Influence of Clarification and Suspended Grape Solid Materials on Sterol Content of Free Run and Pressed Grape Musts in the Presence of Growing Yeast Cells

¹ Director of the Microbiology Section, Istituto Sperimentale per I'Enologia, Via P. Micca, 35 - I, 14100 Asti, Italia

Clarified and unclarified free run and pressed musts were left in contact with suspended solid materials and natural growing yeast cells for 16 hours at room temperature. Free and bound sterols (after saponification) were extracted and analyzed by gas chromatography and GC/MS. Unlike unclarified free run and pressed musts, both clarified musts completely lacked sterols, with the exception of ergosterol which was present at about 10 % of the amount found in the non-clarified must. Free grape sterol content increases proportionately to the time contact of must with grape solid materials in the first four hours; after that, there was a constant decrease in the amount of free sterols, until they almost disappeared at 16 hours. Generally, bound grape sterols decreased during the first two hours, after which they increased. The content of yeast sterols (ergosterol and lanosterol) increased over time and according to the number of viable cells. These changes could be explained by the existence of two processes having antithetic effects: the first due to enzymatic factors of musts and/or yeasts releasing sterols from solid materials and the second due to yeasts uptaking sterols for growth at the same time.

Key words: clarification, musts, sterols, suspended grape solid materials

Submitted on August 4, 1992