Native wine yeasts: potential source of prebiotics to formulate functional foods.

Abstract

This paper presents prebiotics obtention: cell walls, β-glucans and mannoproteins, from native wine yeasts. The identification of yeasts is done by ITS1-5.8S-ITS2 PCR-RFLP and RFLP of mitochondrial DNA, to ensure that microorganisms are GRAS. To optimize biomass production, the effect of 5 variables on culture conditions was tested (carbon source: glucose (2%) or glycerol (3%); stirring: 0 and 100 rpm; temperature: 28 and 37ºC; pH of the medium: 4 and 5; yeast: 8A-9 and 13A-5). Cell walls were obtained by different cell disintegration techniques: autolysis, mechanical rupture (ceramic beads), ultrasound, frozen-thawed, hydrolysis with 4% NaCl or 0.1 N NaOH. Mannoproteins were separated by thermal extraction. Two techniques for the extraction of β-glucans were analyzed: alkali-acid and alkali. Samples were hydrolyzed to study the concentration of reducing sugars (DNS) and glucose (enzymatic assay). Proteins were quantified using Bradford technique. The use of glucose as source of carbon and a temperature of 28ºC increased the obtaining of biomass; no significant differences were observed when evaluating the other variables. The ultrasound and autolysis treatments were chosen to break the cells, which was verified by microscopic observation and methylene blue. The highest proportion of β-glucans was achieved starting from autolysed yeasts, unlike mannoproteins, where their extraction was favored from yeasts treated with ultrasound. It is concluded that different cell rupture should be used depending on the desired product.