Screening of soil yeasts with fermentative capacity from the antarctic continent for their application in the wine industry

Abstract

AIM: In the last years, many wineries are increasing experimentation to produce more distinguishable beverages. In this sense, the reduction of the fermentation temperature could be a useful tool because it preserves volatile compounds and prevents wines from browning, particularly in the case of white wines. However, low fermentation temperatures usually produce an early stop in the fermentation. Hence, the employment of new yeast strains able to operate at low temperatures could solve this problem, giving rise to different characteristics in wines. The Antarctic Continent is a crucial source for the isolation of new microorganisms and bioactive metabolites, given the competitive conditions of this environment with low temperatures, scarce carbon sources and high UV radiation. Considering this, the objective of this study was the isolation and characterization of fermentative yeast from the Antarctic Continent with potential for use in the wine industry.

METHODOLOGY: Six soil samples collected in Fildes Bay, west of King George Island and three soil samples from King George Island were processed for yeast isolation. Samples were suspended in sterile water and dilutions of each suspension were inoculated onto yeast medium (YM) agar plates with antibiotics, which were then incubated at 4, 10, and 18 °C until visible colony growth. Colonies with a non-filamentous appearance were selected, which were reseeded on YM agar without antibiotics. Alcohol tolerance was performed using concentrations of 3, 6, or 9% alcohol. Later on, sugar tolerance was analyzed using fructose and glucose in a 1:1 proportion; with 5, 10, 15, 20, or 25% of sugar in the medium. Those isolates with microscopic characteristics of interest were selected to determine fermentative activity in vitro using a simple colorimetric assay with phenol red, as a pH indicator. To differentiate the isolates, and discard replicates, a fingerprinting assay with arbitrary primers was performed. Identification of the isolates was carried out using PCR and ITS region primers with BLAST bioinformatics tools.

RESULTS: Nine soil samples collected from the Antarctica were processed for yeast isolation. We obtained 125 yeasts from the soil samples, with a growth temperature of 10ºC. Overall, 25 yeasts have fermentative activity and are able to tolerate a culture medium with at least 20% glucose and up to 6% of ethanol. The isolates were also characterized by optical microscopy and fingerprinting using PCR with arbitrary primers to discard identical strains and allowed us to discriminate 10 unique strains with fermentative capacity from the 25 isolates. To determine the identity of the isolated yeasts, the amplification and sequence of the 18S RNA was performed.

CONCLUSION:

The Antarctic continent has proven to be a source of fermentative yeasts with high potential for their use in the wine industry.