Entrapped Psychrotolerant Yeast Cells within Pine Sawdust for Low Temperature Wine Making: Impact on Wine Quality

Root-associated fungal microbiota of the perennial sweet sorghum cultivar under field growth

Root-associated fungal microbiota, which inhabit the rhizosphere, rhizoplane and endosphere, have a profound impact on plant growth and development. Sorghum bicolor (L.) Moench, also called broomcorn or sweet sorghum, is a multipurpose crop. The comparison between annual and perennial sweet sorghum cultivars in terms of plant growth, as well as their interactions with belowground fungal microbiota, is still poorly understood, although there has been growing interest in the mutualism between annual sweet sorghum and soil bacteria or bacterial endophytes. In this study, the perennial sweet sorghum cultivar N778 (N778 simply) and its control lines TP213 and TP60 were designed to grow under natural field conditions. Bulk soil, rhizosphere soil and sorghum roots were collected at the blooming and maturity stages, and then the fungal microbiota of those samples were characterized by high-throughput sequencing of the fungal ITS1 amplicon. Our results revealed that the alpha diversity of the fungal microbiota in rhizosphere soil and root samples was significantly different between N778 and the two control lines TP213 and TP60 at the blooming or maturity stage. Moreover, beta diversity in rhizosphere soil of N778 was distinct from those of TP213 and TP60, while beta diversity in root samples of N778 was distinct from those of TP213 but not TP60 by PCoA based on Bray–Curtis and WUF distance metrics. Furthermore, linear discriminant analysis (LDA) and multiple group comparisons revealed that OTU4372, a completely unclassified taxon but with symbiotroph mode, was enriched in sorghum roots, especially in N778 aerial roots at the blooming stage. Our results indicate that Cladosporium and Alternaria, two fungal genera in the rhizosphere soil, may also be dominant indicators of sorghum yield and protein content in addition to Fusarium at the maturity stage and imply that the perennial sweet sorghum N778 can primarily recruit dominant psychrotolerant bacterial taxa but not dominant cold-tolerant fungal taxa into its rhizosphere to support its survival below the freezing point.

Production of the Polysaccharide Pullulan by Aureobasidium pullulans Cell Immobilization

This review examines the immobilization of A. pullulans cells for production of the fungal polysaccharide pullulan. Pullulan is a water-soluble gum that exists structurally as a glucan consisting primarily of maltotriose units, which has a variety of food, non-food and biomedical applications. Cells can be immobilized by carrier-binding or entrapment techniques. The number of studies utilizing carrier-binding as a method to immobilize A. pullulans cells appears to outnumber the investigations using cell entrapment. A variety of solid supports, including polyurethane foam, sponge, diatomaceous earth, ion-exchanger, zeolite and plastic composite, have been employed to immobilize pullulan-producing A. pullulans cells. The most effective solid support that was used to adsorb the fungal cells was polyurethane foam which produced polysaccharide after 18 cycles of use. To entrap pullulan-producing fungal cells, agents such as polyurethane foam, polyvinyl alcohol, calcium alginate, agar, agarose, carrageenan and chitosan were investigated. Polysaccharide production by cells entrapped in polyurethane foam, polyvinyl alcohol or calcium alginate was highest and the immobilized cells could be reutilized for several cycles. It was shown that the pullulan content of the polysaccharide synthesized by cells entrapped in calcium alginate beads was low, which limits the method’s usefulness for pullulan production. Further, many of the entrapped fungal cells synthesized polysaccharide with a low pullulan content. It was concluded that carrier-binding techniques may be more effective than entrapment techniques for A. pullulans cell immobilization, since carrier-binding is less likely to affect the pullulan content of the polysaccharide being synthesized.

Trials of Commercial- and Wild-Type Saccharomyces cerevisiae Strains under Aerobic and Microaerophilic/Anaerobic Conditions: Ethanol Production and Must Fermentation from Grapes of Santorini (Greece) Native Varieties

In modern wine-making technology, there is an increasing concern in relation to the preservation of the biodiversity, and the employment of “new”, “novel” and wild-type Saccharomyces cerevisiae strains as cell factories amenable for the production of wines that are not “homogenous”, expressing their terroir and presenting interesting and “local” sensory characteristics. Under this approach, in the current study, several wild-type Saccharomyces cerevisiae yeast strains (LMBF Y-10, Y-25, Y-35 and Y-54), priorly isolated from wine and grape origin, selected from the private culture collection of the Agricultural University of Athens, were tested regarding their biochemical behavior on glucose-based (initial concentrations ca 100 and 200 g/L) shake-flask experiments. The wild yeast strains were compared with commercial yeast strains (viz. Symphony, Cross X and Passion Fruit) in the same conditions. All selected strains rapidly assimilated glucose from the medium converting it into ethanol in good rates, despite the imposed aerobic conditions. Concerning the wild strains, the best results were achieved for the strain LMBF Y-54 in which maximum ethanol production (EtOHmax) up to 68 g/L, with simultaneous ethanol yield on sugar consumed = 0.38 g/g were recorded. Other wild strains tested (LMBF Y-10, Y-25 and Y-35) achieved lower ethanol production (up to ≈47 g/L). Regarding the commercial strains, the highest ethanol concentration was achieved by S. cerevisiae Passion Fruit (EtOHmax = 91.1 g/L, yield = 0.45 g/g). Subsequently, the “novel” strain that presented the best technological characteristics regards its sugar consumption and alcohol production properties (viz. LMBF Y-54) and the commercial strain that equally presented the best previously mentioned technological characteristics (viz. Passion Fruit) were further selected for the wine-making process. The selected must originated from red and white grapes (Assyrtiko and Mavrotragano, Santorini Island; Greece) and fermentation was performed under wine-making conditions showing high yields for both strains (EtOHmax = 98–106 g/L, ethanol yield = 0.47–0.50 g/g), demonstrating the production efficiency under microaerophilic/anaerobic conditions. Molecular identification by rep-PCR carried out throughout fermentations verified that each inoculated yeast was the one that dominated during the whole bioprocess. The aromatic compounds of the produced wines were qualitatively analyzed at the end of the processes. The results highlight the optimum technological characteristics of the selected “new” wild strain (S. cerevisiae LMBF Y-54), verifying its suitability for wine production while posing great potential for future industrial applications.

Valorization of Lactic Acid Fermentation of Pomegranate Juice by an Acid Tolerant and Potentially Probiotic LAB Isolated from Kefir Grains

The present study describes the application of an acid tolerant and potentially probiotic L. paracasei SP3 strain, recently isolated from kefir grains, in the production of a novel functional beverage based on the fermentation of pomegranate juice. The fermentation ability of the novel strain was assessed during pomegranate juice fermentations at 30 °C for 24 h and storage at 4 °C for 4 weeks. Various parameters were assessed such as residual sugar, organic acid and alcohol levels, total phenolics content, antioxidant activity, astringency, cell viability, and consumer acceptance. Residual sugar was decreased by approximately 25%, while respectable amounts of lactic acid were determined (4.8 g/L) on the 28th day of storage, proving that the novel strain was effective at lactic acid fermentation. The concentration of ethanol was maintained at low levels (0.3–0.4 % v/v) and low levels of acetic acid were detected (0.6 g/L). The viability of L. paracasei SP3 cells retained high levels (>7 log cfu/mL), even by the 4th week. The total phenolic content (123.7–201.1 mg GAE/100 mL) and antioxidant activity (124.5–148.5 mgTE/100 mL) of fermented pomegranate juice were recorded at higher levels for all of the studied time periods compared to the non-fermented juice. The employment of the novel strain led to a significant reduction in the levels of hydrolysable tannins (42%) in the juice, reducing its astringency. The latter was further proven through sensorial tests, which reflected the amelioration of the sensorial features of the final product. It should be underlined that fruit juices as well as pomegranate juice comprised a very harsh food matrix for microorganisms to survive and ferment. Likewise, the L. paracasei SP3 strain showed a significant potential, because it was applied as a free culture, without the application of microencapsulation methods that are usually employed in these fermentations, leading to a product with possible functional properties and a high nutritive value.

Effect of Yeast Assimilable Nitrogen Content on Fermentation Kinetics, Wine Chemical Composition and Sensory Character in the Production of Assyrtiko Wines

Two wild-type Saccharomyces cerevisiae yeast strains (Sa and Sb) were tested for white wine production using Assyrtiko grape of Santorini. A third commercial Saccharomyces strain was also studied for comparison reasons. Two concentrations of yeast extract and diammonium phosphate (DAP) were added to the must (150 and 250 mg/L) in order to evaluate the effect of nitrogen content on the final wine quality. Analytical methods (HPLC, GC-MS) and sensory analysis were employed to assess the quality of the wines. Fermentation kinetics were monitored throughout the experiment. By the second day of fermentation, all strains showed an approximate consumption of 70% of amino acids. Differences among strains were observed regarding inorganic nitrogen requirements. Sb strain resulted in higher concentrations of higher alcohols (1.9-fold) and ketones (5.6-fold) and lower concentrations of esters (1.2-fold) compared to the control, while Sa strain resulted in higher content of fatty acids (2.1-fold). Both indigenous strains scored better results in aroma quality, body and acidity compared to control. The overall evaluation of the data highlights the great potential of the indigenous S. cerevisiae strains as fermentation starters providing promising results in the sector of terroir wines.

Study of Oenological Fermentation: Which Strategy and Which Tools?

Wine fermentation is a specific and complex research subject and its control is essential to ensure full process completion while improving wine quality. It displays several specificities, in particular, (i) musts with a very high sugar content, low pH, and some limiting nutrients, as well as a great variability in must composition according to the year, grape variety, and so on; (ii) atypical fermentation conditions with non-isothermal temperature profiles, a quasi-anaerobiosis and legal constraints with a limited and predefined list of authorized operations. New challenges have emerged, related to the increasing diversity of commercially available yeast strains; the fluctuating composition of musts, particularly owing to climate change; and sustainability, which has become a key issue. This paper synthesizes approaches implemented to address all these issues. It details the example of our laboratory that, for many years, has been developing an integrated approach to study yeast diversity, understand their metabolism, and develop new fermentation control strategies. This approach requires the development of specific fermentation devices to study yeast metabolism in a controlled environment that mimics practical conditions and to develop original fermentation control strategies. All these tools are described here, together with their role in the overall scientific strategy and complementary approaches in the literature.

Quantification of Volatile Compounds in Wines by HS-SPME-GC/MS: Critical Issues and Use of Multivariate Statistics in Method Optimization

The aim of this review is to explore and discuss the two main aspects related to a HeadSpace Solid Phase Micro-Extraction Gas-Chromatography/Mass-Spectrometry (HS-SPME-GC/MS) quantitative analysis of volatile compounds in wines, both being fundamental to obtain reliable data. In the first section, recent advances in the use of multivariate optimization approaches during the method development step are described with a special focus on factorial designs and response surface methodologies. In the second section, critical aspects related to quantification methods are discussed. Indeed, matrix effects induced by the complexity of the volatile profile and of the non-volatile matrix of wines, potentially differing between diverse wines in a remarkable extent, often require severe assumptions if a reliable quantification is desired. Several approaches offering different levels of data reliability including internal standards, model wine calibration, a stable isotope dilution analysis, matrix-matched calibration and standard addition methods are reported in the literature and are discussed in depth here.

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.

Impacts of Magnetic Immobilization on the Recombinant Proteins Structure Produced in Pichia pastoris System

Pichia pastoris expression system was introduced with post-translation process similar to higher eukaryotes. Preliminary studies were performed toward process intensification and magnetic immobilization of this system. In this experiment, effects of magnetic immobilization on the structure of recombinant protein were evaluated. P. pastoris cell which express human serum albumin (HSA) was used as a model. The cells were immobilized with various concentrations of APTES coated magnetite nanoparticles. HSA production was done over 5 days induction and structure of the product was analyzed by UV-vis, fluorescence, and ATR-FTIR spectroscopy. Second derivative deconvolution method was used to analyze the secondary structure of HSA. P. pastoris cell that were immobilized with 0.5 and 1 mg/mL of nanoparticles were produced HSA with intact structure. But immobilization with 2 mg/mL of nanoparticles resulted in some modifications in the secondary structures (i.e., α-helixes and β-turns) of produced HSA. Based on these data, immobilization of P. pastoris cells with 0.5 or 1 mg/mL of nanoparticles is completely efficient for cell harvesting and has any effect on the structure of recombinant product. These findings revealed that decoration of microbial cells with high concentrations of nanoparticles has some impacts on the structure of secretory proteins.

Next Generation Winemakers: Genetic Engineering in Saccharomyces cerevisiae for Trendy Challenges

The most famous yeast of all, Saccharomyces cerevisiae, has been used by humankind for at least 8000 years, to produce bread, beer and wine, even without knowing about its existence. Only in the last century we have been fully aware of the amazing power of this yeast not only for ancient uses but also for biotechnology purposes. In the last decades, wine culture has become and more demanding all over the world. By applying as powerful a biotechnological tool as genetic engineering in S. cerevisiae, new horizons appear to develop fresh, improved, or modified wine characteristics, properties, flavors, fragrances or production processes, to fulfill an increasingly sophisticated market that moves around 31.4 billion € per year.