No abstract

No abstract

Alternansucrase catalyses the sequential transfer of glucose residues from sucrose onto another sucrose molecule to form a long chain polymer, known as “alternan”. The alternansucrase-encoding gene from Leuconostoc citreum ABK-1 (Lcalt) was successfully cloned and expressed in Escherichia coli. Lcalt encoded LcALT of 2,057 amino acid residues; the enzyme possessed an optimum temperature and pH of 40 °C and 5.0, respectively, and its’ activity was stimulated up to 2.4-fold by the presence of Mn2+. Kinetic studies of LcALT showed a high transglycosylation activity, with Km 32.2 ± 3.2 mM and kcat 290 ± 12 s−1. Alternan generated by LcALT (Lc-alternan) harbours partially alternating α-1,6 and α- 1,3 glycosidic linkages confirmed by NMR spectroscopy, methylation analysis, and partial hydrolysis of Lc-alternan products. In contrast to previously reported alternans, Lc-alternan can undergo self-assembly, forming nanoparticles with an average size of 90 nm in solution. At concentrations above 15% (w/v), Lc-alternan nanoparticles disassemble and form a high viscosity solution, while this polymer forms a transparent film once dried.

No abstract

Durian is an economically important fruit of Southeast Asia. There is, however, a lack of in-depth information on the alteration of its metabolic networks during ripening. Here, we annotated 94 ripening-associated metabolites from the pulp of durian cv. Monthong fruit at unripe and ripe stages, using capillary electrophoresis- and gas chromatography- time-of-flight mass spectrometry, specifically focusing on taste-related metabolites. During ripening, sucrose content increased. Change in raffinose-family oligosaccharides are reported herein for the first time. The malate and succinate contents increased, while those of citrate, an abundant organic acid, were unchanged. Notably, most amino acids increased, including isoleucine, leucine, and valine, whereas aspartate decreased, and glutamate was unchanged. Furthermore, transcriptomic analysis was performed to analyze the dynamic changes in sugar metabolism, glycolysis, TCA cycle, and amino acid pathways to identify key candidate genes. Taken together, our results elucidate the fundamental taste-related metabolism of durian, which can be exploited to develop durian metabolic and genetic markers in the future.