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Item Mathematical modelling of airflow during forced draft precooling operations : 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, 2024-11-01) Tapia Zapata, Nicolas IgnacioBy the year 2020, the kiwifruit industry represents approximately 37 % of the horticultural export industry sector in New Zealand. Thereof, the kiwifruit cold chain aim is to reduce losses due to poor temperature control and energy usage during refrigeration. By forced convection aided by fans in palletised kiwifruit, field heat is removed rapidly prior to storage, thus optimising shelflife of the produce. Previous Computer Fluid Dynamics (CFD) model determined the optimal operating point for palletised kiwifruit during forced-draft cooling. However, CFD requires complex simulation, in detriment to computational efficiency and solving time. Therefore, there is an imperative to provide innovative tools that optimise package design by iterating several designs and that is applicable to the local industry sector for cold chain optimisation. In this spirit, this projects aimed to development of a simplified approach for the prediction of airflow distribution of palletised kiwifruit during forced-draft cooling, that can be coupled with an alternative heat transfer model, thus providing a fast and robust package optimisation routine that can inform cooling performance of several package design and pallet configuration.Item Factors influencing the exertional heat stress response in athletic females : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy, School of Sport, Exercise and Nutrition, Massey University, Palmerston North, New Zealand(Massey University, 2022) Zheng, HuixinClimate change continues to expose an increasing proportion of the global population to more frequent extreme heat events. Concurrently, our society has seen an increase in the number of women that participate in physically demanding leisure time (exercise and sport) and occupational activity. Yet, limited research has been conducted to understand the female physiological responses to exercise-heat stress, especially when considering their various ovarian hormone profiles. This thesis expands our understanding of the female physiological responses to heat stress from different perspectives. Firstly, previous evidence has demonstrated that ambient heat stress amplifies the increase in the cytokine interleukin-6 following exercise, an up-regulator of hepcidin - the hormone that downregulates iron metabolism. In Chapter Five iron sufficient females’ serum iron parameters and hepcidin levels following a self-paced cycling work trial were compared in temperate and hot conditions, and different menstrual phases. IL-6 and hepcidin both increased post-exercise (198% and 38%, respectively), interestingly, neither were affected by ambient temperature or menstrual phase (all p>0.15). Chapter Six determined the measurement error of a 30-min self-paced cycling protocol in moderate, warm-dry and warm-humid environments using thirty-three athletic women distinguished by their ovulatory status and ovarian hormone concentrations. With an ICC=0.90, p<0.01, and a mean CV of 4.7%, SEM of 3.8 kJ (2.1 W) and reliable bias of -2.1 kJ (-1.2 W), it was confirmed that this protocol has high test-retest reproducibility that is not influenced by ambient environment or a female’s hormonal/ovulatory status. Finally, in order to better predict females’ risk for exertional heat stress, Chapter Seven attempted to clarify the role of the ovarian hormones when explaining the variance of the core temperature response using the 30-min self-paced cycling protocol from Chapter Six in thirty-six trained women. It was found that estrogen contributes minimally, whilst baseline core temperature and power output contribute the most to peak core temperature during exercise. Taken together, this thesis deepens our understanding of females’ physiological responses and testing norms for current sport science practices. Specifically, it details iron metabolism responses when exposed to exercise-heat stress, elucidates the role of ovarian hormones regarding exertional heat strain and adds test-retest norms specific to athletic women to the available literature.Item A systematic approach for developing and manufacturing fruit simulators : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Engineering, Massey University, Palmerston North, New Zealand(Massey University, 2023) Huang, HuijianDue to the high cost, variable nature and seasonal availability of fruit, conducting large scale experiments for research purposes is not easy. A fruit simulator is a physical tool that mimics the mechanistic features and properties of the targeted fruit; hence, it can be used as a replacement for the fruit in research experiments. This study focuses on developing simulators for heat transfer experiments, especially in horticultural produce precooling. A framework for developing the simulator was established based on the importance of each mechanistic feature. Depending on the application's needs, the simulator can mimic different length scale levels of the targeted fruit, such as the individual fruit, the bulk stacking of the fruit or sub-units of the fruit (e.g., a punnet/bag of table grapes). The scale level determines whether certain mechanistic features are important and affects the values of the thermal properties that must be matched. For example, a simulator that mimics a punnet of fruit with enclosed air pockets has an effective thermal conductivity and volumetric heat capacity that includes contributions from the thermal properties of the fruit and air, which provides more room for material selection. Based on this framework, a systematic approach for the simulator manufacture and material selection was developed. Three different simulators were developed based on the framework: kiwifruit, apple and table grape simulators. The comparison of a simulator and real fruit precooling trials showed good agreement, validating the approach and demonstrating the feasibility of using simulators in postharvest research. The kiwifruit simulator was validated at different experimental scale levels, from individual kiwifruit to multiple kiwifruit boxes containing numerous individual kiwifruit simulators (which reflected pallet scale precooling). During the simulator development, the concept of a time-scaled approach was identified and was explored. In theory, if the volumetric heat capacity of a simulator becomes smaller while the Bi of the simulator remains the same, the heating/cooling time of the simulator in an experiment will decrease proportionally according to the Fourier number (Fo). This approach was validated via the three simulators developed in this study. The validation of the simulators confirms the feasibility of this time-scaled concept. This approach has a significant advantage in reducing the experimental time and easing the material selection process for the simulator manufacture. In the table grape simulator development, a process of using CT scans of the bulk packaged system to study the bulk shape and effective properties of the fruit subunits (bags) were developed, where the bulk shape and effective thermal properties of a bag of table grape were determined based on the process. A set of bag shaped fruit simulators was then manufactured with equivalent bulk thermal conductivity and used to validate the bulk simulator approach by comparison of cooling rates with real fruit. Overall, this study has successfully developed a generalised heat transfer simulator development framework. In addition, this study validated the feasibility and applicability of the time-scaling approach, which could be helpful for any future experiments. Furthermore, this study has developed a process to use CT scanning to determine a bulk object's bulk shape and effective property. The outcomes of the work pave the way for carrying out postharvest and packaging optimisation experimental trials with reduced variability, greater ease and without seasonal constraints. The simulator development framework provides a basis for further expansion of these concepts into other applications beyond the heat transfer focus that they were developed for in this work.Item The effects of post-training hot water immersion on concurrent training load and treadmill running performance in the heat : a thesis presented in partial fulfilment of the requirements for the degree of Master of Sport & Exercise in Exercise and Sport Science at Massey University, Albany, New Zealand(Massey University, 2019) Stewart, JoshuaBackground: Team-sport athletes of both elite and sub-elite status are often required to travel to hot and/or humid environments for competition; however, preparing for these environmental challenges can be difficult within a team-sport setting. Heat acclimation (HA) strategies for team-sports can typically involve the use of expensive equipment, or travel in advance of competition to naturally acclimatise to the competition environment; these may also affect the quality of concurrent training. These logistical challenges often faced by team-sports when preparing for competition in hot environments often dictate what is (un)available to them. Post-training hot water immersion (HWI) has emerged as a passive approach that is logistically friendly for sporting teams to use during a preparatory period for competition in the heat. Aim: To investigate if 6-days of post-training HWI is an effective HA strategy for sub-elite, male, team-sport athletes, has any detrimental effects on concurrent training load and if it can improve aerobic capacity in the heat. Methodology: In a randomised control study, fifteen, non-acclimatised, moderately-trained males performed an intermittent running protocol in temperate outdoor conditions (18°C, 67% RH) for six consecutive days followed by a post-training cool-down (CON; n=8) or an additional 40 min of HWI in 38°C (n=7). Three days before and two days following the intervention, participants completed a RAMP treadmill run in the heat (33°C, 30% RH). Results: The HWI group displayed a reduced mean heart rate (p=0.02) during immersion from day-1 to day-6 (by 14±10 beats‧min⁻¹) and improved feelings (by 0.9±0.5 AU; p=0.003). Daily HWI had no detrimental effects on concurrent training as no significant differences (all p<0.05) were found between groups for total distance run, session RPE and the composite measure of training load (duration x RPE). Treadmill VO2peak improved from pre-post for the HWI group (by 2.1 ml‧kg⁻¹‧min⁻¹or 4.2%; p=0.003) but not the CON group (0.2 ml‧kg⁻¹‧min⁻¹ or 0%; p=0.88). Conclusions: Six consecutive days of post-training HWI induces partial HA in moderately trained team-sports athletes with no detrimental effects on concurrent training load. This provides a practical acclimation strategy for sporting teams to implement when preparing for competition in the heat that acknowledges the logistical challenges often faced.Item 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 RimkeitForced-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 abstractItem Human temperature regulation during exercise in the heat : effects of the menstrual cycle and ambient thermal profile : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy, School of Sport, Exercise and Nutrition, Massey University, Palmerston North, New Zealand(Massey University, 2018) Lei, Tze-HuanBehavioural thermoregulation is the most effective means with which we regulate our body temperature at rest and during exercise. Yet, research into behavioural thermoregulation during exercise is still at an emergent stage, as it has not included females, or investigated different thermal profiles. In particular, limited studies are available to describe the behavioural and physiological differences between dry and humid heat for both sexes. Furthermore, it remains unknown whether ambient humidity or temperature alone contribute to the initiation of the behavioural responses during exercise in the heat. Therefore, the first part of this thesis investigated the effects of endogenous and exogenous female ovarian hormones on behavioural and autonomic responses, in both dry and humid heat environments matched according to the heat stress index, WBGT (Chapter Five and Six). The results from Chapter Five clearly show that behavioural and autonomic responses were less affected by menstrual phase, but were affected by the environmental conditions. In particular, trained women reduced their power output in order to nullify the autonomic strain from a humid heat environment. Chapter Six then extended this observation to (trained) women taking combined hormonal contraception, compared to eumenorrheic women in Chapter Five. The results from Chapter Six indicate that greater autonomic strain was observed in women with hormonal contraception, compared to eumenorrheic women, in both dry and humid heat, whilst the behavioural response was similar between those two groups. Furthermore, the behavioural response was different between dry and humid heat, with power output being lower in the humid heat environment compared to dry heat. The second part of this thesis investigated the effects of ambient temperature per se on the interaction of thermoregulatory, cardiovascular and perceptual responses to exercise (Chapter Seven), as well as assessing different exercise modalities (variable-intensity versus fixed-intensity exercise) and their effects on thermoregulation when the duration and average power output were matched (Chapter Eight). The results from Chapter Seven indicate that thermoregulatory and cardiovascular responses were not affected by ambient temperature but that perception was, when vapour pressure was matched between two different thermal profiles. The results from Chapter Eight indicate that self-pacing (behaviour) did not modulate thermoregulatory strain, when both self-paced and fixed-intensity were matched at the same exercise intensity and duration. In conclusion, this thesis extends the knowledge-base on behavioural thermoregulation in trained women and also provides evidence that behavioural and autonomic thermoregulation is influenced more by vapour pressure than ambient temperature of the environment in men. Furthermore, the findings of this thesis confirm that behavioural thermoregulation is effective in modulating physiological strain only when there is a reduction in metabolic heat production.Item Growth and physiological responses of asparagus (Asparagus officinalis L.) at high temperatures : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Horticultural Science at Massey University(Massey University, 1993) Yen, Yung-FuAsparagus is now planted in tropical climates, hence a series of experiments were carried out to examine the physiological responses of asparagus to high temperature. These included analysis and modelling of growth, and the measurement of heat tolerance of four asparagus cultivars at high temperatures. Asparagus seeds of four cultivars were sown and grown in controlled climate rooms. These results showed that growth of young asparagus plants was exponential, and thus the parameters RLGR (relative leaf area growth rate), RFGR (relative fern dry weight growth rate), RCGR (relative crown dry weight growth rate), RPGR (relative total plant dry weight) were constant for any specific temperature regime or cultivar. The growth rate could be classified according to the parameters NAR (net assimilation rate), LAR (leaf area ratio) and RGR (relative growth rate), and could be grouped into high : 'D25/N25°C and D30/N30°C', normal : 'D20/N20°C, D30/N20°C, D35/N15°C, and D35/N25°C', and poor growth rates : 'D35/N35°C, D40/N20°C, and D40/N30°C'. The effects of these temperature regimes on growth were greater than the differences among cultivars, although there were different responses at high temperature among cultivars. Generally, NARs decreased with increasing age, while LARs increased with age. Both NARs and LARs varied with temperature regime, plant age and cultivar. The effects of high temperature on NAR or LAR were greater than the differences between cultivars. The leaf production rate was the largest contributor to total plant relative growth rate, followed by the root, the stem, and the rhizome production rate. The stem and the rhizome production rates declined with age, the leaf production rate increased, and the root production rate was maintained nearly constant. The allometric coefficients of root in relation to fern for cultivars and for the various temperature regimes were essentially the same. On the contrary, the allometric intercepts between plants at various temperatures or between cultivars were significantly different, with Tainan No.1 having the highest and Larac the lowest root/ shoot ratio except at supra-optimal temperatures. The lower temperature regimes had the higher root: shoot ratios. The root: shoot ratio was higher with a 10°C day/night temperature differential compared to the equivalent constant temperature regimes. Day or night temperatures around 26.5°C were optimal for RLGR, RFGR and RPGR, but a night temperature of 23.8°C was optimal for RCGR. The experiment on spear yield and fern development showed that not only did high temperature depress spear yield and quality, but it also depressed total fern weight and individual fern height. The plant characteristics such as the first branch height and fern height were also depressed at high temperature. Brocks and UC157 maintained better fern characteristics than the others at high temperatures. From the parameters of Richard's equation on fern, and of the RSGRs on spear, the ability of adaptation to high temperature was in the order: Tainan No.1 > Brocks > UC157 > Larac. In a high temperature study with germinated asparagus seedlings, the higher the temperature was the more stunted the growth. High concentrations of ABA application also markedly depressed seedling growth. There was an additive effect of heat stress and application of high ABA concentration on seedling growth, while there was an ameliorative effect with the application of ABA at a low concentration (0.1 - 1 μM) on heat stressed seedlings. At high temperature the sensitivity difference to ABA between cultivars was clearly expressed and thus the difference in heat tolerance of asparagus cultivars may be determined by ABA insensitivity. The studies of the effect of high temperature on endogenous ABA levels showed that the endogenous ABA levels decreased with temperature and then increased to a peak around 38°C for Larac and Tainan No.1, but peaked at around 36°C or lower for Brocks and UC157 for both roots and shoots. The spears of Tainan No.1 had an extremely high ABA content at 28°C and 33°C and fell to similar levels as the other cultivars at 36°C. It is concluded that the peak of endogenous ABA occurred at supra-optimal temperature and then decreased to low levels at extreme high temperatures. The assay of membrane thermostability (Tm) is a potentially valuable means of determining heat tolerance of asparagus. Tm varied with genotype, age, and heat acclimation. Heat acclimation may increase the membrane thermostability of young tissues. UC157 may be expected to be best adapted to tropical climate on the basis of membrane thermostability, because UC157 had the highest Tm of spears grown at high temperature. Tainan No.1, Larac and Brocks grown at high temperature also had increased heat tolerance, presumably due to heat acclimation. The study on the differences between cultivars in heat shock protein production showed that changes in protein synthesis occurred when asparagus was heat shocked at 34°C or 37°C for 2 or 6 hours. Specific heat shock proteins were produced and the levels of normal proteins changed. Most of the HSPs were of low molecular weight (about 24 kD to 13 kD). A small number of the HSP's appeared to be cultivar specific. A number of ABA induced proteins might be HSPs, but ABA also depressed the production of some HSPs. However most HSPs were induced at high temperature even in the presence of ABA.Item β-Lactoglobulin nanofibrils: Effect of temperature on fibril formation kinetics, fibril morphology and the rheological properties of fibril dispersions(Elsevier Ltd, 2012-05) Loveday SM; Wang XL; Rao MA; Anema SG; Singh HAlmost all published studies of heat-induced b-lactoglobulin self-assembly into amyloid-like fibrils at low pH and low ionic strength have involved heating at 80 C, and the effect of heating temperature on self-assembly has received little attention. Here we heated b-lactoglobulin at pH 2 and 75 C, 80 C, 90 C, 100 C, 110 C or 120 C and investigated the kinetics of self-assembly (using Thioflavin T fluorescence), the morphology of fibrils, and the rheological properties of fibril dispersions. Self-assembly occurred at all temperatures tested. Thioflavin T fluorescence increased sigmoidally at all temperatures, however it decreased sharply with >3.3 h heating at 110 C and with >5 h heating at 120 C. The sharp decreases were attributed partly to local gelation, but destruction of fibrils may have occurred at 120 C. Thioflavin T fluorescence results indicated that maximal rates of fibril formation increased with increasing temperature, especially above 100 C, but fibril yield (maximum Thioflavin T fluorescence) was not affected by temperature. At 100 C and 110 C, fibrils were slightly shorter than at 80 C, but otherwise they looked very similar. Fibrils made by heating at 120 C for 1 h were also similar, but heating at 120 C for 8 h gave predominantly short fibrils, apparently the products of larger fibrils fragmenting. Heating at 100 C gave consistently higher viscosity than at 80 C, and heating for >2 h at 120 C decreased viscosity, which may have been linked with fibril fragmentation seen in micrographs.Item Prediction of the thermal conductivity of porous foods : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Engineering, Massey University, Palmerston North, New Zealand, 2002(Massey University, 2002) Carson, James KA review of the food engineering literature exposed a paucity of information in the area of effective thermal conductivity prediction for porous foods. No useful guidelines were found that could advise a food engineer on the selection of appropriate effective thermal conductivity models for this application. The aims of this study were to increase the understanding in this area and to produce a general procedure for effective thermal conductivity prediction. The specific focus of this study was the influence of porosity on thermal conduction and so the porous foods under consideration were assumed to contain small (<5mm), uniformly distributed void spaces filled with stagnant gas (either air or carbon dioxide), in order that convection and radiation effects could be neglected. It was also assumed that only bound water was present within foods so that moisture migration and its associated heat effects would not be an issue. Two basic classes of porous foods were identified: foods in which void spaces existed in the interstices of particulate foods were referred to as having "external porosity" and foods in which bubbles existed within a solid or liquid matrix were referred to as having "internal porosity". Using a comparative method, thermal conductivity measurements were performed on food analogues comprised of expanded polystyrene (EPS) beads suspended in guar gel. Thermal conductivity data were produced that revealed a basic dependence of the relative effective thermal conductivity (ke/kl) on the porosity (v2) The mean volume of the individual EPS beads used to simulate the air bubbles was varied between 10-6 and 4x10-3 of the total sample volume, but no significant dependence of ke/kl on bead diameter was observed. Thermal conductivity measurements were also performed on samples containing squat aluminium cylinders suspended in guar gel. The results from these samples highlighted the significant influence of the component thermal conductivity on the uncertainties involved in effective thermal conductivity prediction. Using a finite element software package, two-dimensional numerical models were constructed to simulate the measurement of effective thermal conductivity for theoretical material samples having different basic structures. These models allowed the relative significance of several structure-related variables to be examined. The results indicated that the status of the gaseous and solid/liquid components of porous foods, whether continuous or dispersed, and the degree to which pores (in the case of internal porosity) or particles (in the case of external porosity) were in contact with neighbouring pores or particles had a significant influence on the effective thermal conductivity. The sizes and shapes of the individual pores or particles were found to have only minor or negligible influence. The predictions from two basic types of models were compared to the results from the physical experiments: those models that were functions of component thermal conductivity and volume fractions only (referred to as Type A models), and those that were functions of these two variables as well a third variable (referred to as Type B models). None of the Type A models provided accurate predictions for all the experimental data considered and it was concluded that, apart from certain scenarios, the use of Type B models was preferable. Of the Type B models considered, those that were based on isotropic physical models such as the Maxwell and Effective Medium Theory (EMT) based models, provided better predictions on average than those based on anisotropic physical models, such as the Krischer and Chaudhary-Bhandari models. The analysis of the experiments and the results of the model evaluation exercise highlighted an important issue regarding the selection of appropriate effective thermal conductivity models: the effective thermal conductivity of the materials had a strong dependence on the optimum heat conduction pathway for a given structure. Hence an assessment of a material's structure should be performed in order to determine the optimum heat conduction pathway within that material. Two basic optimal heat conduction pathways were identified. In the first scenario the continuous phase of the material has a higher thermal conductivity than the dispersed phase, as is the case with materials having internal porosity, and the optimum heat conduction pathway avoids the gas bubbles that comprise the dispersed phase. In the second scenario, the continuous phase has a lower thermal conductivity than the dispersed phase, as is the case with materials having external porosity, and the optimum heat conduction pathway passes through as many of the solid particles that comprise the dispersed phase as possible. Previous workers have shown that the two forms of the Maxwell-Eucken model provided theoretical upper and lower limits of the effective thermal conductivity of isotropic materials. In this work, it was proposed that the effective thermal conductivities of materials having internal porosity are bounded by the Landauer-EMT model and the form of the Maxwell-Eucken model in which the continuous phase has a higher thermal conductivity than the dispersed phase. Similarly, it was proposed that the effective thermal conductivities of materials having external porosity are bounded by the Landauer-EMT model and the form of the Maxwell-Eucken model in which the continuous phase has a lower thermal conductivity than the dispersed phase. The degree of contact between the pores or particles of the dispersed phase, which was related to the optimum conduction pathway, was identified as the variable having the most significant influence on a material's thermal conductivity, in terms of its position relative to thermal conductivity bounds. For this reason, effective thermal conductivity models for general applications should incorporate some measure of this variable. For isotropic, non-frozen foods, two new models based on the Maxwell and EMT structural models with structure-related parameters were proposed. An advantage of these models was that the values of the structure-related parameters had linear variation between the thermal conductivity bounds, unlike other models in the literature. A simple, general procedure for predicting the effective thermal conductivity of isotropic non-frozen foods was proposed and tested on two types of cake. The predictions from the models recommended by the procedure for the cakes agreed with the experimental data to within ±10%, which would be sufficient for many food industry purposes. It was recommended that further testing of the proposed thermal conductivity prediction procedure be performed to assess its accuracy and practicality. A need to improve the understanding of the relationship between the structure-related model parameter and the extent of contact between pores or particles was also identified.