Affiliation:
1. NIZO Food Research and Wageningen Centre for Food Sciences (WCFS), Ede, The Netherlands
2. State University of Campinas (UNICAMP)
3. Instituto de Tecnologia de Alimentos (ITAL), Campinas SP, Brazil
Abstract
ABSTRACT
The process of acetaldehyde formation by the yogurt bacterium
Streptococcus thermophilus
is described in this paper. Attention was focused on one specific reaction for acetaldehyde formation catalyzed by serine hydroxymethyltransferase (SHMT), encoded by the
glyA
gene. In
S. thermophilus
, SHMT also possesses threonine aldolase (TA) activity, the interconversion of threonine into glycine and acetaldehyde. In this work, several wild-type
S. thermophilus
strains were screened for acetaldehyde production in the presence and absence of
l
-threonine. Supplementation of the growth medium with
l
-threonine led to an increase in acetaldehyde production. Furthermore, acetaldehyde formation during fermentation could be correlated to the TA activity of SHMT. To study the physiological role of SHMT, a
glyA
mutant was constructed by gene disruption. Inactivation of
glyA
resulted in a severe reduction in TA activity and complete loss of acetaldehyde formation during fermentation. Subsequently, an
S. thermophilus
strain was constructed in which the
glyA
gene was cloned under the control of a strong promoter (P
LacA
). When this strain was used for fermentation, an increase in TA activity and in acetaldehyde and folic acid production was observed. These results show that, in
S. thermophilus
, SHMT, displaying TA activity, constitutes the main pathway for acetaldehyde formation under our experimental conditions. These findings can be used to control and improve acetaldehyde production in fermented (dairy) products with
S. thermophilus
as starter culture.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
120 articles.
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