Doctor of Philosophy / Department of Grain Science and Industry / Yong-Cheng Shi / Starch is the most important source of food energy. However, the information about the metabolic quality of starchy foods is scarce. It is well known that native starches with a B-type X-ray diffraction pattern are more resistant to alpha-amylase digestion than those starches with an A-type X-ray pattern, but the underlying mechanism is not well understood. It is not clear whether the enzyme resistance of B-type starch is due to its B-type crystalline structure or the other structural features in starch granules. The objective of this study was to compare the structure and enzyme digestibility of highly pure A- and B-type starch crystals, and understand the roles of crystalline types in starch digestibility. Highly pure A- and B-type starch crystals were prepared from short linear α-glucans (short-chain amylose) generated from completely debranched waxy starches by manipulating the processing conditions such as starch solids concentration, crystallization temperature and chain length. High concentration, high temperature and short chain length favored the formation of the A-type structure, whereas reverse conditions resulted in the B-type polymorph. Digestion results using a mixture of α-amylase and glucoamylase showed that A-type crystals were more resistant to enzyme digestion than B-type crystals. The A-type crystalline product obtained upon debranching 25% waxy maize starch at 50ºC for 24 h gave 16.6% digestion after 3 h, whereas B-type crystals produced by debranching 5% waxy maize starch at 50ºC for 24 h followed by holding at 25ºC for another 24 h had 38.9% digested after 3 h. The A-type crystals had a higher melting temperature than the B-type crystals as determined by differential scanning calorimetry. Annealing increased the peak melting temperature of the B-type crystals, making it similar to that of the A-type crystals, but did not improve the enzyme resistance. The possible reason for these results was due to more condense packing pattern of double helices in A-type crystallites. It seems that the crystalline types are not the key factor that controls the digestibility of native starch granules. The resistance of native starches with B-type X-ray diffraction pattern is probably attributed to the other structural features in starch granules.

In modern forestry, two types of machines are generally used for thinning, harvesters and forwarders. These machines are large and weigh several tens of tons, this means that they damage the ground when they drive around in the woods. AirForestry is a startup company that focuses on manufacturing lightweight and electric forest machines that will do much less damage due to the lower weight. As their ambition is to develop an all-electric harvester, high efficiency in the work process is required to be competitive. The purpose of this thesis was to find which factors affect the debranching process and to find what approximate effect the harvester head's drive motors would need to have to achieve a stable debranching process. If the results of the research were successful, a new knife design would be developed for thinning. The work carried out began with a planning report which included introduction, literature study and method was written. The method chosen was to first develop a test rig to be able to measure what amount of work and what maximum impact force a single branch would need to be cut. Afterwards a study of branches and their distribution on trees in the thinning phase were conducted. The branch distribution and the data from the test rig, would make it possible to estimate the energy required to cut down a tree. Impact forces along the tree provide an opportunity to not only estimate the life cycle of the knives but also an analysis of how the remaining units hold. The branching process was assumed to be affected by both the design of the knives and which branches are present and how these are placed. The literature study showed that frozen wood gives higher forces when sheared, so it was investigated as well. The test rig was designed as a guillotine to make it easy to manufacture and due to potential energy being the only source of energy to power the rig. The work of cutting a branch was measured with a high-speed camera and the maximum impact force was measured with an accelerometer. Different knife designs were tested together with different angles and branch types. All variables tested in the rig were performed on several different branch diameters. The study of branch distribution along the tree was done on trees that were considered to be in the thinning stage and all branches with a diameter greater than 5 mm were noted together with distance and whether it was dead or not. The test rig's test data were later used in a multiple linear regression to determine if a variable effect of not. The regression was then used to estimate the power required to debranch a pine to be 3.1 kW and 6.6 kW for a spruce. Only the diameter of the branches and the tree sort could be proven to have a statistically significant effect on both the work required and the maximum impact force. / I det moderna skogsbruket används i regel två maskintyper vid gallring, skördare och skotare. Dessa maskiner är stora och väger flera tiotals ton vilket gör att de skadar marken när de kör ute i skog och mark. AirForestry är ett startupbolag som riktar in sig på att tillverka lättviktiga och elektriska skogsmaskiner som ska göra mycket mindre skada på grund av deras lägre vikt. Då deras ambition är att utveckla en helelektrisk skördare, krävs en energieffektiv process för att kunna vara konkurrenskraftiga. Målet med detta arbete var att hitta vilka faktorer som påverkar avgreningsprocessen samt hitta vilken ungefärlig effekt skördaraggregatets drivmotorer skulle behöva ha för att uppnå en stabil avgrening. Om resultatet av forskningen var lyckat skulle en ny knivdesign tas fram anpassad för gallring. Arbetet som utfördes började med en planeringsrapport där introduktion, litteraturstudie och metod skrevs. Metoden som valdes var att först utveckla en testrigg för att kunna mäta vilket arbete och vilken maximal slagkraft en gren skulle behöva för att kapas. En studie av grenar och dess distribution på träd i gallringsfasen skulle tillsammans med data från testriggen göra att energin som krävs att ta ner ett träd kan uppskattas. Slagkrafter längs med trädet ger en möjlighet att inte bara uppskatta knivarnas livscykel utan även en analys på hur resterande aggregat håller. Avgreningsprocessen antogs påverkas av både knivarnas design och vilka grenar som finns samt hur dessa är placerade. Litteraturstudien visade på att fryst trä ger högre krafter vid skjuvning, därför undersöktes det med. Testriggen konstruerades som en giljotin för att göra den enkel att tillverka och för att endast potentiell energi används för att driva riggen. Arbetet för att kapa en kvist mättes med höghastighetskamera och maximal slagkraft mättes med en accelerometer. Olika knivdesigner testades tillsammans med olika infallsvinklar och grentyper. Alla variabler som testades i riggen utfördes på flera olika kvistdiametrar. Studien av grenars distribution längs med trädet gjordes på träd som ansågs vara i gallringsstadiet och alla grenar med diameter större än 5 mm noterades tillsammans med avstånd och om den var död eller ej. Testriggens testdata användes senare i en multipel linjär regression för att kunna bestämma vilka variabler som påverkar. Regressionen användes sedan till att uppskatta effekt som krävs till 3.1 kW för en tall och 6.6 kW för en gran. Endast grenarnas diameter och trädsort kunde med statistik säkerställas påverka både arbetet som krävs samt maximala slagkraften.

The main objectives of this study were to develop an effective process to produce modified pea starch with enhanced enzyme resistance property (RS) for food applications. The work compares a non-chemical method (heat moisture treatment) versus a chemical method (crosslinking). One type of commercial pea starch (Nutri-Pea) was used exclusively as the raw material in this study. A number of methods were used to characterize the properties of the modified pea starches: water solubility index (WSI), titration (conversion, iodine value), intrinsic viscosity, infrared spectroscopy (FT-IR), Englyst digestion method, total starch content, and rapid visco analysis (RVA). The effects of heat-moisture treatment on native pea starch and enzyme treated pea starch were examined. The results showed that the produced samples with both native starch and enzyme treated starch exhibited a sharp increase in intrinsic viscosity. Overall, this method was deemed undesirable and not extensively examined past preliminary evaluations. The main focus of the study was on a citric acid crosslinking reaction, chosen for its food compliancy. A temperature of 120 oC was considered ideal for the reaction. FT-IR confirmed the presence of the citric acid incorporation in the starch samples. To improve the extent of reaction, Butanetetracarboxylic acid (BTCA) was considered as a replacement for citric acid and its treated samples showed higher conversion and lower water solubility index than that of the citric acid treated samples. Sodium propionate (NaP) was also considered in the reaction, this time as a food-grade catalyst and found to have minor benefit in cross-linking. BTCA/NaP treated sample reached the highest conversion of the study (96.8±2.3 %) and the lowest WSI (13.1±2.0 %), which increased the RS fraction of the starch from 18% to 32%. The RVA pasting profiles examined were too low to compare due to the high degree of cross-linking. Further improvements to RS were sought by debranching the starch before acid crosslinking. A BTCA/NaP treated sample with enzyme treatment showed a low WSI (31.7±2.3 %) yet substantially higher RS fraction (80.81±0.18 %). Similar to the non-debranched acid modified samples, there were no significant RVA pasting results because of the high cross-linking. Finally, crosslinking with an epoxidized oil was tested to continue looking at food-grade solution yet possible increase the rate of the crosslinking reaction. The results of WSI indicated that this method had little influence on cross-linking, possibly due to the low epoxidation efficiency of vegetable oils, as determined by iodine value. / Thesis / Master of Applied Science (MASc)

There is currently a global increase in Eucalyptus pulpwood plantations. Harvesting systems traditionally utilised in the northern hemisphere are being used in Eucalyptus pulpwood plantations worldwide. However, the small tree size and complexity of debarking Eucalyptus have provided harvesting with productivity and cost challenges not previously experienced in northern-hemisphere conditions. Much research has been invested in these two harvesting methods in northern-hemisphere species and conditions. There is little research available on mechanised processing-machine productivity and costs in Eucalyptus. This investigation aimed to quantify the effect that tree and bundle size has on the productivity of different processing machines in Eucalyptus plantation pulpwood. This was done through regression analysis, whereby productivity models that included tree size and bundle size were constructed. The research also aimed to determine whether or not the multi-stem systems were more cost-effective in smaller tree sizes. The research investigated five mechanised harvesting options that forestry managers could use in Eucalyptus pulpwood plantations. These systems consisted of one CTL system, one full-tree system with single-stem processing and three full-tree systems with multi-stem processing. The CTL system used a harvester to process the trees into logs and to extract them. The full-tree system with single-stem processing used a dangle-head processor (DHP) to process trees into logs. The first full-tree system with multi-stem processing used a chain-flail debrancher debarker (CFDD) to produce debarked and debranched tree lengths, which were slashed into logs. The remaining full-tree, multi-stem systems both produced chips. The first used a chain-flail debrancher debarker chipper (CFDDC) and the second, a CFDD feeding into a stand-alone disc chipper (CFDD&C). The productivity data, measured as m3 per productive machine hour (PMH), was then statistically analysed using regression techniques. Productivity equations were formulated, considering tree size and bundle size, as well as the quadratic functions of these two variables and the interaction between them. Bundle size was only applicable to the multi-stem processing machines. The productivity equations successfully predicted processing-machine productivity, using tree size and bundle size as input variables. Apart from the 0.075 m3 tree size class, the CFDD had the highest overall productivity. The costs of the five systems were then calculated for different tree sizes. No single system was more cost-effective than the others across all tree sizes. In 0.075 m3 trees, the CFDDC system proved the most cost-effective. All systems evidenced high costs in the 0.075 m3 trees, ranging between $19.43 per m3 for the CFDDC system to $28.84 for the harvester system. In 0.40 m3 trees, the cost differences between systems were lower, ranging from $6.91 per m3 for the DHP system to $11.84 per m3 for the CFDD&C. This study confirms that the CTL system was very expensive to operate in the small tree sizes (0.075 m3). There is a cross-over point at 0.25 m3 per tree, where the CTL system costs become lower than those of the full-tree system. At the 0.40 m3 tree size, the full-tree system is slightly more expensive than the CTL system. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Plant Production and Soil Science / unrestricted