engleski

Reversible inhibition of lager Saccharomyces uvarum flocculation ability by specific sugars

INTRODUCTION Yeast flocculation has been traditionally exploited in brewing industry. However, this characteristic might also be useful in modern biotechnology as it is an easy and cheap way of separating the cell biomass from the media at the end of fermentations. The objective of this work was to identify the nutrients than can trigger the loss of flocculation ability under growth conditions in lager-brewing yeast strain, Saccharomyces uvarum. METHODOLOGY The flocculent lager-brewing strain of S. uvarum was grown in YEPD broth and in YNB broth (Difco) (6.7 gL-1 yeast nitrogen base plus 20 gL-1 glucose or galactose, maltose, sucrose and lactose, 5.9 gL-1 succinic acid and 0.46 gL-1 CaCl2.2H2O) ; pH was adjusted to 5.9. Growth was monitored spectrophotometrically (at 600 nm) or by direct microscopic counting, using a counting chamber. After 48 h of growth at 25 oC on an orbital shaker (150 rev min-1), cells were harvested by centrifugation (2000 g, 5 min) and washed twice with 30 mM EDTA solution to ensure floc dispersion. In the experiments with cycloheximide (Sigma), yeast cultures were treated with sterilized cycloheximide (dissolved in deionized water), at a final concentration of 12 mgL-1. Flocculation ability was monitored in standard conditions using a micro flocculation technique. RESULTS AND DISCUSSION Yeast growth with metabolizable carbon sources (glucose, galactose, maltose or sucrose) at 2% (w/v), induced the loss of flocculation ability in yeast that had previously been allowed to flocculate. The yeast remained flocculent when transfer to a medium containing the required nutrients for lager yeast growth and a sole nonmetabolizable carbon source (lactose). Cycloheximide addition (12 mgL-1) to yeast cells stopped flocculation loss. CONCLUSIONS 1. Carbohydrates were the nutrients responsible for stimulating the loss of flocculation in flocculent lager yeast S. uvarum. 2. This work contributes to the elucidation of the role of nutrients in the flocculation ability of lager-brewing yeast strains.

flokulacija; S. uvarum; šećeri

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