Influence of oxygen addition during growth phase on the biosynthesis of lipids in Saccharomyces cerevisiae (M330-9) in enological fermentations

Evidence of the Relationship between the Oxygen Radical Absorbance Capacity (ORAC) and the Potential Exposure of White Wines to Atypical Aging (ATA)

Atypical aging (ATA) is a well-known wine defect that leads to unacceptable off-odors of wet mop, soap, waxy, furniture varnish, and dish rag. The main compound that is responsible for these undesired scents, 2-aminoacetophenone (AAP), results from the oxidative degradation of 3-indole acetic acid. This study aimed to investigate different technological factors for a possible effect on the oxygen radical absorption capacity (ORAC) and ATA development in white wine. Oxygenation during fermentation did not result in a significant effect on the development of ORAC or ATA development. Instead, the addition of ascorbic acid after vinification led to increased ORAC and decreased AAP formation. The first evidence of a tendency toward a correlation between ORAC and potential ATA development was found, with r = 0.365. This study showed the potential of the ORAC assay for an early assessment of the possible formation of ATA during wine storage.

Dosing oxygen from the early stages of white winemaking: Effect on oxidation-reduction potential, browning stability, volatile composition, and sensory properties

This study investigated the effect of controlled oxygen addition during alcoholic fermentation (4 mg/L, at 2nd, 4th, 6th, 10th, 14th, 16th, 20th day) and aging on lees (2 mg/L, every 15 days for 3 months) in a stainless-steel tank for white wine production from a nearly neutral grape. Under less reductive conditions (Ox), alcoholic fermentation was completed in 27 days, whereas one extra week was required under more reductive conditions (no-Ox). The greatest amount of dissolved oxygen in Ox wine triggered the increase of redox potential (EH) starting from the end of alcoholic fermentation and throughout aging (169 and 150 mV in Ox and no-Ox wine, respectively), also improving the wine resistance to browning. Oxygen addition from the early stages of winemaking significantly modulated volatile composition and sensory attributes, which may contribute to the diversification of wine style.

Biotechnological enhancement of lactic acid conversion from pretreated palm kernel cake hydrolysate by Actinobacillus succinogenes 130Z

The aim of this study was to establish an improved pretreatment and fermentation method i.e. immobilized cells for high recovery of fermentable sugars from palm kernel cake (PKC) and its effects on fermentability performance by Actinobacillus succinogenes 130Z in the conversion of the fermentable sugar to lactic acid. The effects of oxalic acid concentrations (1-6% w/v) and residence times (1-5 h) on the sugar recovery were initially investigated and it was found that the highest mannose concentration was 25.1 g/L at the optimum hydrolysis conditions of 4 h and 3% (w/v) oxalic acid. The subsequent enzymatic saccharification of the pretreated PKC afforded the highest enzymatic digestibility with the recovered sugars amounting to 25.18 g/L and 9.14 g/L of mannose and glucose, respectively. Subsequently, the fermentability performance of PKC hydrolysate was evaluated and compared in terms of cultivation phases (i.e. mono and dual-phases), carbonate loadings (i.e. magnesium and sodium carbonates), and types of sugars (i.e. glucose and mannose). The highest titer of 19.4 g/L lactic acid was obtained from the fermentation involving A. succinogenes 130Z in dual-phase cultivation supplemented with 30 g/L of magnesium carbonate. Lactic acid production was further enhanced by using immobilized cells with coconut shell-activated carbon (CSAC) of different sizes (A, B, C, and D) in the repeated batch cultivation of dual-phase fermentation producing 31.64 g/L of lactic acid. This work sheds light on the possibilities to enhance the utilization of PKC for lactic acid production via immobilized A. succinogenes 130Z.

Biotechnological enhancement of lactic acid conversion from palm kernel cake by immobilized Actinobacillus succinogenes 130Z.. [DOI: 10.21203/rs.3.rs-2469941/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The aim of this study was to establish an improved pretreatment and fermentation method i.e. immobilized cells for high recovery of fermentable sugars from PKC and its effects on fermentability performance by Actinobacillus succinogenes 130Z in the conversion of lactic acid. The effects of oxalic acid concentrations (1–6% w/v) and residence times (1–5 h) on the sugar recovery were initially investigated and it was found that the highest mannose concentration was 25.1 g/L at the optimum hydrolysis conditions of 4 h and 3% (w/v) oxalic acid. The subsequent enzymatic saccharification of the pretreated PKC afforded the highest enzymatic digestibility with the recovered sugars amounting to 25.18 g/L and 9.14 g/L of mannose and glucose, respectively. Subsequently, the fermentability performance of PKC hydrolysate was evaluated and compared in terms of cultivation phases (i.e. mono and dual-phases), carbonate loadings (i.e. magnesium and sodium carbonates), and types of sugars (i.e. glucose and mannose). The highest titer of 19.4 g/L lactic acid was obtained from the fermentation involving A. succinogenes 130Z in dual-phase cultivation supplemented with 30 g/L of magnesium carbonate. Lactic acid production was further enhanced by using immobilized cells with coconut shell-activated carbon (CSAC) of different sizes (A, B, C, and D) in the repeated batch cultivation of dual-phase fermentation producing 31.64 g/L of lactic acid. This work sheds light on the possibilities to enhance the utilization of PKC for lactic acid production via immobilized A. succinogenes 130Z.

The metabolism of lipids in yeasts and applications in oenology

Lipids are valuable compounds present in all living organisms, which display an array of functions related to compartmentalization, energy storage and enzyme activation. Furthermore, these compounds are an integral part of the plasma membrane which is responsible for maintaining structure, facilitating the transport of solutes in and out of the cell and cellular signalling necessary for cell survival. The lipid composition of the yeast Saccharomyces cerevisiae has been extensively investigated and the impact of lipids on S. cerevisiae cellular functions during wine alcoholic fermentation is well documented. Although other yeast species are currently used in various industries and are receiving increasing attention in winemaking, little is known about their lipid metabolism. This review article provides an extensive and critical evaluation of our knowledge on the biosynthesis, accumulation, metabolism and regulation of fatty acids and sterols in yeasts. The implications of the yeast lipid content on stress resistance as well as performance during alcoholic fermentation are discussed and a particular emphasis is given on non-Saccharomyces yeasts. Understanding lipid requirements and metabolism in non-Saccharomyces yeasts may lead to a better management of these yeast to enhance their contributions to wine properties.

Effect of Musts Oxygenation at Various Stages of Cider Production on Oenological Parameters, Antioxidant Activity, and Profile of Volatile Cider Compounds

The micro-oxygenation of musts may affect the quality of a finished alcoholic beverage. The aim of this study was to determine the effect of micro-oxygenation at various stages of fermentation on oenological parameters, antioxidant activity, total polyphenol content, and profile of volatile cider compounds fermented with various yeast strains. Rubin cultivar must was inoculated with wine yeast, cider yeast, distillery yeast, and wild yeast strains. Some of the inoculated samples were oxygenated immediately after yeast inoculation, and some on the second and third fermentation days. The control sample was non-oxygenated must fermented in bottles. Higher extract concentration and acidity as well as lower potency were observed in cider treated with micro-oxygenation. Must oxygenation in most cases contributed to the reduction of polyphenol content and to the antioxidant activity of ciders, especially when fermented using wild yeast. The oxygenation of musts before fermentation caused an increase in the content of esters and alcohols in ciders. However, the oxygenation of musts during fermentation reduced the concentration of these volatile components. The oxygenation of musts during fermentation produced a differentiated effect on terpenoid concentration in ciders.

Investigations of the mechanisms of interactions between four non-conventional species with Saccharomyces cerevisiae in oenological conditions

Fermentation by microorganisms is a key step in the production of traditional food products such as bread, cheese, beer and wine. In these fermentative ecosystems, microorganisms interact in various ways, namely competition, predation, commensalism and mutualism. Traditional wine fermentation is a complex microbial process performed by Saccharomyces and non-Saccharomyces (NS) yeast species. To better understand the different interactions occurring within wine fermentation, isolated yeast cultures were compared with mixed co-cultures of one reference strain of S. cerevisiae with one strain of four NS yeast species (Metschnikowia pulcherrima, M. fructicola, Hanseniaspora opuntiae and H. uvarum). In each case, we studied population dynamics, resource consumed and metabolites produced from central carbon metabolism. This phenotyping of competition kinetics allowed us to confirm the main mechanisms of interaction between strains of four NS species. S. cerevisiae competed with H. uvarum and H. opuntiae for resources although both Hanseniaspora species were characterized by a strong mortality either in mono or mixed fermentations. M. pulcherrima and M. fructicola displayed a negative interaction with the S. cerevisiae strain tested, with a decrease in viability in co-culture. Overall, this work highlights the importance of measuring specific cell populations in mixed cultures and their metabolite kinetics to understand yeast-yeast interactions. These results are a first step towards ecological engineering and the rational design of optimal multi-species starter consortia using modeling tools. In particular the originality of this paper is for the first times to highlight the joint-effect of different species population dynamics on glycerol production and also to discuss on the putative role of lipid uptake on the limitation of some non-conventional species growth although interaction processes.

Effects of initial oxygenation on chemical and aromatic composition of wine in mixed starters of Hanseniaspora vineae and Saccharomyces cerevisiae

The use of Saccharomyces and non-Saccharomyces yeast species as mixed starters has potential advantages over pure culture fermentation due to increased wine complexity based on modification of metabolites of oenological interest. In this work, the effects of initial oxygenation on fermentation performance, chemical and volatile composition of French Colombard wine fermented with Hanseniaspora vineae and Saccharomyces cerevisiae in sequential inoculations were investigated in 1 L flasks. Although dominated by S. cerevisiae at the middle-end of fermentation, initial aeration for 1 day boosted H. vineae populations, and allowed H. vineae to coexist longer with S. cerevisiae in mixed cultures compared to no aeration, and suppressed S. cerevisiae later in the fermentation, which resulted in extended fermentation time. More important, the major fermentation products and volatile compounds were significantly modified by aeration and different from no aeration fermentation. The wines produced by aeration of mixed fermentations were characterized with higher amounts of glycerol, lactic acid and acetate esters, and lower levels of ethanol, higher alcohol and ethyl fatty acid esters. The aeration had more potential to shape the quality of wines and diversify the aromatic characteristics relative to simple mixed inoculation, as indicated by PCA analysis. Our results suggested that the impact of early aeration on yeast physiology extends beyond the aeration phase and influences fermentation activity, chemical and aromatic compounds in the following anaerobic stage. The aeration for a short time during the cell growth stage in mixed fermentation is therefore a potential means to increase the aromatic diversity and quality of wine, possibly providing an alternative approach to meet the expectations of wine consumers for diverse aromatic qualities.

Producing Oleaginous Organisms Using Food Waste: Challenges and Outcomes

With organic or food waste being one of the main constituents of the total urban waste generated, it not only makes it essential to seek means for its safe disposal but at the same time reiterates the huge potential that lies with the proper utilization of such a widely available resource. Oleaginous microbes that are effective in producing or storing oil would use food waste rich in carbohydrates, lipids, and proteins, and this oil in turn could be an alternative feedstock for the production of biofuels. However, there are few challenges in the process. The various challenges in this process and methods to address them are discussed in the present chapter.

Micro-oxygenation does not eliminate hydrogen sulfide and mercaptans from wine; it simply shifts redox and complex-related equilibria to reversible oxidized species and complexed forms

This work seeks to assess the effects of micro-oxygenation (MOX) on the present and potential levels of Volatile Sulfur Compounds (VSCs) of wine. With such purpose, three red wines with a tendency to develop sulfury off-odors were subjected to three different MOX conditions (4.4-20mg/L delivered at 0.05 or 0.2mg/L/day). Samples were further subjected to Accelerated Reductive aging (AR) and analyzed for free and Brine Releasable (BR) VSCs and redox potential. Although MOX induced strong decreases in the levels of all free VSCs, hardly affected the ability of the wine to release back hydrogen sulfide and other mercaptans during AR-aging. During aging BR-levels of MOX samples became in most cases similar or higher than non-oxygenated controls. BR-levels and the fractions free/BR follow characteristic sigmoid plots when represented versus redox potential suggesting that all changes are the result of reversible equilibria between free, metal-complexed and oxidized forms of VSCs.

Non-conventional Yeast Species for Lowering Ethanol Content of Wines

Rising sugar content in grape must, and the concomitant increase in alcohol levels in wine, are some of the main challenges affecting the winemaking industry nowadays. Among the several alternative solutions currently under study, the use of non-conventional yeasts during fermentation holds good promise for contributing to relieve this problem. Non-Saccharomyces wine yeast species comprise a high number or species, so encompassing a wider physiological diversity than Saccharomyces cerevisiae. Indeed, the current oenological interest of these microorganisms was initially triggered by their potential positive contribution to the sensorial complexity of quality wines, through the production of aroma and other sensory-active compounds. This diversity also involves ethanol yield on sugar, one of the most invariant metabolic traits of S. cerevisiae. This review gathers recent research on non-Saccharomyces yeasts, aiming to produce wines with lower alcohol content than those from pure Saccharomyces starters. Critical aspects discussed include the selection of suitable yeast strains (considering there is a noticeable intra-species diversity for ethanol yield, as shown for other fermentation traits), identification of key environmental parameters influencing ethanol yields (including the use of controlled oxygenation conditions), and managing mixed fermentations, by either the sequential or simultaneous inoculation of S. cerevisiae and non-Saccharomyces starter cultures. The feasibility, at the industrial level, of using non-Saccharomyces yeasts for reducing alcohol levels in wine will require an improved understanding of the metabolism of these alternative yeast species, as well as of the interactions between different yeast starters during the fermentation of grape must.

The impact of oxygen on the final alcohol content of wine fermented by a mixed starter culture

We have developed a wine fermentation procedure that takes advantage of the metabolic features of a previously characterized Metschnikowia pulcherrima strain in order to reduce ethanol production. It involves the use of M. pulcherrima/Saccharomyces cerevisiae mixed cultures, controlled oxygenation conditions during the first 48 h of fermentation, and anaerobic conditions thereafter. The influence of different oxygenation regimes and initial inoculum composition on yeast physiology and final ethanol content was studied. The impact of oxygenation on yeast physiology goes beyond the first aerated step and influences yields and survival rates during the anaerobic stage. The activity of M. pulcherrima in mixed oxygenated cultures resulted in a clear reduction in ethanol yield, as compared to S. cerevisiae. Despite relatively low initial cell numbers, S. cerevisiae always predominated in mixed cultures by the end of the fermentation process. Strain replacement was faster under low oxygenation levels. M. pulcherrima confers an additional advantage in terms of dissolved oxygen, which drops to zero after a few hours of culture, even under highly aerated conditions, and this holds true for mixed cultures. Alcohol reduction values about 3.7 % (v/v) were obtained for mixed cultures under high aeration, but they were associated to unacceptable volatile acidity levels. In contrast, under optimized conditions, only 0.35 g/L acetic acid was produced, for an alcohol reduction of 2.2 % (v/v), and almost null dissolved oxygen during the process.

Metabolic and transcriptomic response of the wine yeast Saccharomyces cerevisiae strain EC1118 after an oxygen impulse under carbon-sufficient, nitrogen-limited fermentative conditions

During alcoholic fermentation, Saccharomyces cerevisiae is exposed to continuously changing environmental conditions, such as decreasing sugar and increasing ethanol concentrations. Oxygen, a critical nutrient to avoid stuck and sluggish fermentations, is only discretely available throughout the process after pump-over operation. In this work, we studied the physiological response of the wine yeast S. cerevisiae strain EC1118 to a sudden increase in dissolved oxygen, simulating pump-over operation. With this aim, an impulse of dissolved oxygen was added to carbon-sufficient, nitrogen-limited anaerobic continuous cultures. Results showed that genes related to mitochondrial respiration, ergosterol biosynthesis, and oxidative stress, among other metabolic pathways, were induced after the oxygen impulse. On the other hand, mannoprotein coding genes were repressed. The changes in the expression of these genes are coordinated responses that share common elements at the level of transcriptional regulation. Beneficial and detrimental effects of these physiological processes on wine quality highlight the dual role of oxygen in 'making or breaking wines'. These findings will facilitate the development of oxygen addition strategies to optimize yeast performance in industrial fermentations.

Oxygen response of the wine yeast Saccharomyces cerevisiae EC1118 grown under carbon-sufficient, nitrogen-limited enological conditions

Discrete additions of oxygen play a critical role in alcoholic fermentation. However, few studies have quantitated the fate of dissolved oxygen and its impact on wine yeast cell physiology under enological conditions. We simulated the range of dissolved oxygen concentrations that occur after a pump-over during the winemaking process by sparging nitrogen-limited continuous cultures with oxygen-nitrogen gaseous mixtures. When the dissolved oxygen concentration increased from 1.2 to 2.7 μM, yeast cells changed from a fully fermentative to a mixed respirofermentative metabolism. This transition is characterized by a switch in the operation of the tricarboxylic acid cycle (TCA) and an activation of NADH shuttling from the cytosol to mitochondria. Nevertheless, fermentative ethanol production remained the major cytosolic NADH sink under all oxygen conditions, suggesting that the limitation of mitochondrial NADH reoxidation is the major cause of the Crabtree effect. This is reinforced by the induction of several key respiratory genes by oxygen, despite the high sugar concentration, indicating that oxygen overrides glucose repression. Genes associated with other processes, such as proline uptake, cell wall remodeling, and oxidative stress, were also significantly affected by oxygen. The results of this study indicate that respiration is responsible for a substantial part of the oxygen response in yeast cells during alcoholic fermentation. This information will facilitate the development of temporal oxygen addition strategies to optimize yeast performance in industrial fermentations.