Antioxidant properties and global metabolite screening of the probiotic yeast Saccharomyces cerevisiae var. boulardii

Metabolomics analysis of potential functional metabolites in synbiotic ice cream made with probiotic Saccharomyces cerevisiae var. boulardii CNCM I-745 and prebiotic inulin

Probiotic lactic acid bacteria have been widely studied, but much less was focused on probiotic yeasts in food systems. In this study, probiotic Saccharomyces cerevisiae var. boulardii CNCM I-745 was employed to prepare ice cream added with and without inulin (1%, w/v). Metabolomics analysis on the effect of inulin showed 84 and 147 differentially expressed metabolites identified in the ice cream samples from day 1 and day 30 of storage (-18 °C), respectively. Various potential functional metabolites were found, including citric acid, ornithine, D-glucuronic acid, sennoside A, stachyose, maltotetraose, maltopentaose, maltohexaose, maltoheptaose, cis-aconitic acid, gamma-aminobutyric acid, L-threonine, L-glutamic acid, tryptophan, benzoic acid, and trehalose. Higher expression of these metabolites suggested their possible roles through relevant metabolic pathways in improving survivability of the probiotic yeast and functionality of ice cream. This study provides further understanding on the metabolic characteristics of probiotic yeast that potentially affect the functionality of ice cream.

The supplementation of female dogs with live yeast Saccharomyces cerevisiae var. boulardii CNCM I-1079 acts as gut stabilizer at whelping and modulates immunometabolic phenotype of the puppies

Time around parturition is a stressful period for both bitches and their puppies. The use of probiotics has been proposed, e.g., in pigs, to improve health status of sows, their reproductive performances and in turn, the health and performance of their progeny. The objective of the present study was to evaluate the impact, on both dams and puppies, of a supplementation of bitches with the live yeast Saccharomyces cerevisiae var. boulardii CNCM I-1079 (SB-1079) during the second part of the gestation and the lactation period. A total of 36 bitches of medium and large-sized breeds were enrolled. They were divided into two groups, one of which received 1.3 × 109 colony forming units of live yeast per day. At dam's level, SB-1079 yeast shaped a different microbiota structure between the two groups just after whelping, impacted alpha diversity and some plasma metabolites related to energy metabolism. Regarding reproductive performances, SB-1079 improved gross energy of the colostrum (1.4 vs. 1.2 kcal of ME/g) as well as the concentration of protein in milk at Day 7 after parturition (10.4 vs. 7.6%). SB-1079 also reduced the odds of having low birth weight in the litter. At puppy's level, a modulation of immunometabolic phenotype is suggested by the observation of increased growth rates during the early pediatric period (i.e., between 21 and 56 days of life, 225 vs. 190%) and a decrease of the IL-8:IL-10 ratio after vaccination against rabies (4.2 vs. 16.9). Our findings suggest that SB-1079 supplementation during gestation and lactation has the potential to enhance health of bitches and in turn health of puppies through maternal programming.

Anticancer Properties of Saccharomyces boulardii Metabolite Against Colon Cancer Cells

Saccharomyces cerevisiae var. boulardii has been used as a probiotic yeast in the medical and food industries. Colon cancers have been known as the third most common cancer type worldwide. Nowadays, cell-free extract and metabolites of probiotics have been employed for the treatment or prevention of different cancer diseases. This study investigates the anticancer properties of S. boulardii metabolites against human colon carcinoma. We evaluated cytotoxicity, apoptosis induction, and suppression of survivin, IL-8, and NFƙB gene expression effects of SBM against caco-2 cells after 24 and 48 h. IC50 concentrations of SBM were measured at 815 and 1411 µg/mL for 24 and 48 h treatments, respectively. The total proportion of apoptotic caco-2 cells treated with SBM after 24 and 48 h were calculated at 62.23 and 88.7%, respectively. Also, relative expression of survivin, IL-8, and NFƙB genes were significantly suppressed in caco-2 cells treated with SBM after 24 and 48 h. In conclusion, we found that SBM induced apoptosis, inhibited the growth rate, and suppressed the expression of the survivin, IL-8, and NFƙB genes in human colorectal cancer cells and it can be considered as a perspective supplement or drug for the treatment or prevention of colon cancer in humans.

Nutraceuticals: A Promising Therapeutic Approach in Ophthalmology

Oxidative stress represents one of the main factors driving the pathophysiology of multiple ophthalmic conditions including presbyopia, cataracts, dry eye disease (DED), glaucoma, age-related macular degeneration (AMD) and diabetic retinopathy (DR). Currently, different studies have demonstrated the role of orally administered nutraceuticals in these diseases. For instance, they have demonstrated to improve lens accommodation in presbyopia, reduce protein aggregation in cataracts, ameliorate tear film stability, break up time, and tear production in dry eye, and participate in the avoidance of retinal neuronal damage and a decrease in intraocular pressure in glaucoma, contribute to the delayed progression of AMD, or in the prevention or treatment of neuronal death in diabetic retinopathy. In this review, we summarized the nutraceuticals which have presented a positive impact in ocular disorders, emphasizing the clinical assays. The characteristics of the different types of nutraceuticals are specified along with the nutraceutical concentration used to achieve a therapeutic outcome in ocular diseases.

Analysis of Phenolic Compounds in Buckwheat (Fagopyrum esculentum Moench) Sprouts Modified with Probiotic Yeast

Buckwheat sprouts are a source of various nutrients, e.g., antioxidant flavonoids, which have a positive effect on human health. This study analyzed the content of phenolic compounds and assessed their impact on the antioxidant and anti-inflammatory properties and dietary fiber in modified buckwheat sprouts. For this purpose, the buckwheat seeds were modified by adding Saccharomyces cerevisiae var. boulardii. The modified buckwheat sprouts showed a higher content of total phenol compounds (1526 µg/g d.w.) than the control sprouts (951 µg/g d.w.) and seeds (672 µg/g d.w.). As a consequence, a higher antioxidant activity and anti-inflammatory effect were noted. Probiotic-rich sprouts also had the highest content of total dietary fiber and its soluble fraction. A correlation between phenolic compounds and the antioxidant and anti-inflammatory effects, as well as dietary fiber, was shown. The interaction between dietary fiber and phenolic compounds affects the bioaccessibility, bioavailability, and bioactivity of phenolic compounds in food. The introduction of probiotic yeast into the sprouts had a positive effect on increasing their nutritional value, as well as their antioxidant and anti-inflammatory activity. As a consequence, the nutraceutical potential of the raw material changed, opening a new direction for the use of buckwheat sprouts, e.g., in industry.

Synbiotics and Their Antioxidant Properties, Mechanisms, and Benefits on Human and Animal Health: A Narrative Review

Antioxidants are often associated with a variety of anti-aging compounds that can ensure human and animal health longevity. Foods and diet supplements from animals and plants are the common exogenous sources of antioxidants. However, microbial-based products, including probiotics and their derivatives, have been recognized for their antioxidant properties through numerous studies and clinical trials. While the number of publications on probiotic antioxidant capacities and action mechanisms is expanding, that of synbiotics combining probiotics with prebiotics is still emerging. Here, the antioxidant metabolites and properties of synbiotics, their modes of action, and their different effects on human and animal health are reviewed and discussed. Synbiotics can generate almost unlimited possibilities of antioxidant compounds, which may have superior performance compared to those of their components through additive or complementary effects, and especially by synergistic actions. Either combined with antioxidant prebiotics or not, probiotics can convert these substrates to generate antioxidant compounds with superior activities. Such synbiotic-based new routes for supplying natural antioxidants appear relevant and promising in human and animal health prevention and treatment. A better understanding of various component interactions within synbiotics is key to generating a higher quality, quantity, and bioavailability of antioxidants from these biotic sources.

Unique Probiotic Properties and Bioactive Metabolites of Saccharomyces boulardii

Saccharomyces boulardii (S. boulardii) is a probiotic and is widely used to improve the nutritional and functional value of food. This study aimed to compare the probiotic properties of S. boulardii and Saccharomyces cerevisiae. A series of in vitro probiotic experiments was performed, including simulated gastrointestinal digestion, bile salt tolerance, hydrophobicity, self-aggregation, and antioxidant and antibacterial properties. Self-aggregation and hydrophobic properties of S. boulardii were relatively poor, but they showed high tolerance, antioxidant properties, and broad antibacterial properties. In addition, non-targeted metabolomics was used to comprehensively analyze the active metabolites of S. boulardii and the metabolic differences between S. boulardii and S. cerevisiae were compared. Saccharomyces boulardii produced many bioactive metabolites, which generally showed antioxidant, antibacterial, antitumor, anti-inflammatory, and other properties. In contrast to S. cerevisiae, S. boulardii produced phenyllactic acid and 2-hydroxyisocaproic acid. There were also significant differences in their metabolic pathways. These results may be of great significance in the medical and food industries and provide a basis for understanding the metabolism of S. boulardii. It also shows that metabolomics is an effective and novel method for screening microbial functional metabolites and identifying functional differences between similar microorganisms.

Live Yeast Supplementation in Gestating and Lactating Primiparous Sows Improves Immune Response in Dams and Their Progeny

The present study determined the effects of live yeast (LY) supplementation during middle–late gestation and the lactation period in primiparous sows on reproductive parameters, lactation performance, and immunity, and also explores the carryover effects in their offspring. On day (d) 60 of gestation, 16 crossbred primiparous sows were randomly assigned to two dietary treatments (with or without supplementation of 425 mg/kg of live yeast; LYT and CT, respectively) homogeneous for body weight (BW) and backfat thickness. Experimental diets were applied from day 60 of gestation to the end of lactation. At weaning, 60 piglets with an average BW of each treatment were selected based on their source litter and assigned to two groups corresponding to the original treatments received by their mothers. Each group had five replicates of six piglets each and was fed a basal diet for 42 days. The results showed that LY supplementation significantly increased the serum IgA and IgG concentrations of sows at farrowing and weaning stages, and of piglets on day 14 and 28 post weaning. No significant differences were found in reproductive and lactation performance, while minor effects were observed on antioxidant capacity. In conclusion, live yeast addition during middle–late gestation and the whole lactation period resulted in enhanced immunity of primiparous sows and their offspring, therefore, improving maternal and progeny health.

Saccharomyces boulardii exerts renoprotection by modulating oxidative stress, renin angiotensin system and uropathogenic microbiota in a murine model of diabetes

AIMS

We aimed to investigate whether Saccharomyces boulardii strain might exert renoprotective effects by modulating renal renin angiotensin system, oxidative stress and intestinal microbiota in streptozotocin-diabetic mice.

MAIN METHODS

Thirty-six C57BL/6 male mice were divided into four groups: control (C), control + probiotic (CP), diabetes (D), diabetes + probiotic (DP). Diabetes was induced by one intraperitoneal injection of streptozotocin and Saccharomyces boulardii was administered by oral gavage for 8 weeks. Blood glucose, albuminuria and urinary volume were measured. Renal levels of angiotensin peptides (angiotensin I, II and 1-7) and the activities of angiotensin-converting enzyme (ACE) and ACE2 were determined, besides that, renal morphology, serotonin and dopamine levels and also microbiota composition were analyzed.

KEY FINDINGS

Probiotics significantly increased C-peptide secretion and reduced blood glucose of diabetic animals. Saccharomyces boulardii also improved renal antioxidant defense, restored serotonin and dopamine concentration, and activated the renin-angiotensin system (RAS) vasodilator and antifibrotic axis. The modulation of these markers was associated with a beneficial impact on glomerular structure and renal function of diabetic treated animals. The phenotypic changes induced by Saccharomyces boulardii were also related to modulation of intestinal microbiota, evidenced by the decreased abundance of Proteus and Escherichia-Shigella, considered diabetic nephropathy biomarkers.

SIGNIFICANCE

Therefore, probiotic administration to streptozotocin-induced diabetic mice improves kidney structure and function in a murine model and might represent a reasonable strategy to counteract nephropathy-associated maladaptive responses in diabetes.

In vitro bioactivities of coffee brews fermented with the probiotics Lacticaseibacillus rhamnosus GG and Saccharomyces boulardii CNCM-I745

Previously, we demonstrated the production of bioactive metabolites (e.g., indole-3-lactate, 4-hydroxyphenyllactate, 3-phenyllactate, 2-isopropylmalate) by the probiotics Lacticaseibacillus rhamnosus GG and Saccharomyces boulardii CNCM-I745 during coffee brew fermentation. However, it remains unclear if in situ production of bioactive metabolites confers additional health benefits to coffee brews. Here, we aimed to investigate the in vitro bioactivities of freeze-dried cell-free coffee supernatants fermented with L. rhamnosus GG and/or S. boulardii CNCM-I745, compared to non-fermented coffee supernatants. In vitro bioactivity assays pertained to α-amylase and α-glucosidase inhibition, antiglycative activities, anti-proliferation against human cancer cell lines (MCF-7, HCT116, and HepG2), cellular antioxidant activities, and anti-inflammatory activities. We demonstrated that non-fermented coffee supernatants displayed weak starch hydrolase inhibition (IC₅₀ > 36.00 mg/mL), but otherwise displayed strong anti-glycative (IC₅₀ 0.71-0.74 mg/mL), anti-proliferative (IC₅₀ 0.45, 0.36, and < 0.5 mg/mL for MCF-7, HCT116, and HepG2 respectively), cellular antioxidant (85,844.22 µmol quercetin equivalents/100 g coffee supernatant), and anti-inflammatory activities (35.7% reduction in nitrite production at 0.13 mg/mL). In all the assays tested, probiotic fermented coffee supernatants exhibited very similar bioactivities compared to non-fermented coffee supernatants, and improvements were not observed. Overall, in vitro bioactivities of coffee brews were not improved via in situ metabolite production by L. rhamnosus GG and/or S. boulardii CNCM-I745. Therefore, bioactive metabolites produced during probiotic-induced food fermentations may not necessarily confer additional health benefits compared to non-fermented counterparts.

Health-promoting properties of Saccharomyces cerevisiae var. boulardii as a probiotic; characteristics, isolation, and applications in dairy products

Saccharomyces cerevisiae var. boulardii (S. boulardii) has been isolated from lychee (Litchi chinensis), mangosteen fruit, kombucha, and dairy products like kefir. Dairy products containing S. boulardii have been revealed to possess potential probiotic activities owing to their ability to produce organic acids, essential enzymes, vitamins, and other important metabolites such as vanillic acid, phenyl ethyl alcohol, and erythromycin. S. boulardii has a wide spectrum of anti-carcinogenic, antibacterial antiviral, and antioxidant activity, and is known to reduce serum cholesterol levels. However, this yeast has mainly been prescribed for prophylaxis treatment of gastrointestinal infectious diseases, and stimulating the immune system in a number of commercially available products. The present comprehensive review article reviews the properties of S. boulardii related to their use in fermented dairy foods as a probiotic microorganism or starter culture. Technical aspects regarding the integration of this yeast into the dairy foods matrix its health advantages, therapeutic functions, microencapsulation, and viability in harsh conditions, and safety aspects are highlighted.

In Silico Prediction and In Vitro Assessment of Multifunctional Properties of Postbiotics Obtained From Two Probiotic Bacteria

In this study, a global metabolite profile using Raman spectroscopy analysis was obtained in order to predict, by an in silico prediction of activity spectra for substance approach, the bioactivities of the intracellular content (IC) and cell wall (CW) fractions obtained from Lactobacillus casei CRL 431 and Bacillus coagulans GBI-30 strains. Additionally, multifunctional in vitro bioactivity of IC and CW fractions was also assessed. The metabolite profile revealed a variety of compounds (fatty acids, amino acids, coenzyme, protein, amino sugars), with significant probable activities (Pa > 0.7) as immune-stimulant, anti-inflammatory, neuroprotective, antiproliferative, immunomodulator, and antineoplastic, among others. Moreover, in vitro assays exhibited that both IC and CW fractions presented angiotensin-converting enzyme-inhibitory (> 90%), chelating (> 79%), and antioxidant (ca. 22-57 cellular antioxidant activity units) activities. Our findings based on in silico and in vitro analyses suggest that L. casei CRL 431 and B. coagulans GBI-30 strains appear to be promising sources of postbiotics and may impart health benefits by their multifunctional properties.

Recent innovations in the production of selected specialty (non-traditional) beers

Customer demand for product diversity is the key driving force for innovations in the brewing industry. Specialty beers are regarded as a distinct group of beers different from two major types, lagers and ales, without established definitions or boundaries. Specialty beers, including low- to no-alcohol beer, low carbohydrate beer, gluten-free beer, sour beer, probiotic beer, and enriched beer, are exclusively brewed and developed keeping in mind their functionality, the health and wellbeing of the consumer, and emerging market trends. Compared with conventional beer-brewing, the production of specialty beers is technologically challenging and usually requires additional process steps, unique microorganisms, and special equipment, which in turn may incur additional costs. In addition, the maintenance of quality and stability of the products as well as consumer acceptability of the products are major challenges to successful commercialization. A harmonious integration of traditional brewing practices and modern technological approaches may hold potential for future developments. In the present review, latest developments in the fermentative production of selected specialty beers are discussed.

Growth, survival, and metabolic activities of probiotics Lactobacillus rhamnosus GG and Saccharomyces cerevisiae var. boulardii CNCM-I745 in fermented coffee brews

Amidst rising demand for non-dairy probiotic foods, and growing interest in coffees with added functionalities, it would be opportune to ferment coffee brews with probiotics. However, challenges exist in maintaining probiotic viability in high-moisture food products. Here, we aimed to enhance the viability of the probiotic bacteria, Lactobacillus rhamnosus GG, in coffee brews by co-culturing with the probiotic yeast, Saccharomyces cerevisiae var. boulardii CNCM-I745. The yeast significantly enhanced the viability of L. rhamnosus GG, as bacterial populations beyond 7 Log CFU/mL were maintained throughout 14 weeks of storage at 4 and 25 °C. In contrast, the single culture of L. rhamnosus GG suffered viability losses below 6 Log CFU/mL within 10 weeks at 4 °C, and 3 weeks at 25 °C. Growth and survival of S. boulardii CNCM-I745 remained unaffected by the presence of L. rhamnosus GG. Volatile profiles of coffee brews were altered by probiotic metabolic activities, but co-culturing led to suppressed generation of diacetyl and ethanol compared to single cultures. Probiotic fermentation did not alter principal coffee bioactive compounds and antioxidant capacities; however, declines in peroxyl radical scavenging capacities were observed after ambient storage. Overall, we illustrate that yeasts are effective in enhancing probiotic bacterial viability in coffee brews, which may be useful in developing shelf stable probiotic food products.

Saccharomyces boulardii modulates oxidative stress and renin angiotensin system attenuating diabetes-induced liver injury in mice

Type 1 diabetes (T1DM) is a chronic disease characterized by hyperglycemia due to a deficiency in endogenous insulin production, resulting from pancreatic beta cell death. Persistent hyperglycemia leads to enhanced oxidative stress and liver injury. Several studies have evaluated the anti-diabetic and protective effects of probiotic strains in animal models. In the present study, we investigated, through histopathological and biochemical analyses, the effects of eight weeks of administration of Saccharomyces boulardii (S. boulardii) yeast on the liver of streptozotocin (STZ) induced diabetic C57BL/6 mice. Our results demonstrated that S. boulardii attenuates hepatocytes hydropic degeneration and hepatic vessels congestion in STZ-induced diabetic mice. The treatment attenuated the oxidative stress in diabetic mice leading to a reduction of carbonylated protein concentration and increased activity of antioxidant enzymes superoxide dismutase and glutathione peroxidase, compared to untreated diabetic animals. The results also show the beneficial influence of S. boulardii in regulating the hepatic concentration of renin angiotensin system (RAS) peptides. Therefore, our results demonstrated that S. boulardii administration to STZ-induced diabetic mice reduces oxidative stress and normalizes the concentration of RAS peptides, supporting the hypothesis that this yeast may have a role as a potential adjunctive therapy to attenuate diabetes-induced liver injury.

Probiotic Supplementation is Associated with Increased Antioxidant Capacity and Copper Chelation in C. difficile-Infected Fecal Water

Probiotic supplementation plays a key role in maintaining intestinal homeostasis due to its ability to modulate gut microbiota. Although their potential as potent antioxidants have previously been explored, their ability to affect the redox status in the gut lumen of healthy subjects or those with gastrointestinal (GI) disorders remains unclear. In our study, we assessed the ability of single strain and multispecies probiotic supplementation to cause a change in the redox status of normal fecal water and in Clostridium (C.) difficile-infected fecal water using a simulated gastrointestinal model. Changes in redox status were assessed by ferric-reducing antioxidant power (FRAP), 2’,2’-diphenyl-1-picrylhydrazyl (DPPH), and iron and copper chelation assays. The findings from our study showed that in normal fecal water, probiotic supplements, apart from Lactobacillus (L.) rhamnosus R0011, showed a significant increase in iron chelation (p < 0.05), which was associated with lower FRAP and copper chelation. In C. difficile-infected fecal water, all probiotic supplements showed a significant increase in FRAP (p < 0.05) and were associated with increased copper chelation. The DPPH assay showed no treatment effect in either fecal water. These findings suggest that C. difficile mediates dysregulation of redox status, which is counteracted by probiotics through ferric-reducing ability and copper chelation.

Application of Saccharomyces cerevisiae var. boulardii in food processing: a review

Probiotics are increasingly being added to food in order to develop products with health-promoting properties. Particularly, Saccharomyces cereviceae var. boulardii yeast is recently being investigated like a starting-culture for development of functional and probiotic foods. Although the literature is abundant on the beneficial effects of S. boulardii on health, slight information is available on the effects of supplementing this probiotic to food systems. The aim of this paper is to examine the applications of S. boulardii to different food matrices and its implication in food processing (stability, sensorial properties and other technological implications) and the concomitant effects on nutrition and health.

Use of Saccharomyces cerevisiae var. boulardii in co-fermentations with S. cerevisiae for the production of craft beers with potential healthy value-added

In recent years, the awareness of consumers about the impact of food on health is constantly increasing. A high amount of dietary antioxidant intake can be supplied by beverages widely consumed, such as wine, coffee, beer. Recently, an increase in the consumer interest was observed for beer, in consequence of the high phenolic antioxidants and low ethanol content present in this beverage. Among all beer types, in recent years, consumption of craft beers has gained popularity. Being an unpasteurized and unfiltered, craft beer is potentially a new vehicle for delivering health effects. While health benefits of lactic acid bacteria as probiotics are well known, few data are available on probiotic yeasts in fermented food. Therefore, this study was aimed to analyse the effect of integrating the well-known probiotic yeast strain of S. cerevisiae var. boulardii (S.b) in mixed cultures with S. cerevisiae strains for production of beers with increased healthy benefits. The probiotic strain of S.b was tested in mixed cultures with selected S. cerevisiae strains, during wort fermentation. As the viability during processing operations is one of the criteria for selecting suitable strains of probiotic microorganisms, the survival of probiotic yeast during the fermentation and the presence of highly viable cells at the end of fermentations were evaluated. In almost all the mixed fermentations, at the end of the process the probiotic yeast was predominant on S. cerevisiae strain, and the experimental beers contained a high number of viable cells of S.b strain (ranging between 8 × 10⁶ and 7.0 × 10⁷/mL). The analysis of experimental beers for the content of main volatile compounds showed that the inclusion of S.b strain in mixed starter did not affect negatively beer aroma. Moreover, the inclusion of S.b strain in mixed starters determined an increase in the antioxidant activity and polyphenols content, in comparison to beers from single starter fermentations, indicating the influence of S.b strain on these parameters. Some mixed starter cultures tested in this study resulted a very promising tool to increase the healthy quality of the product, such as the improve the antioxidant activity and polyphenols content of beer.

Different specificities of two aldehyde dehydrogenases from Saccharomyces cerevisiae var. boulardii

Aldehyde dehydrogenases play crucial roles in the detoxification of exogenous and endogenous aldehydes by catalysing their oxidation to carboxylic acid counterparts. The present study reports characterization of two such isoenzymes from the yeast Saccharomyces cerevisiae var. boulardii (NCYC 3264), one mitochondrial (Ald4p) and one cytosolic (Ald6p). Both Ald4p and Ald6p were oligomeric in solution and demonstrated positive kinetic cooperativity towards aldehyde substrates. Wild-type Ald6p showed activity only with aliphatic aldehydes. Ald4p, on the contrary, showed activity with benzaldehyde along with a limited range of aliphatic aldehydes. Inspection of modelled structure of Ald6p revealed that a bulky amino acid residue (Met177, compared with the equivalent residue Leu196 in Ald4p) might cause steric hindrance of cyclic substrates. Therefore, we hypothesized that specificities of the two isoenzymes towards aldehyde substrates were partly driven by steric hindrance in the active site. A variant of wild-type Ald6p with the Met177 residue replaced by a valine was also characterized to address to the hypothesis. It showed an increased specificity range and a gain of activity towards cyclohexanecarboxaldehyde. It also demonstrated an increased thermal stability when compared with both the wild-types. These data suggest that steric bulk in the active site of yeast aldehyde dehydrogenases is partially responsible for controlling specificity.