Showing papers by "Sybe Hartmans published in 2000"

Biodegradability of food-associated extracellular polysaccharides.

Abstract: Exopolysaccharides (EPSs) produced by lactic acid bacteria, which are common in fermented foods, are claimed to have various beneficial physiological effects on humans. Although the biodegradability of EPSs is important in relation to the bioactive properties, knowledge on this topic is limited. Therefore, the biodegradability of eight EPSs, six of which were produced by lactic acid bacteria, was compared with microorganisms from human feces or soil. EPS-degradation was determined from the decrease in polysaccharide-sugar concentration and by high-performance size exclusion chromatography (HPSEC). Xanthan, clavan, and the EPSs produced by Streptococcus thermophilus SFi 39 and SFi 12 were readily degraded, in contrast to the EPSs produced by Lactococcus lactis ssp. cremoris B40, Lactobacillus sakei 0-1, S. thermophilus SFi20, and Lactobacillus helveticus Lh59. Clearly, the susceptibility of exopolysaccharides to biological breakdown can differ greatly, implying that the physiological effects of these compounds may also vary a lot.

Transglycosylation by Streptococcus mutans GS-5 glucosyltransferase-D: acceptor specificity and engineering of reaction conditions.

Abstract: The acceptor specificity of Streptococcus mutans GS-5 glucosyltransferase-D (GTF-D) was studied, particular the specificity toward non-saccharide compounds. Dihydroxy aromatic compounds like catechol, 4-methylcatechol, and 3-methoxycatechol were glycosylated by GTF-D with a high efficiency. Transglycosylation yields were 65°50°and 75°respectively, using 40 mM acceptor and 200 mM sucrose as glucosyl donor. 3-Methoxylcatchol was also glycosylated, though at a significantly lower rate. A number of other aromatic compounds such as phenol, 2-hydroxybenzaldehyde, 1,3-dihydroxybenzene, and 1,2-phenylethanediol were not glycosylated by GTF-D. Consequently GTF-D aromatic acceptors appear to require two adjacent aromatic hydroxyl groups. In order to facilitate the transglycosylation of less water-soluble acceptors the use of various water miscible organic solvents (cosolvents) was studied. The flavonoid catechin was used as a model acceptor. Bis-2-methoxyethyl ether (MEE) was selected as a useful cosolvent. In the presence of 15ov/v) MEE the specific catechin transglucosylation activity was increased 4-fold due to a 12-fold increase in catechin solubility. MEE (10-30␟/v) could also be used to allow the transglycosylation of catechol, 4-methylcatechol, and 3-methoxycatechol at concentrations (200 mM) otherwise inhibiting GTF-D transglycosylation activity.

A novel gene encoding xanthan lyase of Paenibacillus alginolyticus strain XL-1.

Abstract: Xanthan-modifying enzymes are powerful tools in studying structure-function relationships of this polysaccharide. One of these modifying enzymes is xanthan lyase, which removes the terminal side chain residue of xanthan. In this paper, the cloning and sequencing of the first xanthan lyase-encoding gene is described, i.e., the xalA gene, encoding pyruvated mannose-specific xanthan lyase of Paenibacillus alginolyticus XL-1. The xalA gene encoded a 100,823-Da protein, including a 36-amino-acid signal sequence. The 96,887-Da mature enzyme could be expressed functionally in Escherichia coli. Like the native enzyme, the recombinant enzyme showed no activity on depyruvated xanthan. Compared to production by P. alginolyticus, a 30-fold increase in volumetric productivity of soluble xanthan lyase was achieved by heterologous production in E. coli. The recombinant xanthan lyase was used to produce modified xanthan, which showed a dramatic loss of the capacity to form gels with locust bean gum.