiotic strains.

Modelling of palladium(II) adsorption onto amine-functionalised zeolite using a generalised surface complexation approach

The many uses of palladium in medicine, catalysts and other industries make it a very important precious element. Many industries using palladium discharge process wastewaters that may release elevated concentrations of palladium into the environment. This study focused on the recovery of palladium from aqueous solutions by zeolite functionalised with spent brewer's yeast. Batch experimental results were used to calibrate a generalised surface complexation model based on coupling parameter estimation (PEST) to the PHREEQC geochemical modelling code. PHREEQC is an acronym which stands for pH, redox, equilibrium and C programming language. Calibration was based on the determination of sorption constants for the reactions of palladium with the adsorbent. The generalised amine surface groups (derived from yeast), the moles of adsorption sites and surface area were specified. The recovery of palladium was assessed as a function of solution pH, adsorbent dosage and initial concentration of palladium in the presence of other cations and anions at different concentrations. The highest recovery of palladium (>97%) was observed at pH 2 and 10 g L−1 adsorbent dosage which, decreased with increasing solution pH. The amount of palladium removed increased in the presence of competing ions and anions. There was no significant difference (p > 0.05) between the modelled and measured data, which indicated that PHREEQC modelling code coupled with PEST can accurately determine the recovery of palladium using amine-based adsorbents when all the required information is specified. This is very useful in instances where limited experimental data is available for non-conventional and novel surfaces to make accurate predictions of sorption processes involving them.

Phosphate-solubilizing Pseudomonas sp., and Serratia sp., co-culture for Allium cepa L. growth promotion

Different genus of bacteria has been reported with the capacity to solubilize phosphorus from phosphate rock (PR). Pseudomonas sp., (A18) and Serratia sp., (C7) isolated from soils at the “Departamento de Boyacá” Colombia, where Allium cepa is cultivated. Bacteria were cultured in MT11B media and evaluated as a bio-fertilizer for A. cepa germination and growth during two months at greenhouse scale. Pseudomonas sp., and Serratia sp., cultured at 30 °C, 48 h in SMRS1 agar modified with PR, (as an inorganic source of phosphorus), presented a phosphate solubilization index (SI) of 2.1 ± 0.2 and 2.0 ± 0.3 mm, respectively. During interaction assays no inhibition halos were observed, demonstrating there was no antagonism between them. In MT11B media growth curve (12 h) demonstrated that co-culture can grow in the presence of PR and glucose concentrations 7.5-fold, lower than in SMRS1 media and brewer's yeast hydrolysate; producing phosphatase enzymes with a volumetric activity of 1.3 ± 0.03 PU at 6 h of culture and 0.8 ± 0.04 PU at 12 h. Moreover, co-culture released soluble phosphorus at a rate of 58.1 ± 0.28 mg L−1 at 8 h and 88.1 ± 0.32 mg L−1 at 12 h. After five days of evaluation it was observed that germination percentage was greater than 90 % of total evaluated seeds, when placing them in contact with the co-culture in a concentration of 1 × 108 CFU mL−1. Furthermore, it was demonstrated that co-culture application (10 mL per experimental unit to complete 160 mL in two months) at 8.0 Log10 CFU mL−1 twice a week for two months increased A. cepa total dry weight (69 ± 13 mg) compared with total dry weight (38 ± 5.0 mg) obtained with the control with water.

Technological features of Saccharomyces cerevisiae var. boulardii for potential probiotic wheat beer development

A comparative controlled study was carried out to evaluate the performance of Saccharomyces cerevisiae var. boulardii to act as brewer's yeast for potential probiotic beer production. The yeast performance on the beer wort (cell growth, sugar consumption and products production) was compared with the conventional top-fermentation Saccharomyces cerevisiae. To improve the yeast metabolism, changes were made in the malt concentration of the wort recipe and in the ramp mash temperature profile, emphasizing β-amylase activity to provide high glucose concentration in the wort. Next, metabolism close to conventional brewer's yeast was achieved. Saccharomyces cerevisiae var. boulardii survivability in the beer and after in vitro gastrointestinal transit was assessed as the indicative of potential probiotic properties in the beer. The yeast population did not decrease dramatically over the storage period, withstanding alive above the minimal dose prescribed to confer health benefit to the host. The present work shows an alternative method to produce potential probiotic wheat beer. However, Saccharomyces cerevisiae var. boulardii metabolism is still not completely understood, especially the metabolism on the wort sugar and the optimized conditions of the wort recipe and ramp mash temperature profile.

The effect of various protein sources in goose diets on meat quality, fatty acid composition, and cholesterol and collagen content in breast muscles

Goose meat is characterized by good quality and a good fatty acid composition. Geese do not need many compounds in their feed to ensure suitable growth. The main source of protein in most feed is soybean meal (SBM). New cultivars of yellow lupin with fewer antinutrients could be a substitute for soybean. The study's aim was to compare the quality of the carcass and meat, as well as the fatty acid composition and the collagen and cholesterol content in the breast muscles from geese fed a diet based on yellow lupin as an replacement for soybean meal. In the study, geese were divided into 2 study groups. The first was a control group (Group 1), fed a feed based on SBM; the second one was an experimental group (Group 2), fed a feed based on yellow lupin “Mister”, potato protein, and brewer's yeast. The rearing period was divided into 3 stages, and the last stage was oat fattening. Each group (105 birds in each group) was divided into 5 replications with 21 birds. After 16 wk of rearing, 10 geese from each group were slaughtered. The carcasses were analyzed for physicochemical traits (dissection, color, water-holding capacity, and chemical composition of the breast and leg muscles, as well as pH level, drip loss, and fatty acid profile of the breast muscles). The drip loss from the breast muscles was higher (P < 0.05) and the water-holding capacity of the leg muscles lower (P < 0.05) in Group 1 than in Group 2. Group 1 also displayed a higher content of protein and water in breast and leg muscles (P < 0.05) but lower fat content than that of Group 2 (P < 0.05). The linoleic acid content of the breast muscles was higher in Group 2 (P < 0.05), whereas the other fatty acid levels were comparable between the groups. The total content of polyunsaturated fatty acid (PUFA) (n-6 and n-3) and the PUFA/ saturated fatty acid ratio was higher in Group 2 (P < 0.05). Moreover, the thrombogenic index was lower (P < 0.05) in the geese fed a lupin-diet. Overall, the yellow lupin–based feed had beneficial effects on the goose meat's traits, and it can be used as a high-protein compound in diets for geese. It is also possible to produce traditional geese fattened by oats.

Innovative Rough Beer Conditioning Process Free from Diatomaceous Earth and Polyvinylpolypyrrolidone.

In large-sized breweries, rough beer clarification is still carried out using Kieselguhr filters notwithstanding their environmental and safety implications. The main aim of this work was to test an innovative rough beer clarification and stabilization process involving enzymatic treating with Brewers Clarex®, centrifuging, rough filtering across 1.4-μm ceramic hollow-fiber membrane at 30 °C, and fine filtering through 0.45-μm cartridge filter. When feeding an enzymatically-pretreated and centrifuged rough beer with permanent haze (HP) of 2 or 14 European Brewery Convention unit (EBC-U), its primary clarification under periodic CO2 backflushing yielded a permeate with turbidity of 1.0–1.5 EBC-U at a high permeation flux (2.173 ± 51 or 593 ± 100 L m−2 h−1), much greater than that typical of powder filters. The final beer was brilliant (HP = 0.57 ± 0.08 EBC-U) with almost the same colloidal stability of the industrial control and an overall log reduction value (~5.0 for the selected beer spoilage bacterium or 7.6 for the brewing yeast) in line with the microbial effectiveness of current sterilizing membranes. It was perceived as significantly different in flavor and body from the industrial control at a probability level of 10% by a triangle sensory test, as more likely related to the several lab-scale beer-racking steps used than to the novel process itself.

Novel microencapsulated yeast for the primary fermentation of green beer: kinetic behavior, volatiles and sensory profile

The development of innovative and more cost-effective approaches of making beer throughout continuous fermentation process remains a challenging problem, which is worthy of serious exploration. The current work focuses on the application of a commercial brewing yeast (S. cerevisiae Nottingham Ale), entrapped into chitosan-calcium alginate double layer microcapsules, for the production of a Pale Ale beer. During the primary alcoholic fermentation, the consumption rate of fermentable brewing sugars and dissolved O2, estimated by the Gompertz equation, was halved in the beer obtained by encapsulated yeast in comparison with the free cell. The physical–chemical parameters of beer (i.e. pH, alcohol content, color and bitterness) were not remarkably affected by the different yeast-inoculating form. However, the volatile profiles identified by means of HS-SPME-GC–MS analysis, significantly differed in terms of terpenes, esters and alcohols content, thus proving that the yeast-inoculating form may typify the odor and flavor descriptors of the green beer.

Sourdough cultures as reservoirs of maltose-negative yeasts for low-alcohol beer brewing

De novo sourdough cultures were here assessed for their potential as sources of yeast strains for low-alcohol beer brewing. NGS analysis revealed an abundance of ascomycete yeasts, with some influence of grain type on fungal community composition. Ten different ascomycete yeast species were isolated from different sourdough types (including wheat, rye, and barley) and seven of these were screened for a number of brewing-relevant phenotypes. All seven were maltose-negative and produced less than 1% (v/v) alcohol from a 12 °Plato wort in initial fermentation trials. Strains were further screened for their bioflavouring potential (production of volatile aromas and phenolic notes, reduction of wort aldehydes), stress tolerance (temperature extremes, osmotic stress and ethanol tolerance) and flocculence. Based on these criteria, two species (Kazachstania servazzii and Pichia fermentans) were selected for 10 L-scale fermentation trials and sensory analysis of beers. The latter species was considered particularly suitable for production of low-alcohol wheat beers due to its production of the spice/clove aroma 4-vinylguaiacol, while the former showed potential for lager-style beers due to its clean flavour profile and tolerance to low temperature conditions.

Changes in carbon pools and enzyme activities in soil amended with pig slurry derived from different feeding diets and filtration process

Monitoring soil carbon content and pools and associated enzyme activities has become an important area of research in terms of the carbon cycle in agricultural lands in order to infer factors regulating soil carbon sequestration. Pig slurry (PS) is considered as a source of organic matter and nutrients for crop production. In recent years, because of the cost of conventional feed applications, manufacturers have preferred liquid feeding diets with decreases of 10–25% in production costs. Furthermore, physical and chemical filtration of PS by new techniques may prevent soil degradation and reduce the negative effects of PS, such as high salt, pathogen, and heavy metal contents. This research aimed to assess the effect of the application of raw pig slurry (R) and treated pig slurry (T) (derived from physical and chemical separation processes) from liquid (L) and solid (S) feeding diets on different soil organic carbon pools and enzyme activities in a sandy loam soil under a rainfed barley cropping system for two years. The solid diet consisted of maize/soya bean, tubers and roots, and supplementary vitamins and minerals. The liquid diet consisted of dairy products such as fresh whey, concentrated cheese or yogurt, skim milk powder, and beer by-products such as brewer's yeast. As a general pattern, the addition of the different types of PS (R or T) had no significant effect on most soil properties, except for microbial biomass C (Cmic), which increased with R. However, the type of diet did have a significant effect on most properties, both for R or T slurries, suggesting that this is more of a determinant factor in explaining changes in soil than the type of pig slurry. Solid diet favors the significant increase of soil organic carbon and arylesterase activity, suggesting higher stabilization of the organic compounds provided by the PS. However, the liquid diet contributed to increasing soluble C and Cmic, suggesting higher availability of nutrients and C sources. Hence, the use of treated pig slurry has no detrimental effect on organic carbon dynamics compared to raw pig slurry and can be suggested as an alternative to reduce the environmental impact, prevent soil pollution, and ensure sustainability.

Increasing the level of 4-vinylguaiacol in top-fermented wheat beer by secretory expression of ferulic acid decarboxylase from Bacillus pumilus in brewer's yeast.

The objective is to explore the effects of enhancing the activity of yeast ferulic acid decarboxylase (FDC1) on the level of 4-vinylguaiacol (4-VG) and the consumption of its precursor ferulic acid (FA) in top-fermented wheat beer. Expression of Bacillus pumilus FDC1 in brewer's yeast showed a better effect on the FDC1 activity than overexpression of the endogenous enzyme. The 4-VG content was increased by 34%, and the consumption time of FA was shortened from 48 to 12h. Since the intracellular accumulation of the FDC1 substrate did not increase over time, to reduce the FA transport burden on cells and shorten the decarboxylation time, B. pumilus FDC1 was further secreted extracellularly. The resulted strain showed a 65% increase in 4-VG content in the FA-containing medium, and produced about 3mg L-1 4-VG in the top-fermented wheat beer, increasing by 61% than control. However, further increasing the secretory expression level of FDC1 only accelerated FA consumption. These results suggested that appropriate secretion of bacterial FDC1 into wort could be used as a potential alternative strategy to increase the level of 4-VG in top-fermented wheat beer.

Caracterização físico-química de cervejas artesanais de atemoia (Annona cherimoia Mill. x Anonna squamosa L) e de sapoti (Manilkara sapota L.)

O objetivo deste estudo foi produzir cervejas artesanais com adição das frutas tropicais atemoia e sapoti em sua composição. Para elaboração dos mostos cervejeiros as matérias primas utilizadas foram malte tipo Pilsen e levedura cervejeira tipo Lager. A polpa de atemoia foi adicionada no mosto cervejeiro na concentração de 8,5% (p/v) e a polpa de sapoti na concentração de 17% (p/v). O processo de fermentação alcoólica ocorreu a 15ºC por 15 dias e o processo de maturação das cervejas verdes ocorreu a 5ºC por 15 dias. Após engarrafamento e carbonatação na própria garrafa realizaram-se as análises físico-químicas das três cervejas produzidas: cerveja sem adição de frutas (cerveja Pilsen), cerveja com polpa de atemoia (cerveja de atemoia) e cerveja com polpa de sapoti (cerveja de sapoti). A adição das polpas de frutas aumentou o teor alcoólico das cervejas de atemoia (5,0ºGL) e de sapoti (5,0ºGL) em relação à cerveja sem frutas (4,6ºGL). Também foi observado um aumento do teor de compostos fenólicos totais das cervejas de atemoia (111,29 mg/100 mL) e de sapoti (77,61 mg/100 mL) em relação à cerveja sem frutas (64,00 mg/100 mL). Outro resultado observado foi o aumento da atividade antioxidante das cervejas de atemoia e sapoti em relação à cerveja sem frutas. A utilização das polpas de atemoia e sapoti mostraram-se tecnologicamente viáveis na produção das cervejas artesanais. As cervejas com frutas valorizam o uso de frutas tropicais e despertam a atenção dos consumidores de cervejas artesanais.

Screening of thermosensitive autolytic mutant brewer's yeast and transcriptomic analysis of heat stress response.

Brewer's yeast has been widely used in the food industry, and the autolysates thereof are increasingly being studied for their valuable nutritional compositions. Yeast autolysis is most affected by medium composition and temperature. In this study, a thermosensitive autolytic brewer's yeast P-510 was obtained with atmospheric and room temperature plasma mutagenesis plus 5-bromo-chloro-3-indolyl phosphate screening. The mutant rapidly autolyzed at 37 °C and the autolysates contained more active components and showed higher antioxidant activities compared with that of the parental strain, which indicated that the mutant's autolysates can potentially be used as functional food and nutritional ingredients. Transcriptomic analysis of the mutant and parental strains at 28 and 37 °C suggested that thermosensitive autolysis of P-510 was probably caused by mitochondrial disfunction, glycogen metabolic flux of glycolysis and pentose phosphate pathway disorder, as well as hexose transport inhibition. The results revealed the important role of mitochondrial metabolism and glycogen utilization regulation in heat stress response of yeast.

Spent brewer's yeast as a source of high added value molecules: a systematic review on its characteristics, processing and potential applications.

Development of new strategies to add-value to agro-industrial by-products are of environmental and economical importance. Innovative and low-cost sources of protein and bioactive peptides have been explored worldwide. Spent brewer's yeast (SBY) is the second most relevant by-product from the brewing industry, and despite its nutritional (about 50% protein, dry weight) and technological potential, it is still underused or needs to be disposed of. SBY cells need to be disrupted to release intracellular and cell wall proteins. This procedure has been performed using autolysis, glass bead milling, enzymatic hydrolysis and ultrasound processing. Enzymatic treatment is usually performed without prior purification and is a challenging process, which involves multiple factors, but has been successfully used as a strategy to add value to agro-industrial by-products. Scope and approach: in this review, we particularly focused on enzymatic hydrolysis as a strategy to promote SBY valorisation, illustrating the state-of-the-art processes used to produce protein extracts from this material as well as exploring fundamental concepts related to the particularities of yeast cell disruption and protein hydrolysis. Furthermore, innovative applications of value-added yeast by-products in food, biotechnological and pharmaceutical industries are presented and discussed. Key findings and conclusions: the discovery of valuable compounds found in spent yeasts as well as the development of new processing methodologies have been widening the possibilities of reuse and transformation of SBY as an ingredient and innovative matrix. Once released, yeast proteins and peptides may be applied as an innovative non-animal protein source or a functional and bioactive ingredient.

Characterization of the structural properties of mannoproteins isolated from selected yeast-based products upon the enzymatic treatment

Four types of yeast-based products (baker's yeast, brewer's yeast, Agrimos® and YCW-b) were subjected to Zymolyase® enzymatic treatment to isolate mannoproteins. In addition to their health promoting properties, yeast-based mannoproteins exhibit high emulsifying and stabilizing properties and play a crucial role in the vinification process. Upon purification, two mannoprotein populations were recovered including a high molecular weight (MP1, 36–620 kDa) composed of a variety of mannoproteins with different mannan to protein ratio (2.5–10), and a low molecular weight (MP2, 2.3–6.8 kDa) being identified as a monocomponent. α-(1,6) Mannanase treatment revealed the presence of α-(1,6) mannose linkages in the high MW MP1 population, but not in the low MW MP2 population. The isolated mannoproteins MP1 were mainly O-glycosylated. Mannoprotein structures were further characterized by 1D and 2D NMR, 7 anomeric carbons were determined in Agrimos® MP1, four of them have very similar chemical shifts than those of mannan standard. The proportion of α-(1,6) linked mannan was found to be the highest in the Agrimos® MP1. The thermal conformational changes of mannoproteins in both solid and liquid states were revealed by FTIR.