Discovering the Influence of Microorganisms on Wine Color

Flavor, composition and quality of wine are influenced by microorganisms present on the grapevine surface which are transferred to the must during vinification. The microbiota is highly variable with a prevalence of non-Saccharomyces yeasts, whereas Saccharomyces cerevisiae is present at low number. For wine production an essential step is the fermentation carried out by different starter cultures of S. cerevisiae alone or in mixed fermentation with non-Saccharomyces species that produce wines with significant differences in chemical composition. During vinification wine color can be influenced by yeasts interacting with anthocyanin. Yeasts can influence wine phenolic composition in different manners: direct interactions—cell wall adsorption or enzyme activities—and/or indirectly—production of primary and secondary metabolites and fermentation products. Some of these characteristics are heritable trait in yeast and/or can be strain dependent. For this reason, the stability, aroma, and color of wines depend on strain/strains used during must fermentation. Saccharomyces cerevisiae or non-Saccharomyces can produce metabolites reacting with anthocyanins and favor the formation of vitisin A and B type pyranoanthocyanins, contributing to color stability. In addition, yeasts affect the intensity and tonality of wine color by the action of β-glycosidase on anthocyanins or anthocyanidase enzymes or by the pigments adsorption on the yeast cell wall. These activities are strain dependent and are characterized by a great inter-species variability. Therefore, they should be considered a target for yeast strain selection and considered during the development of tailored mixed fermentations to improve wine production. In addition, some lactic acid bacteria seem to influence the color of red wines affecting anthocyanins’ profile. In fact, the increase of the pH or the ability to degrade pyruvic acid and acetaldehyde, as well as anthocyanin adsorption by bacterial cells are responsible for color loss during malolactic fermentation. Lactic acid bacteria show different adsorption capacity probably because of the variable composition of the cell walls. The aim of this review is to offer a critical overview of the roles played by wine microorganisms in the definition of intensity and tonality of wines’ color.

Critical Review of Solidification of Sandy Soil by Microbially Induced Carbonate Precipitation (MICP)

Microbially induced carbonate precipitation (MICP) is a promising technology for solidifying sandy soil, ground improvement, repairing concrete cracks, and remediation of polluted land. By solidifying sand into soil capable of growing shrubs, MICP can facilitate peak and neutralization of CO2 emissions because each square meter of shrub can absorb 253.1 grams of CO2 per year. In this paper, based on the critical review of the microbial sources of solidified sandy soil, models used to predict the process of sand solidification and factors controlling the MICP process, current problems in microbial sand solidification are analyzed and future research directions, ideas and suggestions for the further study and application of MICP are provided. The following topics are considered worthy of study: (1) MICP methods for evenly distributing CaCO3 deposit; (2) minimizing NH4+ production during MICP; (3) mixed fermentation and interaction of internal and exogenous urea-producing bacteria; (4) MICP technology for field application under harsh conditions; (5) a hybrid solidification method by combining MICP with traditional sand barrier and chemical sand consolidation; and (6) numerical model to simulate the erosion resistance of sand treated by MICP.

Anaerobic Digestion Characteristics and Key Microorganisms Associated With Low-Temperature Rapeseed Cake and Sheep Manure Fermentation

Qinghai rural household biogas digesters were used to evaluate fermentation characteristics, including gas production and key microbial community changes, associated with low-temperature (15.2-17.8℃) mixed rapeseed cake and sheep manure anaerobic fermentations across 40 days using seven different ratios of material. Different raw material ratios resulted in significantly different effects on biogas yields and microbial community compositions. When the ratio of sheep manure to rapeseed cake was 1:2, the highest level of cumulative gas production was observed (122.92 m3·t−1). Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria were the dominant bacterial phyla among the 29 digester samples (total relative abundances > 79.23%), followed by Synergistetes (4.09%-10.7%). Lactobacillus was the most abundant genus in the biogas digesters with high rapeseed cake contents (average relative abundances: 14.68%), while Peptoniphilus exhibited higher abundances (12.69%) in the mixed fermentation digester treatments. In addition, unclassified Synergistaceae abundances (6.64%) were positively associated with biogas production variation among treatments. Bacteroides (5.74%) and Pseudomonas (5.24%) both accounted for larger proportions of communities in the digesters that used more sheep manure. Methanomicrobiales (66.55%) was the most dominant archaeal group among digesters, with Methanogenium (41.82%) and Methanoculleus (16.55%) representing the main gas-producing archaeal genera; they were more abundant in biogas digesters with higher sheep manure contents and higher rapeseed cake contents, respectively. Regardless of the raw material ratios, Methanoculleus exhibited the highest abundances on the 4th day of fermentation. VFAs and pH were the main factors associated with differences in microbial communities among the 29 samples. Specifically, VFA concentrations were positively correlated with Lactobacillus and Methanoculleus abundances, while pH was positively correlated with Bacteroides, Pseudomonas, Methanobrevibacter, and Methanobacterium abundances.

Visual detection of microbial community during three bacteria mixed fermentation through hyperspectral imaging technology

Hyperspectral imaging technology with chemometrics was used for identifying and counting each species in microbial community during mixed fermentation. Hyperspectral images of microbial community of <i>Enterobacter</i> sp, <i>Acetobacter pasteurianus</i>, and <i>Lactobacillus paracasei</i> colonies were obtained and the spectra of strain colonies were extracted. Identification models were developed using linear discriminant analysis (LDA) and least-squares support vector machine (LS-SVM) by using 23 variables selected by genetic algorithm. The optimal LS-SVM model with identification rate of 96.67 % was used to identify colonies and prepare colony distribution maps in color for strains counting. The counting results by hyperspectral imaging technology agree with that of the manual counting method with average relative error of 3.70 %. The developed counting method has been successfully used to identify and count the specific strain from the mixed strains simultaneously. The hyperspectral imaging technology has a great potential to monitor changes in the microbial community structure.

Impact of Starmerella bacillaris and Zygosaccharomyces bailii on ethanol reduction and Saccharomyces cerevisiae metabolism during mixed wine fermentations

The bulk of grape juice fermentation is carried out by the yeast Saccharomyces cerevisiae, but non-Saccharomyces yeasts can modulate many sensorial aspects of the final products in ways not well understood. In this study, some of such non-conventional yeasts were screened as mixed starter cultures in a fermentation defined medium in both simultaneous and sequential inoculations. One strain of Starmerella bacillaris and another of Zygosaccharomyces bailii were chosen by their distinct phenotypic footprint and their ability to reduce ethanol levels at the end of fermentation, particularly during simultaneous vinification. S. bacillaris losses viability strongly at the end of mixed fermentation, while Z. bailii remains viable until the end of vinification. Interestingly, for most non-Saccharomyces yeasts, simultaneous inoculation helps for survival at the end of fermentation compared to sequential inoculation. S. cerevisiae viability was unchanged by the presence of the either yeast. Characterization of both strains indicates that S. bacillaris behavior is overall more different from S. cerevisiae than Z. bailii. S. bacillaris has a less strict glucose repression mechanism and molecular markers like catabolite repression kinase Snf1 is quite different in size. Besides, S. cerevisiae transcriptome changes to a bigger degree in the presence of S. bacillaris than when inoculated with Z. bailii. S. bacillaris induces the translation machinery and repress vesicular transport. Both non-Saccharomyces yeast induce S. cerevisiae glycolytic genes, and that may be related to ethanol lowering, but there are specific aspects of carbon-related mechanisms between strains: Z. bailii presence increases the stress-related polysaccharides trehalose and glycogen while S. bacillaris induces gluconeogenesis genes.

Identification of Lactic Acid Bacteria in the corn stalk Fermentation by Fluorescence Quantitative PCR

Lactic acid bacteria play an important role in the fermentation of biological feed. In this experiment, Lactobacillus plantarum, Lactobacillus acidophilus, Bifidobacterium longum, Lactobacillus casei and Lactobacillus rhamnosus were used to ferment corn stalk by single and mixed bacteria. The changes of Lactobacillus flora during fermentation were analyzed by fluorescence quantitative PCR. The results showed that the maximum number of lactic acid bacteria appeared on the 7th day of mixed fermentation, and the total bacteria content could be significantly increased by adding five kinds of lactic acid bacteria at the same time, and the number of each bacteria in mixed fermentation was close to that measured by single fermentation, which indicated that these five kinds of lactic acid bacteria could cooperate during fermentation and help to improve the quality of stalk fermented feed.

Variation of bitter components of the asparagus juices during lactic acid bacteria fermentation

To investigate the bitterness status of asparagus juices during lactic acid fermentation, Limosilactobacillus fermentum Xd, Lacticaseibacillus paracasei Yd, Lactiplantibacillus plantarum 5-7-3 and their various combinations were used for single and mixed fermentation of asparagus juices. The fermentation characteristics and variation of the main bitter substances were studied. For the single and co-fermented samples, the viable counts, pH value and acidity were ranged from 8.33 lg CFU/mL to 8.65 lg CFU/mL, 3.58 to 3.86 and 6.29 g/kg to 6.52 g/kg, respectively. By sensory evaluation, the bitterness of every fermented sample was continuously reduced by at least 77% during fermentation and the corresponding content of total saponins, flavonoids and nine bitter amino acids showed varying degrees of declination. These results suggested that it was feasible to develop novel low-bitter asparagus juices fermented by the lactic acid bacteria used in this study.

Brewing and Probiotic Potential Activity of Wild Yeasts Hanseniaspora Uvarum PIT001, Pichia Kluyveri LAR001 and Candida Intermedia ORQ001

Non-conventional yeasts can be isolated from a wide range of environmental sources, often found in beverage industry in mixed fermentations, in which the microorganisms’ inoculum usually is not fully known. It is important to know starter cultures, since in addition to favoring reproducibility, other properties can be discovered. Thus, the objective of this work was to identify and characterize yeasts isolated from environment, evaluating their probiotic potential and possible use in brewery. Isolates were obtained from flowers, fruits, leaves and mixed-fermentation beers, being identified by PCR. Yeasts with promising activity were evaluated regarding their growth under different pHs, temperature and presence of organic acids. To explore probiotic potential, in vitro tests were performed of antimicrobial activity and co-aggregation with food pathogens, auto-aggregation, and survival in simulated gastrointestinal tract conditions. In our study, Pichia kluyveri (LAR001), Hanseniaspora uvarum (PIT001) and Candida intermedia (ORQ001) were selected among 20 isolates. P. kluyveri was the only one that tolerated pH 2.5. Lactic acid was not inhibitory, while acetic acid and incubation at 37 °C had a partially inhibitory effect on yeasts growth. All yeasts tolerated α-acids from hops and NaCl up to 1%. It is suggested that isolates are able to adhere to intestinal cells and influence positively the organism in combating pathogens, as they showed auto-aggregation rates above 99% and antagonistic activity to pathogenic bacteria. The yeasts tolerated gastric environment conditions, however were more sensitive to pancreatic conditions. We conclude that isolated non-conventional yeasts showed probiotic potential and promising application in beer fermentation.