Browsing by Subject "dekstraani"

Brewers’ spent grains (BSG) are by-products of the brewing industry. Utilization of BSG in food applications is challenging, due to its poor technological characteristics. Because of their water retaining properties, interactions with matrix components and impact on texture formation, bacterial exopolysaccharides (EPS) represent a promising tool for improvement of BSG properties. Among bacterial exopolysaccharides, dextran produced in situ by lactic acid bacteria (LAB) during fermentation has shown major improvements in technological and sensorial features of products prepared from various types of plant materials. The nutritious composition of BSG may support the growth of LAB and enable in situ dextran production. The aim of this study was to establish and examine the synthesis of dextran by LAB in BSG. Sixteen dextran producing LAB strains were screened for viscosity formation in BSG fermentation. The strains showing the highest viscosity formation were further assessed for fermentation performance. The more suitable fermentation temperature was traced by comparing the viscosifying performance of selected starters at 20 and 25 °C. Dextran amount was determined semi-quantitatively from selected fermented samples showing optimal results, and the presence of oligosaccharides was assessed. Sucrose, glucose, maltose and fructose amounts were analyzed to observe the relation between sugar consumption and dextran and oligosaccharides formation. Weissella confusa strains A16 and 2LABPTO5 and Leuconostoc pseudomesenteroides strain DSM20193 appeared the most promising starters for viscosity formation and thus dextran synthesis in this matrix. From the examined fermentation temperatures, strains showed the highest potential for dextran synthesis at 25 °C. The amount of synthesized dextran ranged from 1.1 to 1.7 % w/w (of the wet weight of the whole sample matrix). The rheological properties of BSG were modified via LAB fermentation and dextran synthesis, resulting in more viscous texture, and its applicability in food systems was thus potentially enhanced.

Methylation analysis by Ciucanu and Kerek (1984) and Hakomori (1964) and the meaning of circumstances in the reaction, reaction parameters and structure of the sample were reviewed in this study. The experimental work consisted of methylation analysis of glucose, cellobiose, isomaltose, pullulan, commercial dextran and dextrans produced by lactic acid bacteria Weissella confusa and Leuconostoc citreum. The success of the methylation was controlled using the IR-method. Methylated samples were treated by methanolysis and acid hydrolysis. The structure analyses were carried out with GC-MSspectra. Two different columns: DB-1 and HP-5 were compared in the GC-analysis. Two hours methylation in the ultrasonic bath gave good methylation results. It was easy to control the methylation by IR-method. OH-peak (3400 cm-1) was absent and CH3- peaks (2900 and 2800 cm-1) were high after successful methylation. IR-spectroscopy is a valuable tool to check if methylation has been successful. Samples could be remethylated before hydrolysis and derivation if necessary. After methanolysis there were ?- and ?-pyranose forms from each methylated monosaccharides. Due to reduction after the acid hydrolysis method, there was only one methylated form from each product. The structures of glucose, cellobiose, isomaltose and pullulan were solved by both hydrolysis methods. Recovery of these samples was good but the deviation was large. The structure of commercial dextran and dextran produced by W. confusa were solved by methanolysis method and partly by acid hydrolysis method. Recovery of these samples was poor. The methylation succeeded only in one of the dextran samples produced by L. citreum. The methylation analysis of dextrans could be developed in the future by increasing the temperature and the time of mixing and by adding some glycerol.

Hapanleivonta on tuhansia vuosia käytetty prosessi, jota hyödynnetään paljon vielä tänäkin päivänä. Raski eli taikinajuuri on maitohappobakteerien ja hiivojen avulla fermentoitu jauhojen ja veden seos, jonka avulla voidaan nostattaa leipä. Osa raskin maitohappobakteereista tuottaa aineenvaihdunnassaan sakkaroosista eksopolysakkarideja, joista yleisin on dekstraani, jonka perusrunko koostuu α-(1→6)-sidoksellisista glukosyyliyksiköistä. Maitohappobakteerien tuottamilla eksopolysakkarideilla on tutkitusti erilaisia positiivisia vaikutuksia hapanleivonnassa leivän rakenteeseen. Tutkielman tavoitteena oli selvittää sisältävätkö näyteraskit eksopolysakkarideja tuottavia maitohappobakteereita sekä analysoida kyseisten eksopolysakkaridien rakenteet mahdollisimman tarkasti. Tutkimuksessa näyteraskeista eristettiin maitohappobakteerit ja kasvatettiin niitä sakkaroosia sisältävillä MRS-alustoilla. Alustoilta eristettiin kaikki eksopolysakkarideja tuottaneet pesäkkeet ja puhdistettiin ne puhdaskannoiksi. Kantojen tuottamia eksopolysakkarideja hydrolysoitiin entsymaattisesti dekstranaasin ja glukosidaasin avulla, minkä jälkeen HPAEC-PAD-menetelmillä analysoitiin niiden monosakkaridit ja entsyymeille resistentit oligosakkaridit. Eksopolysakkaridien rakennetta analysoitiin myös NMR-tekniikan avulla. Näyteraskeista saatiin eristettyä yhteensä 13 eksopolysakkarideja tuottavaa kantaa. HPAEC-PAD-monosakkaridianalyysin perusteella kaikkien eksopolysakkaridien todettiin olevan dekstraaneja, sillä käytetyt entsyymit pystyivät pilkkomaan niitä. Entsyymiresistenttien oligosakkaridien kromatogrammeista nähtiin, että erilaisia kromatografisia profiileita oli neljä, joten erilaisia näytteitä oli myös neljä. NMR-tulokset varmistivat, että kaikki eksopolysakkaridit olivat dekstraaneja. NMR-tuloksista voitiin myös varmistaa, että yhteensä erilaisia eksopolysakkaridirakenteita oli neljä. Kaikissa eksopolysakkarideissa oli α-(1→3)-sidoksellisia haarautumia. Kahdessa eksopolysakkaridissa oli lisäksi α-(1→2)-sidoksellisia haarautumia. Tutkimuksen avulla saatiin tietoa näyteraskin maitohappobakteerien eksopolysakkaridien tuotosta sekä kyseisten eksopolysakkaridien rakenteista.

The physical stability of plant-based beverages is often weak and is used to be improved by food additives. β-glucan and dextran are hydrocolloids that have been found to increase fluid viscosity and therefore may have the potential to replace E-coded hydrocolloids. The aim of this master's thesis was to investigate the effects of oat β-glucan and microbiologically produced dextran on the physical stability of a drinkable oat snack. In addition, the aim was to determine the importance of the molecular size and concentration of β-glucan for its stabilizing ability. The oat base without any added hydrocolloids served as a control. β-glucan and dextran were added to the oat base as extracts so that they replaced a certain volume of oat base water. To determine the concentration effect of β-glucan, an oat beverage containing a high molecular weight β-glucan extract extracted from oat bran was prepared in three different extract concentrations. To determine the effect of the molecular weight, an oat beverage containing an enzymatically hydrolyzed low molecular weight β-glucan extract was prepared. The effects of dextran were studied by preparing oat beverages containing exopolysaccharide extract (EPS) (dextran positive and negative sample). Samples were stored in a refrigerator for 14 days, during which time their stability was characterized by observing phase separation and measuring viscosity, particle size and turbidity. The stability of the beverage samples decreased because of sedimentation, leading to the visual phase separation at the top of the samples. The high molecular weight β-glucan extracted from the oat bran reduced sedimentation and phase separation, and stability and viscosity increased as the extract concentration increased from 5% to 7.5%, with almost invisible phase separation in the latter. Thereafter, increasing the extract concentration to 10% no longer reduced the phase separation, but resulted in a decrease in viscosity during storage. Low molecular weight β-glucan (extract content 10%) did not increase the stability of the oat base, and the viscosity of the sample decreased by about 60% during storage. The decrease in viscosity in these samples may be due to the aggregation of proteins and / or β-glucan due to the higher β-glucan content. The effects of dextran on the stability of the oat beverage remained unclear, as the dextran-positive and negative samples did not differ significantly in viscosity or phase separation, so further studies are needed. Based on this thesis, high molecular weight β-glucan appeared to be a potential substitute for food additives in oat-based beverage applications.