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    Sweetpotato-based complementary food for infants in Ghana : a thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy in Human Nutrition, Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand
    (Massey University, 2012) Amagloh, Francis Kweku
    Background: In an effort to reduce the prevalence of protein-energy malnutrition among Ghanaian infants after the period of exclusive breastfeeding when complementary food (CF) is introduced, Weanimix, which is a blend of non-dehulled maize, groundnut and non-dehulled soyabean/cowpea, was introduced in Ghana, in 1987 through collaboration between the Nutrition Division, Ministry of Health, Ghana and the United Nations Children’s Fund. Weanimix is an improvement over traditional maize-, millet-, or sorghum-only porridge in protein and energy densities, but it is high in phytate. Phytate limits the bioavailability of nutrients such as iron and zinc, and probably calcium and some proteins. Also, unless fortified, Weanimix is low in β-carotene (vitamin A precursor) as the white maize is the commonly consumed variety in Ghana. Additionally, cereal-based CF (example, Weanimix) forms a very thick porridge that requires dilution with water to get the desirable viscosity, leading to “energy and nutrient thinning” (that is, the reduction of energy and nutrient densities). Thus, the widely used unfortified cereal-based CF could be a major contributing factor to the persistently high occurrence of vitamin A, iron and zinc deficiencies among infants in sub-Sahara Africa. Purpose: The main focus of this study was to develop a CF using locally accessible ingredients in Ghana that will be low in phytate, contain measurable levels of β-carotene and forms a low viscous porridge, which could be produced at home or industrially. Method: A computer-assisted programme (Nutrition Calculator) obtained from Global Alliance for Improved Nutrition- Infant and Young Child Nutrition Programme was used to formulate composite flours containing sweetpotato, soyabean and fish powder from anchovies or skim milk powder to meet the protein, fat and energy specifications in the Codex standards (CAC/GL 8 and STAN 074-1981, Rev.1-2006) for CF. The household-level ComFa formulation with fish powder as an ingredient was toasted in an oven and denoted oven-toasted ComFa, while the industrial-level formulations (roller-dried ComFa and extrusion-cooked ComFa) had skim milk powder (a common ingredient in industrial-processed dry infant cereal) as a component and were produced using a roller drier or an extruder. The nutritional, functional and consumer acceptance analyses of sweetpotato-based CFs were carried out and compared with enriched Weanimix. In this research, Weanimix was slightly modified by using dehulled maize and soyabean flours, and further addition of 17% fish powder and 0.50% sugar to the basic formulation, and referred to as enriched Weanimix. Additionally, the stability of β-carotene in the oven-toasted ComFa was evaluated under simulated average temperature of 32°C and 85% relative humidity, mimicking the ambient conditions of Ghana. Results: The ComFa formulations and the enriched Weanimix met the stipulated energy and fat values specified in the Codex standards. However, the protein content of the industrial ComFa formulations was lower by 17%, but the oven-toasted ComFa and enriched Weanimix met the protein specification. The sweetpotato-based formulations had total dietary fibre that was about twice the Codex specification of less than 5.0%, but was likely to be partly soluble fibre and, thus beneficial. The phytate content in all the ComFa formulations was approximately a quarter of the level of 0.80 g/100 g in the enriched Weanimix. Only the sweetpotato-based infant foods contained measurable levels of β-carotene, resulting in significantly higher vitamin A content of the oven-toasted ComFa compared with enriched Weanimix (28.80 vs. 1.20 μg retinol equivalents/100 kcal). Most of the β-carotene in the oven-toasted ComFa was retained for up to eight weeks when stored in containers with a good moisture barrier under simulated ambient conditions of Ghana. Oven-toasted ComFa, roller-dried ComFa and enriched Weanimix, using an estimated daily ration of 40 g (dry weight), contained less than half of the World Health Organization recommended levels for calcium (400 mg/day), iron (9.3 mg/day) and zinc (4.1 mg/day) from CFs processed for 6 to 8 month-old breastfeeding infants, with the exception of the oven-toasted ComFa, which contained 60% of the recommended calcium level. The two selected ComFa formulations are likely to be less inhibitory regarding calcium, iron and zinc absorption by infants than the enriched Weanimix based on the phytate: calcium, iron and zinc molar ratios, and the level of β-carotene to predict relative availability of these essential minerals. All the CFs had phytate: calcium molar ratios lower than the maximum recommended ratio of 0.17, but their phytate: iron molar ratios exceeded the maximum recommended ratio of 1.0. However, the phytate: zinc molar ratio of the oven-toasted ComFa and roller-dried ComFa were approximately lower by 24% than the recommended ratio of 15. In contrast, the phytate: zinc ratio of enriched Weanimix was higher by 53% compared to the recommended ratio. Also, the ComFa formulations and enriched Weanimix, had levels of total polyphenols (84.70 and 76.96 mg/meal, respectively), which may inhibit iron absorption. On average, sweetpotato-based formulations were higher in maltose (26 times), sucrose (5 times), free glucose (19 times) and fructose (7 times) than levels in enriched Weanimix, but the ComFa formulations contained significantly less starch (10-13 vs. 47 g/100 g). The high simple sugar and low starch levels in the ComFa formulations could explain the lower apparent viscosity (9-, 13- and 20-times, for peak, “consume” and final viscosities), higher water solubility index (7 times), and higher consumer acceptance compared with the maize-based formulation. Conclusion: On the basis of the compositional, functional and sensory findings of this study, the sweetpotato-based formulations have significant advantages as complementary food compared with Weanimix due to the low level of phytate, the high levels of endogenous β-carotene and low viscosity. Importantly, the ingredients used to produce the household-level ComFa formulation could be easily accessed by caregivers in Ghana. However, there is a need to conduct field trial and consumer acceptance studies in Ghana before substantive recommendations on the use of the sweetpotato-based infant formulation could be made. Limitation: The conclusions made are based on compositional, functional and consumer acceptance studies but not on any in vivo experiment or randomised feeding trial among Ghanaian infants. However, because the comparisons were made between the ComFa formulations and Weanimix, the conclusions drawn in this thesis are relevant.
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    The lifecycle and epidemiology of the tomato/potato psyllid (Bactericera cockerelli) on three traditional Māori food sources : a thesis in partial fulfilment for the degree of Master of Science in Plant Protection at Massey University, Palmerston North, New Zealand
    (Massey University, 2011) Puketapu, Aleise
    The tomato/potato psyllid (Bactericera cockerelli (Sulc), TPP) is a species of Psylloidea first detected in New Zealand in 2006. Since its incursion the TPP has proved to be a major insect pest of solanaceous crops, particularly potatoes (Solanum tuberosum), tomatoes (Lycopersicon esculentum) and capsicums (Capsicum L.). The TPP is a vector of Zebra Chip Disease or liberibacter (Candidatus Liberibacter solanacearum syn. psyllaurous), a lethal plant disease related to Citrus greening disease (Candidatus Liberibacter asiaticus). Successive annual population outbreaks coupled with widespread liberibacter infection continues to challenge New Zealand‘s horticulture sector. Three traditional Maori food sources, namely taewa (Solanaceae, Solanum tuberosum L. ssp. andigena and ssp. tuberosum), kumara (Convolvulaceae, Ipomoea batatas (l.) Lam.) and poroporo (Solanaceae, Solanum aviculare G. Forst syn. S. Laciniatum (LINN.), are known to be susceptible to TPP infestation. Kumara and taewa are annual summer plants present during the peak TPP development and population growth period. Poroporo flowers and fruits year-round and is therefore theoretically susceptible to infestation throughout the year and may serve as a potential overwintering host and food source for TPP. Poroporo was assessed as an overwintering host of the TPP and the lifecycle progression of TPP was also compared on the three host plant species; taewa, kumara and poroporo. The role of these three host plants in the annual lifecycle of this insect pest in the New Zealand environment. The results showed that poroporo was not an important overwintering host of the TPP in the Manawatu/Rangitikei region; rather it can be viewed as an alternative or refuge host in the absence of the primary solanaceous host species and other volunteer weed host plants. The results indicated that taewa is a more suitable host of the TPP than poroporo and kumara. In the same vein, poroporo is clearly more suitable as a host than kumara. The relationship seen in this study in terms of host suitability can be pictorially represented as; Taewa> Poroporo> Kumara This study showed that all three host species are capable of supporting TPP and therefore each of the host species should be managed with a view to minimise the impact of TPP across seasons.
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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.