Utilization of brewer's yeast cells for the production of food-grade yeast extract. Part 1: Effects of different enzymatic treatments on solid and protein recovery and flavor characteristics

A Comparative Study of Composition and Soluble Polysaccharide Content between Brewer's Spent Yeast and Cultured Yeast Cells

Yeast, crucial in beer production, holds great potential owing to its ability to transform into a valuable by-product resource, known as brewer's spent yeast (BSY), with potentially beneficial physiological effects. This study aimed to compare the composition and soluble polysaccharide content of Brewer's spent yeast with those of cultured yeast strains, namely Saccharomyces cerevisiae (SC) and S. boulardii (SB), to facilitate the utilization of BSY as an alternative source of functional polysaccharides. BSY exhibited significantly higher carbohydrate content and lower crude protein content than SC and SB cells. The residues recovered through autolysis were 53.11%, 43.83%, and 44.99% for BSY, SC, and SB, respectively. Notably, the polysaccharide content of the BSY residue (641.90 μg/mg) was higher than that of SC (553.52 μg/mg) and SB (591.56 μg/mg). The yields of alkali-extracted water-soluble polysaccharides were 33.62%, 40.76%, and 42.97% for BSY, SC, and SB, respectively, with BSY comprising a comparable proportion of water-soluble saccharides made with SC and SB, including 49.31% mannan and 20.18% β-glucan. Furthermore, BSY demonstrated antioxidant activities, including superoxide dismutase (SOD), ABTS, and DPPH scavenging potential, suggesting its ability to mitigate oxidative stress. BSY also exhibited a significantly higher total phenolic compound content, indicating its potential to act as an effective functional food material.

Influence of yeast growth conditions and proteolytic enzymes on the amino acid profiles of yeast hydrolysates: Implications for taste and nutrition

This study investigated the effects of aerobic and anaerobic growth and proteolytic enzymes on the amino acid content of yeast hydrolysates in relation to taste and nutrition. Saccharomyces cerevisiae ATCC5574 was grown under fed-batch aerobic or batch anaerobic conditions. Intracellular glutamic acid (Glu) concentrations were 18-fold higher in aerobic yeast. Hydrolysis with papain and alkaline protease released more amino acids (AA) than simple autolysis or hydrolysis with bromelain, most significantly when applied to aerobic yeast (∼2-fold increase). Autolysates and bromelain hydrolysates from aerobic yeast had low levels of bitter and essential AAs, with high levels of umami Glu. Papain and alkaline protease hydrolysates of aerobic yeast had high levels of umami, bitter and essential AAs. Autolysates/hydrolysates from anaerobic yeast had moderate, high, and low levels of bitter, essential and umami AAs. Selection of both yeast growth conditions and hydrolysis enzyme can manipulate the free AA profile and yield of hydrolysates.

Protective effects of yeast extract against alcohol-induced liver injury in rats

Oxidative stress, inflammatory response, and gut-liver axis dysbiosis have been suggested as the primarily involved in the pathogenesis of alcoholic liver injury. Previous research established that yeast extract (YE) has antioxidant, immune-boosting or microbiota-regulating properties. However, there is currently lack of information regarding the efficacy of YE on alcoholic liver injury. This study seeks to obtain data that will help to address this research gap using a Wistar male rat experimental model. Histologic and biochemical analysis results showed that the groups treated with both low-dose yeast extract (YEL) and high-dose yeast extract (YEH) had lower degrees of alcohol-induced liver injury. The abundance of Peptococcus and Ruminococcus reduced in the low-dose yeast extract (YEL) group, while that of Peptococcus, Romboutsia, Parasutterella, and Faecalibaculum reduced in the high-dose (YEH) group. Furthermore, Spearman analysis showed that the gut microbes were significantly associated with several liver-related indicators. For the analysis of differential metabolites and enriched pathways in the YEL group, the abundance of lysophosphatidylcholine (16:0/0:0) significantly increased, and then the levels of histamine, adenosine and 5' -adenine nucleotide were remarkedly elevated in the YEH group. These findings suggest that both high and low doses of YE can have different protective effects on liver injury in alcoholic liver disease (ALD) rats, in addition to improving gut microbiota disorder. Besides, high-dose YE has been found to be more effective than low-dose YE in metabolic regulation, as well as in dealing with oxidative stress and inflammatory responses.

Protein recovery from brewery solid wastes

Brewing produces significant amounts of solid waste during the process: spent cereals (BSG), hops and spent yeast (BSY). These residues are sustainable sources of valuable nutrients and functional compounds like proteins, polyphenols, and polysaccharides. This review describes the three solid wastes and the different extraction techniques for protein recovery. The protein obtained can be used as a new source of non-animal protein or as a functional and bioactive ingredient. Particular attention was given to methods using conventional technologies (alkaline and ethanolic extraction) and more innovative approaches (enzymes, microwaves, ultrasound, pressurized liquids and sub-critical water extraction). Although the BSG is used in some industrial applications, studies in operating conditions, cost, energy efficiency, and product performance are still required to consolidate these solid wastes as a source of non-animal protein. The application of proteins is also an important question when choosing the extraction method.

Yeast Extract: Characteristics, Production, Applications and Future Perspectives

Yeast extract is a product prepared mainly from waste brewer's yeast, which is rich in nucleotides, proteins, amino acids, sugars and a variety of trace elements, and has the advantages of low production cost and abundant supply of raw material. Consequently, yeast extracts are widely used in various fields as animal feed additives, food flavoring agents and additives, cosmetic supplements, and microbial fermentation media; however, their full potential has not yet been realized. To improve understanding of current research knowledge, this review summarizes the ingredients, production technology, and applications of yeast extracts, and discusses the relationship between their properties and applications. Developmental trends and future prospects of yeast extract are also previewed, with the aim of providing a theoretical basis for the development and expansion of future applications.

Yeast derivatives as a source of bioactive components in animal nutrition: A brief review

With a long history of inclusion within livestock feeding programs, yeast and their respective derivatives are well-understood from a nutritional perspective. Originally used as sources of highly digestible protein in young animal rations in order to offset the use of conventional protein sources such as soybean and fish meal, application strategies have expanded in recent years into non-nutritional uses for all animal categories. For the case of yeast derivatives, product streams coming from the downstream processing of nutritional yeast, the expansion in use cases across species groups has been driven by a greater understanding of the composition of each derivative along with deeper knowledge of mechanistic action of key functional components. From improving feed efficiency, to serving as alternatives to antibiotic growth promoters and supporting intestinal health and immunity while mitigating pathogen shedding, new use cases are driven by a recognition that yeast derivatives contain specific bioactive compounds that possess functional properties. This review will attempt to highlight key bioactive categories within industrially applicable yeast derivatives and provide context regarding identification and characterization and mechanisms of action related to efficacy within a range of experimental models.

Spent Yeast Valorization for Food Applications: Effect of Different Extraction Methodologies

Over the years, synthetic biology has been growing with the use of engineered yeast strains for the production of sustainable ingredients to meet global healthcare, agriculture, manufacturing and environmental challenges. However, as seen from the brewing industry perspective, these processes generate a substantial amount of spent yeast that contains high nutritional value related to its high protein content, showing its potential to be used as an alternative protein source. Taking into account the rising demand for protein because of the growth in the global population, the present study aims to produce peptide-rich extracts by different potentially scalable and sustainable methodologies in a circular economy approach for the food and nutraceutical industries. The results demonstrated that extraction from genetically modified strains allowed the production of extracts with an excellent nutritional profile and low molecular weight peptides. Furthermore, autolysis was shown to be a potential sustainable approach for this production, though other green metrics need to be explored in order to establish this process at an industrial level.

Comparative Analysis of Mannans Extraction Processes from Spent Yeast Saccharomyces cerevisiae

Mannans are outstanding polysaccharides that have gained exponential interest over the years. These polysaccharides may be extracted from the cell wall of Saccharomyces cerevisiae, and recovered from the brewing or synthetic biology industries, among others. In this work, several extraction processes-physical, chemical and enzymatic-were studied, all aiming to obtain mannans from spent yeast S. cerevisiae. Their performance was evaluated in terms of yield, mannose content and cost. The resultant extracts were characterized in terms of their structure (FT-IR, PXRD and SEM), physicochemical properties (color, molecular weight distribution, sugars, protein, ash and water content) and thermal stability (DSC). The biological properties were assessed through the screening of prebiotic activity in Lactobacillus plantarum and Bifidobacterium animalis. The highest yield (58.82%) was achieved by using an alkaline thermal process, though the correspondent mannose content was low. The extract obtained by autolysis followed by a hydrothermal step resulted in the highest mannose content (59.19%). On the other hand, the extract obtained through the enzymatic hydrolysis displayed the highest prebiotic activity. This comparative study is expected to lay the scientific foundation for the obtention of well-characterized mannans from yeast, which will pave the way for their application in various fields.

Synthetic biology: a new frontier in food production

Concerns regarding food security arise from population growth, global warming, and reduction in arable land. With advances in synthetic biology, food production by microbes is considered to be a promising alternative that would allow rapid food production in an environmentally friendly manner. Moreover, synthetic biology can be adopted to the production of healthier or specifically designed food ingredients (e.g., high-value proteins, lipids, and vitamins) and broaden the utilization of feedstocks (e.g., methanol and CO₂), thereby offering potential solutions to high-quality food and the greenhouse effect. We first present how synthetic biology can facilitate the microbial production of various food components, and then discuss feedstock availability enabled by synthetic biology. Finally, we illustrate trends and key challenges in synthetic biology-driven food production.

Determination of hedonic thresholds by varying three stimuli

The Hedonic Threshold Methodology (HTM), through the determination of compromised acceptance threshold (CAT) and hedonic rejection threshold (HRT), has several applications by the food industry. In order to further increase the field of application of HTM, the objective was to use a mixture design in the Hedonic Threshold Methodology, to enable the determination of hedonic thresholds (CAT and HRT) by varying the intensity of three stimuli simultaneously. It was investigated how much it is possible to replace the NaCl content (1.8% flour weight basis) with two other ingredients (KCL/yeast extract or KCL/enzyme preparation), without compromising the acceptance (CAT) and without resulting in sensory rejection (HRT) of crackers. Reduction in the acceptance started to occur by reducing the NaCl content by around 64% (from 1.81% to 0.651%), with the addition of 1.149% KCl. Two combinations of KCl and yeast extract (1.783% and 0.017%, or 0.693% and 1.107%, respectively) allowed producing a cracker with no NaCl without sensory rejection. The reduction in acceptance also started to occur by reducing the NaCl content by around 40% (from 1.81% to 1.086%), with adding of 0.358% KCl and 0.356% enzyme preparation. A sensory rejection begins to occur by reducing the NaCl content by around 99% (1.81-0.012%), with the addition of 1.215% KCl and 0.573% enzyme preparation (transglutaminase). The use of the mixture design in HTM allowed the unprecedented determination of hedonic thresholds varying three stimuli. This expands the possibilities for applications of sensory thresholds.

Recycling and Conversion of Yeasts into Organic Nitrogen Sources for Wine Fermentation: Effects on Molecular and Sensory Attributes

Organic nitrogen plays a significant role in the fermentation performance and production of esters and higher alcohols. This study assessed the use of yeast protein hydrolysate (YPH) as a nitrogen source for grape must fermentation. In this study, we prepared an enzymatic protein hydrolysate using yeasts recovered from a previous fermentation of wine. Three treatments were performed. DAP supplementation was used as a control, while two YPH treatments were used. Low (LDH) and high degrees of hydrolysis (HDH), 3.5% and 10%, respectively, were chosen. Gas chromatography and principal component analysis indicated a significant positive influence of YPH-supplementations on the production of esters and higher alcohols. Significantly high concentrations of 3-methyl-1-penthanol, isoamyl alcohol, isobutanol, and 2-phenylethanol were observed. Significant odorant activity was obtained for 3-methyl-1-pentanol and ethyl-2-hexenoate. The use of YPH as nitrogen supplementation is justified as a recycling yeasts technique by the increase in volatile compounds.

Valorisation of Brewer’s Spent Yeasts’ Hydrolysates as High-Value Bioactive Molecules

Brewer’s spent yeast (BSY) is produced by the beer industry and has high nutritional value and great potential for producing high-value molecules, such as peptides, for nutraceutical, food and feed applications. In the present research, Flavourzyme® and Protamex® enzymes were selected for protein hydrolysis based on previous studies. The optimum conditions for the enzymatic hydrolysis were defined by response surface methodology (RSM) by the Box–Behnken design composed of four variables: temperature, pH, enzyme dosage and time. Protein content, hydrolysis degree and the anti-microbial and antioxidant bioactivities of obtained hydrolysates were quantified. Obtained results show that time, enzyme dosage and pH had the highest effect on protein extraction yield (PEY), degree of hydrolysis (DH) and antioxidant activity. Response variables ranged from 13.7 to 29.7% for PEY, from 6.3 to 35.7% for DH and from 0.65 to 1.65 g for Trolox equivalent antioxidant capacity. Antimicrobial activity, measured as minimum inhibitory concentration, against Aeromonas salmonicida, Bacillus cereus, Bacillus subtilis and Salmonella enterica, ranged from 6.25 to 50 mg/mL. Antioxidant and antimicrobial activity showed the potential use of BSY hydrolysates as an ingredient for functional foods.

Refining Citrus Wastes: From Discarded Oranges to Efficient Brewing Biocatalyst, Aromatic Beer, and Alternative Yeast Extract Production

Agro-industrial wastes can be valorized as biorefinery raw materials through innovative, environmentally friendly bioprocessing for added value products. In this study, a process for citrus waste valorization within the biorefinery concept is proposed, including the development of an effective biocatalyst, based on immobilized cells, for aromatic beer production, and an alternative yeast extract (AYE) production in the same unit. Specifically, orange pulp from discarded oranges was applied as an immobilization carrier of the alcohol-resistant and cryotolerant yeast strain S. cerevisiae AXAZ-1. The yeast culture was produced by minor nutrient supplementation using diluted molasses as substrate. An effective Citrus Waste Brewing Biocatalyst (CWBB) was produced and applied for beer fermentation. The aroma-related compounds in beer produced with free yeast cells or the CWBB were evaluated by solid-phase micro-extraction (SPME) gas chromatography–mass spectrometry (GC–MS). The analysis showed that the beers produced by the CWBB had a more complex volatile profile compared with beer fermented by the free cells. More specifically, the CWBB enhanced the formation of esters and terpenes by 5- and 27-fold, respectively. In the frame of the proposed multiprocessing biorefinery concept, the spent CWBB, after it has completed its cycle of brewing batches, was used as substrate for AYE production through autolysis. The produced AYE significantly affected the yeast growth when compared to commercial yeast extract (CYE). More specifically, it promoted the biomass productivity and biomass yield factor by 60–150% and 110–170%, respectively. Thus, AYE could be successfully used for industrial cell growth as an efficient and cheaper substitute of CYE. Within a circular economy framework, the present study highlights the potential use of citrus waste to produce aromatic beer combined with AYE production as an alternative way to valorize these wastes.

Dietary Inclusion of Blood Plasma with Yeast (Saccharomyces cerevisiae) Supplementation Enhanced the Growth Performance, Nutrient Digestibility, Lactobacillus Count, and Reduced Gas Emissions in Weaning Pigs

Simple Summary

Since 20th century, the use of yeast (Saccharomyces cerevisiae) supplement has been increased in animals feed due to its promising effects and potential to brighten the livestock industry in future. The feed cost of blood plasma is very expensive and, due to its high cost, it has been used mainly in piglet diets. In this regard, we implemented 3% blood plasma with 3% yeast supplementation to piglets mainly from 0–7 days, and gradually reduced the concentration of blood plasma with yeast supplement to 1.5:1.5% from 8–21 days and observed how it affects the overall performance of pigs on the remaining days 22–42 fed only basal diet. As expected, piglets fed blood plasma with yeast supplement over 0–21 days has a great impact on the growth performance, nutrient digestibility, fecal microbial, and gas emission at the end of the experiment. Thus, we suggest that blood plasma with yeast could be an excellent alternative in the livestock industry.

Abstract

This experiment was performed to examine the hypothesis that blood plasma (BP) with yeast (Saccharomyces cerevisiae) supplement in the diet of weaning pigs could provoke the growth performance, nutrient digestibility, fecal microbial, and reduce harmful gas excretion. A total of one hundred and eighty healthy piglets were taken and assigned (complete random blocks) to three dietary treatments as: Phase 1: Treatment (TRT) 1-6% BP; TRT 2-3% BP + 3% yeast; TRT 3-6% yeast. Phase 2: TRT 1-3%; BP., TRT 2-1.5% BP + 1.5% yeast; TRT 3- 3% yeast. Phase 3: TRT 1- Control (CON) (Basal diet); TRT 2- CON; TRT 3- CON for six- weeks. Each treatment had twelve replicates and five (three gilts and two barrows) pigs per pen. Dietary inclusion of BP with yeast supplementation significantly increased the body weight of piglets during phase 2 (p = 0.003) and phase 3 (p = 0.032). In addition, TRT2 group piglets had a significant improvement in average daily gain at the end of each phase and overall (p = 0.047, 0.025, 0.018 and 0.012, respectively). At phase 3, TRT2 group piglets showed a significant improvement on nutrient digestibility of dry matter (p = 0.012) and nitrogen (p = 0.040). The fecal microbiota of TRT2 group piglets showed a tendency to increase the number of Lactobacillus counts at phase 1 (p = 0.07) and phase 2 (p = 0.06) as well as, a significant improvement at phase 3 (p = 0.021). In addition, TRT2 group piglets had trend to decrease NH₃ (p = 0.074) and H₂S (p = 0.069) during phase 2, and significantly reduced NH₃ (p = 0.038) and H₂S (p = 0.046) at phase 3. However, the fecal score of piglets remains unaffected during the entire trial. At the end of phase 1 piglets’ IgG (p = 0.008) was significantly increased with the inclusion of BP with yeast supplementation. Based on the positive effects on body weight, average daily gain, nutrient digestibility, Lactobacillus count, and reduced gas emission, we suggest that dietary supplement with BP and yeast in the diet of weaned piglet could serve as an excellent alternative to antibiotics growth promoters.

Spent Brewer's Yeast as a Source of Insoluble β-Glucans

In the brewing process, the consumption of resources and the amount of waste generated are high and due to a lot of organic compounds in waste-water, the capacity of natural regeneration of the environment is exceeded. Residual yeast, the second by-product of brewing is considered to have an important chemical composition. An approach with nutritional potential refers to the extraction of bioactive compounds from the yeast cell wall, such as β-glucans. Concerning the potential food applications with better textural characteristics, spent brewer’s yeast glucan has high emulsion stability and water-holding capacity fitting best as a fat replacer in different food matrices. Few studies demonstrate the importance and nutritional role of β-glucans from brewer’s yeast, and even less for spent brewer’s yeast, due to additional steps in the extraction process. This review focuses on describing the process of obtaining insoluble β-glucans (particulate) from spent brewer’s yeast and provides an insight into how a by-product from brewing can be converted to potential food applications.

Advances in yeast autolysis technology - a faster and safer new bioprocess

Abstract The yeast autolysis process - an endogenous and irreversible lytic event, which occurs in cells caused by the action of intracellular enzymes, proteases and carbohydrases - is a well-known and an economic process, however, there is a constant risk of serious microbial contamination since there are many nutrients in the broth and this process is slow, favoring the growing of pathogens. The present work comes up with an attempt to accelerate the autolysis of Saccharomyces cerevisiae with focus on the high yield of yeast extract production through a fast, economic and simple technology. The proposed strategy is based on decreasing the pH of the yeast suspension at the beginning of autolysis through an acid shock to activate the cell autolytic system under stressful conditions of temperature and pH. The influence of cell concentration, temperature, time and acid shock at the beginning of the autolysis on yeast extract yields were studied. The best yields of proteins and total solids were observed for autolysis treated with acid shock (H2SO4 10 µL/g of dried yeast and final pH 4.4) at 60 °C (36, 84% of protein and 48, 47% of total solids extracted) and gradual increase of temperature 45 to 60 °C (41.20% of protein and 58.48% of total solids extracted). The shock could increase the speed of the process since the control reached about 30% of extract at 60 °C and the same experiment, however, with acid shock reached more than 43% in 12 h. When considering time in an industrial scale, it could be noted that the time was very important for the productivity as well as avoiding risk of pathogen contamination in autolysis. These results were very relevant for industrial purposes in the production of yeast extract, autolyzed yeast and glucan and mannan.

Membrane Fractionation of Protein Hydrolysates from By-Products: Recovery of Valuable Compounds from Spent Yeasts

Spent brewer’s yeast (Saccharomyces sp.), the second most generated by-product from the brewing industry, contains bioactive and nutritional compounds with high added value such as proteins (40–50%), polysaccharides, fibers and vitamins. Molecules of interest from agro-industrial by-products need to be extracted, separated, concentrated, and/or purified so that a minimum purity level is achieved, allowing its application. Enzymatic hydrolysis has been successfully used in the production of peptides and protein hydrolysates. The obtained hydrolysates require efficient downstream processes such as membrane technology, which is an important tool for the recovery of thermolabile and sensitive compounds from complex mixtures, with low energy consumption and high specificity. The integration of membrane techniques that promote the separation through sieving and charge-based mechanisms is of great interest to improve the purity of the recovered fractions. This review is specifically addressed to the application of membrane technologies for the recovery of peptides from yeast protein hydrolysates. Fundamental concepts and practical aspects relative to the ultrafiltration of agro-industrial protein hydrolysates will be described. Challenges and perspectives involving the recovery of peptides from yeast protein hydrolysates will be presented and thoroughly discussed.

Insight into the advantages of premixing yeast-wheat gluten and combining ultrasound and transglutaminase pretreatments in producing umami enzymatic protein hydrolysates

This study aimed to utilize effectively industrial byproducts, yeast suspension (Y) and wheat gluten (W), to produce umami protein hydrolysates as seasonings. Y and W were mixed to yield YW, followed by a pretreatment (ultrasound, transglutaminase (TG), or their combination) and then proteolysis with a yeast extract enzyme and trypsin. Premixing Y and W promoted their dispersibility, and suppressed gluten aggregation and hydrolysate's bitterness. All pretreatments increased protein recovery. Ultrasound alone or ultrasound with TG increased the embedding of yeasts in W, umami and salty tastes, hydrolysis degree and proportion of molecules < 3 kDa of the YW hydrolysate. For the first time, premixing Y and W, and pretreating YW (by ultrasound then TG-catalyzed protein crosslinking), were found to increase the β-sheet and random coil contents and decreased the β-turn content and surface hydrophobicity, leading to a low-cost umami and non-bitter protein hydrolysate with 56% of species < 1 kDa.

Biological Properties of Yeast-based Mannoprotein for Prospective Biomedical Applications

BACKGROUND

Natural products constitute more than half of all biomolecules lately being used in clinical settings. Mannoprotein derived from the yeast cell wall has found full biotechnological applications.

OBJECTIVE

This study was intended to investigate the antioxidant, anticancer, and toxicological properties of Kluyveromyces marxianus mannoprotein (KM).

METHODS

The KM extract was obtained through a sequence of operations, including centrifugation for cell isolation, precipitation with potassium citrate/sodium metabisulfite, and recovery and purification. Its antioxidant, growth inhibition, macrophage mitogenic, and toxic activities were evaluated for its future use in the biomedical field.

RESULTS

Significant inhibitory effects of KM were obtained on reactive species. It showed antiproliferative activity against HeLa (human cervical adenocarcinoma) and MCF-7 (human breast cancer) cell lines with no toxic effects on HUVECs (human umbilical vein endothelial cells). The in vitro model of CHO-K1 (Chinese hamster ovary) cell lines did not show the cytotoxic and genotoxic of KM. Moreover, it enhanced macrophage activity in terms of nitric oxide (NO) production and viability. No sign of acute toxicity was found in BALB/c mice, and body weight remained unchanged in guinea pigs over three months.

CONCLUSION

Comprehensive biological evaluations in this study are expected to expand the potential of KM as a natural material.

Maillard conjugates from spent brewer's yeast by-product as an innovative encapsulating material

Yeast-based by-products are greatly available, have a rich nutritional composition and functional properties. The spent brewer's yeast (SBY) cells after enzymatic hydrolysis may be a sustainable and low-cost alternative as carrier material for encapsulation processes by spray drying. Our work had as main purpose to characterise the hydrolysed SBY cell debris after the Maillard reaction and to study their potential as a microencapsulation wall material. SBY-based Maillard reaction products (MRPs) were used to encapsulate ascorbic acid (AA) by spray drying. The Maillard Reaction was able to improve the solubility of solids and proteins by 15% and promoted brown color development (230% higher Browning Index). SBY-based MRPs resulted in particles of a high encapsulation yield of AA (101.90 ± 5.5%), a moisture content of about 3.4%, water activity of 0.15, hygroscopicity values ranging from 13.8 to 19.3 g_H2O/100 g and a glass transition temperature around 71 °C. The shape and microstructure of the produced particles were confirmed by scanning electron microscopy (MEV), indicating very similar structure for control and AA encapsulated particles. Fourier Transform Infrared Spectroscopy (FT-IR) results confirmed the presence of yeast cell debris in the surface of particles. Ascorbic acid was successfully encapsulated in Maillard conjugates of hydrolyzsd yeast cell debris of Saccharomyces pastorianus and maltodextrin as confirmed by optical microscopy, differential scanning calorimetry, MEV and FT-IR.

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.

Continuous Self-Cycling Fermentation Leads to Economical Lycopene Production by Saccharomyces cerevisiae

The economic feasibility and waste treatment problem are challenges to the industrialization of lycopene production from Saccharomyces cerevisiae. In this study, fermentation wastewater, biomass residue, and residual D-galactose are recycled for lycopene production. Results show that when fresh water is totally replaced by wastewater, lycopene titer attains 1.21 ± 0.02 g/L, which is 14.2% higher than the fresh water group (P < 0.05). An 80% replacement ratio of yeast extract by biomass residue causes no significant difference to lycopene production while 100% replacement ratio significantly lowers lycopene titer compared with the yeast extract group. Then, a novel fermentation medium containing wastewater and biomass residue with supplementing 3 g/L yeast extract and D-galactose is used for lycopene production. Lycopene titer increases 22.4% than the traditional fermentation in shake flasks (P < 0.05). Continuous self-cycling strategy using wastewater and biomass residue was tested in shake flasks. The mean lycopene titer of the first five recycles shows no significant difference with the start batch. Scaling up to 70 L fermenter, the mean lycopene titer attains 5.88 ± 0.15 g/L in three recycles, which is 22.25% higher than the start batch (P < 0.05). Economic analysis shows that the lowest unite product cost is achieved when four recycles are accomplished, which is 29.6% lower than the traditional fermentation while the chemical oxygen demand decreases 64.0%. Our study shows that continuous self-cycling fermentation process for lycopene production is feasible for the first time. The comprehensive utilization of wastewater and biomass residue from lycopene production by S. cerevisiae and achievement of high lycopene titer will hopefully accelerate industrialization of microbial production of lycopene.

Autolysis, plasmolysis and enzymatic hydrolysis of baker's yeast (Saccharomyces cerevisiae): a comparative study

Saccharomyces cerevisiae is being used for long as a rich source of proteins, sugars, nucleotides, vitamins and minerals. Autolyzed and hydrolyzed yeast biomass has found numerous applications in the health food industry as well as livestock feeds. Here, we have compared three lysis methods for production of yeast lysates using autolysis, plasmolysis (ethyl acetate 1.5%), and enzymatic hydrolysis (Alcalase 0.2%). The efficiency of each process was compared according to soluble solid and protein contents, cell lysis monitoring, and release of intracellular materials, cell viability and microscopic analysis. Results showed that plasmolysis by ethyl acetate was found to be more efficient compared to autolysis, with a higher recovery of yeast extract (YE) content. In comparison, the content of released solids and proteins were higher during the enzymatic hydrolysis using Alcalase compared to autolysis and plasmolysis treatments. The highest decrease in optical density of 600 nm was monitored for the hydrolyzed cells. Besides, we defined "Degree of Leakage (DL)" as a new index of the lysis process, referring to the percentage of total released proteins from the cells and it was estimated to about 65.8%, which represents an appropriate indicator of the cell lysis. The biochemical and biophysical properties of the hydrolyzed yeast product as well as its biological activity (free radical scavenging activity and bacterial binding capacity) suggest that Alcalase could be used to accelerate the lysis of yeast cells and release the valuable intracellular components used for foodstuffs, feed and fermentation media applications. Production of baker's yeast lysates using autolysis, plasmolysis, and enzymatic hydrolysis methods.

Investigating characteristics and possible origins of off-odor substances in various yeast extract products

Yeast extract (YE) is rich in amino acids, nucleotides, peptides, and other flavor substances, and is a natural nutrient, umami, and flavor enhancer. However, certain YE samples impart a yeasty flavor that affects the quality parameters of YE. We compared solid-phase microextraction (SPME), solvent-assisted evaporation (SAFE), dynamic headspace sample preparation (DHS), stir bar sorptive extraction (SBSE), and other pretreatment methods for the extraction of volatiles substances in YE. SPME was selected as a suitable extraction method, and aroma extract dilution analysis (AEDA) was combined with gas chromatography-olfactometry-mass spectrometry (GC-O-MS) for identification of key odor-active compounds in 23 YE samples. The yeast off-odor substances were screened from these compounds. Principal component analysis (PCA) was used to investigate the relationship between strains and the processing of YE products and their yeasty flavor. PRACTICAL APPLICATIONS: YE is prepared primarily from baker's yeast or waste beer yeast by autolysis or enzymatic hydrolysis, and is rich in nucleotides, peptides, amino acids, and other flavor compounds. It is used globally as a common umami and flavor enhancer. However, consumers have observed that YE imparts a certain yeasty flavor that influences the overall flavor negatively. Hence, the yeasty flavor-imparting substances from 23 YE samples were investigated in this study, and the observations (including strains, processing techniques, etc.) were integrated to explain the relationship between the yeasty flavor of the YE products with strain (different yeast strain for production) or processing of YE products (enzymes used, enzymatic hydrolysis conditions, composition of products, concentration conditions of YE, etc.), or storage conditions (temperature, humidity, duration, package, etc.), providing a scientific basis for removal/lowering or masking of yeasty flavor and the improvement of flavor quality of YE products.

Pulsed electric field-assisted extraction of valuable compounds from microorganisms

Microorganisms (bacteria, yeast, and microalgae) are a promising resource for products of high value such as nutrients, pigments, and enzymes. The majority of these compounds of interest remain inside the cell, thus making it necessary to extract and purify them before use. This review presents the challenges and opportunities in the production of these compounds, the microbial structure and the location of target compounds in the cells, the different procedures proposed for improving extraction of these compounds, and pulsed electric field (PEF)-assisted extraction as alternative to these procedures. PEF is a nonthermal technology that produces a precise action on the cytoplasmic membrane improving the selective release of intracellular compounds while avoiding undesirable consequences of heating on the characteristics and purity of the extracts. PEF pretreatment with low energetic requirements allows for high extraction yields. However, PEF parameters should be tailored to each microbial cell, according to their structure, size, and other factors affecting efficiency. Furthermore, the recent discovery of the triggering effect of enzymatic activity during cell incubation after electroporation opens up the possibility of new implementations of PEF for the recovery of compounds that are bounded or assembled in structures. Similarly, PEF parameters and suspension storage conditions need to be optimized to reach the desired effect. PEF can be applied in continuous flow and is adaptable to industrial equipment, making it feasible for scale-up to large processing capacities.

Effects of different expression systems on characterization of adenylate deaminase from Aspergillus oryzae

Adenylate deaminase (AMPD) is an amino hydrolase that catalyzes the irreversible hydrolysis of adenosine monophosphate (AMP) to inosine monophosphate (IMP) and ammonia. In this study, the effect of different hosts on the enzymatic properties of AMPD from Aspergillus oryzae GX-08 was investigated and showed that Bacillus subtilis WB600 was more suitable for producing AMPD with a higher activity of 2540 U/mL. After purification, the optimal temperature and pH of recombinant AMPD were 55 °C and pH 6.0, respectively, and its activity was significantly enhanced by 10 mM Fe³⁺ with an increase of 236%. More importantly, the recombinant AMPD specifically and effectively catalyzed the conversion between AMP and IMP, in which 10 mL of crude AMPD achieved a conversion ratio of 76.4% after 40 min. Therefore, B. subtilis WB600 provides a potential platform for producing AMPD with excellent catalytic ability and catalytic specificity.

Recovery of Natural Antioxidants from Agro-Industrial Side Streams through Advanced Extraction Techniques

Large amounts of agro-industrial waste are being generated each year, leading to pollution and economic loss. At the same time, these side streams are rich source of active compounds including antioxidants. Recovered compounds can be re-utilized as food additives, functional foods, nutra-/pharmaceuticals, cosmeceuticals, beauty products, and bio-packaging. Advanced extraction techniques are promising tools to recover target compounds such as antioxidants from agro-industrial side streams. Due to the disadvantages of classical extraction techniques (such as large amounts of solvents, increased time of extraction, large amounts of remaining waste after the extraction procedure, etc.), and advanced techniques emerged, in order to obtain more efficient and sustainable processes. In this review paper aspects regarding different modern extraction techniques related to recovery of antioxidant compounds from wastes generated in different industries and their applications are briefly discussed.

The Impact of Pyroglutamate: Sulfolobus acidocaldarius Has a Growth Advantage over Saccharolobus solfataricus in Glutamate-Containing Media

Microorganisms are well adapted to their habitat but are partially sensitive to toxic metabolites or abiotic compounds secreted by other organisms or chemically formed under the respective environmental conditions. Thermoacidophiles are challenged by pyroglutamate, a lactam that is spontaneously formed by cyclization of glutamate under aerobic thermoacidophilic conditions. It is known that growth of the thermoacidophilic crenarchaeon Saccharolobus solfataricus (formerly Sulfolobus solfataricus) is completely inhibited by pyroglutamate. In the present study, we investigated the effect of pyroglutamate on the growth of S. solfataricus and the closely related crenarchaeon Sulfolobus acidocaldarius. In contrast to S. solfataricus, S. acidocaldarius was successfully cultivated with pyroglutamate as a sole carbon source. Bioinformatical analyses showed that both members of the Sulfolobaceae have at least one candidate for a 5-oxoprolinase, which catalyses the ATP-dependent conversion of pyroglutamate to glutamate. In S. solfataricus, we observed the intracellular accumulation of pyroglutamate and crude cell extract assays showed a less effective degradation of pyroglutamate. Apparently, S. acidocaldarius seems to be less versatile regarding carbohydrates and prefers peptidolytic growth compared to S. solfataricus. Concludingly, S. acidocaldarius exhibits a more efficient utilization of pyroglutamate and is not inhibited by this compound, making it a better candidate for applications with glutamate-containing media at high temperatures.

Estimating effects of yeast extract compositions on Escherichia coli growth by a metabolomics approach

Bioprocess stability depends on the variety of yeast extract, which varies from lot-to-lots and between brands, thereby leading to variable bacterial growth and productivity in manufacturing processes. As a model experiment for good stability of bioprocesses, Escherichia coli growth in media containing different brands of yeast extract was evaluated and predicted using component-profiling and multivariate data analysis (metabolomics approach). The components of yeast extract were extracted from media containing varying concentrations of yeast extract and analyzed using gas chromatography-mass spectrometer. The yeast extract was categorized into three clades by principal component analysis (PCA). The E. coli growth using yeast extract showed approximately 30% difference at equivalent amount of supplementation. The bacterial growth in the media was estimated for the component profiles by partial least squares regression analysis (PLS-R). A predictive model was developed from the relationship between bacterial growth (as subjective attributes) and component profiles (as objective attributes), and correlation coefficients were calculated. Most of the amino acids in the media stimulated growth; however, methionine had negative effect on growth. In a culture validation, Asp, Val, Glu, and Try stimulated the bacterial growth, but Met inhibited. The other amino acids tested, Ser, Ile, Asp, Lys, Phe, Leu, Thr, and Gly did not show significant effects on the growth. The results indicate that the metabolomics approach can provide useful feedback information to improve the cultivation.

Effects of dietary yeast extract supplementation on growth, body composition, non-specific immunity, and antioxidant status of Chinese mitten crab (Eriocheir sinensis)

This study was conducted to evaluate the effects of dietary supplementation with yeast extract on growth, body composition, non-specific immunity, and antioxidant status of Chinese mitten crab (Eriocheir sinensis). A total of 432 crabs (initial average weight, 4.62 ± 0.11 g) were randomly distributed into four treatment groups with six replicates of 18 crabs. The crabs were fed a basal diet or the same diet supplemented with 2.5, 5, and 10 g/kg yeast extract for 8 weeks. The results showed that dietary yeast extract inclusion enhanced the edible viscera index (linear, P < 0.001), edible viscera crude protein (CP) content (linear, P = 0.025) and serum phenoloxidase (ProPO) activity (quadratic, P = 0.023) at 56 day, increased the total superoxide dismutase (T-SOD) activity at 28 day (quadratic, P = 0.037) and catelase (CAT) activity at 56 day (quadratic, P = 0.034) of edible viscera, and muscular T-SOD activity (quadratic, P = 0.020) at 56 day in Chinese mitten crab. Compared with the control group, the inclusion of 5 g/kg yeast extract in the diet increased the edible viscera index, enhanced the CAT activity of edible viscera at 56 day in Chinese mitten crab (P < 0.05). Dietary 10 g/kg yeast extract inclusion enhanced the edible viscera index at 56 day in Chinese mitten crab than that of the control group (P < 0.05). These results implied that dietary yeast extract inclusion improved the edible viscera index and crude protein content of edible viscera, enhanced serum immunity, and increased the antioxidant status of edible viscera and muscle in Chinese mitten crab, especially when it is supplemented at 5 g/kg yeast extract in the diet.

Effect of supplementation with brewer's yeast hydrolysate on growth performance, nutrients digestibility, blood profiles and meat quality in growing to finishing pigs

Objective

This study was aimed to investigate the effects of brewer’s yeast hydrolysate (YH) on growth performance, nutrients digestibility, blood profiles and meat quality of growing pigs.

Methods

A total of 200 growing pigs ([Landrace×Yorkshire]×Duroc) (initial body weight, 25.31±1.29 kg) were allotted to 5 treatments as follow: CON, basic diet; and YH treatment, CON+0.05%, 0.1%, 0.5%, and 1.0% of YH, respectively.

Results

On wk 11, 16 and overall phase, pigs fed YH diet showed a linear improvement in average daily body gain and gain/feed (p<0.05). The pigs that received YH linearly increased the digestibility of dry matter, nitrogen, and energy on wk 11 and 16. The concentration of serum urea nitrogen was linearly increased in YH treatments on wk 16. However, the carcass weight, back fat and lean muscle percentage of pigs receiving YH had no significant change. Besides, no difference was observed in creatinine and total protein in the blood among treatments.

Conclusion

The pigs fed a graded YH diet had improved growth performance and nutrient digestibility, meanwhile, the YH increased the serum urea nitrogen in the growing pigs.

Saccharomyces cerevisiae containing 28% polyphosphate and production of a polyphosphate-rich yeast extract thereof

Currently, inorganic polyphosphate is chemically synthesized from phosphate rock and added directly to food products. Yeast extract is a concentrate of soluble fractions of Saccharomyces cerevisiae and is, as a food additive, generally regarded as safe. The aim of this study was to biotechnologically produce a naturally polyphosphate-rich yeast extract. Polyphosphate-rich cells were produced with a wild type (non-genetically modified) S. cerevisiae by orthophosphate-starvation and subsequent orthophosphate-feeding, and contained 28% (w/w) polyphosphate (as KPO3) in cell dry weight, which is the highest content reported so far. Four yeast extract production protocols (autolysis, plasmolysis, enzymatic hydrolysis without and with prior heat inactivation) were tested, whereas the latter was the most promising. From the polyphosphate-rich cells, yeast extract paste and powder were produced containing 20% and 14% (w/w, as KPO3) polyphosphate with an average chain length of 31 and 3 P-subunits, 7% and 14% (w/w, as K1.5H1.5PO4) orthophosphate, 22% and 0% (w/w) water, respectively. For the first time, naturally polyphosphate-rich yeast extracts were produced, which possibly can be used as a clean-label food additive and biological alternative to chemically synthesized polyphosphate in food products.

Metabolic regulatory mechanisms and physiological roles of functional amino acids and their applications in yeast

In yeast, amino acid metabolism and its regulatory mechanisms vary under different growth environments by regulating anabolic and catabolic processes, including uptake and export, and the metabolic styles form a complicated but robust network. There is also crosstalk with various metabolic pathways, products and signal molecules. The elucidation of metabolic regulatory mechanisms and physiological roles is important fundamental research for understanding life phenomenon. In terms of industrial application, the control of amino acid composition and content is expected to contribute to an improvement in productivity, and to add to the value of fermented foods, alcoholic beverages, bioethanol, and other valuable compounds (proteins and amino acids, etc.). This review article mainly describes our research in constructing yeast strains with high functionality, focused on the metabolic regulatory mechanisms and physiological roles of "functional amino acids", such as l-proline, l-arginine, l-leucine, l-valine, l-cysteine, and l-methionine, found in yeast.

High-level production of valine by expression of the feedback inhibition-insensitive acetohydroxyacid synthase in Saccharomyces cerevisiae

Valine, which is one of the branched-chain amino acids (BCAAs) essential for humans, is widely used in animal feed, dietary supplements and pharmaceuticals. At the commercial level, valine is usually produced by bacterial fermentation from glucose. However, valine biosynthesis can also proceed in the yeast Saccharomyces cerevisiae, which is a useful microorganism in fermentation industry. In S. cerevisiae, valine biosynthesis is regulated by valine itself via the feedback inhibition of acetohydroxyacid synthase (AHAS), which consists of two subunits, the catalytic subunit Ilv2 and the regulatory subunit Ilv6. In this study, to improve the valine productivity of yeast cells, we constructed several variants of Ilv6 by introducing amino acid substitutions based on a protein sequence comparison with the AHAS regulatory subunit of E. coli. Among them, we found that the Asn86Ala, Gly89Asp and Asn104Ala variants resulted in approximately 4-fold higher intracellular valine contents compared with those in cells with the wild-type Ilv6. The computational analysis of Ilv6 predicted that Asn86, Gly89 and Asn104 are located in the vicinity of a valine-binding site, suggesting that amino acid substitutions at these positions induce conformational change of the valine-binding site. To test the effects of these variants on AHAS activity, both recombinant Ilv2 and Ilv6 were purified and reconstituted in vitro. The Ilv6 variants were much less sensitive to feedback inhibition by valine than the wild-type Ilv6. Only a portion of the amino acid changes identified in the E. coli AHAS regulatory subunit IlvH enhanced the valine synthesis, suggesting structural and/or functional differences between the S. cerevisiae and E. coli AHAS regulatory subunits. It should also be noted that these amino acid substitutions did not affect the intracellular pools of the other BCAAs, leucine and isoleucine. The approach described here could be a practical method for the development of industrial yeast strains with high-level production of valine or isobutanol.

Heterologous expression and characterization of Penicillium citrinum nuclease P1 in Aspergillus niger and its application in the production of nucleotides

Nuclease P1 gene (nuc P1) which was cloned from Penicillium citrinum and expressed in A. niger Bdel4 with the low-background extracellular protein. The expression strategy of multi-copy nuc P1 in the A. niger with the linker of 2A peptide was applied to improve the enzyme activity of nuclease P1, the highest activity up to 77.6 U/mL. After Ni-chelate purification, the specific enzyme activity, the optimum temperature and pH were 32.4 U/mg, 65 °C and 5.3 respectively. The recombination nuclease P1 was activated by addition of Mg²⁺, Zn²⁺ and Cu²⁺, and inhibited by addition of Ca²⁺, Fe²⁺, Mn²⁺, Ni²⁺, Co²⁺, Mg²⁺, K⁺ and EDTA. Furthermore, the enzyme hydrolyses yeast RNA efficiently into 5'- nucleotides. Through enzymolysis, the highest concentration of nucleotides achieved 15.12 mg/mL, and 75U nuclease P1 is suitable amount should be added to the enzymolysis system.