Sorghum waxy and high protein digestibility traits and their relationship with malting and dough-based product making quality

Sorghum is a critical cereal crop in Africa, owing to its heat- and drought- tolerance, its role in nutrition and potential in commercial food and beverage manufacture. However, sorghum has limitations for producing quality foods and beverages e.g. malt, breads and biscuits. This is due to its high starch gelatinization temperature and poor protein functionality, specifically its inability to form a viscoelastic dough like wheat. Novel sorghum lines with combined waxy (high amylopectin) and high protein digestibility (HD) traits have been developed through conventional breeding. These lines are hypothesized to have superior functionality in food and beverage applications due to their higher digestibility and improved dough functionality. The objective of this work was to determine the relationship between waxy and HD traits in sorghum and malting quality as well as dough-based product (injera-fermented flatbread and biscuit) making quality. Novel white tan-plant sorghum lines with differing endosperm traits: waxy, heterowaxy, waxy-HD, non-waxy-HD and non-waxy-normal digestibility traits were malted at a laboratory scale and their malting qualities were studied. Additionally, injera and biscuits were prepared using standard methods and their qualities were evaluated using a trained descriptive sensory panel (DSP) and instrumental texture analysis. The endosperm of the waxy lines had a pale waxed floor-like appearance (typical of waxy sorghum), high starch amylopectin and intermediate to corneous texture. Transmission electron microscopy revealed that the HD lines had protein bodies which were not densely packed in the protein matrix, of irregular shape and small size (0.48-0.56 mm diam.), and had a floury endosperm. Malt produced from waxy and heterowaxy sorghum lines generally had improved endosperm modification and starch granule degradation. Only non-waxy-HD and one waxy line malts exhibited clear evidence of endosperm protein degradation. Malt α- and β-amylase activities were not evidently affected by the traits. Malt from waxy lines had improved hot water extract (HWE) and free amino nitrogen (FAN). Principal component analysis (PCA) showed that the waxy lines were associated with high HWE, FAN, starch and protein loss. DSP showed that injera made from waxy sorghums were softer, more rollable, and flexible compared to normal sorghum injera and were much closer to teff injera reference. Instrumental texture analysis of fresh and stored injera revealed that waxy sorghums gave lower stress and higher strain compared to injera from non-waxy lines, indicating that the injera were softer and more flexible. There was no clear trend as to whether the HD-trait affected injera quality. The textural properties of the injera measured by texture analyser and DSP showed significant correlation. Also, the instrumental texture profile of the injera prepared using full-scale (traditional) and small-scale (microwave) methods were significantly correlated. DSP and instrumental texture analysis showed that sorghum biscuit quality was not affected by the traits. The waxy trait either alone or in combination with the HD-trait appears to improve sorghum malting quality, probably due to the better starch granule swelling property of amylopectin, which could facilitate hydrolysis by amylases and proteases. The improved injera quality is most likely due to the slower retrogradation and better water holding of amylopectin starch. This study shows that white tan-plant waxy sorghum can produce better quality malt and flatbreads than regular sorghums, and thus has considerable potential to partially replace barley malt and teff, respectively in these products in areas in Africa where sorghum is a major cereal crop. Hence, either white tan-plant waxy or normal sorghum can be used to partially replace wheat for biscuit making in regions that have shortage of wheat.Thesis (PhD)--University of Pretoria, 2018.Food SciencePhDUnrestricte

Effects of plant-fungal interactions on volatile emission of Hordeum vulgare and aphid preference

Barley is one of the most economically important cultivated crops in the world. However, barley is a host for many insect pests and plant pathogenic fungi which is a threat to the production. Rhopalosiphum padi is an economically important insect pest that leads to large economical losses in agricultural crops such as barley. An increased understanding of interactions between insects, plants and microorganisms is an important step in developing non-chemical control strategies to prevent major outbreaks of aphids and other pests. This study firstly aims to study the effect of barley inoculated with the beneficial fungi Trichoderma atroviride and the plant pathogen Fusarium graminearum on emission of volatile organic compounds. Secondly, it aims to analyse aphid behavior and preference to odours from barley plants inoculated with T. atroviride, F. graminearum and non-inoculated controls through olfactometer tests. Volatile organic compounds were collected on volatile traps from barley-plants inoculated and grown under controlled conditions in a growth chamber. The volatile organic compounds were analysed and quantified in a Gas chromatography – mass spectrometry (GC-MS) and then in the Automated Mass Spectral Deconvolution and Identification System (AMDIS). The result of the volatile analysis showed no significant differences in the total volatile organic compound (VOC) composition between plants inoculated with F. graminearum, T. atroviride and non-inoculated plants. The olfactometer test result shows no significant difference in aphid preference between plants inoculated with F. graminearum and non-inoculated plants. However, R. padi did significantly prefer non-inoculated plants over plants inoculated with T. atroviride. As a conclusion, based on the results in this study, VOCs induced by T. atroviride could possibly work as repellents for R. padi. However, further studies on the interaction between plants, insects and microorganisms are needed to develop new control strategies and possibly use it as biological control and in Integrated Pest Management (IPM).Korn är en av de ekonomiskt viktigaste odlade grödorna i världen och är värd för flera skadeinsekter och växtpatogena svampar, vilka utgör hot mot produktionen. Havrebladlusen Rhopalosiphum padi är en ekonomiskt viktig skadeinsekt som leder till stora ekonomiska förluster i jordbruksgrödor som exempelvis i korn. En ökad förståelse för interaktioner mellan insekter, växter och mikroorganismer är ett viktigt steg för att utveckla andra icke-kemiska kontrollstrategier för att förhindra stora utbrott av bladlöss. Denna studie syftade för det första till att studera hur inokuleringen av korn med nyttosvampen Trichoderma atroviride och den växtpatogena svampen Fusarium graminearum påverkar volatila ämnen från plantan. För det andra syftade den till att analysera bladlössens beteende och preferens för volatiler från kornplantor inokulerade med T. atroviride, F. graminearum och ej inokulerade kontrollplantor genom olfaktometer tester. Volatiler samlades in på fällor från kornplantor som hade växt under kontrollerade förhållanden i en tillväxtkammare. Volatilerna analyserades och kvantifierades med GC-MS och AMDIS. Resultaten visade inga signifikanta skillnader i den totala sammansättningen av volatiler från plantor inokulerade med T. atroviride, F. graminearum och ej inokulerade plantor. Olfaktometertestet visade ingen signifikant skillnad i bladlössens preferens mellan plantor inokulerade med F. graminearum och ej inokulerade plantor. Rhopalosiphum padi föredrog däremot ej inokulerade plantor framför plantor inokulerade med T. atroviride. Som en slutsats, baserat på resultaten i denna studie, kan volatiler inducerade av T. atroviride möjligen fungera frånstötande för R. padi. Det behövs dock ytterligare studier om interaktionen mellan växter, insekter och mikroorganismer för att utveckla nya kontrollstrategier och för att använda denna strategi inom biologisk kontroll och i IPM-strategier

Effects of physical parameters in mashing on lautering performance

This thesis investigates performance parameters of unit operations in the brewery. It describes effects of the parameters temperature and agitation during mashing on mash properties. Mainly two properties are influenced by these parameters, the viscosity and the particle size distribution in the fines. It could be shown that both factors have significant influence on filterability of mash. In pilot scale and laboratory trials particle size effects in mash were investigated systematically. The importance of fine particles for lautering performance could be confirmed and quantified. The precipitation and aggregation of fine particles with increasing temperatures in the mash could be monitored for the first time. It could be shown that this parameter is not malt dependent. Mashes from different malts react in the same way. In laboratory trials it could be proved that the particle size parameter is more important than viscosity for filterability of mash. The parameters described above have been quantified and correlated with mash filtration parameters. This work provided a basis for the development of a computer model which describes mash separation in a lauter tun

Optimisation of brewery yeast management: a study incorporating image analysis

Changes in cell volume occur when yeast is propagated in worts of increasing original gravity (OG) in the range 7 5 to 17 5°P Using image analysis to measure cell volume, the mean individual cell volume of ale and lager yeast increased by up to 30% as OG increased to 17 5°P. Propagation of yeast in high-gravity wort (17 5°P) has a deleterious effect on yeast quality during subsequent high-gravity fermentations. The mean cell volume of yeast changes during storage and this has been identified as a contributing factor to over-pitching of fermentations. A reduction in mean cell volume of up to 19% for ale yeast and up to 7% for lager yeast has been observed. Using image analysis, a new pitching regime was developed which improves fermentation consistency. A rapid technique has been developed to determine the glycogen content of yeast on an individual cell basis using a combination of image analysis technology and staining of yeast cells with an I2 KI solution. Analysis of the distribution of yeast glycogen during fermentation indicates that a fraction of yeast cells do not dissimilate glycogen. Therefore, conventional glycogen analysis of yeast used to inoculate fermentations is of limited use, unless information regarding the proportion of cells which utilise glycogen is known. Thermal gradients in yeast crops of 3 5°C were recorded within 5 hours of unmixed storage, using a specially designed cooling rig. These gradients increased with increasing yeast metabolic activity to a maximum of 11°C. Using a custom-built yeast storage vessel, it was determined that mechanical agitation achieves better mixing than recirculation of slurry through an external loop. In all trials, a dense biomass layer (up to 75% w/w) developed on the slurry surface (due to CO2 evolution), in which the yeast viability was up to 13% lower than in the remainder of the vessel