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    Effects of postharvest treatments on sweetpotato (Ipomoea batatas) storage quality : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, New Zealand
    (Massey University, 2015) Pankomera, Pilirani
    After harvest, sweetpotato (Ipomoea batatas) storage root quality is reduced due to weight loss, sprouting and rots. There are also hidden quality losses relating to loss of nutritional compounds. In order to maintain sweetpotato quality during storage, sweetpotatoes need to be stored at 13 - 15 °C and 80 - 90% RH. However, controlled temperature methods are difficult to achieve for subsistence farmers in less developed countries who have limited access to electric power. This work was undertaken to determine the potential postharvest techniques that would extend sweetpotato storage life without compromising phytochemical concentration. Postharvest treatments investigated in this work were hot water dipping (with or without coating) and ethylene (with or without 1-MCP) treatments. The work was undertaken using mainly ‘Owairaka Red’ and ‘Clone 1820’ sweetpotato cultivars. Following treatments, these sweetpotatoes were stored at 25 °C and 80 - 90% RH for 4 to 12 weeks. Hot water dipping (HWD) at 51 °C for 11 min delayed sprout growth by 2 weeks but increased weight loss. Coating (carnauba wax 5%) significantly reduced weight loss, but increased sprout growth in ‘Owairaka Red’. A combination of HWD and coating was effective in reducing both sprout growth and weight loss. ß-carotene content measured in ‘Clone 1820’ ranged from 17.3 to 25.6 mg/100 g dry weight. The concentration was not affected by HWD or coating, but declined by about 30% during 12 weeks storage. The calculated retinol activity equivalent (RAE) ranged from 363 to 537 RAE, per 100 g of edible portion of sweetpotato. Based on the recommended daily intake for vitamin A, a serve of 100 g would supply more than 25% of daily retinol requirement for all age groups, suggesting that even after storage ‘Clone 1820’ is a good source of vitamin A. In addition, no treatment adversely affected the phenolic acid and anthocyanin concentrations. Roots that were HWD showed a subtle increase in total phenolic content, phenolic acids and anthocyanin concentration when compared to control roots, but the effect was shortlived. Previous studies have demonstrated that ethylene is a potential sprout inhibitor, but causes darkening of flesh colour and the development of off-flavours after cooking. Ethylene-induced responses may be inhibited by 1-methylcyclopropene (1-MCP). 1- MCP and ethylene combined effects on sweetpotato physiological, flesh colour and phytochemical variables were assessed during storage. Ethylene treatment with or without 1-MCP inhibited sprout growth, increased root respiration rates by 2-fold, and caused root stem-end split leading to high weight loss and rots. Ethylene treatments also caused flesh darkening, and this was not prevented by a single 1- MCP (1 µL L-1) pre-storage treatment. When roots stored in continuous ethylene were subjected to multiple 1-MCP (1 µL L-1) treatments, the ethylene-induced root splitting and flesh darkening were delayed/reduced whilst maintaining minimal sprout growth. This implies that ethylene-induced negative responses in sweetpotato can be mitigated with on-going 1-MCP treatment. The sensory results showed that roots stored in air were highly preferred by consumers over roots stored in ethylene; nevertheless, acceptance means scores of all treatments were above five, indicating that ethylene-induced flesh darkening was not severe enough to cause consumer rejection. Based on these findings, it is proposed that a combination of HWD and coatings can be used to extend non-refrigerated storage life of sweetpotato with no major effect on phytochemical content. The results on ethylene are consistent with previous findings that ethylene suppresses sprout elongation. However, the associated negative effects outweigh the benefits of using ethylene as a sprout control. Future research therefore should focus on finding ways to get the benefit of ethylene for sprout reduction without incurring risk of root splitting.
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    Traditional knowledge systems and crops : case studies on the introduction of kūmara (Ipomoea batatas) and taewa Māori (Solanum tuberosum) to Aotearoa/New Zealand : a thesis presented in partial fulfilment of the requirement for the degree of Master of AgriScience in Horticultural Science at Massey University, Manawatū, New Zealand
    (Massey University, 2015) Estrada de la Cerda, Rodrigo
    Kūmara (Ipomoea batatas) and taewa Māori, or Māori potato (Solanum tuberosum), are arguably the most important Māori traditional crops. Over many centuries, Māori have developed a very intimate relationship to kūmara, and later with taewa, in order to ensure the survival of their people. There are extensive examples of traditional knowledge aligned to kūmara and taewa that strengthen the relationship to the people and acknowledge that relationship as central to the human and crop dispersal from different locations, eventually to Aotearoa / New Zealand. This project looked at the diverse knowledge systems that exist relative to the relationship of Māori to these two food crops; kūmara and taewa. A mixed methodology was applied and information gained from diverse sources including scientific publications, literature in Spanish and English, and Andean, Pacific and Māori traditional knowledge. The evidence on the introduction of kūmara to Aotearoa/New Zealand by Māori is indisputable. Mātauranga Māori confirms the association of kūmara as important cargo for the tribes involved, even detailing the purpose for some of the voyages. Less conclusive is the earlier introduction of kūmara to the Pacific from South America. In the case of taewa, both traditional Māori knowledge and early literature confirm the potato as an introduction during the first decade of recorded European contact. The aim of this thesis was to look to various knowledge sources and determine what can contribute to a discussion around the early introduction of key food crops to Aotearoa / New Zealand and also to understand the most important factors affecting each crop’s mode of introduction, assisted or not. Various key factors which clearly define the Māori relationship to these foods have been identified. These include: the conduit the crops provided in determining and continuing a relationship between cultures across the South Pacific and including the South American continent and cultures; the contribution of scientific knowledge from western science including oceanography, ethnography, ethnobotany and horticulture generally; the perceived importance of these crops as witnessed at the time of European contact, by both the Spanish and Portuguese in the wider Pacific region, and subsequently the British, French, and other peoples including their missionary cohorts in Aotearoa / New Zealand, and; the extended value of these crops to the endurance of Māori culture (physically, socially and spiritually). Both crops retain an importance to Māori society which is beyond doubt.
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    Optimal processing of kumara : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Bioprocess Engineering, Massey University, Palmerston North, New Zealand
    (Massey University, 2004) Canumir-Veas, Juan Antonio
    The colour and texture change of kumara (Ipomoea batatas L.) during the cooking process has been studied. A model was developed as a tool to understand how of these characteristics could be optimised in terms of cooking temperature and time. After cooking, kumara undergoes an intensive darkening discolouration due to a reaction between iron and phenolic compounds. The discoloration mechanism was separated into three consecutive steps. Cell modification occurs during cooking allowing iron and/or phenolic compounds (principally chlorogenic acid) to leave the cell. Once free, both elements combine to form a colourless iron-phenolic complex. In the presence of oxygen this complex oxidises to form a blue-black Fe3+ complex that is responsible for the dark colour. This mechanism was confirmed experimentally on roots of Owairaka Red and Toka Toka Gold kumara by measuring the colour parameters (a, b, L) over a range of cooking and storage conditions using a Minolta colorimeter. Kinetics parameters for cellular modification during cooking and colour formation upon exposure to oxygen were determined. The results showed that the cell modification reaction followed first order kinetics with an activation energy and Arrhenius constant of 101kJmol-1 and 4.56mim-1 respectively. Upon exposure of cooked kumara to oxygen, colour formation occurs at a rate dependent on diffusion of oxygen into the kumara flesh. By chelation of iron through the use additives such as sodium pyrophosphate (SAPP) it is possible to prevent post cooking darkening in kumara. Textural change was also studied and the mechanism was found to be a result of two main reactions, starch gelatinisation and cell wall disruption. Experiments were carried out to confirm this textural mechanism. Experiments were carried out to measure the kinetics of textural change (fracture force) using Owairaka Red and Toka Toka Gold kumara. The results showed that texture kinetics were temperature dependent and followed first order kinetics and the Arrhenius Law with activation energies of 162 and 125kJ/mol, and Arrhenius constants of 5.59E22 and 2.54E17min-1 for red and gold kumara respectively. Attempts to measure cell wall disruption kinetics from changes in alcohol insoluble solids and total reducing sugars were not successful but literature data for pectin losses in potatoes showed close agreement with overall texture loss in kumara, suggesting that breakdown of the middle lamella is the primary cause of softening during cooking. Using the kinetics data a model was formulated to predict temperature, texture and colour profiles through the product during cooking. Good comparisons were found between experimental data predictions from the model, for large kumara samples providing a partial validation of the model. The model was used to demonstrate the sensitivity of kumara quality and consistency to processing conditions. The use of the model was demonstrated with two industrially focussed case studies.
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    Storage root production in sweetpotato (Ipomoea batatas (L.) Lam.) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, New Zealand
    (Massey University, 2004) Lewthwaite, Stephen L.
    Sweetpotato (Ipomoea batatas (L.) Lam.) is a root crop well established throughout the world's tropical and sub-tropical regions. Despite sweepotato's importance, it has been under-researched relative to many other major crops. The main objective of this thesis is to contribute to a fuller understanding of the genetic and physiological factors underlying the production of sweetpotato storage roots for human consumption. The sweetpotato genome is diverse and subject to high levels of natural somatic mutation. Applying the AFLP (amplified fragment length polymorphism) technique allowed a direct comparison of inter and intra-cultivar DNA (deoxyribonucleic acid) base sequence variation. Analysis of the variation indicated that although sweetpotatoes are clonally propagated, clones show a lack of genetic fidelity to their source. Further, the level of genetic variation within the cultivar 'Owairaka Red' indicated the continuing emergence of distinct new strains. Plant field establishment represents the interaction of both propagation and growth phases of storage root production. A range of establishment techniques were investigated in a field trial under commercial conditions. Sprouts cut from seed roots and held for six days rather than immediate planting improved establishment as measured by growth, at little expense. Plug raised plants also improved establishment, while potentially reducing the degree of intra-cultivar genetic variation. Plant carbohydrate partitioning in three cultivars, 'Beauregard', 'Beniazuma' and 'Owairaka Red' was examined by field trial over the period of storage root growth. While cultivars differed in the proportions of dry matter partitioned to leaf, stem and root organs, the cultivar specific ratios of leaf to stem dry weight were relatively stable over time. Total storage root dry weight increased with time for all cultivars, but the distribution of storage root grades by size was cultivar specific. Within the storage roots % dry weight increased over time in all cultivars, but total sugar concentration only increased for 'Beauregard' and 'Beniazuma'. Finally, a storage root disorder called 'brown centre' curtails the temperate growing season so was investigated using low temperature storage and a field trial with various nutrition regimes. The disorder was found to be associated with susceptible germplasm, high soil nitrogen and harvest time.