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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Preparation, characterisation and functionality of kafirin microparticles

Taylor, Janet 18 November 2008 (has links)
Whilst working on a Masters degree on alternative solvents and extractants for the sorghum prolamin protein, kafirin, the author serendipitously found an ethanol-free method of making kafirin microparticles in dilute organic acid. Further, on drying a suspension of kafirin microparticles in dilute organic acid, a clear, transparent film was found to be formed. Microparticles from zein, the maize prolamin protein, have shown potential for food and pharmaceutical applications. Kafirin is more hydrophobic and less digestible than zein so it was hypothesised that it may form microparticles with superior properties. However, the structural and functional characteristics of kafirin microparticles and films made from them needed to be known before any potential applications could be exploited. Kafirin microparticles were made by dissolution of kafirin in glacial acetic acid followed by precipitation on addition of water. They were characterized by Light microscopy (LM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) and were found to be mainly spherical, porous and between 1-10 ìm in diameter. The kafirin microparticles had very large internal surface area due to the presence of many smooth walled holes or vacuoles of variable sizes, probably caused by entrapment of air during microparticle formation. Increasing the final acetic acid concentration resulted in kafirin microparticles of increased size, with an increasing number of internal holes. At 40% acetic acid the spherical microparticle structures completely disappeared and were replaced by an open matrix which resembled an expanded foam. The kafirin microparticles were found to form very thin (<15 ìm) free standing films and coatings. A minimum concentration of organic acid (10.8 percent) is required to form a cohesive kafirin microparticle film relative to the concentration of protein (1 percent for acetic acid). Some functional properties, e.g. smooth film surface properties, low water vapour permeability (WVP) and low protein digestibility of these films are superior to those of similar conventionally cast kafirin films. With the aim of exploiting the porous nature of kafirin microparticles for encapsulation of nutrient additives, several factors were examined for their influence on retarding protein digestibility. Retardation of digestibility of kafirin microparticles would allow controlled release of the encapsulated agent in the stomach and gastrointestinal tract. The importance of disulphide cross-linking and sorghum condensed tannin protein interactions were confirmed as major causal factors of the poor protein digestibility of sorghum. Gamma-kafirin was found to bind the most condensed tannins compared to the a-and b- kafirins, probably due to its high proline content. As expected, the protein digestibility of kafirin-tannin complexes was much lower than unbound kafirins. This seems to slow the biodegradation of kafirin films made with bound tannins. The antioxidants, catechin and sorghum condensed tannins were encapsulated within kafirin microparticles and the antioxidant release profiles investigated under simulated gastric conditions. Over a period of four hours, catechin and condensed tannin encapsulated kafirin microparticles showed virtually no protein digestion but released approximately 70% and 50% respectively total antioxidant activity. The mechanism for the formation of kafirin microparticles and films formed from them seems to involve controlled aggregation of kafirin molecules. Models for the formation of both were proposed based on an analogy with protein body formation and the potential ability of -kafirin to undergo a structural inversion exposing either hydrophilic or hydrophobic ends depending on the prevailing conditions. Research into cross-linking by physical or chemical agents is needed before practical applications can be exploited. However, encapsulation of catechin and sorghum condensed tannins within kafirin microparticles seems to be an effective way to use the binding properties of polyphenols with protein to enhance potential health benefits by controlled release of antioxidant activity within the stomach and gastrointestinal tract. Copyright / Thesis (PhD)--University of Pretoria, 2009. / Food Science / unrestricted
2

Improvement in the size and antioxidant activity of kafirin microparticles by treatment with sorghum polyphenols

Muronzwa, Juliet January 2013 (has links)
Microparticles (KEMs) made from the sorghum prolamin protein, kafirin, have internal vacuoles. Hence, they have potential as delivery vehicles for nutraceuticals. However, their physico-chemical properties need to be improved for this application. The influence of kafirin extracted from white tan-plant and red non-tannin sorghum types of 81% and 84% protein content respectively and the rate of water addition on the formation of KEMs from kafirin in acetic acid solution by coacervation on their morphology was investigated. A water flow rate of 1.4 and 0.7 ml/min during coacervation using 81% kafirin resulted in spherical-shaped KEMs between 1 and 10 μm in diameter and vacuoles up to 2 μm. KEMs made with 84% kafirin at a flow rate of 0.7 ml/min were large and oval-shaped with an average length and width of 43 and 21 μm respectively and numerous vacuoles up to 3 μm. At a flow rate of 1.4 ml/min, the KEMs were oval-shaped with larger vacuole sizes (5 μm), a length and width of 91 and 30 μm respectively. However, SDS-PAGE indicated that neither the source of kafirin, nor the conditions of microparticle preparation had an effect on KEMs protein molecular size.As the presence of phenolic compounds in the kafirins might have been responsible for the differences in KEMs morphology, the effect of sorghum-derived polyphenols (extracted from condensed-tannin and non-tannin black sorghum brans) on the physico-chemical properties of KEMs was then investigated using 81% kafirin. Aqueous condensed tannin (10.1 mg CE (catechin equivalent)/100 mg extract) and black non-tannin (4.6 mg CE/100 mg extract) extracts in varying concentrations, were substituted for the water used for coacervation. KEMs made with condensed tannin extracts were oval-shaped and much larger, than control KEMs ranging from 20 to 400 μm, with rough surfaces and enlarged vacuoles. The enlarged vacuoles were probably due to more air being trapped within the particles during formation. However, KEMs made from non-tannin phenolic extracts were smaller and spherical with average diameters up to 18 μm. Tannins are known to bind strongly to kafirin through hydrogen and hydrophobic bonds, which probably resulted in the larger microparticles. The KEMs made from condensed tannins also had high antioxidant capacities compared to KEMs made from non-tannin phenolic extracts, attributed to tannins being more potent antioxidants. Thus, condensed tannin extracts are the most beneficial as they contributed towards the antioxidant activity of the KEMs, resulting in the development of innovative KEMs with added antioxidant benefits and enlarged size. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Food Science / unrestricted

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