Abstract

EFFECT OF pH ON ETHANOL AND INVERTASE PRODUCTION BY SACCHAROMYCES CEREVISIAE GROWN IN BLACKSTRAP MOLASSES

Prof. Michele Vitolo*

ABSTRACT

Blackstrap molasses (a residue from sucrose crystallization) and sugarcane juice are among the most used raw materials for alcohol production by fermentative yeast Saccharomyces cerevisiae. After fermentation, residual yeast cells become source of other commercial products as yeast extract, nucleic acids, and enzymes (invertase, for instance). This study evaluates the effect of mash pH (4.0, 4.5, 5.0, 5.5, 6.0, and 6.5) on the ethanol and invertase production of S. cerevisiae. The highest ethanol (8.5 g/L) and invertase (237.6 U/L) productions were obtained at pH 4.5 and 5.5, respectively. Moreover, the invertase activity of intact yeast cells and total reducing sugars concentration in the mash were shown to be inversely correlated, indicating the submission of invertase biosynthesis to catabolite repression, although a fraction of invertase formation could be subjected to a constitutive mechanism. The kinetic constants (KM= 14.8 mM and Vmax = 184.4 U/L) of yeast cell wall invertase were calculated using the Eadie-Scatchard plot.

Keywords: Invertase, yeast, ethanol, molasses.