Massey Documents by Type
Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294
Browse
18 results
Search Results
Item Shear work induced changes in the rheology of model Mozzarella cheeses : 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, 2016) Sharma, PrateekMozzarella cheese is a pasta filata type of cheese. Its manufacture includes a kneading – stretching step that creates a fibrous protein network and distributes fat-serum channels to attain desirable melt functionality on a pizza. During processing and manufacturing of pasta-filata cheese, large deformations take place. For appropriate characterization of a food material, rheological evaluation should be conducted in similar operating conditions, length scales and time scales to those taking place in the actual process. Development of the typical fibrous pasta-filata structure of mozzarella cheese depends on composition and process variables. Critical process variables in the development of cheese structure are time, temperature and shear. In this study we studied the effect of shear work on rheology, structure and melt functionality of model Mozzarella cheese. Three types of model cheeses (full-fat, non-fat and full-fat with added tri-sodium citrate) were prepared by working cheese components together at 70 oC in a twin screw Blentech cooker. Varied amounts of shear work input (2.8-185 kJ/kg) were given to the cheese samples using 50, 150 and 250 rpm screw speeds. Samples were subjected to a range of rheological tests, confocal laser scanning microscopy, fat particle size measurements (DLS) and melt functionality evaluation. While measuring steady shear viscosity of Mozzarella-type cheeses in a rotational rheometer at 70oC, three main difficulties were encountered; wall slip, structural failure during measurement and viscoelastic time dependent effects. A flow curve method was successfully devised to measure steady shear rheology by using serrated plates as surface modification to avoid wall slip, giving enough measurement duration at low shear rate to avoid viscoelastic effects and selecting limited shear steps to cause minimum structural changes. These techniques enabled successful measurement of steady shear viscosity of molten Mozzarella-type cheeses at 70oC at shear rates up to 250 s-1. Strong work thickening was observed for full fat Mozzarella cheese from steady shear rheology, oscillatory rheology, creep, elongational viscosity and tensile testing data. Steady shear rheology and melt functionality were found to be strongly dependent on total shear work input. An exponential increase in consistency coefficient (K from power law model) was observed with increasing amounts of accumulated shear work, indicating work thickening behaviour. An exponential work thickening equation is proposed to describe this behaviour. Excessively worked cheese samples exhibited liquid exudation, poor melting and poor stretch. Nonfat cheese exhibited similar but smaller changes after excessive shear work input. At lower shear work inputs (<30 kJ/kg), cheese behaved like a viscoelastic liquid exhibiting typical entangled polymer melt behaviour with moderate frequency dependence and at excessive shear work levels (>70 kJ/kg) it behaved like a viscoelastic solid with low frequency dependence. A definite critical point for structural and viscoelastic transition was identified at a medium shear work level (~ 58 kJ/kg at 150 rpm). Similar viscoelastic property changes occurred in non-fat cheese suggesting that major changes were taking place in the protein matrix during working. Confocal microstructures plus macroscopic observations showed systematic changes in structure with increased shear work inputs with unmixed buttery liquid observed at <5 kJ/kg, typical Mozzarella type microstructures (elongated fat-serum channels) at 6-15 kJ/kg and homogeneously distributed, small size fat droplets at >58 kJ/kg. At very high shear work inputs, > 75 kJ/kg, striations or anisotropy in the microstructures had disappeared and small micro-cracks were evident. Volume-weighted mean fat particle size decreased with shear work input and particle size distributions also changed. To account for the short and long term relaxation response behaviour, a 4-element Burger‘s model was found adequate for fitting the creep data of model cheese at 70 oC but a 6-element model was required at 20 oC. As shear work input increased, retarded compliance decreased and zero shear viscosity increased indicating the more elastic behavior of the cheeses with higher shear work input. Fracture stress and strain for longitudinal samples from elongated full fat cheese did not vary significantly with shear work input up to 26.3 kJ/kg then decreased dramatically at 58.2 kJ/kg. Longitudinal samples with shear work input <30 kJ/kg, demonstrated significant strain hardening. At shear work inputs <30 kJ/kg strong anisotropy was observed in both fracture stress and strain. After a shear work input of 58.2 kJ/kg anisotropy and strain hardening were absent. Perpendicular samples did not show strain hardening at any level of shear work input. A good correlation was found between the steady shear, oscillatory shear and transient rheological properties and the melting properties of the cheeses. The order for the rheological properties in terms of their sensitivity towards both shear work input and melt functionality is ηapp > G‘ > elongational viscosity > consistency coefficient, K. It was concluded that the dominant contributor to the changes in rheology, structure and melt properties with increased shear work was shear induced structural changes to the protein matrix. An increase in calcium induced protein-protein interactions after high shear work at 70 oC. In summary, this thesis provides useful insights to shear work induced changes in material properties. It proposes useful linkages between the manufacturing process and the application of model Mozzarella cheese using appropriate rheological methods. Since the linkages were validated for only one composition and in only one processing environment, it is proposed that they should be tested in other conditions. In order to build a more complete picture, a molecular level study is proposed for future work to elucidate chemical changes during working and find appropriate linkages with physical and functional characteristics.Item Preparation of nano- and microemulsions using phase inversion and emulsion titration methods : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Auckland, New Zealand(Massey University, 2014) Wang, YueThe formation of nano- and microemulsions with droplet size smaller than 100 nm in diameter and stabilised by non-ionic surfactants was investigated by using two different methods, emulsion phase inversion and emulsion titration. A series of ternary systems consisting of three components (lemon oil, Tween 20 or 80 and water) were prepared at different ratios via gentle agitation by the phase inversion composition method involving the spontaneous formation of microemulsion. The phase behaviour and nano- and microemulsion formation of the ternary mixtures prepared were characterised by visual observation for their phase separation and optical clarity (e.g. transparency and opacity). The samples were also analysed for their particle size and size distribution, viscosity, conductivity and birefringence. As a consequence, phase diagrams based on two different types of small molecule surfactants (Tween 20 or Tween 80) were constructed which define the ratios of three components in the composition of the ternary mixtures that allow the formation of oil-in-water (o/w) or water-in-oil (w/o) nano- and microemulsions. Overall, the o/w microemulsions were found to form at a small region of the ternary phase diagrams with a relatively large ratio of water, compared to w/o nanoemulsion, along dilution lines 1 and 2. On the other hand, w/o microemulsions were determined at the corner of surfactant-rich region along dilution lines 1, 2, 3 and 4 in the ternary phase diagrams. Between the two ternary phase diagrams based on Tween 20 and 80, there were some differences in their composition regions responsible for the formation of nano- and microemulsions as well as for other types of phases formed, including bi- and multiphase, liquid crystals, gel and coarse emulsions. In this study, nano- and microemulsions were also produced by a method called =titration method‘ involving a two-step process; i) preparation of non-ionic small molecule surfactant-stabilised o/w emulsions by high pressure homogenisation and ii) titration of the o/w emulsions into non-ionic surfactant micelle solutions. Types and concentrations of surfactants (Tween 20, 40, 60 and 80) and oils (sunflower oil, lemon oil, tributyrin, isopropyl myristate and Imwitor 308) were investigated for their influence on the solubilisation of oil molecules from emulsion droplets into surfactant micelles, thus the formation of nano- and microemulsion. The results showed that Tween 60 and Tween 80 had the better capacity of oil droplet solubilisation compared to Tween 20 and Tween 40. The system containing a higher concentration of 2 wt% Tween 80 micelles had the larger capacity of droplet solubilisation than the other systems containing 0.5 wt% or 1 wt% Tween 80 micelles. In terms of the types of oil used, microemulsions could be fabricated using lemon oil, tributyrin, isopropyl myristate and Imwitor 308, whereas it could not be formed by using sunflower oil due to its high viscosity. Among the oils with relatively low viscosities, the order of the maximum amount of oil incorporated in 1 wt% Tween 80 micelles was Imwitor 308 > lemon oil > isopropyl myristate > tributyrin. This implies the lower viscosity oil has a higher rate of solubilisation in non-ionic surfactant micelles. The effects of pH, salt concentration and heat treatment on the stability of microemulsions were also determined. The results found that the nano- and microemulsion systems prepared by the emulsion titration method were relative stable to pH and ionic strength but sensitive to thermal treatment. This study provides useful information for the rational design of transparent nano- and microemulsions as delivery systems potentially for bioactive compounds for applications in food, beverage and non-food areas.Item Objective differentiation of cheese type and maturity : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology, Riddet Centre and Institute of Food, Nutrition and Human Health, College of Sciences, Massey University, Palmerston North(Massey University, 2003) Puryer Coker, Christina JuneThe main objectives of this study were to develop instrumental methods for determining cheese maturity and for differentiating variety irrespective of maturity. Traditionally this has been done by sensory (texture and taste) evaluation, but it is desirable to systematise the process, for both non-varietal cheese that is destined to become an ingredient in a complex food and for table cheese. An initial study developed a size exclusion (high performance liquid) chromatography (SE-HPLC) method for the characterisation of proteolysis in cheese. The method provided predictable elution of peptide and amino acid standards on the basis of hydrodynamic volume (which equates well with molecular weight), although the presence of a net positive charge caused smaller peptides and amino acids to elute slightly earlier than anticipated. The repeatability of the elution time and peak intensity of a range of molecular weight standards was excellent, and their elution time was used to develop a standard curve for determining molecular weight. The potential of the SE-HPLC method for characterising proteolysis in cheese was compared with commonly used methods by examining seven cheeses of different types. Non-casein nitrogen and non-protein nitrogen were useful for demonstrating differences in the overall amounts of protease and peptidase activity; alkaline urea-polyacrylamide gel electrophoresis (urea-PAGE) of the urea-soluble fraction (USF) of cheese was useful for comparing the amounts of chymosin and plasmin action; urea-PAGE of the water-soluble fraction (WSF) of cheese was useful for comparing the amounts of several large peptides (>~5000 Da) and reverse phase (RP)-HPLC of the WSF was useful for comparing patterns of peptides in different cheese types. SE-HPLC was useful for demonstrating differences in the pattern of molecular weight distribution of the peptides and amino acids present in the WSF of different cheese types, but was less useful for demonstrating the molecular weight distribution of the caseins (which eluted as a single peak), peptides and amino acids present in the USF. Good repeatability of the extraction of the WSF was demonstrated. A larger study compared the SF-HPLC (WSF) method with alternative methods (urea-PAGE of the USF and WSF, and RP-HPLC of the WSF) for following the maturation of five cheese types (New Zealand-style Cheddar, Elsberg, Gouda, Mozzarella and Swiss) from pressed curd to beyond normal maturity. Principal component analysis (PCA) was used to reduce the data from a large number of peaks to a few principal components that accounted for most of the variation in the data set. Depending on the method of sample analysis, the correlation form of PCA accounted for between 72% and 83% of the variation in the data within the first three principal components, and generally provided better differentiation of cheese type than the covariance form of PCA which accounted for between 85 and 97% of the variation in the data and was better for determining maturity. Plots of the first three principal components showed that urea-PAGE of the USF and SE-and RP-HPLC of the WSF could be used to differentiate the cheese types throughout ripening; urea-PAGE of the USF, which measured primary proteolysis, provided useful maturity trends in the early stages of ripening of most cheese types and throughout the ripening of slowly maturing cheese while RP- and SE-HPLC of the WSF, which mainly measured secondary proteolysis, provided useful maturity trends throughout the ripening of each cheese type. The final study used RP- and SE-HPLC of the WSF to examine the diversity of a range of first grade mild to mature commercial cheese of one type (Cheddar), and to examine the potential of the instrumental methods for establishing a cheese maturity index that could accurately predict a sensory maturity score (SMS; 1.00 - 9.00 scale) provided by a trained sensory panel. Each cheese sample (77 samples of Cheddar cheese manufactured at 8 New Zealand factories over 2 seasons and ripened at 5, 10 or 13°C for 3, 6, 12 or 15 months) was analysed using both methods, as well as traditional methods for determining maturity (non-protein nitrogen (NPN), water-soluble nitrogen (WSN)). The relationship between each set of instrumental results and the SMSs was modelled using multivariate statistics and equations were developed for predicting cheese sensory maturity. Multiple linear regression (MLR) analysis showed that the simplest measures of maturity provided a reasonable correlation with the SMS (R = 0.88, R2 (adj) = 0.77 for NPN and total nitrogen (TN); and R = 0.90 and R2 (adj) = 0.80 for WSN and TN). The covariance form of PCA accounted for the most variation in the data (PC1 to PC3 = 88% for RP-HPLC; and PC1 to PC3 = 93% for SE-HPLC) and provided trends that were more closely associated with sensory maturity. MLR analysis showed the close correlation between the first three principal components and the SMSs (RP-HPLC: R = 0.94, R2 (adj) = 0.87 for PC1, PC2, PC3 and TN; and SE-HPLC: R = 0.92, R2 (adj) = 0.84 for PC1, PC2, PC3 and TN). The PCA factor loading scores were used to select influential peaks and MLR was used to demonstrate their close correlation with the SMS (RP-HPLC: R = 0.99, R2 (adj) = 0.98 for 32 peaks and TN (Model K); and SE-HPLC: R = 0.96, R2 (adj) = 0.90 for 15 'peaks' and TN (Model M)). The regression equations for Models K and M were validated. RP-HPLC or SE-HPLC could be used to provide effective indices of maturity. It was possible to conclude that: varietal differences could be captured using either the SE-HPLC method or RP-HPLC; differentiation of the source of cheese within a variety was not possible using SE- or RP-HPLC methods; a standardised SE-HPLC procedure or a RP-HPLC procedure could be developed for accurately predicting the sensory maturity Cheddar cheese; and that the SE-HPLC procedure provided the most practical instrumental means of estimating the sensory maturity of Cheddar cheese.Item Studies on the preparation, processing and properties of soymilks : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University(Massey University, 1971) Khaleque, AbdulThe effect that presoaking of soybeans in solutions of various chemicals has on the reduction of "beany" flavour in soymilk was investigated. Of the chemicals used, sodium carbonate and sodium hydroxide had a significant effect. Sodium carbonate soaking at 0.4 M concentration for 18 - 24 hours was significantly better than any other presoak treatment. Soymilk prepared from carbonate presoaked beans contained more protein and had a higher viscosity than milks prepared from water or sodium hydroxide presoaked beans. Beans presoaked in carbonate were easier to process than beans presoaked in water or hydroxide. There was no significant difference in the amino acid pattern of the proteins in the soymilks prepared by the three methods. The activity of lipoxidase as a major source of "beany" flavour in soymilk has been questioned. The rate of inactivation of trypsin inhibitors in soymilks prepared from carbonate presoaked beans was faster than that in the water presoaked preparation when heated to 98°C. This effect was primarily associated with the rise in pH that occurred in the soymilks from carbonate presoaked beans. The effect of alkaline pHs at 98°C on the inactivation of trypsin inhibitor was examined and it was found that the rate of inactivation was changed from zero order at pH 6.8 to first order kinetics at pH 9.9. This effect of pretreatment was not noticeable when both milks were processed at 115°C in sealed cans because of the constancy of pH under these conditions. The influence of heat processing conditions on the enzymatic digestibility of proteins in both soymilks was also studied. The digestibility with trypsin increased with the degree of heat treatment up to the point where the trypsin inhibitor had been destroyed, after which further heating resulted in lower digestibilities. The optimum heat processed soymilks prepared from carbonate presoaked beans gave higher digestibilities than those of the water presoaked preparations under the conditions used. Pepsin digestion (at 0.125% of 1 : 2,500 pepsin) showed no appreciable differences between soymilks prepared by either presoaking procedures. The degree of digestibility with pepsin plus trypsin of the proteins in the optimum heat processed carbonate presoaked preparation was similar to the digestibility of acid precipitated freezedried casein under identical conditions. The changes in viscosity during processing of soymilks prepared from carbonate presoaked beans was different from that of the water presoaked soymilk. Of the factors which affect the viscosity of soymilk during processing, denaturation, aggregation and hydration-dehydration processes probably play the most important roles. Nevertheless, the proteins in both soymilks were very stable under the processing conditions used. About 0.1 percent of sodium chloride was formed in the carbonate presoaked preparation during neutralisation with hydrochloric acid. When this amount of sodium chloride was added to the water presoaked preparation either in the raw state or during heat treatment, the proteins became unstable. This effect could be eliminated if the addition of sodium chloride was made after even slight denaturation of the proteins. Addition of up to 0.25 percent of sodium chloride had no effect on the stability of proteins in the carbonate presoaked preparation. The instability of proteins in soymilks in presence of sodium chloride was considered to be primarily due to aggregation. Soymilk that has been heat treated to destroy the trypsin inhibitor is difficult to concentrate because its viscosity increases exponentially with increase of solids content. This imposes a concentration limit of around 17 - 18 percent total solids due to the formation of a gel-like structure beyond this. The possible factors which contribute to this gel formation during concentration were investigated. A sulphydryl-disulphide interchange reaction was mostly responsible for the increase in viscosity of the concentrate up to about 16 percent total solids but above this concentration other forces predominated. The possibility that gelation occurred through intermolecular cross-linkages by calcium ions was eliminated. Sodium sulphite and N-ethyl maleimide were effective in reducing this viscosity increase to some extent but when the concentrate was heat sterilised sodium sulphite ceased to have any effect on the viscosity and with N-ethyl maleimide the viscosity of the sterilised concentrate was about 50 percent of the unstabilised sample. Forewarming by heating to 115°C/5 min. caused an increase in viscosity during concentration but effectively stabilised the product against further increases in viscosity on sterilisation. The effect of processing conditions on the nutritional quality of proteins in soymilks was studied using a number of in vitro methods. The results indicated that the nutritive values of the soymilks prepared from carbonate presoaked beans by three different processes (98°C for 40 minutes; 115°C for 18 minutes; preheated at 115°C for 5 minutes, concentrated to 15.5 percent solids content and then sterilised to a FO value of 5.5) were about the same and were better than that prepared from the water presoaked preparation processed at 115°C for 18 minutes. Methods of process control and quality assessment of soymilk are discussed. Flow and mass balance sheets for the process developed have been presented.Item The development of a chemical analogue of thermal destruction of bacterial spores : a thesis presented in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Massey University(Massey University, 1967) Packer, Gordon John KitchCanning as a method of food preservation has its origin in the work of Nicolas Appert (1750-1841) who was the first to use heat as a means of preserving food in hermetically sealed containers. Although he did not understand the principles of his method, his systematic experimentation (and generous sharing of his discoveries) laid the foundations of thermal food preservation methods. Appert initially processed his food in cork sealed glass jars and bottles in boiling water baths for periods varying from 15 minutes to two and a half hours. Storage trials were the basis of his processing methods, some foods being kept up to ten years. His products ranged from meats, soups and vegetables to fruit and even cream and evaporated milk. He recognized the value of quick clean handling of good quality raw materials. Blanching was used with some products, and he was also aware of the distinction between acid and low-acid foods in regard to their length of processing. Appert's understanding of the process was that heating eliminated the "air" which was believed to be the cause of spoilage. This belief was to persist for nearly 100 years. Appert's work in glass containers led to the development in England about 1815-20 of tin containers for preserved foods. Appert himself used cans in some of his later work. Some time before 1830 the autoclave was introduced (apparently by Appert) as a means of cooking canned foods under pressure. By 1870, autoclaves were being used quite widely in industrial canning.Item Solvent fractionation of New Zealand mutton tallow : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biotechnology at Massey University(Massey University, 1981) Ramsay, Grant AlexanderSamples of inedible bulk mutton tallow were collected monthly throughout two killing seasons from one meat killing plant. These samples plus one sample from another plant, were analysed for fatty acid and triglyceride composition. In these samples, four fatty acids (myristic (14:0), palmitic (16:0), stearic (18:0) and oleic (18:1)) comprised 88.6% of the total fatty acids, and there was an average of 16% trisaturated triglycerides, 38% disaturated triglycerides and 46% of triglycerides with a greater degree of unsaturation. Overall, there was a significant decrease in the proportion of 14:0, and a significant increase in the proportion of 18:0, from November to June; and there was a significant difference in the mean proportion of 16:0, and also 18:1, between the two seasons. There was a significant difference in the proportion of cis monounsaturated triglycerides, and the more highly unsaturated triglycerides, between some of the different tallows analysed. There was a significant decrease in the proportion of 2-oleo disaturated triglycerides from November to June, with a range from 10.0% (May, 1978) to 20.5% (November, 1976). An acetone fractionation scheme was developed with the main aim of concentrating these 2-oleo disaturated triglycerides into one fraction (the intermediate fraction) which may be useful as a cocoa butter replacer. The first precipitate (the hard fraction was separated by filtration, and the filtrate was adjusted for solvent : fat ratio and then further cooled to precipitate the intermediate fraction. After separation of this precipitate, acetone was distilled from the filtrate to produce a final fraction (the soft fraction). A screening experiment showed that the solvent : fat ratio at each crystallisation, the temperature to which the fat solution was cooled at each crystallisation, the water content of the acetone and the degree of agitation during crystallisation all affected the fractionation. The effect of these variables upon one sample of mutton tallow was studied, and mathematical models were developed to predict the yields of the three fractions and the melting properties of the intermediate fraction, The model predicting the melting properties of the intermediate fraction was used to estimate the fractionation conditions which would give an intermediate fraction with melting properties most similar to those of cocoa butter. From this, a fractionation was performed with first and second crystallisation temperatures of 9.2°C and 5.2°C respectively, solvent to fat ratios at the first and second crystallisations of 1.0:1 and 10.0:1 respectively, a water concentration in the acetone of 0.6% and a defined agitation condition. The yields of the hard, intermediate and soft fractions were 34.5 wt %, 2.5 wt % and 63.0 wt % of the tallow respectively. The intermediate fraction contained 51.0% of 2-oleo disaturated triglycerides (compared to 68.9% in cocoa butter) and had very similar melting properties to cocoa butter. Then the fractionation scheme was modified to give a greater yield of the intermediate fraction (8.3 wt %) but the melting properties of this intermediate fraction were less similar to those of cocoa butter. This latter fractionation scheme was scaled up (from 20 g tallow to 200 g and 1 kg). On each scale an intermediate fraction with consistent yield and melting properties was obtained. The yields of the other two fractions varied, however, and overall there was a considerable difference in the behaviour of the fractionations on each scale. Attempts on the 1 kg scale to produce an intermediate fraction with properties similar to those of the best 20 g intermediate fraction (i.e. similar to cocoa butter) were unsuccessful. The highest proportion of the important 2-oleo disaturated triglycerides attained in a 1 kg scale intermediate fraction was 36.8%, and this fraction melted, over a wider temperature range than cocoa butter. This intermediate fraction may be useful as a cocoa butter substitute in a coating chocolate, but is unlikely to be able to replace cocoa butter in chocolate. The hard fraction produced from this 1 kg fractionation (23.0 wt % of the tallow) showed promise in a baking shortening blend with butter, but was too hard to be useful as a pastry shortening. The soft fraction performed well as a deep-frying medium and in mayonnaise.Item A quality control system for the manufacture of spray dried milk powders :a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Technology at Massey University(Massey University, 1981) Bloore, Christopher GrosvenorIn the last decade the New Zealand dairy industry has greatly increased its spray drying capacity in response to the world market demand for spray dried milk products. Powder specifications are becoming increasingly complex and smaller quantities of each product are required as the number of different products grows. These factors have made it necessary to learn more about the way processing variables influence the product quality in order to improve product quality control. A computer simulation model providing a complete description of the drier behaviour was developed from a series of experiments on a pilot scale spray drier. This took the form of regression equations relating the quality parameters of skim milk powder to the drier operating variables and the composition and physical properties of the skim milk. The model was then used in the development of a quality control system and also to simulate and evaluate a variety of commercial operating practices. The characteristics of the spray drying process were investigated using the pilot plant evaporator and spray drier at the New Zealand Dairy Research Institute, which had been fully instrumented and interfaced to a process control computer. The drier studies confirmed the importance of low concentrate viscosity in the production of good quality milk powder. This could be achieved by keeping concentrate holding times to a minimum and by using high temperature, short time preheat treatments. The protein content of the skim milk was found to be the major determinant in the seasonal changes observed in concentrate viscosity, high protein contents giving high viscosities. The study of the hydrodynamics of centrifugal pressure nozzle atomisers revealed that the nozzles used in milk powder drying fall into two distinct categories, each with characteristic behaviour in response to variations in fluid viscosity. The magnitude of the viscosity effect depends on the ratio of the swirl chamber and orifice diameters. The large capacity nozzles used in tall-form driers exhibit a marked decrease in pressure drop at constant flowrate as the viscosity of the concentrate fed to them is increased. This was found to play a very important part in determining the overall behaviour of the drier. Five operating variables; the inlet air temperature and the concentrate total solids, feedrate, atomising pressure and temperature, proved to be necessary and sufficient to describe the drier performance and to predict the properties of the powder. Simulation studies of two outlet air temperature control strategies clearly demonstrated the superiority of inlet air temperature manipulation over that of concentrate feedrate, for driers employing large capacity nozzles. The drier model was used in the selection, tuning and evaluation of a quality control system based on the SIMPLEX Evolutionary Operation scheme of Spendley et al. The process of spray drying milk powders presents several control problems. There are a number of quality parameters assessed by laboratory analysis, which means that feedback is multivariable, delayed and subject to error. Furthermore, the processing characteristics of milk change with time. A single measure of the powder quality was obtained from penalty functions based on economic considerations. After selection of the SIMPLEX step sizes with the help of simulation model, a pilot plant trial of the scheme was conducted. The Simplex evolutionary operation method was found to be a simple robust procedure which rapidly improved the product quality and maintained it in the face of disturbances typical of those likely to occur in commercial operation. The method provides two sets of plant conditions in advance, a feature which permits a substantial increase in the speed of attainment of optimum conditions for processes with setpoint response times similar to the time required to analyse the product quality. The Simplex method is therefore particularly suited to the manufacture of spray dried milk powders.Item Effects of high pressure processing on carrot tissue : a microstructure approach : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand(Massey University, 2011) Trejo Araya, Ximenita IsabelleHigh pressure processing (HPP) has the potential of extending the shelf life of fruits and vegetables whilst preserving nutrients and, importantly, many sensory attributes. Although there is a developing body of literature identifying the advantages of this technology for specific products under specific conditions, it is important to gain further understanding of why undesirable quality changes can also be enhanced by this process. For this reason, this work focused on the changes that HPP promotes within the microstructure of the product (carrots, Daucus carota L.) considering that macroscopic quality is determined at a cellular level. This project was part of a government funded flagship programme at CSIRO Australia, where carrots were chosen as a model product of study. The effects of HPP on this commodity were studied for a range of pressures (100-600 MPa) applied for different holding times (2, 10 and 30 minutes) at ambient temperatures (20 °C). The effects were measured qualitatively and quantitatively by using several microscopy techniques, textural, physiological, biochemical and sensory analysis and through comparison with unprocessed (raw), frozen and heat processed (boiled, steamed and sous vide) carrots. The information collected provided understanding of how different pressure levels affected the physical and physiological responses of carrots based on cellular changes. It also allowed HPP to be positioned within the range of other preservation techniques and to identify relationships between quantitative and sensory quality attributes. The key findings of the study can be divided into HPP effects below and above 200 MPa, as near this pressure a “tissue break point” was identified. Pressures below 200 MPa only slightly affected the cellular structure arrangement according to microscopy techniques, which explained small textural changes, but there was an interesting shift in the metabolic response from aerobic to anaerobic metabolism, presumably due to stress. Above 200 MPa, cell structures became less organized and more disrupted resulting in significant loss of textural characteristics such as hardness and cutting forces compared to raw carrots. This texture loss was related to cellular leakage and loss of turgidity. Considering that ii texture is one of the most important quality attributes in carrots, this study searched for ways of ameliorating the impact of pressure by manipulating turgidity before and after the HPP process. One possibility was by weight loss prior to high pressure processing, but this approach did not help to overcome texture losses after HP treatments above 200 MPa, as structures were irreversibly damaged. Below 200 MPa, cells were still able to regain some turgor pressure (pressure of the cell content against the cell wall); however changes in cell permeability were evident. The addition of calcium chloride solutions in samples high pressure treated at above 200 MPa showed no quantitative texture improvements, confirming membrane damage as the principle mechanism and limited influence of biochemical reactions (pectin degradation by pectin methylesterase) affected cell walls at the conditions studied. Sensory perception by a trained panel showed a positive response toward HPP carrots treated at 600 MPa for 2 minutes. It was interesting to observe no significant differences in many sensory attributes in comparison to raw and sous vide samples, while boiled carrots showed low acceptability due to loss of most volatiles, texture and colour attributes. Storage trials confirmed that high pressure treated samples retained higher quality after 14 days at 4°C by supporting a lower count of lactic acid bacteria and consequently having less ethanol and acetic acid production in the pack. Overall, this research has provided a greater understanding of the application of high pressure on whole vegetable pieces by following microstructural changes. Based on this work, HPP can be considered equivalent to other ‘lightly processed’ technologies such as sous vide and may offer benefits as a complementary process to this or other similar preservation techniques. Future opportunities could be investigated taking advantage of the changes observed in cell permeability (< 200 MPa) for diffusion processes such as salting and candying. Health benefits arising from nutrients being more exposed and preserved after pressure treatments should be further studied by following nutrient availability and body absorption. Furthermore, studies on altering rates of compression or decompression and various pressure cycling effects could assist in optimisation of future commercial HPP applications.Item The functional properties of milk protein concentrates : a thesis presented for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand(Massey University, 1999) Carr, Alistair JamesThe aim of this thesis was to explore aspects of the functional properties of MPC85 (milk protein concentrate, 85% protein). A rheological study of milk protein concentrate (52°C) prior to spray drying showed a slight age-thinning behaviour which lasted about one hour, after which the apparent viscosity of the concentrate remained constant. This result is the opposite of skim milk concentrate which age-thickens at evaporator temperatures. The flow behaviour of the concentrate was adequately described by a Power Law rheological model. The rheological properties of reconstituted commercial MPC85 were studied at various temperatures and concentrations. At low concentrations (<10% w/w total solids) MPC85 solutions were Bingham Plastics. The yield stress was found to increase with temperature and concentration. At high concentrations (>15% w/w total solids) the logarithm of apparent viscosity was found to increase linearly with protein concentration. These solutions were also found to be Bingham Plastics. At lower temperatures (<35°C), however, these MPC85 solutions (>15% w/w total solids) were pseudoplastic and did not possess a yield stress. The solubility of commercial MPC85 was found to be dependent on the temperature at which the solution was prepared, increasing from ≈59% at 20°C to 100% at 50°C Homogenisation was shown to improve the solubility of MPC85 at 20°C. The rheological properties of MPC85 were profoundly influenced by the presence of any insoluble solids. The effect of preheat treatments during the pilot-scale manufacture of MPC85 on functionality was investigated. Heat treatment had no effect on heat stability of reconstituted MPC85 solutions for whey protein denaturation (WDN) values up to 86%. Heat treatments resulting in ≥90% WDN produced a dramatic loss in heat stability. The variations in rheology and rennet coagulation properties among the pilot plant powders were found to be correlated with the apparent diameter of the casein micelles. In reconstituted solutions the apparent diameter of the casein micelles increased gradually with heat treatments up to 86% WDN and dramatically at higher WDN levels. The main effect of preheat treatments during manufacture on the rheology of MPC85 solutions was the linear increase in apparent viscosity with apparent diameter of casein micelles. The variation in apparent viscosity with apparent diameter of casein micelles was found to be greater at low shear rates. A schematic model was proposed to account for these observations. A factorial design experiment was used to identify the components and interactions of components which play a significant part in determining the functionality of MPC85. This work demonstrated techniques for modelling heat stability - pH profiles and thereby allowing the quantitative comparison of the entire profiles of different solutions rather than comparisons at just single pH values or qualitative comparisons regarding the shape of the profile. The addition of divalent cations in the absence of added phosphate resulted in solutions that were completely unstable at 120°C. Overall this work has provided a detailed characterisation of commercial MPC85, both of the rheology of the concentrate prior to spray drying and of the functional properties of the powder. The research presented here has implications for both processing and product formulation.Item Development of a microencapsulation technique for probiotic bacteria Lactobacillus casei 431 using a protein-polysaccharide complex : a thesis presented in partial fulfillment of the requirements of the degree of Masters of Technology in Food Technology at Massey University, Palmerston North, New Zealand(Massey University, 2011) Nag, ArupAccording to the Food and Agriculture Organization (FAO) and the World Health Organization (WHO), probiotics are defined as ‘‘live microorganisms which when administered in adequate amounts confer a health benefit for the host’’ (FAO/WHO, 2001). Lactobacilli and Bifidobacteria are two major group of organisms considered to have probiotic properties. Probiotic bacteria are accepted universally for conferring beneficial effects to human gut health. However, the successful delivery of these bacteria to the human intestine via a proper food matrix is challenging because the stresses encountered by the probiotics during processing, storage and gastric transition cause major loss of viability. The primary objective of this study was to develop a novel protection system using a complexation product of dairy protein and a bacterial exo-polysaccharide which should be able to protect the probiotic bacteria during their gastric transit and also release them under suitable conditions in the intestine. Lactobacillus casei 431, a commercial strain from Chr Hansen, Denmark, was chosen as the experimental strain and the protein-polysaccharide complex was made up of sodium caseinate and gellan gum. Gelation of the sodium caseinate and gellan gum mixture was achieved by a gradual decrease of pH with slow hydrolysis of glucono-delta-lactone (GDL) and Lactobacillus casei 431 cells were successfully entrapped into this gel matrix. An intermediate step of forming a water-in-oil emulsion was involved in this process for producing micron level gel particles. The appropriate combination of ingredients, based on final elastic modulus to attain adequate gel strength, was finally decided as 10% (w/w) sodium caseinate, 0.25% (w/w) gellan gum and 2.5% (w/w) GDL. This combination resulted in a very fine and uniform capsule size distribution and up to 89% encapsulation efficiency was achieved. The gelled microcapsules were freeze dried to obtain better shelf stability and easy handling properties. The particles obtained had diameters ranging from 40 to 1100 μm for wet and 46 to 631 μm for freeze dried microcapsules. The mean diameters (D32) of wet and freeze dried microcapsules were found as 287 and 152 μm, respectively. II Scanning electron microscopic examination of the freeze dried particles showed irregular surfaces and the presence of numorous pores. Tolerance of free and encapsulated bacterial cells in simulated gastric juice at pH 2.0 was tested in an in vitro model and the results showed better survivability of encapsulated cells in both wet and dry microcapsules as compared to the free cells. The log CFU reduction figures after a 2 hour incubation period, were 4.56 for free cells, 3.03 for cells inside wet capsules and 2.28 for cells protected inside freeze dried particles. Incubation of free and encapsulated cells in the presence of 1% (w/v) bile extract for 8 hours showed 2.51 log CFU/gm reductions for free cells with almost no detrimental effect on wet microencapsulated cells and 2.44 log CFU reductions for freeze dried cells. Further research work was undertaken to improve the post freeze drying survivability of the L. casei 431 cells by including cryoprotective solutes in both the culture growth and the drying media. Trehalose and lactose were chosen as cryoprotecting agents. Compared to an average 1.70 log CFU reduction in case of control (no cryoprotectant) samples, trehalose and lactose containing samples both showed a much better survival rate; only 0.84 and 0.37 log CFU/gm reduction respectively, in cell population, were recorded. A membrane coating over the produced microcapsules was applied and the properties of such coated samples were checked separately. The coating process aided in the post drying survivability and only 0.53 and 0.13 log CFU/gm reductions were recorded for trehalose and lactose supplemented samples, respectively. The presence of cryoprotecting compounds proved to be beneficial against the simulated gastric environment and the membrane coating gave additional improvement in this regard. During the gastric fluid incubation tests, cryoprotected samples (freeze dried) containing trehalose and lactose shown a higher survival of 3.13 log CFU/gm and 2.04 log CFU/gm respectively, compared to cells in free form. Improvements offered by the membrane coating were recorded as an additional 0.23 log CFU/gm and 0.66 log CFU/gm higher survival for trehalose and lactose respectively. The same trend was observed for bile salt tolerance also. Cryoprotected samples (freeze dried) containing trehalose and lactose showed a higher survival of 0.41 log CFU/gm and 0.84 log CFU/gm respectively, compared to cells in free form. Additionally, the membrane coating process contributed III towards further improvement in viability of 0.25 log CFU/gm and 0.26 log CFU/gm for trehalose and lactose respectively. Overall, lactose has been found to be a marginally better protectant of cells than trehalose against freeze drying, acid and bile salt stresses. The membrane coating process helped in forming a very smooth surface morphology devoid of any visible pores. Perhaps the presence of a membrane coating was responsible for this better protective nature of coated microcapsules. But as a drawback, this coating process resulted into higher particle mean diameters, both for wet and freeze dried beads. Storage of freeze dried samples at 37°C proved to be more detrimental to the entrapped cells than at 4°C. But the results obtained were better compared to the situation where no protective compounds were used. It was found that lactose and trehalose helped in maintaining high levels of viable cell populations during the storage period but the cell degradation rate was positively correlated with the storage temperature. Therefore, it can be concluded that a low pH sodium caseinate-gellan gum gel matrix can offer adaptation and protection to the probiotic cells before encountering a high acid stomach environment and therefore can be utilized as an effective microencapsulation technique. The survibility of the L. casei 431 cells could be further improved during freeze drying as well as gastrointestinal transit by incorporation of protectants, viz., lactose or trehalose and applying a membrane coating of gellan gum. High acid food preparations such as, yogurt and fruit juice could be the probable applications for the current findings.