Browsing by Subject "Viscosity"

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  • Viidik, Laura; Seera, Dagmar; Antikainen, Osmo; Kogermann, Karin; Heinämäki, Jyrki; Laidmäe, Ivo (2019)
    Printing technologies combined with a computer-aided design (CAD) have found an increasing number of uses in pharmaceutical applications. In extrusion-based printing, the material is forced through a nozzle to form a three-dimensional (3D) structure pre-designed by CAD. The aim of this study was to evaluate the 3D-printability of biocompatible aqueous poly(ethylene oxide) (PEO) gels and to investigate the effects of three formulation parameters on the 3D printing process. The impact of PEO concentration (gel viscosity), printing head speed and printing plate temperature was investigated at three different levels using a full factorial experimental design. The aqueous PEO gels were printed with a bench-top extrusion-based 3D printing system at an ambient room temperature. The viscosity measurements confirmed that the aqueous PEO gels follow a shear-thinning behaviour suitable for extrusion-based printing. Heating the printing plate allowed the gel to dry faster resulting in more precise printing outcome. With the non-heated plate, the gel formed a dumbbell-shaped grid instead of straight lines. Higher concentration and more viscous PEO gels formed the best structured 3D-printed lattices. In conclusion, the accuracy and precision of extrusion-based 3D printing of aqueous PEO gels is highly dependent on the formulation (PEO concentration) and printing parameters (printing head speed, plate temperature). By optimizing these critical process parameters, PEO may be suitable for printing novel drug delivery systems.
  • Yassami, Shiva (Helsingfors universitet, 2016)
    Wheat bran is obtained after conventional milling of wheat grains for the production of white flour, which is an important source of dietary fiber, vitamins and minerals, but still remains underutilized in food manufacturing. In spite of the increasing evidence about the health effects of whole-meal and fiber-rich foods, refined white flour is still preferred. Bran also has a negative influence on dough rheology, texture and the sensory quality of bread, which limits its use in bran bread baking. The use of starter culture for sourdough fermentation can drive the fermentation process and confer specific changes on the matrix. Exopolysaccharides (EPS) produced by some lactic acid bacteria (LAB) are important due to their physicochemical properties affecting dough rheology and bread texture, as well as their health-promoting potential. The screening of EPS-producing strains has been carried out mostly on wheat and rye sourdough, and very few studies have considered different matrices. The objective of this work was to determine and compare whole-wheat flour and wheat bran fermentation by two strains of LAB (Leuconostoc spp. and Weissella spp.) in the presence of added sucrose and without, and to study the effect of sourdough obtained with a selected EPS-producing LAB strain on the quality of bread and its shelf-life. Sourdough quality was studied by means of microbiological, rheological and chemical analysis by comparing the growth and acidification performance in the different matrices, and by evaluating EPS production using viscosity measurements. The physical and mechanical properties of fresh bread made using the best EPS producer LAB were investigated to study the product shelf-life by using the seed replacement method and texture analysis test. The results showed that dough prepared with Weissella confusa with added sucrose had a positive impact on viscosity, as well as providing mild acidic sourdough leading to better bread quality properties, whereas in the presence of Leuconostoc pseudomesenteroides, no positive viscosity has observed in whole-wheat sourdough. Bran sourdough samples with Weissella confusa showed a higher volume, better color and shelf-life during storage than samples with un-soured bran, confirming the effect of sourdough and the positive role of EPS on the functional properties of high-fiber bread making.
  • Yang, Lingxi (Helsingin yliopisto, 2018)
    Oat β-glucans are water soluble non-starch polysaccharides. The health benefits of β-glucan including reduction of post-prandial glycemic response are correlated to its ability of forming viscous solutions. Phytate has also been reported to reduce starch digestion due to its potential of binding starch-digestion-related enzymes such as α-amylase or enzyme co-factors. The previous study showed that a significant amount of phytate was found in both oat β-glucan extract and highly purified β-glucan. The aim of this research was to study the role of residual phytate in the oat β-glucan extracts in starch hydrolysis. Oat β-glucan (OBG) was extracted from oat bran concentrate. OBG with phytate-removal treatment (OBG-PR) was prepared with ion-exchange resin and dialysis. The content of β-glucan, phytate and starch in OBG and OBG-PR were determined with Megazyme kits. The protein and calcium content was also measured. Before adding into the gelatinized wheat starch solution, the β-glucan solutions or phytic acid solution were pre-incubated with porcine pancreatic α-amylase. The starch hydrolysis was induced at physiological pH 6.9 and 37°C. Aliquots were collected at 20 min and 120 min digestion time. Digested starch was calculated based on the released glucoses. Both OBG and OBG-PR inhibited the starch hydrolysis. OBG contained a higher amount of phytate. And it had a stronger inhibitory effect (46%) than that of OBG-PR (34%). Pure phytic acid showed a comparable inhibitory effect on the starch hydrolysis as the OBG intrinsic phytic acid did, when the pure phytic acid was used at the same level as the concentration of intrinsic phytic acid in OBG. The decrease of intrinsic calcium in OBG-PR was found due to the ion-exchange and dialysis process. Consequently, the same amount of calcium was added to OBG-PR. The inhibitory effect of phytic acid on starch hydrolysis was completely reversed by the addition of calcium. Moreover, degradation of β-glucan by lichenase increased starch hydrolysis rate, which confirmed the role of β-glucan viscosity in the reduction of starch hydrolysis. In summary, the residual phytic acid of oat β-glucan, in addition to viscosity, reduced starch hydrolysis, while calcium contributed to promote starch hydrolysis.
  • 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.
  • Mäkelä, Noora; Brinck, Outi; Sontag-Strohm, Tuula (2020)
    The physiological functionality of cereal beta-glucan (beta-glucan) has been mainly attributed to its ability to form viscous solutions in the gastrointestinal (GI) tract. The viscosity is dependent on the concentration, extractability and molecular weight of beta-glucan, and to enable maximal functionality, these factors should therefore be acknowledged and their role in the physiological functionality of cereal beta-glucan further studied. An in vitro GI simulation with separate oral, gastric and small intestine phases was used to model the state of beta-glucan from various oat products in the GI tract. A rather large variation (from 26% to 99%) was observed in the extractabilities between product categories, with the highest extractabilities observed in spoonable products. The viscosities also varied highly within categories. When the comparison was done at similar concentration levels, the highest viscosities were observed in the products produced through dry processes, and moisture content during processing was suggested to be essential to the extent of beta-glucan degradation. The viscosity in samples that were likely to exhibit enzymatic activity was shown to be rather low, and thus the physiological functionality of beta-glucan may be threatened if the product also contains grain ingredients other than kiln-dried oat. Clear differences were observed in the functionality of beta-glucan in the GI tract model depending on a product type, and these were explained by differences in ingredients and processes. However, further studies are needed to specify the influence of each factor and to clarify the factors determining the physiological functionality of beta-glucan in food products.