Gum arabic is a natural gummy exudate from acacia trees and exhibits natural built-in variations commonly associated with hydrocolloids. This study is concerned with the determination of factors which could influence its properties and functionality. These factors include origin (location, soil type, rainfall), different collections, age of the trees and storage condition. Previous studies acknowledged the influence of some of these factors but somehow lack providing definitive answers to questions being asked by the end user and required for the development of Gum arabic industry in Sudan. Local knowledge as well as the various stages of gum collection and processing were reviewed in order to provide a clear background and the justification for the experimental design. In this study samples were collected from six plantations located in the west and east regions in Sudan. Samples were collected from trees of different age (5, 10, 15 and 20 years old) and also from different picking interval (1-4). Each sample was divided into three portions (UK, Khartoum and Port Sudan) and stored for 5 years in order to determine the effect of the respective location. Various analytical parameters (% loss on drying, Optical rotation, % protein, intrinsic viscosity, molecular weight and molecular weight distribution) were measured to fully characterise the gum samples and to determine their functionality (emulsification). The results obtained for all samples were consistent with those previously reported in the literature (see Chapter 4). The only exception, identified in a number of samples from the western region, is the high proportion (~30%) of high molecular weight fraction termed arabinogalactan-protein complex (AGP). The results clearly demonstrated significant variations between plantations located in western region compared with the eastern region. However, the variations between the plantations within the same region are statistically not significant. High values of % protein, viscosity, Mw and % AGP were obtained from the 1st pick, from both regions, and then significantly decreased thereafter to the fourth pick. Samples from west region in Sudan, from 1st and 2nd pick and from tree age (15) years gave the highest viscosity, molecular weight, % AGP and superior emulsification performance compared to other samples from different tree ages. The regression statistical analysis for the physiochemical properties correlation with emulsification performance demonstrated the role of % AGP to be the most influential factor followed by viscosity. The major finding of this study is the effect of storage condition on the properties and functionality of Acacia senegal. An increase in the molecular weight for all stored samples (for 5 years) irrespective of region was evident and statically significant. However, this increase was more prominent for samples from the western region compared to the eastern region. The AGP fraction was increased by the storage treatment up to 40% in Port-Sudan, 20% in Khartoum-Sudan and 15% in UK. The result clearly demonstrated that the temperature and humidity are the crucial factors to induce the natural maturation process in acacia gums. Statistical analysis (linear regression) suggested statistically significant models and equations to predict and explain the variations in the physiochemical and functional properties based on the environmental factors, picking set and age of the tree.

O presente trabalho teve como objetivos estudar a distribuição diamétrica de acácia negra em povoamentos independentes, selecionar a equação que melhor descrevesse as distribuições e estudar as variações das distribuições em diferentes idades. Os dados provem da Fazenda Dona Bernarda, de propriedade da TANAC S.A. em Montenegro, Rio Grande do Sul (nas coordenadas geográficas de 30° de latitude sul e 52° de longitude oeste e clima do tipo Cfa , subtropical , segundo Köeppen). Foram estudados os diâmetros quanto a distribuição e estabilidade em relação a curva normal nas idades de 3,5 a 7,5 anos , através do pacote de computação MLESD - Maximun Likelihood Estimation for Selected Distributions. As distribuições testadas foram Normal, Log-normal, Gama, Weibull, SB e Beta. Estas foram ajustadas pelo método de Máxima Probabilidade e selecionadas pelo critério do Logarítmo da Probabilidade e Kolmogorov-Smirnov. A distribuição SB foi a selecionada para descrever os dados de diâmetros nas cinco idades estudadas. No entanto, a distribuição Beta nas idades de 3,5 , 5,5 , e 7,5 e a Weibull na idade de 3,5 anos, também podem ser utilizadas, porém, com ajustes um pouco inferiores que os proporcionados pela distribuição SB. As equações Normal, Log-normal e Gama não ofereceram bons ajustes em nenhuma das idades estudadas, sendo desaconselháveis as suas utilizações para descrever a distribuição de diâmetros de acácia negra.

No description available.

Thesis (M. Sc. (Agriculture)) -- University of Limpopo, 2004 / National Research Foundation (NRF)

The ecology of plant species at Sandford Rocks Nature Reserve (SRNR) was studied. The study site is an important nature reserve that contains relatively undisturbed natural vegetation. It has a mosaic of exposed granite rocks, scrublands and woodlands. The study involved: a description of the structure and composition of the vegetation; the population characteristics of selected Acacia species; aspects of reproduction in Acacia; germination and seedling characteristics of some Acacia and grass species that dominate the reserve; the effect of seed size on germination and seedling characteristics; and, the relationship of seed size to seed coat thickness in selected Acacia species. Five different areas were studied using the point centered quarter method to sample the woody perennial species. Thirteen Acacia species were examined for reproduction characteristics; and in 2 selected Acacia species, the effects of phyllode and/or inflorescence removal on reproduction was investigated. Germination tests were conducted to identify germination characteristics in 8 Acacia and 7 grass species dominant at SRNR. The possible effects of variation in seed size on germination; seedling characteristics; and, seed coat thickness were investigated in Acacia fauntleroyi and Acacia prainii. A total of 85 species from 20 families of woody perennials were collated. All areas were dominated by the Myrtaceae, Mimosaceae and Proteaceae families. There was considerable variability in the structure and composition of vegetation. Most species were present in particular sites and the composition of communities appears to be related to the heterogeneity of the habitat within the reserve. In areas of shallow or rocky soil, vegetation types present include Allocasuarina huegeliana woodland, Grevillea paradoxa low scrubland and Acacia neurophylla medium shrubland. / In a seasonally wet area, vegetation types present include low open grassland; Eucalyptus capillosa (wandoo) woodland; and, Acacia saligna thicket. In deep, dry sandy soil, vegetation types include Phebalium tuberculosum shrubland, Acacia acuminata and Acacia coolgardiensis thickets. On relatively flat areas that gain water from adjacent large granite hills, the vegetation consists mainly of tall, open woodlands of Eucalyptus species. Vegetation types include: medium tall Eucalyptus salmonophloia woodland with Kunzea pulchella shrubland at the periphery of the Eucalyptus woodland. At rock areas, vegetation types present include dense Leptospermum erubescens thicket, low open Acacia prainii and Dodonaea viscosa shrubland. Of the Acacia populations studied, in A. lasiocalyx no recent seedling establishment was observed. It is hypothesised that recruitment occurs in particular periods. As the plants are associated with rock and soils are generally shallow, it appears that recruitment depends on run-off water from the rocks in winter. Continuous recruitment seems to be the pattern in A. prainii with both seedlings and saplings represented. A. fauntleroyi forms relatively small populations; apparently long drought periods (>l00 d) result in mass death and limit its population size. In A. hemiteles, no seedling stage was found, root competition (for water) from associated Eucalyptus species presumably limits its recruitment. Reproductive success of Acacia is affected by rainfall. A wet winter is required to induce flowering and further rain is required after flowering to promote pod development and good seed set. / All Acacia species suffer from drought in the reproduction season, however they differ in their degree of susceptibility. Leaflessness and tree shape also affect Acacia fecundity. Plants bearing more phyllodes produce more flowers and pods, and branches in the upper part of the crown bear heavier inflorescences. In 1998, all Acacia species at SRNR produced mature seed of low weight, with many immature and diseased seed, which gave poor germination. A late spring frost in 1998 is believed to be responsible for limited seed development. In two selected Acacia species, removal of phyllodes reduced the number of pods produced. Presumably, phyllode removal reduces photosynthate produced, therefore the competition among inflorescences (or pods) for resources is more intense and subsequent abortions are likely to occur. All Acacia species studied showed best germination in the cool winter temperature range. Apparently, seeds are adapted to germinate in winter when seasonal moisture is more likely to be available. The best temperature however, varied slightly between species. The grass species dominant in the reserve, except for Aristida contorta, also had more germination in cooler rather than warmer temperatures. The flora of SRNR is similar to typical vegetation of the Southwest. Generally, Acacia species are present only in particular sites, presumably were habitat moisture allows. Seedlings of Acacia species growing in naturally dry areas have greater root: shoot masses than those growing in seasonally wet areas. Biomass partitioning is an apparent strategy to conserve water. Of the 7 grass species, Amphipogon strictus appears to have fastest growth. / Eriachne ovata has greater root than shoot mass, while in all other species, shoot mass is greater than root mass; a characteristic of species that grow well in moist habitats. The longest shoots and roots are in Austrostipa elegantissima, an understorey species of eucalypt woodland. In A. fauntleroyi, the degree of hard-seededness varies between seed sizes. There is a higher proportion of soft seed in smaller seed. Seed of different sizes show some responses to different pre-treatments and incubation temperatures for germination. Larger seeds generally germinate in greater numbers after higher treatment temperatures. The best treatment for small seeds is pre-treatment at 75°C and incubated at 15°C. For medium and large seed, best pre-treatment is at 75°C with incubation at 30°C or soaking in boiling water and incubation at either 15 or 3°C. In A. prainii, seed size; pre-treatment; incubation; and, their interaction all affected germination; larger seeds are more viable. The best treatment to promote germination of A. prainii is soaking in boiling water and incubation at 25°C. In both A. fauntleroyi and A. prainii, larger seeds produce larger seedlings. Seedlings from large seeds have the potential for more rapid pre-photosynthetic growth. Larger, heavier seed has a thicker seed coat. The seed coat of A. prainii is thicker than in A. fauntleroyi; the difference in seed coat thickness is reflected by more soft seed in A. fauntleroyi (35%) than in A. prainii (6%).

As part of an investigation into traditional Australian Aboriginal bush medicine a range of Acacia species have been examined. Several species have been reported to be utilised for the preparation of antimicrobial washes and lotions by Aboriginal tribes. Initial bioactivity screening focussed on antimicrobial activity of the polar/and or non-polar extracts of air dried plant material, and a range of interesting activity has been found. Specifically, of the 94 extracts of Acacia species screened, five showed activity against the fungus C.albicans, 47 showed activity showed activity against the gram positive bacteria S.aureus and five showed activity against the gram negative bacteria E.coli. A retrosynthetic analysis and total synthesis of the novel anisidine alkaloid isolated from Acacia trineura was attempted. A variety of methodologies to generate the lithiate of anisidine and subsequently trap with an appropriate electrophile were attempted. While the results only indicated which methods were appropriate, they did give strong leads for future work in this direction / Doctor of Philosophy (PhD)

A series of laboratory oxygen delignification were performed in this study at constant oxygen pressure and consistency to study the response of the pulp to the different process parameters, i.e. reaction temperature, reaction time, soda addition, and mechanical pretreatment, to the zero span tensile strength loss. The basic chemistry of the oxygen delignified pulps was under study including fiber charge, celluloses/hemicelluloses, and hexenuronic acid. The fiber structure such as curl, kink, fines, and fiber length were also discussed. NaOH charge can be reduced as much as 50 % by applying mechanical pretreatment to obtain the same level of selectivity at the oxygen delignification conditions described in this study.Mechanical pretreatment prior to oxygen delignification promoted a better selectivity for both Acacia mangium and MHW pulps. MHW kraft pulp did not show a significant extractive removal in all pretreatment methods during oxygen delignification. The ultrasonic pretreatment followed by filtering induced the best extractive removal among the other three methods.

Thesis (M. Ag. Sc.)--University of Adelaide, Dept. of Horticulture, Viticulture and Oenology, 1997. / Copies of author's previously published material inserted. Includes bibliographical references (leaves 212-227).

Acacia ants evolved obligate protective mutualisms with acacia trees, which they defend against herbivores, food parasites and encroaching vegetation. In this mutualism, the fitness of one partner entirely depends on the other. Other ant species are parasitic on acacia trees; they nest on the tree, harvest food rewards, do not defend their own tree, and occasionally try to steal food from other trees, usually inhabited by mutualistic ants. To understand the behavioral and anatomical effects of the interaction between ants and host trees, I integrated brain anatomy, morphology and field experiments to study parasitic and mutualistic species of Pseudomyrmex ants associated with acacia trees. In Chapter 1, I describe a previously unknown behavior of stealing food from other ant-defended acacia trees in the parasitic acacia ant P. nigropilosus, and I evaluate four strategies that may allow parasitic ants to overcome the usually effective defenses of the robbed mutualistic ants protecting a host tree. In Chapter 2, I study how colony size correlates with the degree of division of labor and brain anatomy of workers, focusing on a species of acacia ant lacking morphological castes among workers, P. spinicola. In Chapter 3, I study acacia-ant behavior of killing vegetation encroaching on a host tree. I document the interspecific differences among acacia ants in the size of the area around the host tree that workers clear from encroaching vegetation. I further test for interspecific variation in pruning behavior, and whether mandibular force correlate with worker pruning decisions. In Chapter 4, I test whether ant species that routinely leave the host tree to forage or to prune encroaching vegetation are better at orienting themselves when returning to their host tree, compared to ant species that rarely leave their host tree. This dissertation documents how the obligate protective mutualism of an ant with a tree has consequences for division of labor, navigational skills, behavioral specializations, head shape and brain anatomy of ant workers. / text

Three pen trials were conducted to evaluate the value of A. saligna as a source of feed for ruminants. In Trial 1 A. saligna was inadequate as the sole source of nutrients for sheep. Furthermore, the level of detannification achieved in Trial 1, with the addition of PEG 4000 or PEG 6000, failed to improve the diet sufficiently. The antinutritional effects on the animals were largely attributed to the excessive biological activity of the phenolics in the A. saligna leaves. Feeding of these leaves, without PEG, had a definite defaunating effect on the ruminal fluid. The ruminal ammonia levels were all well below the threshold for maximal microbial growth. Given the results of Trial 1, the second trial was undertaken to determine if A. saligna was more useful as a supplement rather than a basal diet. The benefits of including A. saligna as a supplement to a basal diet of lupins and wheat straw were not clear. The benefits of including a detannification agent with the A. saligna were also not evident. Ruminal ammonia levels were much higher than in Trial 1 and animals generally maintained weight. Trial 2 revealed that the sheep were capable of consuming significantly more A. saligna than they did in Trial 1, but it was not clear whether this was due to the basal diet providing adequate nutrients or if it was due to differences in the A. saligna fed in the respective trials. Total phenolics, CT and PPC were considerably lower than those of Trial 1. Trial 3 was designed to investigate the use of A. saligna as the basal source of nutrients, with or without a supplement of N in the form of urea or PEG. Total phenolics, CT and PPC were lower than those of Trial 1, but higher than those of Trial 2. Animals consumed more A. saligna than in Trial 2 and generally maintained weight. / The results from Trial 3 suggest that A. saligna could be a useful feed source for ruminants. The substitution of straw with A. saligna indicates that its incorporation into a grazing system could significantly decrease grazing pressure on dry summer pastures. In Trial 3 goats were not shown to have a superior ability than sheep in utilising A. saligna as a source of nutrients.