Lingvistiskā variācija elektroniskajā akadēmiskajā diskursā

Promocijas darbā ir atspoguļota jauna īpaša angļu valodas diskursa veida, kas notiek akadēmiskajās aprindās ar datora starpniecību, leksisko un gramatisko formu sastopamības variācijas teorētiskā un empīriskā izpēte. Ir izstrādāta oriģināla elektroniskā akadēmiskā diskursa (EAD) definīcija. EAD piemīt specifiskas lingvistiskās īpašības, kas to atšķir no citiem angļu valodas diskursa veidiem. Ir piedāvāta oriģināla tipoloģiska EAD klasifikācija. Ir norādīti seši tipiskākie EAD veidi: akadēmiskie e-pasti, sinhronās konferences, tiešsaistes diskusijas, emuāri, hiperteksti un elektroniskie semināri. Katra EAD veida raksturošanai tika izveidoti seši specializēti tekstu sakopojumi. Lingvistisko leksisko un gramatisko formu sastopamības daudzdimensiju analīze (Biber 1988) tika izmantota kā galvenais kvantitatīvais izpētes paņēmiens. Būtiskas izmaiņas ir atklātas piecdesmit piecu leksisko un gramatisko formu. Pretēji tradicionālajam uzskatam, ka elektroniskais akadēmiskais diskurss būtiski nemainās, pētījumā iegūtie rezultāti pierāda būtisku multidimensiju variāciju dažādu EAD veidu lingvistisko līdzekļu sastopamības biežumā. Šajā pētījumā iegūtie rezultāti var būt noderīgi pētījumu veicējiem, kas pēta elektroniskās valodas atšķirības, valodas pasniedzējiem un citiem speciālistiem lietišķajā valodniecībā.The dissertation presents the undertaken theoretical and empirical research investigating a new specific type of English discourse that takes place in academic settings and is mediated by computer. An original definition of computer-mediated academic discourse (CMAD) has been elaborated. The author has demonstrated that CMAD has specific linguistic characteristics distinguishing it from other types of English discourse. An original typological classification of CMAD has been proposed. The following six most typical types of CMAD have been distinguished: academic e-mails, synchronous conferencing, online discussions, weblogs, hypertexts and computer-mediated seminars. Six specialised corpora were complied to represent each type of CMAD. Multidimentional analysis of variance of linguistic features (Biber 1988) was applied as the main quantitative research method. Considerable changes have been revealed in the use of fifty-five types of linguistic features in the corpus. Contrary to the traditional view, which regards academic discourse mediated by computer not significantly varying, the research results provide the evidence of significant multidimensional variation in the frequency of appearance of linguistic features in different types of CMAD. The findings obtained in the present research may be of interest to the researchers investigating varieties of computer-mediated language, language educators and other specialists in applied linguists

Efficient Synthesis and Characterization of Lactulosucrose by <i>Leuconostoc mesenteroides</i> B‑512F Dextransucrase

This work describes an efficient enzymatic synthesis and NMR structural characterization of the trisaccharide β-d-galactopyranosyl-(1→4)-β-d-fructofuranosyl-(2→1)-α-d-glucopyranoside, also termed as lactulosucrose. This oligosaccharide was formed by the <i>Leuconostoc mesenteroides</i> B-512F dextransucrase-catalyzed transfer of the glucosyl residue from sucrose to the 2-hydroxyl group of the reducing unit of lactulose. The enzymatic reaction was carried out under optimal conditions, i.e., at 30 °C in 20 mM sodium acetate buffer with 0.34 mM CaCl₂ at pH 5.2, and the effect of factors such as reaction time (0–48 h), enzyme charge (0.8, 1.6, and 2.4 U mL^–1), and sucrose:lactulose concentration ratios (20:40, 30:30, and 40:20, expressed in g/100 mL) on the formation of transfer products were studied. The highest formation in lactulosucrose was attained at 8 and 24–32 h by using 20%:40% and 30%:30% sucrose:lactulose mixtures, respectively, with 1.6 or 2.4 U mL^–1 dextransucrase, leading to lactulosucrose yields of 27–35% in weight respect to the initial amount of lactulose. Furthermore, minor tetra- and pentasaccharide, both probably derived from lactulose, were also detected and quantified. Likewise, the capacity of lactulosucrose to act as d-glucosyl donor once the sucrose was consumed, could explain its decrease from 16 to 24 h when the highest charge of dextransucrase was used. Considering the chemical structure of the synthesized oligosaccharides, lactulosucrose and its derivatives could potentially be excellent candidates for an emerging prebiotic ingredient

Synthesis and Characterization of a Potential Prebiotic Trisaccharide from Cheese Whey Permeate and Sucrose by <i>Leuconostoc mesenteroides</i> Dextransucrase

The production of new bioactive oligosaccharides is currently garnering much attention for their potential use as functional ingredients. This work addresses the enzymatic synthesis and NMR structural characterization of 2-α-d-glucopyranosyl-lactose derived from sucrose:lactose and sucrose:cheese whey permeate mixtures by using a <i>Leuconostoc mesenteroides</i> B-512F dextransucrase. The effect of synthesis conditions, including concentration of substrates, molar ratio of donor/acceptor, enzyme concentration, reaction time, and temperature, on the formation of transfer products is evaluated. Results indicated that cheese whey permeate is a suitable material for the synthesis of 2-α-d-glucopyranosyl-lactose, giving rise to yields around 50% (in weight respect to the initial amount of lactose) under the optimum reaction conditions. According to its structure, this trisaccharide is an excellent candidate for a new prebiotic ingredient, due to the reported high resistance of α-(1→2) linkages to the digestive enzymes in humans and animals, as well as to its potential selective stimulation of beneficial bacteria in the large intestine mainly attributed to the two linked glucose units located at the reducing end that reflects the disaccharide kojibiose (2-α-d-glucopyranosyl-d-glucose). These findings could contribute to broadening the use of important agricultural raw materials, such as sucrose or cheese whey permeates, as renewable substrates for enzymatic synthesis of oligosaccharides of nutritional interest

Intestinal Anti-inflammatory Effects of Oligosaccharides Derived from Lactulose in the Trinitrobenzenesulfonic Acid Model of Rat Colitis

Intestinal microbiota modulation is becoming an interesting approach to manage inflammatory bowel disease and can be achieved by the administration of prebiotics. Previous studies showed the intestinal anti-inflammatory effects of the prebiotic lactulose. The aim of the present study was to test the preventative effects of oligosaccharides derived from lactulose with prebiotic properties (OsLu) in the trinitrobenzenesulfonic acid model of rat colitis and compare them with those of lactulose. Both treatments modified bacterial profile in intestinal contents, increasing the bifidobacteria and lactobacilli counts and up-regulating the production of short-chain fatty acids, although OsLu generated a larger amount. OsLu also inhibited to a greater extent different pro-inflammatory markers such as interleukins (IL) 1, 6, 12, and 23 and chemokines (MCP-1 and CINC-1). However, both prebiotics equally restored colonic epithelial integrity, evaluated both with a histological score (OsLu, 9.8 ± 2.2; and lactulose, 12.1 ± 2.1, vs colitic control, 27.3 ± 3.3) and by measuring several key proteins of the mucosal barrier (MUC-2, MUC-3, and TTF-3). OsLu effect was also associated with an inhibition of iNOS expression and a reduction of Th17 cell activity in the inflamed tissue that facilitated the intestinal mucosa barrier recovery. In conclusion, OsLu showed a better anti-inflammatory profile than lactulose in this model of experimental colitis