Biodiversity of yeasts isolated during spontaneous fermentation of cool climate grape musts.

Biodiversity of native yeasts, especially in winemaking, has hidden potential. In order to use the value of non-Saccharomyces strains in wine production and to minimise the possibility of its deterioration, it is necessary to thoroughly study the yeast cultures present on grape fruits and in grape must, as well as their metabolic properties. The aim of the study was to characterise the yeast microbiota found during spontaneous fermentation of grape musts obtained from grape varieties 'Rondo', 'Regent' and 'Johanniter'. Grapes from two vineyards (Srebrna Góra and Zadora) located in southern Poland were used for the research. Succession of subsequent groups of yeasts was observed during the process. Metschnikowia pulcherrima yeasts were identified both at the beginning and the end of the process. Hanseniaspora uvarum, Wickerhamomyces onychis and Torulaspora delbrueckii strains were also identified during the fermentation. Torulaspora delbrueckii and Wickerhamomyces onychis strains were identified only in grape musts obtained from grapes of the Zadora vineyard. These strains may be characteristic of this vineyard and shape the identity of wines formed in it. Our research has provided specific knowledge on the biodiversity of yeast cultures on grapes and during their spontaneous fermentation. The research results presented indicate the possibility of using native strains for fermentation of grape musts, allowing to obtain a product with favourable chemical composition and sensory profile.

Evaluation of yeasts from Ecuadorian chicha by their performance as starters for alcoholic fermentations in the food industry.

Yeasts involved in the spontaneous fermentation of traditional beverages like chicha (indigenous Andean beer) may have the potential to be used as starter cultures to improve the quality and microbiological safety of these products, but also as non-conventional alternatives to other food alcoholic fermentations. In this research, we isolated, identified and characterised yeast strains from four Ecuadorian chichas made by using four different raw materials: rice (RC), oat (OC), grape (GC) and a mixture of seven corn varieties (yamor, YC). Finally, 254 yeast isolates were obtained and identified by molecular methods. Eleven yeast genera and 16 yeast species were identified with relatively few isolates belonging to Saccharomyces cerevisiae (9.1% belonging to 6 strains) and Torulaspora delbrueckii (18.6% belonging to 2 strains). In order to select good candidates for fermentative starter production, different analyses were performed. The results of the stress response tests showed a wide variability between species and strains, and identified some yeasts displaying high stress tolerance, similarly to commercial wine strains. Amylase production was screened as being indicative of the capacity to degrade and ferment starch-rich substrates. A Cryptococcus sp. isolate showed the highest amylase activity. The growth rate and fermentative capacity in molasses medium was measured for three S. cerevisiae, T. delbrueckii and Candida sp. strains as tests for yield and performance in biomass production. Based on their excellent behaviour, three S. cerevisiae strains and one T. delbrueckii strain were selected for further analyses, including dehydration tolerance and invertase activity as additional desired traits for chicha starters. All the S. cerevisiae strains exhibited high invertase activity and one also displayed high resistance to dehydration. The yeasts selected in this study can thus be suitably used as dry starters for the microbiologically controlled production of traditional beverages, and also for other alcoholic fermentations.

Torulaspora nypae sp. nov., a novel yeast species isolated from nipa (Nypa fruticans Wurmb.) inflorescence sap in southern Thailand.

Two strains (YSP-384 and YSP-399), representing a novel Torulaspora species, were isolated from two nipa inflorescence sap samples collected in Trang province in the southern part of Thailand. The two strains had identical sequences of the D1/D2 domains of the large subunit (LSU) rRNA gene and the internal transcribed spacer (ITS) regions. The two strains were closest to Torulaspora maleeae CBS 10694T, but with 1.1 % nucleotide substitutions in the D1/D2 domains of the LSU rRNA gene and 5.2 % nucleotide substitutions in the ITS regions. Phylogenetic analysis based on the concatenated sequences of the ITS regions and the D1/D2 domains of the LSU rRNA gene supported that the two strains represented a distinct species in the genus Torulaspora. Some phenotypic characteristics of the two strains differed from T. maleeae including the two strains have ability to assimilate d-xylose, d-glucono-δ-lactone and melizitose, and inability to ferment maltose and raffinose, whereas T. maleeae has opposite results. Therefore, the two strains are described as representing a novel species, for which the name Torulaspora nypae sp. nov. was proposed.

ETHANOL PRODUCTION FROM STARCH BY YEASTS ISOLATED FROM CROPS AND DAIRY PRODUCTS.

The aim of this work was to study the ability ofyeasts isolated from crops and dairy products to convert starch to ethanol. The isolated yeasts were screened for their ability to hydrolyze starch. Six most active strains were identified as Lipomyces mesembrius spp. 5.4, 5.5 and 6.4, Shwanniomyces vanrijiae var yarowii F33, Torulaspora sp. F7 and Candida sp. S26. The selected yeasts produced low levels of ethanol from starch under aerobic conditions - 0.006-0.129 g/l (0.3-0.87 % of theoretical yield) and microaerobic conditions - 0. 089-0.35 g/l (1.61-6.07 % of theoretical yield). These amylolytic yeast strains will be studied as the potential candidates for the cocultivation with efficient ethanol producers which do not possess the ability to directly hydrolyze starch.

Torulaspora indica a novel yeast species isolated from coal mine soils.

Four yeast strains (APSS 805, APSS 806, APSS 815 and AP-18) belonging to a novel Torulaspora species were isolated from coal mine soils of Singareni in Andhra Pradesh state, India. Another strain (PBA-22) was isolated from agricultural field soil from Gujarat state, India. The vegetative cells of all these strains were round, haploid and produced asci by conjugation between independent cells or mother cell and bud, with rough ascospores, suggesting their possible relation to ascomycetous yeast genus Torulaspora. Phylogenetic analysis of the D1/D2 domain of the large subunit (LSU) rRNA gene and Internal Transcribed Spacer (ITS) regions revealed that, among the five strains, three viz. APSS 805, APSS 806 and APSS 815 have identical sequences. The other two strains (AP-18 and PBA-22) differed from the other three strains in less than 1% nucleotide substitutions in the combined D1/D2 domain and ITS sequences, indicating that all of them (five strains) may belong to the same species. These five strains were closely related to Torulaspora globosa, but showed more than 3-7% sequence divergence from T. globosa and all other species in the genus Torulaspora in the combined sequence analysis of D1/D2 domain and ITS region of rRNA gene. In addition, these strains also showed distinct microsatellite finger-printing pattern from related species and differed in several physiological responses suggesting that these strains belong to a novel species of Torulaspora. We propose to name these strains as Torulaspora indica sp. nov., and designate APSS 805(T) = MTCC 9772 (T) = CBS 12408 (T) as the type strain of this novel species. The Mycobank number of the novel species is MB 563738.

Torulaspora quercuum sp. nov. and Candida pseudohumilis sp. nov., novel yeasts from human and forest habitats.

Strains XZ-46A, XZ-105, XZ-129 and XZ-281(T) isolated from the oral cavities of healthy Tibetan volunteers were revealed to represent two novel ascomycetous yeast species by molecular taxonomic characterizations. Strain XZ-281(T) was most closely related to Candida humilis, but differed from the type strain of the species by eight (1.2%) substitutions in the 26S rRNA gene D1/D2 domain and by >100 (>20%) mismatches in the internal transcribed spacer (ITS) region. Strains XZ-46A, XZ-105 and XZ-129 had identical or similar D1/D2 and ITS sequences with each other and with strain 17YF(T) isolated from a leaf of an oak tree (Quercus sp.). The closest relative of this group was Torulaspora microellipsoides. They differed from the type strain of the species by five (0.9%) substitutions in the D1/D2 domain and >70 (>15%) mismatches in the ITS region. A sexual state was observed in strain 17YF(T), but not in the other four oral strains. An anamorphic name Candida pseudohumilis sp. nov. is proposed for strain XZ-281(T) (=AS 2.3956(T)=CBS 11404(T)) and a teleomorphic name Torulaspora quercuum sp. nov. is proposed for strain 17YF(T) (=AS 2.3768(T)=CBS 11403(T)) and the other three oral strains.

Production of shelf-stable ranch dressing using high-pressure processing.

High-pressure processing (HPP) can reduce or eliminate microorganisms of concern in food without deteriorating product quality; however, quality benefits must justify the substantial capital investment for the utilization of this technology. HPP is particularly a beneficial preservation technology for products damaged by thermal treatments or when product quality could be improved by reformulation to raise pH or eliminate chemical preservatives. The primary objectives of this study were to determine the efficacy of HPP to protect premium ranch dressing (pH 4.4) from microbial spoilage and to assess changes in physical, chemical, and sensory attributes throughout the product's shelf life. In inoculated-packages studies, the efficacy of HPP was measured against ranch dressing spoilage organisms: Pediococcus acidilactici, Lactobacillus brevis, and Torulaspora delbrueckii. HPP treatment (600 MPa, 3 min) decreased population of P. acidilactici, the most pressure-resistant spoilage organism tested, by >or= 6.4 log CFU/g. During a shelf-life study of edible product, treating ranch dressing at 600 MPa for 5 min effectively prevented microbial spoilage throughout the storage period (26 wk at 4 and 26 degrees C). The pH and emulsion stability of ranch dressing were not adversely influenced by HPP. Extended storage of HPP product for 16 to 26 wk at 26 degrees C resulted in a decrease in consumer acceptance and significant changes in color and organic acid profile (specifically, increased pyroglutamic acid). These changes were consistent with those expected during extended storage of commercially available products. HPP may be used to produce premium ranch dressing, with defined shelf-life and storage conditions, without significantly changing product attributes.

Isolation and identification of spoilage microorganisms using food-based media combined with rDNA sequencing: ranch dressing as a model food.

Investigating microbial spoilage of food is hampered by the lack of suitable growth media and protocols to characterize the causative agents. Microbial spoilage of salad dressing is sporadic and relatively unpredictable, thus processors struggle to develop strategies to minimize or prevent spoilage of this product. The objectives of this study were to (i) induce and characterize spoilage events in ranch-style dressing as a model food, and (ii) isolate and identify the causative microorganisms using traditional and food-based media, coupled with rDNA sequence analysis. Ranch dressing (pH 4.4) was prepared and stored at 25 degrees C for 14 d and microbial populations were recovered on MRS agar and ranch dressing agar (RDA), a newly formulated food-based medium. When isolates suspected as the spoilage agents were inoculated into ranch dressing and held at 25 degrees C for 9-10 d, three unique spoilage events were characterized. Using rDNA sequence comparisons, spoilage organisms were identified as Lactobacillus brevis, Pediococcus acidilactici, and Torulaspora delbrueckii. P. acidilactici produced flat-sour spoilage, whereas Lb. brevis resulted in product acidification and moderate gas production. The RDA medium allowed for optimum recovery of the excessive gas-producing spoilage yeast, T. delbrueckii. The isolation and identification strategy utilized in this work should assist in the characterization of spoilage organisms in other food systems.