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Item 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 NadjihaSpray 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.Item 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, SebastianTo 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.Item The stickiness curves of dairy powder : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Bioprocess Engineering at Massey University(Massey University, 2004) Zuo, Jenny YPowder stickiness problems encountered during spray drying are important to the dairy industry. Instantaneous stickiness is a surface phenomena that is caused by exceeding the glass transition temperature of the amorphous sugar in the powder, usually lactose in dairy powders. Instantaneous stickiness occurs at a certain temperature above the Tg of amorphous lactose and has been denoted as the critical "X" value. Whether powder particles are sticky or not depends on whether there is enough liquid flow on the surface between the particles. Two particles stick to each other when there is enough liquid flow to form a bridge between them after the contact. This project aimed to measure the instantaneous sticky point conditions for various dairy powders and to relate these to the operating conditions to give a commerical outcome for the dairy industry. The particle-gun rig was developed to simulate the conditions in the spray drier and the ducting pipe and cyclone. The stickiness of powder particles occurs after a short resident time in the particle-gun. Thus, stickiness is a surface phenomenon and the point of adhesion is the instantaneous sticky point. The amount of deposit on the plate was measured at a temperature, with increasing relative humidity. At a particular temperature and relative humidity, the powder stuck to the stainless steel plate instantaneously. This was observed by a sudden change in % deposition on a % deposition verse RH plot. The T-Tg plot and stickiness curve profile were developed to determine the critical "X" value for the dairy powders. The critical 'X' value is the temperature which exceeds the Tg of amorphous lactose when instantaneous stickiness occurs. The critical "X" values tor various dairy powders including WMP, SMP, MPC, whey protein, buttermilk, white cheese powder and GLUMP powder were found to be 33-49°C. 37-42°C. 42-51C. 50°C, 37-39°C, 28.5°C, and 40.7°C respectively. In addition, the slope of the trend line in the T-Tg plot, indicates how quickly the particular powder becomes sticky once the instantaneous sticky point has been exceeded. The particle-gun rig demonstrated that powders with greater than 30% amorphous lactose are more likely to cause blockage than powders with less than 30%. Both the critical 'X' value and the slope are unique to the powder. The stickiness curve was used to relate the powder surface stickiness condition with the drier outlet temperature and relative humidity. It was recommended to operate at conditions below the stickiness curve for a powder to avoid any chamber or cyclone blockages caused by stickiness. The slope enables a decision to be made about how close to the critical point a plant should be run for a particular powder. The inlet air temperature or concentrate feeding rate can be used to move the operating conditions towards or away from the stickiness curve, according to the operating situations.Item Characterising stickiness of dairy powders : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Bioprocess Engineering, Massey University(Massey University, 2004) Chatterjee, RajeshThe stickiness phenomenon, one of the major operational problems, in the spray drying process is strongly related to changes in the powder particle surface. During the course of drying, powder particles with intermediate moisture pass through a very cohesive and adhesive 'plastic' phase. This phase has shown to be influenced by surface composition, moisture content, particle size, manufacturing method, surrounding air humidity and temperature. During spray drying, the powder particle experiences varied temperature and humidity conditions, which were replicated under controlled dynamic conditions to some extent in a 'Bench-top-scale Fluid Bed Rig' or in a 'Particle Gun Rig'. In these two set-ups, stickiness-end-point or deposition rates at a particular temperature and humidity combination were plotted to develop 'Stickiness Curves' after testing different dairy-based powders. Further improvements in the 'Particle Gun Rig' has been identified to minimise heat loss for future experimentation. It has been demonstrated that the stickiness property is a surface phenomenon. This is governed by the composition of a particular powder, manufacturing methods and the temperature / humidity conditions surrounding the powder particles. The low fat powders (<42%) tested followed a single step 'Lactose based stickincss model' and high fat powders (>42%) followed a combined 'Fat and lactose based stickiness model'. The 'lactose based model' followed the predicted glass transition (Tg) trend of amorphous lactose, shifted by some degree (X) upwards, depending on the product composition or the amount of amorphous lactose present - to be specific. These quick and easy methods to identify a safe and non-sticky operating window to minimise product adhesion to the equipment wall would be of huge benefit to the dairy industry in process optimization, as fore knowledge of likely difficulties and specified operating conditions will help efficient and economic operation. Attempts have been made to rectify the humidity tracking system in a spray drier and relate the 'stickiness curves' with its drying parameters. Further work should be done by taking commercial trial runs at recommended or allowable operating conditions with reference to 'Stickiness Curves', in order to maximise the throughput and to minimise the drying cost without compromising the product quality. Looking into the effects of other variables like air velocity, angle of impact, different impact surface materials and particle size on powder stickiness would be of much interest to the dairy industry.Item Stability of the probiotic Lactobacillus paracasei CRL 431 under different environmental conditions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatu, New Zealand(Massey University, 2015) Poddar, DevastotraProbiotics are live microorganisms which provide health benefits to the host upon consumption. There is a wealth of information available on the health benefits associated with the consumption of probiotics. However, currently probiotic microorganisms are delivered mainly through refrigerated, short shelf-life products. When incorporated into ambient shelf-life products, the products generally fail to meet the regulatory criteria, which require probiotic bacteria to be viable in high numbers at the end of shelf-life. Storage temperature, oxygen and residual moisture content often result in loss of viability of probiotics during storage and distribution. A preliminary study was carried out to explore the effects of matrix composition (fat, protein and carbohydrate) on the probiotic bacterial (Lactobacillus paracasei CRL 431) viability, during fluidized bed drying and subsequent storage. The finding suggests that whole milk powder provided a superior protection to bacteria during fluidized bed drying and subsequent storage, compared to skim milk powder or milk protein isolate. Moreover, water activity of the powders during storage played a key role in determining the probiotic viability. The effects of drying techniques, moisture content and water activity on the storage stability of L. paracasei in a whole milk matrix were studied. Whole milk powder-bacteria mixtures were dried using spray drying, freeze drying or fluidized bed drying and stored at 25 ºC under controlled water activity ( 0.11 aw, 0.33 aw and 0.52 aw) for 105 days. At 0.11 aw, cell viability loss was minimal, while at 0.52 aw viability was lost in all powders within 22 days. At the intermediate 0.33 aw, there were marked differences among stored powders. Further, various analytical techniques (X-ray diffraction, FT-IR, Raman, NMR spectroscopy) were used to explore why and how structural differences in the matrix-bacteria mixtures, produced using different drying technologies, under different water activity storage conditions, influence bacterial viability. The results suggest that fluidized bed drying provided a better protection to the bacteria during storage, which was attributed to unique powder structure that reduced the absorption of water. The lower absorption of water resulted in the maintenance of a more rigid structure, which limited molecular mobility. Lactobacillus sp. is known to accumulate large amounts of inorganic manganese which apparently provides defense against oxidative damage by scavenging free radicals. The ability of L. paracasei to maintain viability during long term ambient storage may be enhanced by the ability of microorganism to accumulate manganese, which may act as free radical scavenger. To investigate this hypothesis, X-ray fluorescent microscopy (XFM) was employed to determine the changes in the elemental composition of L. paracasei during growth in MRS medium with or without manganese as a function of physiological growth state (early log vs. stationary phase). The results revealed that lower level of manganese accumulation occurred during the early log phase of bacterial growth compared with the stationary phase cells. The lower level of manganese accumulation was found to be related to the loss in bacterial viability during storage. Manganese has been known to possess pro- and anti-oxidant properties, and understanding of the changes in the manganese oxidation state was considered to provide some further insights into the bacterial death mechanisms. In view of the relatively high concentration of manganese in lactobacilli, it was of interest to better understand the oxidation state, coordination number and ligands of the manganese in the bacteria. It was possible to characterize the changes of manganese within bacteria using XANES. The results confirmed that manganese present within L. paracasei is in Mn(II) oxidation state and no changes in the manganese ligands could be observed during storage. In summary, the thesis provides a mechanistic insight into the ways to improve the stability of probiotics for application into ambient long shelf-life products. Future studies on tracking the genetic and proteomic aspects of the bacteria during storage might be useful for further understanding and process optimization.Item Computer control of the manufacture of spray dried milk powder : a thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy in Industrial Management and Engineering at Massey University(Massey University, 1979) Wong, OwenThis thesis describes the development and application of modern control techniques to an industrial processing plant. The plant is made up of a pilot scale triple effect Wiegand falling film evaporator and a De Lavel tall form spray drier situated at the laboratories of the New Zealand Dairy Research Institute. The continuous version of the standard state space and measurement equations for linear, time-invariant, multi-variable systems provides the basis for the development. This standard representation is not well suited for direct application to the plant because of the difficulty in defining a suitable state vector and the difficulty in knowledge of the process dynamics. The standard representation is therefore enhanced to provide a modified structure that exhibits several significant features:- i) only measurable outputs, control inputs and measurable disturbances are involved in the process descriptions; ii) the equation structure is similar to that of the standard discrete state space equations, so that state space time domain control system design methods are applicable; iii) the structure is suitable for the direct application of statistical modelling; iv) maximum flexibility is offered for selection of discrete intervals for measurement samples and controls; v) precise knowledge of process time delays is not required. Application of the control strategies is performed using an IBM System/7 minicomputer. A suite of computer programs, developed in FORTRAN, is used. These programs are suitable for transferring to any other minicomputer supporting a multi-tasking mode of operation with the major system dependent area being the actual sampling of process data. Whilst a control engineer would be required for the installation of the software and initial control system design, further tuning of the controllers could be performed by a suitably trained operator. The procedures described allow an operator to apply sophisticated control techniques by following a sequence of relatively simple steps:- a) apply perturbations to normal plant operating conditions; b) use the interactive graphics facility to identify process models using the generalised least squares technique; c) choose appropriate design weightings and use a dynamic programming algorithm to obtain controller gains; d) simulate operation of the controller using the process model; e) apply the controller to the actual plant. Steps b), and c) and d may need to be repeated until a suitable controller is obtained. The results of the implementation of controllers on the pilot scale plant are presented. Consistent control of the product density and flowrate from the evaporator is obtained. As an hierarchical control structure has been used on the evaporator, the development of lower level controllers on variables such as steam flowrate, preheat temperature, inlet milk flowrate and condenser water temperature is also described. On the spray drier environmental control on concentrate flowrate, gas flowrate and drier chamber pressure is obtained.Item Air-suspension coating of dairy powders : a micro-level process approach : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Technology at Massey University, Palmerston North, New Zealand(Massey University, 2005) Werner, Stephen R. L.Air-suspension particle coating is a process by which thin coatings are applied to powder particles. The coatings can be formulated to act as permeable barriers to increase powder shelf-life or to impart controlled release character. The ultimate objective of a coating operation is to produce individual particles, each with a well-controlled, even coating. This project was focused on the air-suspension coating of fine powders of ~100 µm in diameter for the dairy industry. Despite the widespread use of the technology in the pharmaceutical industry, its use in the food industry has been limited. Little is known about the fundamental mechanisms, and so published work to date is product and equipment specific and is statistical in the way the experimental design and analysis has been approached. This 'black box' approach is time consuming and costly. Better methods based on an understanding of the physical and chemical mechanisms are needed to deal with the numerous products and constantly changing formulations typical of the dairy industry. This thesis proposes a new approach to air-suspension particle coating research. The basis of this 'micro-level process approach', is to deconvolute the complex coating process into smaller manageable parts based on classical physical phenomena for which descriptions already exist. The thesis identifies and develops an understanding of the key micro-level processes controlling coated product quality and process performance. Four were selected for further study: drying, droplet impact and spreading, and stickiness which encompasses the two key micro-level processes of droplet impact and adherence and inter-particle agglomeration. They were studied separately to deconvolute the variable effects and interactions. Kinetic data were collected for the drying droplets containing maltodextrins, whey protein isolate and gum arabic. A mathematical model, based on 'ideal shrinkage' was developed to predict the drying kinetics of single droplets with particular interest in the development of the surface glass transition temperature. The model accurately predicted the kinetics until significant morphological changes occurred in the droplet. To better predict the kinetics late in the drying process, the droplet radius was set to be constant at a time based on the surface proximity to the surface glass transition temperature (critical X concept). This was done to arrest droplet shrinkage in line with experimental observations and to more accurately depict the drying of high molecular weight, amorphous glass forming polymers. After this point, a new flexible calculation scheme was used to better predict the variation in internal droplet structure as either a dense, 'collapsed shell' structure or a 'dense skin-porous crumb' structure. Further study should focus on the surface and internal droplet structure (porosity and mechanical integrity) development during drying, particularly the conditions leading to the arresting of the droplet radius and the subsequent rate of skin thickness progression. The critical X concept was used to make industrial-scale predictions of the optimum drying conditions that ensure maximum droplet impact and adherence efficiency and minimum inter-particle agglomeration in a Würster-style coating operation. This enabled the prediction of two key design parameters, the nozzle distance from the powder impact point and the Würster insert height. The span in design parameters showed that there is significant opportunity for design optimisation based on the critical X concept. A probe tack test was used to map the level of stickiness of droplets of different coating materials as they dried. As skin formation progressed, the stickiness passed through a maximum, in most cases to arrive at a point at which the droplet was no longer sticky at all (non-adhesive state). The maximum point of stickiness represents the ideal state to ensure successful droplet-substrate impact and adherence. The minimum point of stickiness represents the ideal state to prevent unwanted inter-particle agglomeration. The time interval between the onset of stickiness and the non-adhesive state was particularly dependent on the addition of plasticisers, but also on the formulation and the drying air conditions. Future work should look to establish a possible relationship between the surface glass transition temperature and the probe tack test stickiness measurements. The impact and spreading of droplets containing maltodextrin DE5 on to solid anhydrous milkfat was studied using a high speed video camera. It was found that the final spread diameter was able to be fixed close to the maximum spread diameter by using surfactants, thus avoiding significant recoil. Because existing literature focuses on predicting the maximum spread diameter, this work defines a need for adequate prediction methods for the final spread diameter, as this is the significant parameter in coating applications. Formulation and operating guidelines were established to independently optimise each micro-level process. These were used in a series of population based coating experiments in a pilot-scale Würster coater. This study highlighted the limited flexibility of the standard 'off-the-shelf' Würster coating apparatus for the coating of fine sized dairy powders. Because of this, the validation of the guidelines were inconclusive and optimisation could not be carried out. Further validation work is required on a custom-built apparatus for dairy powders. This work has advanced the fundamental knowledge of the coating process and is independent of material, equipment and scale. This knowledge, based on physical and chemical mechanisms, can be used to develop coating formulations and identify optimum process conditions for successful coating in less time and at less expense than is current practice. The next step is to put the guidelines into practice and craft the engineering of a continuous coating apparatus for dairy powder applications.