Browsing by Subject "Molecular weight"

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  • Chen, Yike Jr (Helsingin yliopisto, 2018)
    Cereal β-glucan, or (1→3)(1→4)-β-D-glucan, has unique viscous and gelling properties, which are related to its physiological effects. The increased viscosity in human gastrointestinal tract by β-glucan is considered a key factor for its health benefits. However, the possible gelling ability of β-glucan in human intestine and its relation to the physiological functionality have not been investigated. The aims of this study were to investigate the possible structure formation of β-glucan at physiological conditions and to understand gelation difference between oat and barley β-glucan (OBG and BBG, respectively). Additionally, the effects of phytate and molecular weight (MW) on structure formation of β-glucan were studied. Oat (ROBG14, ROBG22) and barley bran concentrates (RBBG18) were used for in vitro studies in upper gut model. OBG14 was extracted from oat concentrates and used for further producing phytate-removed OBG (PR-OBG) or enzymatically degraded OBG (ENZ-OBG). The effect of phytate or molecular weight on gelation of beta-glucan was studied by comparing the gelation of PR-OBG or ENZ-OBG to OBG14 after 2 h and 1 d. The effect of β-glucan source was studied with medium viscosity oat (MOBG) and barley (MBBG) β-glucan with same molecular weight and concentration on day 1 and day 4. The extracted samples were first dissolved at physiological T 37°C for 2 h and the gel properties of the samples were measured with oscillatory measurements. OBG showed more structure formation than BBG at low concentrations in both studies with in vitro digestion model and extracted β-glucan samples at physiological temperature. In vitro RBBG18 (β-glucan content of the in vitro extract 0.6%) showed liquid-like behavior and no hysteresis obtained, indicating no structure formation. ROBG14 (β-glucan content 0.5%) and ROBG22 (β-glucan content 0.6%) showed entangled network, with similar crossover frequencies, 0.07 and 0.1 Hz, respectively. 1.5% MOBG showed liquid-like behavior on day 1, but storage modulus (G’) increased during storage. The undissolved particles in watery medium of MBBG indicated 37°C was not enough for partial dissolution which could lead to gel. At the same concentration (1%), both PR-OBG and OBG14 showed weak gel structure, with slightly higher G’ in PR-OBG. This indicated that phytate is not the reason for better gelation of OBG than BBG, which was hypothesized due to higher residual phytate in OBG than BBG. ENZ-OBG (0.7%) had lower G’ than OBG14 (0.7%), which indicated more structure formed in higher MW OBG at 2 h. To conclude, OBG is more prone to structure formation than BBG at physiological conditions. Phytate was not the reason for better gelation of OBG than BBG.
  • Carvalho, Danila M.d.; Berglund, Jennie; Marchand, Célia; Lindström, Mikael E.; Vilaplana, Francisco; Sevastyanova, Olena (2019)
    The impact of various degrees of acetylation on improving the thermal stability of xylan isolated from different botanical source has been studied; methylglucuronoxylan from birch and eucalyptus, arabinoglucuronoxylan from spruce and glucuronoarabinoxylan from sugarcane bagasse and straw. The lower molecular weight of nonacetylated methylglucuronoxylan (17.7-23.7 kDa) and arabinoglucuronoxylan (16.8 kDa) meant that they were more soluble in water than glucuronoarabinoxylan (43.0-47.0 kDa). The temperature at the onset of degradation increased by 17-61 degrees C and by 75-145 degrees C for low and high acetylated xylans respectively, as a result of acetylation. A glass transition temperature in the range of 121-132 degrees C was observed for the samples non-acetylated and acetylated at low degree of acetylation (0.0-0.6). The acetylation to higher degrees (1.4-1.8) increased the glass transition temperature of the samples to 189-206 degrees C. Acetylation proved to be an efficient method for functionalization of the xylan to increase the thermal stability.
  • Zhan, Ruzhen (Helsingin yliopisto, 2017)
    Cereal β-glucans are soluble non-starch polysaccharides. Both the health benefits and industrial applications of β-glucan have been correlated to its capability of forming viscous solutions. Oxidative degradation has been demonstrated to be the critical factor that causes the viscosity drop of β-glucan solutions. In oats and barley, more than 90% of the phytate was found in the soluble fiber fraction, most of which is β-glucan. Phytate has chelating ability to form phytate-mineral complexes. Therefore, phytate has the potential to suppress iron-catalyzed oxidative reactions and is hypothesized to protect β-glucan from oxidative degradation. The aim of this research was to study the role of both intrinsic and added phytate in the oxidative degradation kinetics of β-glucan. Fenton reaction was used to induce oxidation in both oat β-glucan (OBG) and barley β-glucan (BBG) solutions. Degradation of OBG and BBG was indicated by the decrease in molecular weight and viscosity. When the concentration of hydrogen peroxide kept constant, the extent of OBG degradation was found to be greater with increased iron concentration. Most degradation occurred in the beginning of the oxidation and OBG degradation in the initial 3 hours fitted well in the second order kinetics. The reaction rate constant (k) which stands for the degradation rate demonstrated a positive relationship with the iron concentration. Intrinsic phytate in OBG had a protective effect on β-glucan degradation induced by Fenton reaction. After phytate removal by ion exchange resin, degradation of OBG solution became faster with the same amount of oxidative reagents. As to the degradation kinetics, under the same oxidative condition, the k value increased after phytate removal. Added phytic acid also had a protective effect on the degradation of BBG solution, but the effect was not as strong as the intrinsic phytate in OBG. Furthermore, the strength of the protection was related to the PA/iron ratio. When the PA/ iron ratio was 2:5 , there was no protective effect of added phytic acid observed on the degradation of BBG. When the PA/ iron ratio was 2, the added phytic acid had protective effect. When PA/ iron ratio was 1:5, the added phytic acid had a more profound protective effect. In summary, our results demonstrated that both intrinsic phytate and additional phytic acid had a protective effect against the oxidative degradation of β-glucan. Addition of phytic acid in a proper ratio is of importance to maintain the stability of products containing β-glucan. Phytate or phytic acid is commonly considered as an antinutrient related to the mineral bioavailability in food intake. This study however showed an anti-oxidant effect of phytate in β-glucan solutions which suggests that it may have a beneficial effect in physicological conditions.