Factors affecting yeast ethanol tolerance and fermentation efficiency.

Alcohol fermentation is a key process in wine, beer, alcoholic beverage production, bioethanol production by means of carbohydrate sources, and food industry byproducts. There are three key points in these kinds of processes determining their efficiency; enzymatic cellulose lysis into simple sugar molecules, alcohol fermentation rate, and ethanol tolerance of yeast cells. The first process is usually carried out by either the use of pure cellulolytic enzymes, which is a high cost procedure, or by the production of these enzymes from cellulolytic bacteria and filamentous fungi. Lately, Saccharomyces cerevisiae and several other yeasts were genetically modified to express recombinant cellulases in media or display them on the cell surface. Many studies have indicated that the genetic engineering of yeast cells can be a useful approach in increasing the alcoholic fermentation rate as well as their ethanol tolerance. These modifications could be the overexpression of a key protein using a strong promoter or the modification of a specific domain or amino acid which can also lead to the desired outcome. This review focuses on the modifications of a single protein and/or pathways that can lead to the augmentation of ethanol tolerance and alcoholic fermentation efficiency of Saccharomyces cerevisiae.

Investigation of the Microbiome of Industrial PDO Sfela Cheese and Its Artisanal Variants Using 16S rDNA Amplicon Sequencing and Shotgun Metagenomics.

Sfela is a white brined Greek cheese of protected designation of origin (PDO) produced in the Peloponnese region from ovine, caprine milk, or a mixture of the two. Despite the PDO status of Sfela, very few studies have addressed its properties, including its microbiology. For this reason, we decided to investigate the microbiome of two PDO industrial Sfela cheese samples along with two non-PDO variants, namely Sfela touloumotiri and Xerosfeli. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), 16S rDNA amplicon sequencing and shotgun metagenomics analysis were used to identify the microbiome of these traditional cheeses. Cultured-based analysis showed that the most frequent species that could be isolated from Sfela cheese were Enterococcus faecium, Lactiplantibacillus plantarum, Levilactobacillus brevis, Pediococcus pentosaceus and Streptococcus thermophilus. Shotgun analysis suggested that in industrial Sfela 1, Str. thermophilus dominated, while industrial Sfela 2 contained high levels of Lactococcus lactis. The two artisanal samples, Sfela touloumotiri and Xerosfeli, were dominated by Tetragenococcus halophilus and Str. thermophilus, respectively. Debaryomyces hansenii was the only yeast species with abundance > 1% present exclusively in the Sfela touloumotiri sample. Identifying additional yeast species in the shotgun data was challenging, possibly due to their low abundance. Sfela cheese appears to contain a rather complex microbial ecosystem and thus needs to be further studied and understood. This might be crucial for improving and standardizing both its production and safety measures.

The Rising Role of Omics and Meta-Omics in Table Olive Research.

Table olives are often the result of fermentation, a process where microorganisms transform raw materials into the final product. The microbial community can significantly impact the organoleptic characteristics and safety of table olives, and it is influenced by various factors, including the processing methods. Traditional culture-dependent techniques capture only a fraction of table olives' intricate microbiota, prompting a shift toward culture-independent methods to address this knowledge gap. This review explores recent advances in table olive research through omics and meta-omics approaches. Genomic analysis of microorganisms isolated from table olives has revealed multiple genes linked to technological and probiotic attributes. An increasing number of studies concern metagenomics and metabolomics analyses of table olives. The former offers comprehensive insights into microbial diversity and function, while the latter identifies aroma and flavor determinants. Although proteomics and transcriptomics studies remain limited in the field, they have the potential to reveal deeper layers of table olives' microbiome composition and functionality. Despite the challenges associated with implementing multi-omics approaches, such as the reliance on advanced bioinformatics tools and computational resources, they hold the promise of groundbreaking advances in table olive processing technology.

The Effects of Insect Infestation on Stored Agricultural Products and the Quality of Food.

In this review article, we focus on the effects of insect pests on the quality of stored cereals and legume grains. The changes in the amino-acid content, the quality of proteins, carbohydrates, and lipids, and the technological characteristics of the raw materials when infested by specific insects are presented. The differences reported concerning the rate and kind of infestation effects are related to the trophic habits of the infesting insect species, the variation of the component distribution in the different species of grains, and the length of the storage period. For example, wheat germ and brans feeders such as Trogoderma granarium may cause a higher reduction in proteins than endosperm feeders such as Rhyzopertha dominica, since the germ and brans contain higher concentrations of proteins. Trogoderma granarium may also cause higher reduction in lipids than R. dominica in wheat, maize and sorghum, in which most of the lipids exist in the germ. Furthermore, infestation with insects such as Tribolium castaneum may downgrade the overall quality of wheat flour, by increasing the moisture content, the number of insect fragments, the color change, the concentration of uric acid, the microbial growth, and the prevalence of aflatoxins. Whenever possible, the significance of the insect infestation and the concomitant compositional alterations on human health are presented. It should be highlighted that understanding the impact of insect infestation on stored agricultural products and the quality of food will be crucial for the required food security in the future.

The Low-FODMAP Diet, IBS, and BCFAs: Exploring the Positive, Negative, and Less Desirable Aspects-A Literature Review.

The literature about the association of branched short-chain fatty acids (BCFAs) and irritable bowel syndrome (IBS) is limited. BCFAs, the bacterial products of the catabolism of branched-chain amino acids, are proposed as markers for colonic protein fermentation. IBS is a gastrointestinal disorder characterized by low-grade inflammation and intestinal dysbiosis. The low-FODMAP diet (LFD) has increasingly been applied as first-line therapy for managing IBS symptoms, although it decreases the production of short-chain fatty acids (SCFA), well known for their anti-inflammatory action. In parallel, high protein consumption increases BCFAs. Protein fermentation alters the colonic microbiome through nitrogenous metabolites production, known for their detrimental effects on the intestinal barrier promoting inflammation. Purpose: This review aims to explore the role of BCFAs on gut inflammation in patients with IBS and the impact of LFD in BCFAs production. Methods: A literature search was carried out using a combination of terms in scientific databases. Results: The included studies have contradictory findings about how BCFAs affect the intestinal health of IBS patients. Conclusions: Although evidence suggests that BCFAs may play a protective role in gut inflammation, other metabolites of protein fermentation are associated with gut inflammation. Further research is needed in order to clarify how diet protein composition and, consequently, the BCFAs are implicated in IBS pathogenesis or in symptoms management with LFD+.

Fermentation Efficiency of Genetically Modified Yeasts in Grapes Must.

Winemaking is a stressful procedure for yeast cells. The presence of high levels of carbohydrates at the beginning of the fermentation and the subsequent increase of ethanol levels alongside with other environmental factors force the cell to undergo a continuous adaptation process. Ideally, yeast strains should be able to adapt to this changing environment fast and they must be able to ferment at low temperatures with the highest possible fermentation rates. Additionally, the balanced utilization of glucose and fructose-the two major hexoses in grapes-is also important as any residual fructose may confers unwanted sweetness. As proteins, Msn2/4 are known to play pivotal roles in cell stress response, the question that arise regards the differentially cell response driven by specific point mutations in these two proteins, and the subsequent effects on alcoholic fermentation. Four different mutants in which serine residues have been replaced by alanine are studied in this paper. Our results indicate that substitution at position 533 of Msn4 protein (W_M4_533) significantly increases the fermentation rate even at low temperatures (12 °C), by lowering the fermentation's activation energy. Similar results but to a lesser extent were obtained by the S582A substitution in Msn2 protein. In addition, W_M4_533 seems to have a more balanced utilization of must hexoses. From the present work it is concluded that genetic modification Msn2/4 represents a promising procedure for shortening the fermentation time, even at low temperatures, which in many cases constitutes an important technological requirement.

Ser625 of msn2 transcription factor is indispensable for ethanol tolerance and alcoholic fermentation process.

The genetic modification of yeast strains can be used as an approach for the improvement of ethanol fermentation. msn2p transcription factor is implicated in yeast stress response and its activation is controlled by protein kinase A (PKA). PKA activation inhibits the translocation of msn2p to the nucleus. An in silico analysis of msn2 protein sequence revealed serine residue at position 625 as a potent target of PKA. Thus, substitution of this serine residue with alanine increases the susceptibility of the cells to ethanol challenge reducing IC50 from 3% vol/vol to 2.42% vol/vol. Additionally, cells carrying this substitution were shown a significantly reduced fermentation rate at 30°C and 18°C increasing the total fermentation time by approximately two and three times, respectively. These results clearly indicate that Ser625 is absolutely necessary for yeast to retain its fermentation ability and ethanol tolerance.

Specific serine residues of Msn2/4 are responsible for regulation of alcohol fermentation rates and ethanol resistance.

Despite the fact that Saccharomyces cerevisiae has suicide tendencies since its product affects cell function, it is a key player in alcoholic fermentation. The presence of ethanol in the medium affects membrane integrity and fluidity, as well as the rate of ethanol production. The Msn2/4p transcription factors are key regulators in stress response and play a critical role in cell response to ethanol challenge. Protein kinase A (tpk1/2/3) is controlling the activation/inactivation of a multitude of proteins through phosphorylation at specific serine residues. Targets of Protein Kinase A (PKA) are also msn2/4 and phosphorylation of these two transcription factors by PKA resulting in obstruction of their translocation to the nucleus. This work attempts to reveal the significance of specific serine residues of Msn2/4p, as possible targets of PKA, through substitution of these serine residues with alanine. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2759, 2019.

Reversed-Flow Gas Chromatography as a Tool for Studying the Interaction between Aroma Compounds and Starch.

The versatile technique of reversed-flow gas chromatography was introduced to calculate physicochemical quantities for the interaction between aroma compounds and starch. Adsorption, adsorption/desorption, and surface reaction rate constants as well as surface diffusion coefficients for the vapors of aroma compounds over the different starch surfaces were calculated in the temperature range of 303.15-333.15 K. Enthalpies of adsorption between -45.5 and -109.0 kJ mol-1 and enthalpies of physicochemical interaction between 6.8 and 47.4 kJ mol-1 were also calculated for all the systems studied. From the obtained results, it is concluded that the interaction forces between aroma compounds and starch correspond to weak energy bonds such as hydrogen bonds and dipole-dipole interactions. For all the systems studied, except for the system heptanal/potato, physical sorption of aroma compounds on starch granules was indicated according to the calculated activation energies.

Study of the influence of surfactants on the activity coefficients and mass transfer coefficients of methanol in aqueous mixtures by reversed-flow gas chromatography.

This work focuses on the influences of surfactants on the activity coefficients, γ, of methanol in binary mixtures with water, as well as on the mass transfer coefficients, kc, for the evaporation of methanol, which is a ubiquitous component in the troposphere, from mixtures of methanol with water at various surfactant's and methanol's concentrations. The technique used is the Reversed-Flow Gas Chromatography (R.F.G.C.), a version of Inverse Gas Chromatography, which allows determining both parameters by performing only one experiment for the kc parameter and two experiments for the γ parameter. The kc and γ values decrease in the presence of the three surfactants used (CTAB, SDS, TRITON X-100) at all methanol's and surfactant's concentrations. The decrease in the methanol's molar fraction, at constant number of surfactant films leads to a decrease in the kc and γ values, while the decrease in the surfactant's concentration, at constant methanol's molar fraction leads to an increase in both the kc and γ parameters. Mass transfer coefficients for the evaporation of methanol at the surfactant films, are also calculated which are approximately between 4 and 5 orders of magnitude larger than the corresponding mass transfer coefficients at the liquid films. Finally, thicknesses of the boundary layer of methanol in the mixtures of methanol with water were determined. The quantities found are compared with those given in the literature or calculated theoretically using various empirical equations. The precision of the R.F.G.C. method for measuring γ and kc parameters is approximately high (94.3-98.0%), showing that R.F.G.C. can be used with success not only for the thermodynamic study of solutions, but also for the interphase transport.

Time distribution of adsorption entropy of gases on heterogeneous surfaces by reversed-flow gas chromatography.

The reversed-flow gas chromatography (RF-GC) technique has been applied to measure the adsorption entropy over time, when gaseous pentane is adsorbed on the surface of two solids (gamma-alumina and a silica supported rhodium catalyst) at 393.15 and 413.15K, respectively. Utilizing experimental chromatographic data, this novel methodology also permits the simultaneous measurement of the local adsorption energy, epsilon, local equilibrium adsorbed concentration, c(s)(*), and local adsorption isotherm, theta(p, T, epsilon) in a time resolved way. In contrast with other inverse gas chromatographic methods, which determine the standard entropy at zero surface coverage, the present method operates over a wide range of surface coverage taking into account not only the adsorbate-adsorbent interaction, but also the adsorbate-adsorbate interaction. One of the most interesting observations of the present work is the fact that the interaction of n-pentane is spontaneous on the Rh/SiO(2) catalyst for a very short time interval compared to that on gamma-Al(2)O(3). This can explain the different kinetic behavior of each particular gas-solid system, and it can be attributed to the fact that large amounts of n-C(5)H(12) are present on the active sites of the Rh/SiO(2) catalyst compared to those on gamma-Al(2)O(3), as the local equilibrium adsorbed concentration values, c(s)(*), indicate.

New gas chromatographic instrumentation for studying the action of sulfur dioxide on marbles.

Reversed-flow gas chromatography, which is a sub-technique of inverse gas chromatography, is an experimental arrangement simulating a simple model for the action of air pollutants on buildings and monuments, in laboratory scale. By using a commercial gas chromatograph and an appropriate mathematical analysis, kinetic parameters such as rate constants for adsorption k1, adsorption/desorption kR and surface reaction k2, as well as surface diffusion coefficients Dgamma, deposition velocities Vd and reaction probabilities gamma of SO2 on marble surfaces at different temperatures (303.15-353.15 K) in the presence or in the absence of protective materials (an acrylic copolymer, Paraloid B-72 or a siloxane, CTS Silo 111) were calculated. From the above mentioned physicochemical quantities the ability of the examined materials to minimize the dry deposition of SO2 on marble is carrying out and a possible mechanism for the interaction between SO2 and Paraloid B-72 was suggested. Both materials (CTS SILO 111 and Paraloid B-72) are good enough for protecting marble against SO2 at low temperatures (303.15-323.15), while at high temperatures (333.15-353.15), siloxane seems to protect marble better than acrylic copolymer.

Heterogeneous catalysis on solids of gases diffusing through a liquid layer, studied by inverse gas chromatography.

Physicochemical parameters for heterogeneous catalytic reactions when the catalytic bed was under a liquid phase have been determined, using a non-linear adsorption isotherm by the reversed-flow version of inverse gas chromatography (RF-GC). The mathematical analysis developed in heterogeneous catalysis, mass transfer across gas-liquid boundaries, and diffusion coefficients of gases in liquids was associated with a non-linear adsorption isotherm to find the relevant equations pertaining to the problem. These equations were then used to calculate the adsorption/desorption rate constant, the rate constant for the first-order catalytic reaction and the equilibrium constant for the non-linear adsorption isotherm. The diffusion coefficients of the reactant in the liquid and gaseous phases and the partition coefficients for the distribution of the reactant between the gaseous and liquid phase were also determined.

Surface energy of solid catalysts measured by inverse gas chromatography.

The time separation of experimental surface energy on Pt-Rh bimetallic catalysts, together with the time-independent rate constants for adsorption and desorption of O(2), CO, and CO(2) on them, is described, applying the reversed-flow version of inverse gas chromatography. The standard free energy of adsorption DeltaG(z.plims;) and its probability density function over time, together with the geometrical mean of the London parts of the total surface free energy (gamma(L)(1)gamma(L)(2))(1/2) of the adsorbed probe and the solid surface, accompanied by the relevant probability density functions over time are also calculated. The time-resolved phenomena lead to quite varying values of DeltaG(z.plims;), (gamma(L)(1)gamma(L)(2))(1/2), and the distribution functions as time passes, their maximum values being given by the catalyst containing a Pt:Rh = 3:1 weight ratio of the active phase for all adsorbed gases. The conclusion is reached that the surface energy measured as described can be used as a good measure for catalyst characterization.

Kinetic study of aggregation of milk protein and/or surfactant-stabilized oil-in-water emulsions by sedimentation field-flow fractionation.

Milk proteins are able to facilitate the formation and stabilization of oil droplets in food emulsions. This study employed Sedimentation Field-Flow Fractionation (SdFFF) to monitor changes in particle size distribution of freshly prepared emulsions with varying weight contributions of sodium caseinate (SC) and whey protein concentrate (WPC). The effect of the addition of Tween 80 (T) on the initial droplet size was also investigated. The results indicated that emulsifying ability follows the order Tween 80>WPC>SC, with corresponding weight average droplet diameter of 0.319, 0.487 and 0.531µm respectively, when each of the above emulsifiers was used solely. The stability of sodium caseinate emulsions was studied at 30.5 and 80.0°C by measuring the particle size distribution for a period of 70h. Emulsions withstood the temperatures and exhibited an initial increase in particle size distribution caused by heat-induced droplet aggregation, followed by a decrease to approximately the initial droplet size. The rate of droplet aggregation depends on the severity of thermal processing, as revealed by the kinetics of particle aggregation during aging at different temperatures. Comparison of the experimental rate constants found from SdFFF, with those determined theoretically gives invaluable information about the oil droplet stability and the aggregation mechanism. Based on the proposed mechanistic scheme various physicochemical quantities, which are very important in explaining the stability of oil-in-water emulsions, were determined. Finally, the advantages of SdFFF in studying the aggregation of the oil-in-water droplets, in comparison with other methods used for the same purpose, are discussed.