Selection of native yeast for producing reduced etanol wines: oxidative capacity and sugar assimilation

MATURANO Y.P.; MESTRE M.V.; MERCADO L.; TORO M.E.; VAZQUEZ F.; COMBINA M.

Recife

Jornada; V Jornadas Latinoamericanas de Biología y Biotecnología de Levaduras; 2015

Red Latinoamericana de Levaduras

Nowadays, strongly colored full-bodies and ripe fruit flavored wines are highly appreciated by the market. Nevertheless, grapes with very high phenolic maturity frequently present high sugar concentrations. Furthermore, climate change, mainly the increase in temperature and the variations in rainfall distribution, impact directly on the fruit sugar levels resulting in wines with excessive alcohol (sometimes more than 15% v/v). High levels of alcohol can alter the sensorial quality of wines, have psychological and physiological effects on health and can raise economic issues (some countries impose taxes on alcohol content). On the other hand, the effects of climatic change can induce the increment of the proportion of fructose respect to glucose in grapes. This fact can lead to sluggish or stuck fermentations because yeasts prioritize glucose consumption. Several strategies are being developed to decrease ethanol concentration in wines. Among them, we concernm about the use of co-inoculation of non-Saccharomyces and Saccharomyces selected yeasts. Objective: To select wild yeasts with oxidative metabolism and producinglow levels of ethanol and metabolite undesirable, to use in co-cultures. One-hundred and twenty two non- Saccharomyces yeasts belonging to 33 species (11 genera) and 9 S. cerevisiae yeasts were screened. Assimilation of non-fermentable substrate (glycerol), cytochrome-c-oxidase and catalase activities and oxidative stress tolerance were assayed. Microfermentations were carried out at 25°C under static conditions for 21 days. Ethanol, pH, volatile acidity, total acidity, density, residual sugars, glycerol, , glucose, fructose, sucrose, lactic, malic, citric and tartaric acid contents were analyzed by F-TIR spectrophotometer. All assays were performed in triplicate and statistically analyzed using ANOVA. According to the results of the screening for the oxidative metabolism tests and the fermentative performance 21 non-Saccharomyces (10 Hanseniaspora uvarum, 4 Starmerella bacillaris (synonym Candida zemplinina), 4 Pichia occidentalis, 1 Pichia fabianii, 1 Debaryomyces hansenii, and 1 Cryptococcus laurentii) and 2 S. cerevisiae were selected. These yeasts were able to assimilate glycerol, tolerate severe conditions of oxidative stress and registered catalase and cytochrome-c-oxidase activities. Besides, in fermentative conditions, these yeasts showed inefficiencies in conversion of sugar to ethanol, using between 19 and 27g/L of sugars per degree ethanol produced. Also, they produced high glycerol (> 5g/L) and low acetic acid (< 0,7g/L) levels and registered high affinity by the fructose, glucose/fructose ratio in the fermentative medium was high (0,5-9). Selected yeasts presented optimal performance to be employed in co-inocula for the production of wines reduced in ethanol and with good organoleptic profile.