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    Using non-destructive laser backscattering imaging technology for kiwifruit quality assessment : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatū, New Zealand
    (Massey University, 2024) Yang, Zhuo
    Kiwifruit is one of the most important exported horticultural products in New Zealand. The supply of kiwifruit to both national and international markets can be extended by harvesting kiwifruit unripe and storing with proper postharvest practice. During kiwifruit storage, quality monitoring is required for inventory planning and consistent quality maintenance. Currently, the industry is using sampled data to represent a batch of kiwifruit. However, kiwifruit quality is difficult to estimate based on destructively measured samples due to the heterogeneous population quality distribution. Therefore, a non-destructive technology is preferred allowing quality measurement for all kiwifruit prior to and during storage, as well as before exporting and marketing. Commercial spectral-optical devices, such as near-infrared (NIR) spectroscopy, have been employed by the industry for fruit grading and sorting at harvest, and have achieved good performance in total soluble solid content (SSC) and dry matter content (DMC) estimation. However, NIR spectroscopy had a poorer performance in estimating kiwifruit flesh firmness (FF), the primary quality indicator. During light and fruit tissue interaction, those optical devices capture data containing primarily the absorption signal related to kiwifruit’s chemical composition. Therefore, the FF estimation is indirect and the accuracy of FF measurement is affected when both textural structures and SSC change during postharvest ripening. Laser backscattering imaging (LBI) records the backscattered signal after a single laser beam interacts with kiwifruit tissue. These light-tissue interactions include light absorption and scattering. The back-scattered signal could be analysed as an attenuation profile, and this attenuation profile is determined by optical properties of absorption (μa) and reduced scattering (μs’) coefficients, which correlate with fruit chemical compositions and physical properties, respectively. Therefore, LBI data is potentially helpful for FF estimation and early-stage internal disorder symptoms detection. This PhD work developed a non-destructive approach based on the LBI technique to segregate kiwifruit with internal disorders [brown marmorated stink bug (BMSB) feeding injury and chilling injury (CI)], as well as soft fruit at FF threshold of 9.8 N. Estimation of μa and μs’ was achieved with 56.6 % and 91.5 % accuracy respectively, using a pre-classification method and validated against optical phantoms of known optical properties. Additionally, LBI parameters directly extracted from the images were utilised to develop segregation models owing to the uncertainties in μa and μs’ estimation. For internal disorder detection, using the estimated kiwifruit μa and μs’, the segregation accuracy for kiwifruit with BMSB damage was 84 % and 62 % for ‘Zesy002’ (n=198) and ‘Hayward’ (n=198). Using extracted kiwifruit LBI parameters, the segregation accuracy for kiwifruit with CI was 92 % and 39 % for ‘Zesy002’ (n=396) and ‘Hayward’ (n=400). In addition, ‘Zesy002’ (n=30) and ‘Hayward’ (n=30) LBI during the postharvest ripening for kiwifruit were collected through a 15-day shelf life at 20 °C, where extracted LBI parameters were used to develop a time-series model. Absolute values of kiwifruit LBI parameters increased during the kiwifruit ripening process for both cultivars and the trend of LBI parameters may be correlated with kiwifruit softening. For segregating kiwifruit based on FF, the kiwifruit FF segregation model was calibrated, cross-validated and externally tested using kiwifruit LBI and corresponding FF data collected from 2 seasons with varying at-harvest maturity stages and stored at 2 temperatures. The segregation model accuracy for classifying fruit based on the 9.8 N FF threshold was 75 % and 70 % for ‘Zesy002’ (n=2247) and ‘Hayward’ (n=3558) in test sets. In conclusion, this work confirms that LBI technology has the potential for segregating soft kiwifruit or kiwifruit with early internal disorder symptoms and be adapted to the packhouse sorting system. However, in this work, FF segregation uncertainty at the 9.8 N threshold was observed when ‘Zesy002’ FF (N) ∈ (5,15) and ‘Hayward’ FF (N) ∈ (5,20) due to LBI parameter overlapping. Improved image analysis and segregation algorithms need to be investigated to enhance the segregation sensitivity for kiwifruit FF in the lower firmness range.
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    Assessment of the relationship between kiwifruit skin topography and its quality and storability using fringe projection : 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. EMBARGOED until 22 November 2025.
    (Massey University, 2023) Lai, Po-Han (Leo)
    Kiwifruit harvested from different growing locations tends to have variable fruit quality and storage performance due to many preharvest factors that contribute to fruit variation at harvest. This variability of fruit between batches makes the prediction of postharvest storage quality difficult, causing postharvest fruit losses. One of the preharvest factors that introduces fruit variability is the growing environment in which the fruit are exposed to. Fruit skin, a protective layer that covers the entire fruit, plays an important role in fruit development and is the first point of interaction with the surrounding environment. The objective of this research was to investigate a novel non-destructive technique that utilised at-harvest skin topography to link with fruit quality and storage performance of kiwifruit. The ‘G3’ (marketed as SunGoldᵀᴹ) kiwifruit cultivar was chosen for consideration in this thesis because it has distinctive skin properties with protruding lenticels and is a high-value cultivar that is of considerable importance to the New Zealand kiwifruit industry. The potential for fringe projection to extract skin physical properties in kiwifruit was demonstrated through surface roughness quantification and image analysis technique. Characterisation of lenticels on the surface of kiwifruit was achieved by developing an automated image processing algorithm. The knowledge of the skin properties of kiwifruit was revealed through a comparison of skin topography and cuticle compositions of different kiwifruit cultivars. Skin topography differences revealed genotype related diversity as well as the effect of environmental factors that fruit were exposed to. The most abundant cutin monomer composed mainly of C₁₈. Predominant cuticular waxes such as fatty acids and phenolics were identified. The knowledge of lenticel development was confirmed through monitoring the skin topography during fruit development and fruit bagging. Lenticel formation becomes visible from 45 DAFB and is dictated in the early stage of fruit growth before 77 DAFB. Lenticel properties are set and established before harvest. An orchard bagging experiment revealed that the difference in the growing environment modified the development of lenticels in kiwifruit. The lenticel coverage was positively correlated with the humidity condition that the fruit is exposed to during fruit development. Lenticel density and size at harvest had little influence on the water loss and storage performance of fruit. Lenticels were found to become a low resistance pathway for water loss if there is evidence of microcraking and splitting. The hypothesis of using at-harvest skin topography to predict the post-storage quality of kiwifruit was explored by developing a blackbox machine learning model. Unfortunately, both quantitative and qualitative predictions of soluble solids and flesh firmness in storage were not successful due to a low level of accuracy across models. The storability of fruit is affected by many factors, and improvements can be made to include additional information such as other non-destructive techniques to help in prediction. While skin topography using fringe projection may not be a good indicator of kiwifruit storability, the application is useful to characterise skin properties that are related to fruit quality. The work found that skin roughness generally increases after storage which is likely to be caused by shrivel development or skin scuffing. There is an opportunity to rapidly and reliably quantify skin defects. Another potential application for fringe projection is to use in a kiwifruit breeding program as a high-throughput phenotyping tool to capture the surface properties of different genotypes, enabling the identification of desirable traits.
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    Identification of mechanical parameters to be used as a firmness standard on quality evaluations of stored blueberry : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatu, New Zealand
    (Massey University, 2022) Rivera Smith, Sebastian
    Blueberry firmness is considered a relevant quality variable influencing consumer acceptability of fresh blueberries. However, the blueberry supply chain and research community have not yet adopted a standard method to measure firmness on postharvest quality evaluations. This thesis has focused on characterising the mechanical properties of blueberry ‘Nui’ and ‘Rahi’ as influenced by different factors such as storage relative humidity (i.e., fruit water loss), controlled atmosphere and harvest maturity. The mechanical parameters were obtained by using the instrumental methods of texture profile analysis (TPA) equipped with a flat plate and the penetration test equipped with a 0.39 mm round tip diameter needle probe. Mechanical parameters of hardness slope (BHS, also known as chord stiffness) of TPA and displacement at skin break (DSk) of the penetration test can be used to track water loss changes in stored blueberries. The DSk and BHS can also accurately detect quality changes induced by controlled atmosphere storage. In addition, BHS can detect maturity differences in stored blueberries, but the force at skin break (FSk) provides better detection of maturity differences at harvest evaluations. To demonstrate the relevance of chord stiffness evaluations at a commercial level, sensory evaluation of texture of hand-touch firmness using a formal sensory panel setting and trained assessors was related to instrumental mechanical parameters. Chord stiffness measured as BHS using a flat plate compression and skin break slope (SSk) measured using a needle probe were strongly related to consumer sensory perception of hand-touch firmness. A blueberry batch with an average BHS ≤0.47 kN m⁻¹ or SSk ≤0.13 kN m⁻¹ was associated with a very high likelihood of unmarketable berries (i.e., berries are ‘soft’ or ‘very soft’). In summary, BHS was an informative parameter of blueberry quality across factors inducing the textural changes and providing commercially relevant information about consumer acceptability. These results can assist the development of a standard instrumental method to measure postharvest firmness on blueberry quality evaluations for research and commercial purposes. Further studies should focus on validating the feasibility of BHS to determine blueberry quality across other sources of textural variation, such as calcium and ethylene-related treatments. In addition, threshold values for mechanical parameters related to consumer acceptance (sensory analysis) may be identified across an extensive range of blueberry genotypes and using other sensory descriptors also relevant to the consumers, such as crispness. Finally, this research identifies alternative areas for further studies, such as the blueberry firming (an increase of firmness during storage) occurring consistently on blueberries ‘Nui’ stored under high RH in regular air or a controlled atmosphere of 5 kPa CO₂ + 4 kPa O₂.
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    Temperature and atmosphere composition influence on colour change of apples : a dissertation presented in partial fulfilment of the requirements for a Masterate of Horticultural Science, Massey University, Palmerston North, New Zealand
    (Massey University, 1993) Dixon, Jonathan
    In apples colour is a major quality parameter used by consumers to determine apple maturity. A full understanding of the nature of the relationship between storage conditions and apple fruit colour change would be of advantage in formulating models to predict how changes to handling systems would affect fruit colour. While much is known in a general way about how environmental conditions affect colour change, little information is available to characterise the nature of the relationships between temperature, oxygen and carbon dioxide. The postharvest change in colour was measured for two export apple cultivars; Cox's Orange Pippin and Granny Smith. Previous research on these and other apple cultivars has determined that colour change is from green to yellow. The colour of Cox's Orange Pippin and Granny Smith apples were measured by subjective and objective methods during experiments to investigate the effect of temperature and atmosphere composition on colour change. The objective methods used were: chlorophyll extraction and colour using a Minolta chromameter. The subjective method was colour matching for Granny Smith using the NZAPMB maturity colour charts. When related to changes in chlorophyll, the principal skin pigment, the colour parameters used had non-linear relationships. Lightness, hue angle and colour chart score all reflect pigment changes occurring as apples change colour from green to yellow. Lightness values were the least variable followed by hue angle then colour chart score. All methods used showed more sensitivity to changes in chlorophyll content when chlorophyll content was low compared to when chlorophyll content was high. The objective measurements were highly correlated with the subjective measurements and the conclusion was that the use of hue angle or lightness to follow colour change in the skin of Granny Smith and Cox's Orange Pippin apples is an accurate indirect measure of chlorophyll and other pigments. The rate constant of colour change (k), measured using a declining exponential function, from green to yellow, at eleven temperatures over two seasons, two harvests per season and several growers was investigated in order to characterise the relationship between yellowing and temperature. All the methods of colour measurement used had the same relationship with temperature which was described by a modified form of the Arrenhius equation. Re-worked published data also fitted the modified Arrenhius equation. The modified Arrenhius equation was used to generate k for the various colour parameters measured (chlorophyll, hue angle, lightness and colour charts score). The value of k, as a function of temperature, increases slowly between 0°C and 6°C (the lag phase), increases exponentially between 6°C and 20°c and reaches a maximum at 25.3°C for Cox's Orange Pippin and 23.5°C for Granny Smith before declining. Pattern of response to temperature was the same for each cultivar although Granny Smith yellowed more slowly than Cox's Orange Pippin. For Cox's Orange Pippin apples more variation was accounted for by differences between growers than years or harvests within a year. For Granny Smith fruit most variation was accounted for by differences between years. Sixteen atmospheres were used each year for Cox's Orange Pippin and Granny Smith apples from one harvest in order to characterise the relationship between yellowing and oxygen or carbon dioxide. Cox's Orange Pippin and Granny Smith apples differ in their response to oxygen. For Cox's Orange Pippin the value of k as a function of oxygen level increased slowly from 0% to 6% and thereafter increased exponentially from 6% to 19%. This function may be sigmoidal as the k values increase slows above 17% oxygen. The relationship for Granny Smith was poorly defined by this function, k values increased slowly as the oxygen level rose. This could be due to a fundamental physiological or biochemical difference between these two cultivars. Each cultivar had a similar response to carbon dioxide, described by a declining exponential function, with the relationship for Granny Smith being better defined than for Cox's Orange Pippin. The relationship of carbon dioxide with colour change was poorly defined as the effects of oxygen on colour change were not removed from the analysis. Oxygen appears to have a greater influence on colour change than carbon dioxide. Atmospheres for Cox's Orange Pippin apples were not scrubbed for carbon dioxide in 1989 but were in 1990. The pattern of response to oxygen in the absence of levels of carbon dioxide above 1% in the atmosphere did not alter the sigmoidal relationship found. This may be evidence that the effect on yellowing by oxygen and carbon dioxide is by separate processes. Ethylene levels in the atmosphere appeared to have little effect on the rate of yellowing in all the atmospheres studied. The carbon dioxide and oxygen functions were combined into a single equation for use as a predictive model. The temperature function, the modified Arrenhius equation, and the atmosphere functions were combined into one equation to which different environmental values were added. The use of such a model and other practical applications for the information gathered for this thesis are discussed and a chart drawn comparing the hue angle, lightness and colour chart score to chlorophyll level.
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    Development of a rapid liquid freezer : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatū, New Zealand
    (Massey University, 2021) Morel, Jolin
    Small sheep dairy farms often make insufficient volumes of milk for economic daily collection and are limited by transport distances to processors. A method of long-term on-farm storage of milk would enable the industry to grow. Freezing would allow extended milk storage on farms. But existing methods of freezing for on-farm applications have shortcomings around materials handling, labour requirements and product quality. The project reported in this thesis aimed to develop the engineering science behind an economically viable freezing method that would improve on current methods. The first period of this project focused on two freezer designs which were thought to be promising: Rolling Droplet Freezing (RDF) and Falling-Film Flake freezing (FFF). RDF was selected as the initial focus of the research program and consisted of a system where droplets of milk would roll down an angled super-hydrophobic surface against a cold air flow and freeze. RDF was abandoned due to concerns about construction costs and operating reliability. In a condensing atmosphere, droplets rolling on superhydrophobic surfaces occasionally transitioned from a Cassie-Baxter wetting state to a Wenzel wetting state, which caused the droplets to stick. FFF was then developed further. A pilot scale unit was designed and constructed, and preliminary pilot-scale trials that were conducted with pure water and ovine milk reconstituted from powder. The partition coefficient of FFF was measured as 0.946 at an operating temperature of -30°C. At higher operating temperatures the partition coefficient was reduced. Detaching frozen solids by applying a burst of heat to the freezer/ice interface was studied and this method of detachment was successful with pure water, but ineffective for ovine milk. The development of FFF was put on hold with the conception and development of the continuous tubular freezer. Ice formed in a solution can show morphologies ranging from highly dendritic structures with entrapped solutes, which are homogenous on a gross scale, to large crystals of pure ice with solutes rejected and compressed into inter-crystalline spaces. To investigate which sheep milk components influence ice morphology at various freezing rates, whole milk was separated into skim milk and into a casein-free serum phase. A simulated sheep milk ultrafiltrate was also prepared. The morphology of the ice/sample interface was observed in a custom-built microscope stage at freezing front velocities from <0.5 μms⁻¹ to 50 µms⁻¹ with a spatial temperature gradient of 35-38 Kcm⁻¹. The morphology arising from extremely rapid freezing front velocities was investigated by supercooling slides on a temperature-controlled stage and observing the nucleation and recalescence of the samples. The morphology of ice at the interface changed from a planar to columnar and then to dendritic as freezing front velocity increased, with the transitions from one morphology to another occurring at lower speeds in more complicated solutions. A map of freezing front behaviours was developed. The transition between interface morphologies was at different velocities and transition differed based upon the interface velocity. At lower interface velocities a columnar interface grew directly from a planar starting condition. At higher velocities an intermediate dendritic zone formed, which then settled into a columnar interface. The ice formed by rapid freezing from subcooled solutions was highly dendritic, with ice growth rates of approximately 21,000 μms⁻¹, which was close to the diffusion-limited ice growth rate in water of similar degrees of supercooling. The morphology of frozen ovine milk was also studied by Cryogenic Scanning Electron Microscopy (Cryo-SEM): Milk was frozen by three different methods-slow quiescent freezing (SF), rapid directional freezing (DF), and droplet freezing in LN₂. Ice crystals rejected unfrozen solids into the region between crystals in all samples, including those frozen by immersion into liquid nitrogen. There was a distinct difference in morphology between the SF and DF samples, with the bands of unfrozen solids being significantly smaller in DF samples, and the long axes of ice crystals were aligned with the direction of heat flow. SF samples lacked any particular ice growth direction, and ice crystals were orders of magnitude larger. Lactose crystallisation was observed in some SF samples but was not observed in any DF samples. Fat globules were engulfed in ice crystals in DF samples, but rejected in SF samples. To study the effects of frozen storage temperature and time, samples of raw ovine milk were stored frozen at -10°C, -18°C and -28°C to -30°C for up to 8 weeks. Further samples were stored below -20°C for 6 months. After thawing at 20°C, samples were tested for a range of properties and serum samples were collected by separating the fat phase and micellar casein phase by centrifugation. A gel was observed in milk stored at -10°C for 4 weeks and 8 weeks but was not observed in milk stored at lower temperatures. The gel dispersed under heating and homogenisation. There was no change observed in the pH, or serum protein level of thawed samples after frozen storage at any temperature. The whiteness of the milk decreased during frozen storage and the yellowness increased. Both of these changes were reversed on homogenisation. The serum Ca²⁺ levels in milk stored at -10°C and -18°C dropped over the storage period, while no trend was seen in milk stored below -28°C, indicating that the migration of Ca²⁺ may play a role in the formation of gels after frozen storage. Milk that had been stored below -20°C for 6 months had a similar viscosity and appearance to fresh milk. A possible mechanism for the formation of gels at -10°C, but not -18°C or -28°C lies in the altered solute environment, and the physical agglomeration of milk components in the spaces between ice crystals, driving the gelation of closely packed casein micelles, with Ca²⁺ stabilising this network. It is well established in literature that the viscosity of an unfrozen phase increases by several orders of magnitudes as it decreases in temperature and approaches a glassy state. This increased viscosity reduces protein mobility and solute diffusion, which reduces the rate of gel formation. The tendency for frozen milk particles to bind together during frozen storage was evaluated. Frozen pellets of whole ovine milk were stored under weights at -10°C and -18°C and pellets of frozen concentrated milk stored at -18°C and -28°C. Ovine milk pellets bound together at -10°C but not -18°C, while concentrated milk bound together at -18°C, but not -28°C. This can be linked to the volume and viscosity of the unfrozen phase in these samples. Differential scanning calorimetry was used to determine the fraction of freezable water frozen at any temperature. The melting onset temperature was observed, and this was used to determine the solids content maximally freeze concentrated solution (𝑋𝑠(𝑇𝑚)). 𝑋𝑠(𝑇𝑚)=0.875 for whole ovine milk 𝑋𝑠(𝑇𝑚)=0.85 for skim milk, and 𝑋𝑠(𝑇𝑚)=0.81 for ovine milk serum. This was also determined for whole ovine milk by the magnitude of the overall latent heat release during melting, which gave a value for whole milk of 𝑋𝑠(𝑇𝑚)=0.85±0.016. A partial phase diagram for ovine milk was generated from the data collected. The insights generated from observing both the dendritic morphology of high velocity ice fronts and progressive freezing behaviour led to conceptualising a novel tubular freezer, subsequently constructed. It was hypothesised that reducing the volume or area of ice in contact with the freezer wall, due to the inclusion of unfrozen product, could reduce the adhesion strength between a frozen product and the freezer wall. By controlling the outlet temperature, the volume fraction of unfrozen product could be controlled. The adhesion strength could thereby be controlled, and a set of operating conditions could be found that would allow a mostly frozen product to be extruded as a solid from a cooled tube by a high-pressure pump. This was tested on a benchtop scale (up to 5mL/minute, with a freezer internal diameter of 4.2mm and cooled length of 500mm), with ovine milk, fruit juice, fruit pulp, concentrated coffee, bovine cream and concentrated milks. The system successfully froze all samples. The operating pressure was found to increase with increased frozen fraction, and therefore with decreased operating temperature. The ice morphology of milk and juice frozen by this equipment was imaged by cryo-SEM and by optical microscopy. The ice crystals were radially aligned, increasing in size closer to the centre of the frozen product plug, which was expected due to the heat flows and the relationship between freezing front velocity and feature sizing. This positive preliminary result led to the construction of a larger scale prototype unit which consisted of a spiral tube with a length of 5000 mm, and an internal diameter of 10 mm. This was used successfully for a product flowrate of approximately 6 kghr⁻¹.
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    Ethylene related ripening of 'SunGold™' kiwifruit : 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. EMBARGOED until 31 January 2026.
    (Massey University, 2020) Tongonya, Jeritah
    A key component of the success of the New Zealand kiwifruit industry is the consistent provision of high-quality produce. The projected increase in kiwifruit volumes necessitates the widening of harvest and marketing windows. Two different kiwifruit export marketing strategies are currently deployed: i) Early season fruit are delivered for immediate sale (‘KiwiStart’), ii) later season fruit have a maturity that enables extended postharvest cool storage (‘MainPack’). These marketing strategies determine harvest criteria and subsequent postharvest management practices employed in the supply cool chain. The introduction of new cultivars, e.g. ‘SunGold™’, necessitates a re-evaluation of the postharvest ripening and storage practices, tuning the requirements to the specific responses of each cultivar. Since there is minimal information on ethylene related responses for ‘SunGold™’, research to develop a fundamental understanding of these responses is crucial for optimal management and performance of the product in the market. The purpose of this PhD is to determine the effect of industry-relevant ethylene concentrations on ‘SunGold™’ quality progression (firmness and soluble solids content (SSC)). With that understanding, a semi-mechanistic model for the simultaneous description of firmness decline and soluble solids increase under dynamic temperature conditions and ethylene concentrations was developed.--Shortened abstract
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    Characterising texture and cellular level responses of 'Centurion' blueberries during storage in different weight loss conditions : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Albany, New Zealand
    (Massey University, 2019) Franklin, Deena Kelsey
    Postharvest blueberry softening hinders consumer acceptance and correlates with high moisture loss during storage. Such textural variations have been attributed to factors such as turgor, cell wall modifications and other microstructural changes in the outer cell layers of the fruit. This thesis investigated the impact of moisture loss on blueberry quality, as well as the structure/function relationships associated with fruit texture characteristics during postharvest using an integrated physical and microstructural approach. Four different weight loss conditions (62%, 76%, 93% and 98% RH) were evaluated over a three week postharvest storage period to assess blueberry texture parameters using a texture analyser, where microstructural changes were assessed by light microscopy and optical coherence tomography (OCT). Under high weight loss conditions there was an increase in berry softening and a decrease in texture characteristics whereas an increase in berry firmness, hardness and gumminess was observed during storage under low weight loss conditions. Light microscopy clearly illustrated microstructural differences among ‘Centurion’ blueberries stored in different weight loss conditions, in retention of cell shape, degree of cell to cell wall contact, the amount of space between cells and cell wall integrity. When berries lost moisture during storage, epidermal and subepidermal cells retained their integrity, and parenchyma cells lost integrity leading to collapse which may contribute to overall fruit quality during postharvest. 3D OCT images showed no obvious differentiation between large cells at each weight loss treatment, however significant differences were observed in the microstructure between each storage period. In general the microstructure of medium to large cells in the parenchyma tissue showed an increase in average surface area and total surface area after each storage period. In summary, low weight loss storage conditions help to preserve blueberry texture and quality, whilst maintaining cellular structure and integrity during postharvest storage. It is recommended blueberries are stored between 95 – 99% RH and at a low temperatures to prevent moisture loss during postharvest.
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    Stabilisation of dried Lactobacillus rhamnosus against temperature-related storage stresses : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatū, New Zealand
    (Massey University, 2019) Priour, Sarah
    In the past few years, research has established a link between gut health and overall health and wellbeing. A diverse microbiome is a major step towards a healthy gut. Probiotics could help by improving the gut microbiome diversity and thus, are being added to a wide range of food products. However, maintaining them in a viable state within these food products is a considerable challenge. In order to increase the shelf-life of probiotics, numerous encapsulation systems have been developed to help protect them. Techniques such as emulsification, coacervation, or drying methods have all been employed with varying levels of success. While the final encapsulated bacteria may have enhanced protection and stability, a range of stresses are imposed on the bacterial cells during the actual encapsulation process, including mechanical, physical and chemical. Drying is the technique that confers the most protection to the probiotics, potentially stabilising them for up to several years. However, water plays a structural role and upon its removal, forces appear between cell components leading to the denaturation of proteins or the phase transition of the phospholipids membrane. Thus, bacterial cells need to be dried in the presence protectants that can prevent detrimental events from occurring and damaging the cells. It is thought that there are three main mechanisms by which protectants will confer superior stability. Firstly, the protective matrix can form a glassy system preventing further chemical reactions from happening, and thus protecting the bacteria. Secondly, if protectants are introduced for a period prior to drying, they can interact with the cellular biomolecules, replacing the structural role of the water, and maintaining the biomolecules in their native state when the water is removed from the system. Finally, the protectants can increase the free energy of water, maintaining it in the vicinity of the biomolecules, so that when the water is removed, the biomolecules are still hydrated and in their native state. Therefore, it is obvious that the role of protectants during the drying step is critical. The question that has remained largely unanswered, however, is how long and under what conditions should the protectants be introduced, and what type of protectants work best? Once the probiotics are successfully dehydrated, storage stresses may impair their stability on the shelf. Among these stresses, high temperatures of the surrounding environment is one that has been well documented to be detrimental to the cells and generally leads to a rapid drop in shelf stability. These temperatures can be experienced not only during the life of the product on the supermarket shelves, but also during transport of these consumables around the globe. The effect of changes in temperature on bacterial cell viability is an area which has not been explored in great depth, and the impact that encapsulation may have on the viability under these conditions even less so. Once again, like in the case of the protectants, the materials used to encapsulate the bacteria will be critical to final stability. Materials such as ‘phase change materials’ (PCM), which can absorb and release heat over different temperature ranges could be the key to protecting bacteria under extreme conditions. The aim of this thesis was thus to stabilise a model probiotic: Lactobacillus rhamnosus HN001 to high temperatures occurring during storage and transport. In order to do so, the study was separated into four principal research questions. Firstly, can a pre-drying step (for example the uptake of protectants) help the stability/viability of the bacteria during storage? Secondly, what are the best protectants for long-term storage of Lb. rhamnosus HN001, and why? Thirdly, is it possible that combinations of the most suitable protectants act in synergy, bringing increased storage stability compared to either protectant on its own? Finally, can the inclusion of PCM in the encapsulation matrix give extra protection to the cells during storage? This question would be of particular significance when examining the effect of the fluctuating temperatures experienced during the transport of the probiotics. The first study, therefore, consisted of establishing a protocol to prepare the cells for drying, by finding the early stationary phase where cells are known to be most stable to stress, and then optimising the exposure of the cells to potentially protective solutions of glucose and sucrose at 4 and 20°C. The uptake of the solutes was explored using HPLC, before drying the cells and evaluating the effect that their uptake had on the shelf-life stability of freeze-dried cells. In order to try and understand any interactions between the intracellular biomolecules and the protectants, the Nano DSC was used. Results showed that when cells were exposed to glucose at 20°C, metabolisation took place, and the longer the exposure, the lower the stability of the cells after drying and over storage. Overall, the study revealed that cells exposed to sucrose at 20°C for 4 hours presented best stability indicating that both the type of protectant, and exposure settings are critical to a successful outcome. The results from the Nano DSC showed that sucrose interacted with some of the cell biomolecules, rendering them more stable. The exposure temperature for the rest of the experiments was thus set at 4°C to avoid metabolisation, and the time was set at one hour so that exposure settings would be adapted for both sugars. In the second part of the study, a range of nine protectants (glucose, fructose, galactose, sucrose, lactose, trehalose, betaine, monosodium glutamate (MSG) and sorbitol) were compared for their ability to stabilise freeze-dried Lb. rhamnosus at 30°C for 6 months. Inulin was used as a carrier. The impact of galactose, sucrose, betaine, MSG and sorbitol was studied using a Nano DSC to again try and establish links between biomolecule interaction and stability during storage. Interestingly, MSG led to the best stability overall with a cell loss of 0.19 /month, even though it had the highest water activity of all the samples following freeze-drying. This is contradictory to general thought on how water activity affects bacterial cell stability, with higher water activity generally resulting in increased cell death over time. It was shown, using the Nano DSC, that MSG interacted with most of the cell biomolecules rendering them more stable. MSG was thus selected for further study. Three additional protectants were selected (galactose, sucrose and sorbitol) to look for potential synergistic effects with MSG in terms of protecting the bacteria during storage. The study followed a mixture design of experiment (DoE) in order to obtain an optimal protective matrix. The powder structure was also studied at this point by microscopy along with analysis using the DSC to try and comprehend the importance of the powder structure on the stability of the dried cells. Multivariate analysis was used to link all factors and their relative impact on the cell death rate together. Interestingly, it was found that neither a high glass transition temperature (Tg) nor a low water activity helped to stabilise the bacteria. Instead, the amount of MSG was clearly shown to improve the shelf-life, and a synergy was found between sorbitol and MSG. Microscopy showed that this powder led to a unique structure that most likely collapsed during drying resulting in the shrinkage of the cake and the loss of the porous structure, thus lowering the exposure of the bacteria to oxygen. In addition, a small amount of the sorbitol present in the matrix seemed to help in stabilising additional biomolecules as shown by the Nano DSC. The slowest death rate results obtained were 0.04 /month when MSG alone was mixed with inulin, but the model predicted an even lower death rate due to the synergy occurring between MSG and sorbitol. Finally, this optimised stabilisation matrix was used to study the impact of further protection, in the form of an encapsulate containing a PCM, on the stability of the bacteria. Powders with two different structures were compared using freeze-drying and spray drying techniques. The viability of the resulting powders was assessed during two separate storage studies designed to test the cells against fluctuating temperatures (20 to 50°C) and at constant temperature (35°C). The results showed that PCM appeared to have little impact on the overall stability of the powder. However, it was confirmed that a dense and smooth powder structure helped to maintain the bacteria in a viable state for a longer time than a more porous structure. This was most likely due to the lower surface-area ratio decreasing the exposure with the environment and preventing detrimental reaction such as oxidation. The bacteria in the optimised stabilisation matrix had the best stability, with a death rate of 0.07 /month at 35°C and 0.18 /month under fluctuating temperature from 20 to 50°C. In conclusion, it was found that the interaction of the protectants with cells is of paramount importance in maintaining the cells in a dried, viable state for longer periods at elevated temperatures. In addition, the structure of the powder should also be considered as one of the main mechanisms for protecting the bacteria, as it has a substantial impact on the shelf-life of the powder. Conversely, in this body of work it was shown that a high glass temperature did not enhance, or indeed help to maintain cell viability as has been suggested by many previous studies. A dense structure is, however, believed to protect the bacteria through preventing exchanges with the environment, especially with oxygen. If future work is to be done, it should follow the oxidation of the cells during storage and link it with measures of the powder porosity to gain further insight into the impact of the structure on oxidation stress.
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    An integrated modelling approach to inform package design for optimal cooling of horticultural produce : 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, 2018) Olatunji, Jamal Rimkeit
    Forced-air cooling is a widely used pre-cooling process that enables the New Zealand horticultural industry, valued at over NZD $8B in 2016, to maintain the quality of perishable exports. In the typical systems used in New Zealand’s horticultural industry, forced-air cooling involves stacking fruit boxes into pallets, which are stacked together in a refrigerated room, and a fan is used to create a pressure drop through the pallets. This forces cold air through the packaging ventilation and over the fruit, facilitating heat transfer and rapidly cooling the product from the field heat (~20 °C) to the storage temperature (0-2 °C), thus prolonging shelf life and preserving fruit quality. Package design is linked with cooling performance, as the specifics of the ventilation (i.e. placement and size of vents in the boxes) results in different airflow patterns. Unfortunately, it is not well understood how to predict the performance of a hypothetical design, which is partly why in industry and academia there has been a focus on package design testing – where through experimental or computational means, the performance of a given design is thoroughly tested. Trial-and-error experimental work represents a steep materials cost, and construction and validation of detailed mathematical models can be a highly arduous and specialised task. It would therefore be beneficial to the New Zealand horticulture industry and academia to have a suite of methodologies that can simply and rapidly predict performance of a hypothetical package design. It was proposed that such methods are based upon mathematical modelling, with a focus on flexibility, computational efficiency, and automation. The goal is that such a model can be used to rapidly develop mathematical descriptions of a wide variety of products and cooling scenarios, and if integrated with optimisation routines, will allow swift iteration toward an optimised design.--Shortened abstract
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    Curing kiwifruit : physical, physiological and storage impacts : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Food Technology at Massey University, Auckland, New Zealand
    (Massey University, 2018) Doleh, Leila
    Curing of ‘Hayward’ kiwifruit is a postharvest approach to reduce decay and maintain quality during long-term storage. Curing occurs immediately after harvest, with fruit placed in picking bins in a covered packhouse space for a few days. Curing contributes to fruit quality by allowing the picking scar to heal (resulting in reduced Botrytis rot) and allows a proportion of water loss, resulting in fruit cells that are less turgid and hence less prone to mechanical damage during packing. In the contemporary packhouse, curing is also used to buffer logistical challenges, since stockpiling fruit has advantages in ensuring the packing line continues to process fruit. In kiwifruit, the rates of cooling to storage temperature have previously been identified as an influence on long-term storage outcomes, including firmness and storage breakdown development (SBD). Little is known about how curing contributes to long-term storage, yet there is potential to impact post-storage fruit quality given that curing occurs immediately prior to packing and cooling. There is a lack of knowledge regarding the range of conditions which fruit are exposed to when bins are stacked under non-controlled conditions. It is also unknown how these conditions may influence fruit quality (i.e. fruit softening and SBD development) after long-term storage. This thesis incorporates monitoring of within bin environmental conditions to assess possible in-stack heterogeneity during curing.