Technical and economic study of plantain food products

Plantain (Banana-Musa AAB) is a widely growing but commercially underexploited tropical fruit. This study demonstrates the processing of plantain to flour and extends its use and convenience as a constituent of bread, cake and biscuit. Plantain was peeled, dried and milled to produce flour. Proximate analysis was carried out on the flour to determine the food composition. Drying at temperatures below 70ºC produced light coloured plantain flour. Experiments were carried out to determine the mechanism of drying, the heat and mass transfer coefficients, effect of air velocity, temperature and cube size on the rate of drying of plantain cubes. The drying was diffusion controlled. Pilot scale drying of plantain cubes in a cabinet dryer showed no significant increase of drying rate above 70ºC. In the temperature range found most suitable for plantain drying (ie 60 to 70ºC) the total drying time was adequately predicted using a modified equation based on Fick's Law provided the cube temperature was taken to be about 5ºC below the actual drying air temperature. Studies of baking properties of plantain flour revealed that plantain flour can be substituted for strong wheat flour up to 15% for bread making and up to 50% for madeira cake. A shortcake biscuit was produced using 100% plantain flour and test-marketed. Detailed economic studies showed that the production of plantain fruit and its processing into flour would be economically viable in Nigeria when the flour is sold at the wholesale price of NO.65 per kilogram provided a minimum sale of 25% plantain suckers. There is need for government subsidy if plantain flour is to compete with imported wheat flour. The broader economic benefits accruing from the processing of plantain fruit into flour and its use in bakery products include employment opportunity, savings in foreign exchange and stimulus to home agriculture.

Saccharomyces Cerevisiae as a biotechnological tool for ageing research:studies on translation and metabolism

The yeast Saccharomyces cerevisiae is an important model organism for the study of cell biology. The similarity between yeast and human genes and the conservation of fundamental pathways means it can be used to investigate characteristics of healthy and diseased cells throughout the lifespan. Yeast is an equally important biotechnological tool that has long been the organism of choice for the production of alcoholic beverages, bread and a large variety of industrial products. For example, yeast is used to manufacture biofuels, lubricants, detergents, industrial enzymes, food additives and pharmaceuticals such as anti-parasitics, anti-cancer compounds, hormones (including insulin), vaccines and nutraceuticals. Its function as a cell factory is possible because of the speed with which it can be grown to high cell yields, the knowledge that it is generally recognized as safe (GRAS) and the ease with which metabolism and cellular pathways, such as translation can be manipulated. In this thesis, these two pathways are explored in the context of their biotechnological application to ageing research: (i) understanding translational processes during the high-yielding production of membrane protein drug targets and (ii) the manipulation of yeast metabolism to study the molecule, L-carnosine, which has been proposed to have anti-ageing properties. In the first of these themes, the yeast strains, spt3?, srb5?, gcn5? and yTHCBMS1, were examined since they have been previously demonstrated to dramatically increase the yields of a target membrane protein (the aquaporin, Fps1) compared to wild-type cells. The mechanisms underlying this discovery were therefore investigated. All high yielding strains were shown to have an altered translational state (mostly characterised by an initiation block) and constitutive phosphorylation of the translational initiation factor, eIF2a. The relevance of the initiation block was further supported by the finding that other strains, with known initiation blocks, are also high yielding for Fps1. A correlation in all strains between increased Fps1 yields and increased production of the transcriptional activator protein, Gcn4, suggested that yields are subject to translational control. Analysis of the 5´ untranslated region (UTR) of FPS1 revealed two upstream open reading frames (uORFs). Mutagenesis data suggest that high yielding strains may circumvent these control elements through either a leaky scanning or a re-initiation mechanism. In the second theme, the dipeptide L-carnosine (ß-alanyl-L-histidine) was investigated: it has previously been shown to inhibit the growth of cancer cells but delay senescence in cultured human fibroblasts and extend the lifespan of male fruit flies. To understand these apparently contradictory properties, the effects of L-carnosine on yeast were studied. S. cerevisiae can respire aerobically when grown on a non-fermentable carbon source as a substrate but has a respiro-fermentative metabolism when grown on a fermentable carbon source; these metabolisms mimic normal cell and cancerous cell metabolisms, respectively. When yeast were grown on fermentable carbon sources, in the presence of L-carnosine, a reduction in cell growth and viability was observed, which was not apparent for cells grown on a non-fermentable carbon source. The metabolism-dependent mechanism was confirmed in the respiratory yeast species Pichia pastoris. Further analysis of S. cerevisiae yeast strains with deletions in their nutrient-sensing pathway, which result in an increase in respiratory metabolism, confirmed the metabolism-dependent effects of L-carnosine.