Molecular and Phenotypic Diversity of Indigenous Oenological Strains of Saccharomyces cerevisiae Isolated in Greece

During 3 years, we explored the biodiversity of the indigenous yeast flora in five Greek wine regions by collecting five varietal grape samples, conventionally and biologically cultured. Spontaneous wine fermentations were carried out by the native microbiota of the grape juice, without the inoculation of selected industrially produced yeast. The indigenous yeast flora, isolated at three phases of these fermentations, was purified and characterized using different oenological and technological criteria. The pre-selected Saccharomyces cerevisiae strains, with the most promising oenological characteristics, were evaluated in microvinifications of Malagousia must and the quality of the produced wines was subjected to a sensorial descriptive analysis.

Increased Varietal Aroma Diversity of Marselan Wine by Mixed Fermentation with Indigenous Non-Saccharomyces Yeasts

The common use of commercial yeasts usually leads to dull wine with similar aromas and tastes. Therefore, screening for novel indigenous yeasts to practice is a promising method. In this research, aroma discrepancies among six wine groups fermentated with indigenous yeasts were analyzed. Three Saccharomyces yeasts (FS36, HL12, YT28) and three matched non-Saccharomyces yeasts (FS31, HL9, YT2) were selected from typical Chinese vineyards. The basic oenological parameters, aroma compounds, and sensory evaluation were analyzed. The results showed that each indigenous Saccharomyces yeast had excellent fermentation capacity, and mixed-strain fermentation groups produced more glycerol, contributing to sweeter and rounder taste. The results from GC-MS, principal components analysis (PCA), and sensory evaluation highlighted that the HL mixed group kept the most content of Marselan varietal flavors such as calamenene and β-damascone hereby ameliorated the whole aroma quality. Our study also implied that the indigenous yeast from the same region as the grape variety seems more conducive to preserve the natural variety characteristics of grapes.

Selection of Indigenous Saccharomyces cerevisiae Strains and Exploitation of a Pilot-Plant to Produce Fresh Yeast Starter Cultures in a Winery

The inoculation of grape juice with Saccharomyces cerevisiae strains selected from indigenous yeast populations can be a suitable tool to control alcoholic fermentation, contributing to producing wines with typical flavor and aroma and, hence, the demand for native starter cultures is increasing. However, since low amounts of indigenous yeast biomasses are usually required for local winemaking, the industrial production of these yeasts can be expensive. Therefore, in this study, after selecting an indigenous S. cerevisiae strain based on relevant oenological and technological features, a pilot-plant for easy and rapid production of fresh yeast biomass directly in a winery located in Tuscany, was exploited. The selected yeast strain was used as a starter to carry out 25 and 100 hL fermentations and its enological performance was compared with that of the commercial starter normally used in the winery. Chemical and sensory analysis of the resulting wines showed that they differentiated according to the used yeast strain, with the wines produced by the indigenous S. cerevisiae strain being characterized by a distinctive aromatic and sensory profile. In conclusion, the pilot-plant effectively resulted in producing fresh yeast starter cultures in the winery to be successfully used to carry out alcoholic fermentations.

Oenological property analysis of selected Hanseniaspora uvarum isolated from Rosa roxburghii Tratt

Oenological yeasts play a crucial role in the winemaking process by converting sugar into ethanol, carbon dioxide and flavor substances that contribute to the wine aroma profile. Eighty strains of yeast were isolated from Rosa roxburghii Tratt. Three of the indigenous yeast strains (numbered as C26, C31 and F110) were selected based on having the strongest fruity-aroma producing ability to further evaluate theirs oenological properties, and they were identified as Hanseniaspora uvarum based on morphological and molecular analyses. Strains tolerance results showed that the selected strains have glucose, citric acid and sulfur dioxide tolerances that are comparable to commercial Saccharomyces cerevisiae X16, but they are ethanol sensitive. Additionally, the H. uvarum strains had similar β-glucosidase production abilities to the control, but they do not produce hydrogen sulfide. Moreover, the selected H. uvarum strains reduced the acidity and increased the volatile aroma richness and complexity of R. roxburghii wine during laboratory-scale fermentation. Thus, the selected H. uvarum strains (C26, C31 and F110) show potential in the production of unique R. roxburghii wine.

Renewable Plant Waste As Substrates for Enzyme Production, Saccharification and Direct Bioethanol Production by Indigenous Yeast Strain Pichia Exigua

Renewable plant wastes constitute environmental nuisance. Their conversion by enzymes into bioethanol can be beneficial. We investigated the use of renewable plant waste as substrate for enzyme production and hydrolysis of the plant waste for ethanol production using an indigenous yeast strain. Five yeast strains; MCC-1, MCC-2, MCC-3, MCC-4 and MCC-5 were evaluated for production of sugars, α-amylase, glucoamylase and bioethanol using soluble starch. Phylogenetic analysis using partial sequence of the ITS gene classified MCC-4 as Pichia exigua. Proximate composition of plant wastes – cassava, wild yam, mango seed, udara seed and breadfruit were determined. Results showed total carbohydrate of (83.9%) for cassava flour. The ability of yeast to utilize these substrates and the effect of culture conditions (inoculum, pH, nitrogen source and substrate concentration) were also determined. Cassava pulp flour was the best substrate producing reducing sugar (1.471 ± 0.056mg/mL), α-amylase (0.573 ± 0.019U/mL), glucoamylase (1.605 ± 0.119U/mL), and ethanol (4.440 ± 0.014g/L). Culture conditions revealed optimum for inoculum concentration as (1mL), pH (4), nitrogen source (soya bean, 3g/L) and substrate concentration of (8%). Pichia exigua (MCC-4) a natural yeast strain isolated from the soil has the potential for both enzyme and ethanol production in a single step process.

In Vitro Evaluation of Probiotic Properties of Indigenous Yeasts Isolated from Nigerian Fermented Food Products

Probiotics are living microbial food supplements which beneficially affect the host by improving the intestinal microbial balance. Before an organism can be designated as probiotic there are certain criteria that must be fulfilled. These include acid and bile tolerance, antimicrobial activity, ability to co-aggregate, hydrophobicity etc. One hundred and eighty one indigenous yeast isolates recovered from various fermented food products of Nigeria were characterized and grouped using phenotypic methods. Forty two selected yeast isolates were identified using molecular method which involved sequencing of D1 and D2 domain of the large subunit of ribosomal DNA. Then nine indigenous Saccharomyces cerevisiae were evaluated for their probiotic characteristics such as acid and bile tolerance, transit in simulated gastric and intestinal juices, autoaggregation and hydrophobicity. Saccharomyces cerevisiae SC10 was included as a positive control. The S. cerevisiae were able to grow in the presence of acidic medium with pH as low as 2 and 3. In the minimum inhibitory concentration test with 0-1% ox bile, all the S. cerevisiae tested were able to grow. The growth for 3% bile tolerance test ranged from 4.81 to 5.35 log cfu/ml. These isolates were able to survive in simulated gastro-intestinal transit. All the yeast isolates exhibited bile salt deconjugation activity against sodium glycodeoxycholate and were able to grow in the presence of all other bile salts investigated. Autoaggregation ability (an adhesive property) of the indigenous yeast isolates ranged from 89.80% for S. cerevisiae BK19 to 99.91% for S. cerevisiae OB03. The native yeast isolates also exhibited high percentage hydrophobicity, another adhesive property of probiotics. The values obtained ranged from 31.62 to 83.45% for isolates AG23A and OB 17. These observations indicate that the native yeast isolates from Nigerian fermented foods have the potential of being use as probiotics for making functional foods.

Inactivation of Indigenous Microorganisms and Salmonella in Korean Rice Cakes by In-Package Cold Plasma Treatment

The antimicrobial effects of in-package cold plasma (CP) treatment on Korean rice cakes (KRC) were evaluated. The CP treatment (25 kV) inactivated indigenous mesophilic aerobic bacteria by 0.8–1.0 log CFU/g, irrespective of the position of KRC in the package. The addition of a shaking step during CP treatment increased the reduction in microbes by ~1 log CFU/g. The microbial inactivation efficiency increased significantly when the treatment time increased from 1 to 3 min. Microbial inactivation activity was highest for packages containing eight rice cakes. The optimized CP treatment achieved a 2.0 ± 0.1 log CFU/g reduction in indigenous bacteria. In addition, the optimum CP treatment inactivated indigenous yeast and molds and Salmonella in KRC by 1.7 ± 0.1 log CFU/g and 3.9 ± 0.3 log CFU/g, respectively. No significant changes in color and firmness were observed, and the surface temperature of KRC did not exceed 22 °C after CP treatment. Moreover, CP treatment damaged the cellular membrane of Salmonella, mainly by inducing lipid peroxidation. This study demonstrates the potential use of in-package CP treatment for the non-thermal microbial inactivation of KRC.