Browsing by Subject "food Technology"

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  • Bhattarai, Mamata (Helsingin yliopisto, 2020)
    Galactoglucomannans (GGMs) are principal hemicelluloses in softwood tissues. Spruce GGM obtained from different recovery approaches are currently studied for applications as emulsifiers and stabilizers of dispersed systems. Natural polysaccharides, owing to their origin from a complex matrix, have an intrinsic affinity for the association. Their associative properties are affected by the recovery approach since it influences purity and intrinsic characteristics (e.g., molar mass, degree of substitution). Understanding the impact of the GGM recovery approach on its associative behavior, currently limited, is essential to comprehend the stabilization mechanism of GGM in dispersed systems as well in the expansion of its functional applications. This doctoral project investigated the associative behavior of GGM at a semi-dilute concentration of 1% in an aqueous medium and its effect in an oil-in-water emulsion system, with GGM recovered from spruce sawdust/wood chips using pressurized hot water extraction, BLN process (modified pressurized hot water extraction process), and effluent of the thermo-mechanical pulping process. All studied GGM samples existed in the form of polysaccharide molecules and supramolecular fraction. It was observed that the recovery approach and sample purity affected the molar mass of the polysaccharide fraction as well as the share and structural properties of the supramolecular fraction. The supramolecular fraction was observed to be either colloidal aggregates, agglomerates, solid particles, or a combination in varying proportions. Next, these samples were studied in emulsions. Differences in the macromolecular state of samples were found to influence interfacial morphology and stability of emulsions. Following, the associative behavior of purified GGM obtained from the pressurized hot water extraction process was studied at acidic, neutral, and alkaline pH and upon addition of sodium chloride. Associative behavior of the sample displayed a positive correlation with acidic pH condition and time, improving emulsion stability. The sample exhibited an upper limit of GGM to oil ratio for efficient emulsification and stabilization ability, implying the presence of a limited amount of active emulsifying component. Currently, novel biomaterials are being developed from wood biomass. The findings of this study contributed to the characterization of colloidal properties of GGM at a nanometric scale, thereby enhancing its scope of future applications. These findings regarding the solubility of GGM would also be relevant in existing operations of paper and pulping industries, as well as for aspiring biorefineries in identifying optimal GGM recovery approach.
  • Alam, Syed Ariful (Helsingin yliopisto, 2020)
    This study focused on modification of rye bran to produce high fibre extruded cereal foods with a good texture and structure. Rye bran addition during extrusion is challenging due to high levels of insoluble dietary fibre, which leads to less expanded products and a hard texture. Bran modification by particle size reduction or fermentation significantly improved both the structural and textural properties of extrudates. Moreover, optimization of the processing parameters such as increasing the screw speed, lowering the water feed rate, as well as the use of in-barrel hydration regimens further improved the textural properties. The applicability of rye bran in extruded products could thus be improved by particle size reduction and fermentation. The extruded food structure and texture had a direct effect on the mastication and bolus formation process in the mouth. A hard and dense extrudate structure required more mastication effort than a crispy structure. Crispy and porous structures easily disintegrated in the mouth and produced smaller bolus particles than a hard and dense structure. A smaller particle size of the bolus was associated with increased starch hydrolysis. The bolus particle size was more effective than the matrix composition in altering the starch digestibility. Increased dietary fibre intake via appealing snack products could help reduce chronic diseases. Knowledge obtained in this thesis on cereal matrix formation and digestion and the effects of added dietary fibre on the structural and textural properties of extruded solid foams will help the food industry to develop healthy and appealing products. Understanding process-structure-digestibility relationships of high fibre extruded matrices is essential for designing health promoting foods.