Chapter 1. General Introduction
1.6 Weissella confusa
Hydrocolloids have been reported to improve bread quality (Rosell et al., 2001). The exopolysaccharides influence the product texture, mainly due to their ability to influence viscosity. Weissella sp. has emerged as potential in-situ dextran producer in sourdough. Katina et al., 2009 established the potential of Weissella confusa VTT E-90392 in sourdough fermentation. Weissella confusa VTT E-90392 produced significant amounts of polymeric dextran and isomaltooligosaccharides in wheat sourdough without strong acidification (Katina et al.,2009).
The endogenous cereal proteases of flours have been shown to degrade cereal prolamins under acidic conditions (Kawamura and Yonezawa, 1982, Brijs et al., 1999). Increased proteolysis during sourdough fermentation leads to the liberation of amino acids in wheat and rye dough (Spicher and Nierle, 1988, Collar et al., 1991, Gobbetti et al., 1994). Furthermore, sourdough fermentation results in a solubilization and depolymerization of the gluten macropolymer (Thiele et al., 2004). Lactic acid bacteria also produce volatile compounds which is strain-specific. Homofermentative Lactobacilli are characterized by the high production of diacetyl, acetaldehyde, hexanal and heterofermentative strains are characterized by the production of ethyl acetate, alcohols and aldehydes. Isoalcohols (2-methyl-1-propanol, 2,3-methyl-1- butanol), with their respective aldehydes and ethylacetate are characteristic volatile compounds of yeast fermentation (Damiani et al., 1996).
carrot juice, milk, fermented foods and beverages and human and animal samples (Bjorkroth et al., 2002; Dworkin et al., 2006, Fusco et al., 2011; Kumar et al., 2011).
It is more commonly found in many fermented cereals and vegetables (Bjorkroth et al., 2002; Dworkin et al., 2006, Fusco et al., 2011).
1.6.1 Phylogentic relationship of Weissella confusa
The phylogeny of the bacteria classified currently in the genus Weissella was clarified in 1990. The genus Weissella is phylogenetically related to Leuconostoc and Oenococcus and arose from the reclassification of Leuconostoc paramesenteroides and some related atypical heterofermentative Lactobacilli (Björkroth and Holzapfel, 2006). In a study of Leuconostoc-like organisms originating from fermented sausages (Collins et al., 1993) the taxonomy of these species was further assessed. Thus there are currently eight species in the genus Weissella, Weissella confusa, Weissella halotolerans, Weissella hellenica, Weissella kandleri, Weissella minor, Weissella paramesenteroides, Weissella thailandensis and Weissella viridescens. Weissella confusa was formerly known as Lactobacillus confuses. Weisella confusa possessed the highest 16S rDNA sequence similarity to Weisella cibaria, but the DNA-DNA reassociation experiment showed hybridization levels below 49% between the strains studied (Bjorrkroth et al.,2002).
1.6.2 Identification of Weissella confusa
The identification of Weissella confusa and the other Weissella species traditionally relies on their biochemical and physiological features. These biochemical and physiological features include the production of gas from carbohydrates, the presence within the cell wall of lysine and alanine joined with an intrapeptide bond,
the hydrolysis of arginine, the formation of D, L-lactate and the ability to ferment different sugars (Björkroth et al., 2002; Collins et al., 1993; De Bruyne et al., 2008;
Koort et al.,2006). Given its widespread use for biotechnological applications, Fusco et al.,2011 developed rapid and reliable method involving polymerase chain reaction (PCR) using Amplified Fragment Length Polymorphism (AFLP) derived primers for the identification of Weissella sp. Recently, the first genome sequence for the Weissella confusa LBAE C39-2 species has become available (Amari et al., 2012). A total of 86,967 filtered reads corresponded to 33 Mb and 14-fold coverage of in the genome sequence of Weissella confusa LBAE C39-2 were obtained (Amari et al., 2012), The phylogenetic analysis of the genome sequence of Weissella confusa LBAE C39-2 showed that less than 30% contig sequences matched with Weissella ciberia KACC11862 (Amari et al., 2012).
1.6.3 Metabolic traits of Weissella confusa
Weissella confusa shows multiple metabolic traits which can be exploited for biotechnological applications. Weissella confusa has been successfully employed in a multi-species semi-liquid ready-to-use sourdough starter (Gaggiano et al., 2007). Di Cagno et al., 2009 used strains of Weissella confusa as autochthonous starters to ferment tomato juice as well as red and yellow peppers. Some metabolic traits other than lactic acid fermentation, such as exopolysaccharide production from sucrose (Maina et al., 2008; Shukla and Goyal, 2011) and antifungal activity (Ndagano et al., 2011; Beak et al., 2012), have been reported, highlighting that W. confusa could be attractive for diverse biotechnological applications. W. confusa is also present in the normal microflora of human intestines (Mitsuoka, 1992) and has been described as a potential probiotic species (Lee, 2005). Three Weissella confusa and five Weissella
cibaria strains were isolated from human faeces and their potential as probiotics was examined by Lee et al., 2012. W. confusa is a suitable alternative to the widely used Leuconostoc mesenteroides NRRL B-512F in the production of high amounts of linear dextran (Maina et al.,2008). Weissella confusa has been successfully employed for in-situ production of dextrans and isomaltooligosaccharides in wheat sourdoughs without strong acidification (Katina et al.,2009).
1.6.4 Dextransucrase, dextran and oligosaccharide production from Weissella confusa
There are very few reports where the dextran production capacity of Weissella confusa has been explored. While dextransucrase from Leuconostoc are inducible by sucrose, it has been reported that dextransucrase from several Weissella sp. are constitutive in nature (Bounaix et al. 2010). Dextransucrase of 180 kDa size from Weissella ciberia and Weissella confusa (LBAE-C39-2 and DSM 20196) have been reported in medium containing sucrose or glucose as the carbon source (Bounaix et al., 2010). Bounaix et al., 2010 also reported an additional sucrose inducible dextransucrase of approximately, 300 kDa for W. confusa DSM 20196 which did not form in the medium containing glucose. Malik et al., 2009 characterized three glucantransferase genes (gtf) and one fructantransferase gene (ftf) from Weissella confusa strains MBF8-1 and MBF8-2. Amari et al., 2012 reported the first complete gene sequence encoding dextransucrase from a W. confusa strain (LBAE C39-2) along with the one from a W. cibaria strain (LBAE K39). A recombinant dextransucrase (rDSRC39-2) of approximately, 180 kDa from Weissella confusa isolated from sourdough has been characterized (Amari et al., 2012). The dextran produced by Weissella confusa has gained importance recently due to its linear structure (Maina et al., 2008). Dextran produced by Weissella sp. is more linear in
nature (Maina et al., 2008) as compared to 95% linearity in glucan formed from Leuconostoc mesenteroides NRRL B-512F (Seymour and Knap, 1980). Bounaix et al., 2010 also reported that Weissella strains isolated from sourdoughs which produce linear dextran containing α-(1→6) glucose residues with few α-(1→3) linkages from sucrose produced by a constitutive dextransucrase of 180 kDa size. The production of exopolysaccharide by Weissella strains, isolated from a traditional Thai food (plasom) was investigated using sugarcane molasses and white sugar from sugarcane as substrates in comparison to analytical grade sucrose (Tayuan et al., 2011). The dextran (rDSRC39-2 dextran) produced by a recombinant dextransucrase from Weissella confusa C39-2 contained consecutive α-(1→6)-linked D-glucopyranosyl units with few α-(1→3)-linked branches (Amari et al.,2012). Several reports suggest that Weissella sp are very promising candidates for sourdough fermentation due to the production of significantly high dextran (Katina et al., 2009; Galle et al.,2010). Galle et al., 2010 reporeted in-situ production of panose and glucosylated panose with a degree of polymerization of up to 14 from Weissella ciberia MG1. Katina et al.,2009 also reported similar observation of oligosaccharide production in wheat sourdough.