PhD Vermeiren Lieve Compleet - Hogeschool Gent

temperature (4°C) and high salt (9% NaCl). Although these conditions influence growth,
survival was enhanced and differences in cell morphology were observed. In 2004, Marceau
et al. found six proteins to be affected during growth of L. sakei at 4°C or in the presence of
4% NaCl. Two were proteins from general carbon metabolism, four were general stress
proteins.
Lactobacillus sakei is known to have the most fastidious nutritional requirements of all
lactobacilli (Lauret et al., 1996). Although L. sakei can generate energy by degrading
arginine, leading to NH3 and ATP production, via the arginine deiminase pathway, this amino
acid alone does not allow growth of L. sakei but rather survival during the stationary phase
(Champomier-Vergès et al., 1999; 2002). Instead, this species uses other energy sources to
grow on meat. Among the few sugars present in meat, glucose and ribose are the only sugars
that L. sakei can utilise for its growth (Stentz et al., 2001). Glucose is fermented via the
homofermentative EMP-pathway while ribose is fermented via the heterofermentative
phosphoketolase pathway. During sugar fermentation, D- and L-lactic acid are produced
although only L-lactate dehydrogenase is present. The conversion of L- to D-lactic acid is
catalysed by a lactate racemase (Carr et al., 2002; Champomier-Vergès et al., 2002).
Little is known about nucleotide and vitamin requirements. Thiamin is required for growth on
pentoses such as ribose (Champomier-Vergès et al., 2002). In the study of Moretro et al.
(1998), riboflavin was essential for growth, while biotin had no effect on the growth of two
L. sakei strains. Furthermore, both strains needed purines and pyrimidines for growth.
1.5. Antimicrobial activity of lactic acid bacteria
Since ancient times, LAB are used in the production of a wide range of fermented foods.
Lactic acid bacteria contribute to the stability and safety of these products mainly due to the
acidic conditions they create during their development and this souring effect is primarily due
to the fermentation of carbohydrates to organic acids. Although the preservative effect of
LAB is known for a long time, only in the last twenty years it became clear that the
antimicrobial activity of LAB is more than organic acid production alone. A whole range of
antagonistic systems have been described for LAB (De Vuyst & Vandamme, 1994a).
Chapter 1 – Antagonistic micro-organisms for biopreservation of food products 8