To combat insect infestation of maize and maize products during storage without using chemical fumigants, a possible physical treatment method, microwave technology was investigated. Through its selective heating between cereals and insects, microwave technology is a possible physical treatment for eradication of insects and their eggs. Eradication of five insect species, namely Sitophilus zeamais, Rhizopertha dominica, Ephestia cautella, Cryptolestes ferrugineus and Tribolium Confusum was studied. Different microwave parameters such as power dosage, microwave mode, length of microwave cavity, maize exposure method and exposure time were investigated. The effective microwave treatment conditions were then selected, and used to treat maize kernels at laboratory scale. The effect of microwave treatment on the physicochemical properties of maize kernels was investigated. Microwave single exposures did not result in total insect mortality when maize was dropped through the microwave cavity (free falling) as the exposure times were too short. But utilising a pulley system, total insect mortality was achieved in a single exposure of 9 sec. A long microwave cavity (728 mm) resulted in maize kernel damage in terms of swelling, popping and discolouration. Redesigning the cavity by shortening it appeared to reduce these effects. The pulsed microwave mode was found to be better than continuous mode. The selected treatment that eradicated all five insect species with no visible kernel damage was pulsed mode at 2450 MHz frequency, using a 483 mm long microwave cavity, at a power level of 1.5 kW, with an exposure time of 9 sec. The selected conditions (normal treatment) and a more harsh treatment (2 kW power dosage, 18 sec exposure time) were applied to 4 kg samples of white and yellow maize kernels. The normal microwave treatment significantly decreased the moisture content and kernel weight of maize kernels but had no significant effect on test weight, stress cracks, germination and translucency. The harsh microwave treatment also had significant adverse effects on test weight, translucency, germinability, hardness and stress cracks. Additionally, reduced extractability of certain proteins was observed by 2D PAGE with the harsh microwave treatment. Both normal (power dosage of 1.5 kW, for 9 sec exposure time) and harsh (2 kW, 18 sec exposure time) treatment conditions eradicated adult insects and their eggs, but only the former maintains maize quality. The use of microwave technology has potential to be used as an insect control measure of maize products prior to packaging of the products. It is recommended that the effect of pulsed microwave disinfection on nutritional quality (starch and protein digestibility of maize products) be studied. Heat transfer phenomena should be studied and improved if possible to reduce the power usage and possibly shorten the exposure time from 9 sec. / Dissertation (MSc)--University of Pretoria, 2009. / Food Science / unrestricted

Fermentation is a process by which primary food products are modified biochemically by the action of microorganisms and/or their enzymes. Several societies have, over the years, intentionally carried it out to enhance the taste, aroma, shelf-life, texture, nutritional value and other properties of food. It is used in many parts (lithe world. However, there are regional differences in use and these depend on the availability of raw materials, consumption habits. and other socio-cultural factors. This study was aimed at (comparatively) assessing, local commercial and homemade amahewu with respect to nutritional value, hygiene and other health benefits to the commirn ity. Methods employed were Thin Layer Chromatography (TLC) (mycotoxins), High Perliffmance Liquid Chromatography (HPLC) (mycotoxins, sugars and amino acids), Dumas (proteins), SOxhlet (lipids) and intubation technique (metabolisable energy) to analyse maize meal and amahewu samples from various regions. The regions sampled included mal3heleni (South Coast) and kwaNgcolosi (North Coast) villages. Commercial amahewu was analysed with kind permission from Clover SA. Species from the following genera were isolated and identified from amahewu samples: Lactobacillus, Saccharonivccs, Lcuconostoc, Lactococcus, Panioca, Entcrobacter and kleb•iella. Saccharotnyces was detected in commercial samples only. Gram-negative strains were identified in most of manheleni village samples. No traceable amounts of aflatoxin BI (AFB1), fumonisin B 1 (FBI) and zearalenone (ZEA) were found in Clover SA samples. AFB I was detected in 40% of both maize meal and amahewu samples from maBheleni (range 0.55 — 0.84ng/g and 8.3x10 5 — 9.1x10-5ng/g respectively). From the same village, 100% of the maize meal and 80% of the amahewu samples were contaminated with FBI (range 4.1 47.2ng/g and 1.4 ---- 6.9ng/g respectively). ZEA was detected in all maize meal samples (range 0.9 — 4.3ng/g). None of the amahewu samples contained detectable levels of ZEA. All maize meal and amahewu samples from kwaNgcolosi were contaminated with AF13 1 (range 8.3 — 30.I ng/g and 0.04 - 0.102ng/g respectively). FB I was detected in 75% of both maize meal and amahewu samples from the same village (range 0.5 — 4.1ng/g and 0.04 0.56ng/g respectively). ZEA was also found in all maize meal samples and 75% of amahewu samples (range 3.7 — 16.4ng/g and 0.03 -- 0.06ng/g respectively). MaBheleni, Clover SA and kwaNgcolosi maize meal and amahewu samples contained vitamins B1, 13 2 and B6 with a range of 0.31+0.21 - 4.48±0.81 B 1 ; 0.15±0.14 - 1.67±0.33 B2 and 0.05±0.07 - 0.77±1.45 lig/g B6. Fat levels ranged from 0.28±0.40 to 4.54±0.05 percentage by weight. The levels of proteins varied from 4.02±0.02 to 8.40±0.04 percentage by weight. Starch concentrations ranged from 31.51.5.28 to 75.911.92g/100g. Maize meal samples contained glucose and maltose, while glucose, fructose, sucrose, maltose, M-triose, DP 4 and 5 and DP >15 were detected in amahewu. Apparent and true metabolisable energy for homemade and commercial Freeze-dried amahewu was 13.194 and 13.696MJ/kg (AME N ); and 13.605 and 14.106M.Ekv ( 1 MEN ), respectively. This study has shown that lactic acid maize fermentation reduce' the levels of AF13 1 , FB I and ZEA toxins in maize meal, inhibits the growth of most Gram-negative bacteria, and in some instances, fermentation did improve the nutritional value. Metabolisable energy analysis represents an important tool to assess whether or not compounds ingested are converted to sources of energy in the body and utilised. Amahewu fermentation yielded beneficial products (probiotics: reduced mycotoxins levels and reduced starch). In conclusion, natural lactic acid maize fermentation to produce amahewu will do more good than harm to the consumer, therefore, people need to be advised on how to safely store their maize and also to be encouraged to consume their stored maize in fermented form. / Thesis (M.Med.Sc.)-University of Natal, Durban, 2003.

Orientador: Jose de Assis Fonseca Faria / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-03T16:20:14Z (GMT). No. of bitstreams: 1 Azanha_AlvaroBarbosa_M.pdf: 3398484 bytes, checksum: 16232746a9c01d957bd78ac9a6b08ef3 (MD5) Previous issue date: 2003 / Resumo: Este estudo avaliou a utilização de três modelos matemáticos (Linear, Ponto Médio e Intervalo Logaritmo) para estimar a vida útil durante a estocagem de flocos de milho em embalagens plásticas flexíveis. Para verificar a adequação dos modelos matemáticos, foram realizados alguns experimentos reais com o produto como subsidio para as devidas comparações. Para a caracterização do produto foram determinados a isoterma de adsorção e os teores de umidade inicial e crítica. Esta última foi obtida, utilizando-se um método sensorial (Diferença de Controle) e um método instrumental. Para os ajustes das isotermas foram utilizados os modelos linear, polinomial cúbico e GAB. Foram determinadas as taxas de permeabilidade ao vapor de água (TPV A) das embalagens, as quais foram utilizadas nas simulações matemáticas. O modelo GAB foi o que apresentou melhor ajuste pelo valor de RMS (valor médio quadrático relativo). Dentre os modelos matemáticos estudados, o do Ponto Médio e o do Intervalo Logaritmo foram os que apresentaram uma melhor aproximação do modelo experimental real, com erro entre 4 a 6 %. A validação destes modelos para estimar a estabilidade de flocos de milho será muito valiosa para a indústria, pois se torna uma ferramenta importante no desenvolvimento de produtos, melhorias na formulação, processos e embalagens / Abstract: The objective of this work was to evaluate three different mathematical models (Linear, Middle Point and Logarithm Interval) to predict the stability of commercial corn flakes in flexible packages. The limit factor of corn flakes shelf life is the gain of moisture from the external environment, which causes loss of crispness becoming unacceptable to the consumer. In order to verify the adequacy of the different models, some laboratory experiments were done with the product to provide the necessary information to compare the performance of each mode!. The sorption isotherm of the product was determined by the desiccator method and adjusted by the following methods: linear, GAB and cubic polynomial. The water vapor transmission rates of the packages (High Density Polyethylene) were determined. Among the mathematical models studied, the Middle Point and Logarithm Interval had the best approximation with the shelf life determined experimentally, with error from 4 to 6%. The validation of these models to estimate the shelf life of corn flakes will become a very powerful tool for the industry, once it will help the research and development of new products, processes and packaging / Mestrado / Mestre em Tecnologia de Alimentos