One other amino acid increasing markedly upon fermentation of
the must was L-leucine; this result is consistent with those of
Valero, Millan, Ortega, and Mauricio (2003) in fermented musts
from fresh grapes. The high L-proline content observed in the sweet
wines can be explained considering its high concentration in grape
must as well as both the limitation of molecular oxygen during the
alcoholic fermentation that avoids its degradation and the fact Lproline
is hardy metabolized by yeast (Lasko & Brandriss, 1981). In
addition, L-proline is important because serves to maintain the
redox balance and prevent osmotic stress of the yeast cell (Mauricio
et al., 2001; Takagi, 2008).