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Subject: search.filters.subject.400406 Powder and particle technology

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    A study on the physicochemical properties of defatted New Zealand green-lipped mussel protein concentrates (MPC) dispersions : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology, Massey University, Auckland, New Zealand. EMBARGOED until 28th July 2026
    (Massey University, 2024) Lin, Jingying
    This thesis investigated changes of physicochemical properties of mussel protein concentrates (MPC) dispersions at different pH affected by ultrasound treatment and the viscoelastic properties of heat-induced MPC gels with varying concentrations of different starches. The first study evaluated the effect of pH (3,5,7,9) and ultrasound treatment (15 min) on the physicochemical and functional properties of desalted MPC, including particle size, solubility, zeta potential, emulsification, and gelation. Compared with control groups, it was found that the particle size of all samples at all pH decreased greatly after ultrasound treatment, as reflected in a 7~17 times reduction in D [3,2] and a 3~8 times reduction in D [4,3]. Ultrasound treatment also improved absolute values of zeta potential and made MPC dispersions more stable. In addition, ultrasound treatment increased the solubility of MPC dispersions at all pH values. The most significant increase in solubility was observed for samples at pH 3, from ~1.2% to ~57.4%; followed by pH 7 and pH 9 samples, from ~1% to ~20.8% and ~2% to ~18.7%, respectively; pH 5 showed the smallest change, from ~0.5% to ~0.8%, which was because it closed to the isoelectric point of MPC (pI~4.55). SDS-PAGE results showed that MPC composed of actin (43-46 kDa) and paramyosin (98–107 kDa), ultrasound treatment and pH changes did not result in significant changes in the mussel protein bands. All untreated and sonicated MPC samples were observed to form interconnection dense and fine gel network structures under confocal laser scanning microscopy (CLSM) after heat treatment, untreated MPC gels at pH 3 and pH 9 showed dense network structures compared to other gels. Also, ultrasound treatment led to finer and more homogeneous gel network structures. Microstructure images and rheological measurements of emulsions revealed that emulsions stabilized by sonicated MPC at pH 3 had the smallest oil droplet size with D [3,2] ~6.5 µm and D [4,3] ~12.7 µm, respectively. The gel strength (G' (1 Hz)) of pH 3 emulsion was the highest and reached ~502.3 Pa. Emulsion stabilized by sonicated MPC at pH 5 had the lowest G' (1 Hz) at ~107.9 Pa, the oil droplet was the greatest among all emulsions with D [3,2] ~20.4 µm and D [4,3] ~66.9 µm, respectively. This could be attributed to MPC dispersion at pH 5 having the lowest solubility and the greatest particle size. For heat induced MPC gels, ultrasound treatment declined the gel strength at all pH values; gels without ultrasound treatment at pH 9 and pH 3 had the highest G'. The study may provide useful information for MPC applications in the food field. The second study examined the viscoelastic properties of heat-induced defatted mussel protein gels with varying concentrations (0%, 2.5%, 5%, 10% w/w) of native rice starch (NRS), waxy rice starch (WRS), waxy corn starch (WCS), and waxy potato starch (WPS). CLSM images showed that a 10 w/w % mussel protein concentrate (MPC) sample cannot form a gel after heating at 90 ℃ for 30 min. When 5% starch was added to MPC samples, dense gel network structures were observed after heating, suggesting a crucial role of starch in MPC gelation. Rheological measurements indicated that starch addition can increase the strength of MPC gels. Both G′ and Gʺ raised significantly in the protein-starch system when the starch concentration increased. Compared to the control (10% MPC without starch), in the presence of 10% starches, the G′ of MPC-NRS, MPC-WRS, MPC-WCS, MPC-WPS gels increased ~120, ~32, ~50, ~185 times, respectively. MPC-WPS gel appeared the highest G′ among all MPC-starch gels with a 10% starch addition. In the protein-starch system, the combination of MPC and starch resulted in a stronger gel, showing a greater effect than the sum of MPC and starch separately. Additionally, the pasting temperature of starch in the protein-starch system was higher compared to when it was in water.
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    Atomization of fruit juice with fibres as drying aid : nozzle : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemical and Process Engineering at Massey University, Palmerston North, New Zealand
    (Massey University, 2019) Mohd Rozali, Siti Nadjiha
    Spray drying of fruit juices is desirable as it produces dry powders which extend the shelf-life, reduce storage and transport costs, and produce a free-flowing powder which makes it easier to blend as an ingredient. Commercially, maltodextrin is added to the juices as a drying aid to increase the efficiency of the spray drying process. In this project, pomace fibres were investigated as an alternative drying aid. The main attraction of pomace fibres as a drying aid is the pomace fibres are originally derived from the fruits itself. This study explores the rheological behaviour of juice-fibre suspensions inside the spraying device, specifically the nozzle, to ensure high efficiency powder production by enabling atomization of the mixtures. This study also sought to determine the type of nozzle and operating conditions for efficient atomization of the juice-fibre suspensions inside the spray dryer. Flow-fields inside a nozzle consists of shear and extensional flows. Previous studies on the shear rheology of fibre suspensions revealed the addition of fibres creates a non-Newtonian shear-thinning liquid. The studies on extensional rheology of fibre suspensions, however, were absent. It is widely known the atomization of liquids with both shear and extensional resistances, require additional energy for atomization when compared to Newtonian liquids or viscous non-Newtonian liquids of a similar intrinsic viscosity. In this work, four types of fibres with different aspect ratios were investigated. Some of the significant and notable methods achieved during the study include 1) the use of capillary viscometer to examine the shear rheology of fibre suspensions at shear rates up to 20 000 s⁻¹, which represents the calculated shear rate experienced during atomization, 2) the building of a portable capillary breakup extensional rheometer to accurately characterize the extensional rheology of the fibre suspensions at high extensional strain rates and 3) the use of flash photography technique to capture the atomization patterns. Important findings from this work include: • Fibre suspension is a non-Newtonian shear thinning liquid with shear viscosity dependents on the fibre aspect ratio. The shear thinning behaviour continued until the shear rate of 25 000 s⁻¹ and a plateau occurred at 25 000 s⁻¹ shear rate. The plateau is independent of the fibre aspect ratio. • The fibre suspension exhibited extensional resistance. The extensional rheological properties of the fibre suspensions were dependent on fibre aspect ratio. When comparing between the shear and extensional rheology of a specific fibre suspension, the transient extensional viscosity, 𝜂⁺𝐸 of the fibre suspension was relatively greater than its corresponding shear viscosity. • The entrance pressure drop into the nozzle was significantly increased with the addition of fibre. This made the use of a pressure nozzle inefficient. It was advised by personal discussion with industry experts that rotary atomizers usually fail in atomizing extensional liquids, so its application was not explored in this study. • Spray visualization showed the extensional resistance of the fibre suspensions significantly affected the atomization behaviour and pattern (droplet size distribution) by forming filament structures connecting successive droplets together. This pattern was absent in Newtonian atomization. • Successful atomization of fibre suspensions was achieved by using a two-fluid nozzle at high atomizing air velocities and at air-to-liquid ratio above 0.25. At an atomizing air velocity of 150 m/s, the atomization performance is dependent on the fibre aspect ratio, but this effect was reduced at higher atomizing air velocities. At the highest tested atomizing air velocity of 240 m/s, all fibre suspensions yielded a volume-based average droplet size, D(v,50), of 200 – 250 µm. • Using a two-fluid nozzle at high atomizing air velocities, the droplets sizes of the fibre suspensions insignificantly reduced when the temperature of the inlet fibre suspensions was increased. No change was observed to the atomization performance when an ultrasonic mechanism was added to the two-fluid nozzle as an attempt to improve the atomization performance. • A method of predicting the atomization performance of a given two-fluid nozzle from its dimensionless numbers, for actual spray dryer applications, was demonstrated and the results showed that the two-fluid nozzle can be used inside a spray dryer if the air-to-liquid ratio exceeds 0.25. Overall, the methodology used in this thesis provides a systemic means of investigating the suitability of an atomization method for the spraying of a non-Newtonian fluid with extensional rheological properties.
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    Prediction of the glass transition temperature of fruit juice powders : a thesis presented in partial fulfilment of the requirements for the degree of Doctor in Philosophy in Process Engineering at Massey University, Manawatu, New Zealand
    (Massey University, 2019) Linnenkugel, Sebastian
    To overcome the limited shelf life of fresh fruit juice, manufacture aim to reduce the juice to a powdered form that can be available all year around. One technique of powder formulation is the use of spray dryer. However fruit juices are rich in fruit sugars and organic acids, which make them difficult to spray dry. Their low glass transition temperatures lead to stickiness problems in the spray dryer. This work investigates the prediction of the glass transition temperature (Tg) of fruit juice powders and mixtures including high molecular weight components often used as drying aids of their mixtures. The ability to predict glass transition temperatures enables optimization of powder formulations and spray dryer operation to avoid sticking problems. A semi-empirical model is presented to predict the glass transition temperature of fruit juice powders on the basis of the chemical composition and the Tg values of the individual pure components. The Flory-Huggins Free Volume theory is used to describe the relation between the water activity of the powders and the glass transition temperature based on the composition of the powders. These prediction models were tested for different freeze dried multicomponent systems and validated against the glass transition temperatures measured by Differential Scanning Calorimetry (DSC). The model was then applied to predict the Tg of values freeze dried juice and vegetable powders prepared from commercial juice concentrate. The six fruit and vegetable juice powders exhibited higher measured Tg values at zero water activity those that predicted from the model. The 6-14˚C difference between the measured and predicted Tg values cannot be explained purely by the main sugar and organic acid components, but are rather linked to the presence of residual breakdown products of pectins and other polysaccharides from the base fruit. For several powders, a second glass transition temperature was visible in the DSC thermogram, which can be attributed to these additional components. The prediction of the glass transition temperature of the pure juice powders at various water activities showed better agreement with the experimental data the closer the predicted and measured Tg value of the powders was at zero water activity. The Tg values of different low molecular weight components and the polysaccharide maltodextrin DE 9-13 often used as a drying aid was studied. The Tg for the binary and multicomponent systems was well estimated by the prediction model at zero water activity. The addition of higher amounts of maltodextrin DE 9-13 up to a weight fraction of 0.7 in the mixture resulted in a widening of the transition observed in the DSC thermogram, which can be attributed to dynamic heterogeneity of the samples due to the dynamic response times of different domains in the solid matrix. This could be demonstrated by annealing the samples below their glass transition temperatures for 16 hours. The analytical semi-empirical model proved to be a viable method for predicting the glass transition temperature of mixtures of low and high molecular mixtures. Multicomponent systems consisting of more than one high molecular weight component in the form of various soluble polysaccharides and the monosaccharide glucose were investigated for their Tg values at zero water activity. The different mixtures of the low molecular weight components and polysaccharides showed a shift in the glass transition temperature that depended strongly on the Tg value of the pure polysaccharide. However, the overall trend of Tg values for the mixtures of low and high molecular weight components was found to be similar for all mixtures. The Tg values of all systems with various polysaccharides were well predicted. It also highlighted that a weight fraction of above 0.5 for the polysaccharides with a degree of polymerization of sugar units above 5 is necessary in the solid matrix to have a significant impact on the glass transition temperature. Salts were tested as an alternative drying aid to high molecular weight components at various ratios to the monosaccharide glucose. The salts increased the glass transition temperature of the blends at lower concentrations. A weight fraction of 0.2 of salts in the system has the same effect on the Tg values as a 0.5 weight fraction of a higher molecular weight component. The difference in necessary amount to increase Tg can be attributed to the different mechanisms of salts and polysaccharide in the solid matrix. To demonstrate the utility of the model, it was applied to optimize the spray drying of blackcurrant juice concentrate, with the aid of maltodextrin DE 9-13. It has been reported that sticking can be avoided during drying if the operating temperature does not exceed T=Tg + 25˚C. By combining the prediction of the Tg of the solid mixture at various water activities and a mass and energy balance over the spray dryer, reasonable feed composition and operational conditions were found. This allowed the successful conversion of blackcurrant juice into a powder in a single trial without relying on trial-and-error approaches.