Browsing by Author "Onyango, Calvin"
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Publication Composition of Polyphenols in Wheat Bread Supplemented with Pleurotus ostreatus Mushroom(American Journal of Food Technology, 2015) Ndung'u, Stella W.; Otieno, Christina A.; Onyango, Calvin; Musieba, FredrickPleurotus ostreatus mushrooms were blanched, milled into flour and incorporated into wheat flour at 5, 10 and 15%. These composite flours, together with composite breads developed from these formulations were evaluated for polyphenols, namely flavones and isoflavones. Wheat flour and wheat bread were used as control samples. Extraction of polyphenols was done using ethanol as a solvent and analyzed using gas chromatographmass spectrometry. It was not possible to make bread with 15% mushrooms. Quantities of different flavones and isoflavones evaluated increased significantly (p<0.05) with increasing supplementation of mushroom flour in wheat flour. Composite breads were also observed to have higher contents of flavones and iso flavones as compared to bread prepared from wheat flour only. Composite flour with 15% mushrooms had highest quantities of flavones and isoflavones while composite bread with 10% mushroom flour had significantly higher (p<0.05) levels of these compounds. Caffeic acid was the most abundant amongst all the flavones analyzed in wheat mushroom blends while genistein was the most abundant isoflavone. Flavones and isoflavones in human nutrition protect against oxidative stress and also provide medicinal properties such as antimicrobial, antiviral and anticancer benefits. Pleurotus mushrooms are a good source of these important compounds hence incorporating them in daily diet like bread would ensure constant supplementation for improved health and nutrition.Publication Effect of Drying Lactic Acid Bacteria Fermented Uji on Its Pasting Properties and Content of Carboxylic Acids(University of Nairobi Department of Food and Nutrition Technology, 1999-01-01) Onyango, Calvin; Okoth, Michael; Mbugua, SamuelThe effect of fermentation and drying on the pasting properties and carboxylic acids of pure flours of maize, finger millet and cassava and of composite flours of maize-finger millet and cassava-finger millet were studied. The pasting properties were measured between 30°C and 96°C in a Brabender Amylograph while carboxylic acids from the uji slurries were determined on thin layer chromatography plates coated with 0.25 mm silica gel. Irrespective of the treatment given, the cereal flours of maize, finger millet and the composite of maize-finger millet consistently had higher onset and peak gelatinization temperatures than pure cassava or the composite of cassava-finger millet. Also the latter two flours developed higher peak viscosities and disintegrated more rapidly after attaining the peak than either pure maize, finger millet or the composite of maize-finger millet. The higher viscosities of the root flours was also reflected in the higher swelling powers and solubility values at 85°C. Fermentation increased the viscosity of the slurries. The greatest increases were recorded by maize (500BU) and the composite of maizefinger millet (780 BU). Fermentation did not affect gelatinization temperatures except for the maize-finger millet composite whose gelatinization temperature decreased by 10°C. Fermentation and drying resulted in increased viscosity when compared to the non-fermented flours, except for the drum dried cassava-finger millet composite. For all the drum dried flours there was a spontaneous increase in viscosity at 30°C when the Brabender Amylograph was switched on. The drum dried flours absorbed about four times their own weight of water; and since the starch granules were pregelatinized, reconstitution in cold water was difficult, as the flour particles tended to lump together, getting wetted on the surface and inhibiting the penetration of water into the interior. In contrast, sun and cabinet dried flours absorbed about 1.9 times their own weight of water and formed smooth slurries in cold water. Fermentation increased total titratable acidity and fixed acidity of the slurries to about 3.9% and 3.6% respectively, while the pH declined from 5.5 to 3.9. On drying there were no significant changes in (p0.05) from the uji prepared from fermented and nondehydrated slurries.Publication Effect of Resistant Cassava Starch on Quality Parameters and Sensory Attributes of Yoghurt(Current Research in Nutrition and Food Science, 2017-12-04) Mwizerwa, Herve; Abong’, George Ooko; Okoth, Michael Wandayi; Ongol, Martin Patrick; Onyango, Calvin; Thavarajah, PushparajahResistant starch is known to impart a number of health benefits to consumers. It is therefore desirable to increase the content of resistant starch in popular foods such as yoghurt. The current research investigated the effect of cassava resistant starch synthesized by heat-moisture treatment of starch from I92/0057 cassava variety on physico-chemical properties and sensory attributes of yoghurt. Cassava starch rich in resistant starch was incorporated into yoghurt in the proportions of 0, 0.1%, 0.5% and 1%. Corn starch (0.6%) was used as control. Yoghurt was stored at 4oC for 21 days and the effect of starch modification on resistant starch content, viscosity, syneresis, total solids, acidity, lactic acid bacteria count and sensory properties were determined on weekly basis. Applying cassava starch rich in resistant starch into yoghurt in the proportions of 0.5% and 1% had significantly higher (p≤0.05) resistant starch content of yoghurt reaching 3.40 g/100 g and 5.58 g/100 g on day one and 1.92 g/100 g and 4.47 g/100 g on day 21, respectively. There was a significant correlation (p≤0.05) between resistant starch concentration and the physicochemical properties of yoghurt. Yoghurt treated with 1% resistant starch enriched cassava starch had the highest viscosity during cold storage which was determined as 2721.5 mPa s, mPa s, 2650.0 mPa s and 1034.5 mPa s at day 1, day 7, day 14 and day 21 respectively and it had the least syneresis (22.25%). Addition of cassava starch rich in resistant starch significantly increased (p≤0.05) the total solids content of yoghurt but did not significantly (P>0.05) change the sensory properties of yoghurt. The application of 1% of resistant starch enriched cassava starch as yoghurt thickener produces significant quantity of resistant starch in yoghurt with acceptable sensory and physico-chemical properties.Publication Optimization of the Performance of Hybrid Solar Biomass Dryer for Drying Maize Using ANSYS Workbench(Journal of Energy Research and Reviews, 2020-02-03) Aukah, Jackis; Muvengei, Mutuku; Ndiritu, Hiram; Onyango, CalvinIn this paper ANSYS workbench was used to optimize the performance of hybrid solar biomass dryer for drying shelled maize in order to find the optimal operating input variables when the air temperature within the drying chamber set within the permissible range at reasonably high flow velocity. Hybrid Solar dryer with biomass as a source of fuel for auxiliary heating during absence or low solar insolation is a feasible option for small scale maize farmers [1]. At times high temperatures are induced in this dryer which may result in grain fissures and breakage during milling, thus reducing the grain quality. Optimization results indicate that in order to keep the air temperature within drying chamber to permissible range [2], the air velocity at collector inlet and biomass heat exchanger outlet should be improved to 3 m/s and 2.8 m/s respectively while the capacity of the biomass heat exchanger should also be enhanced to provide hot air at 85°C. It be concluded from the study that HSBD is suitable for drying maize as well as other agricultural products since continuous interrupted drying can be achieved. The capability of the dryer to maintain uniform temperature and air flow within the drying chamber enable high quality dried products within a short duration.Publication Physical Properties of Dry-Milled Maize Meals and Their Relationship with the Texture of Stiff and Thin Porridge(African Journal of Food Science, 2014-08-31) Onyango, CalvinSelected physical properties of white maize meal, obtained by different dry-milling techniques were evaluated and correlated to the texture of stiff and thin porridge. Sifted or par-cooked maize meals had finer particles than hammer-milled maize meals. Hammer-milled maize meals had lower water absorption indices (17-38%) and higher water solubility indices (WSI, 4-5%) than sifted (41-42 and 2-3%, respectively) or par-cooked (114 and 2%, respectively) maize meals. Sifted or par-cooked maize meals had lower breakdown viscosities (0-19 BU) and higher final viscosities (818-1925 BU) than hammer-milled maize meals (89-173 BU and 530-780 BU, respectively). Stiff porridge prepared from par-cooked maize meal (34% w/v), and thin porridge from dehulled and hammer-milled maize meal (10% w/v) had the firmest textures at 80.93 and 1.28 N, respectively. There was a negative correlation (P < 0.05, r = -1.00) between the WSI and total shearing force of stiff porridge prepared from par-cooked maize meal.Publication Prediction of Airflow and Temperature Distribution in Hybrid Solar-Biomass Dryer using Computational Fluid Dynamics(JOURNAL OF SUSTAINABLE RESEARCH IN ENGINEERING, 2018-09-15) Aukah, Jackis; Muvengei, Mutuku; Ndiritu, Hiram; Onyango, CalvinHybrid solar-biomass dryers present a viable option for drying maize since continuous drying can be achieved. However,non-uniform drying of the product may occur in the drying chamber due to poor airflow distribution. Several studies have beenreported on modeling of solar dryers for drying of agricultural products but most researchers use one dimensional models basedon thermal analysis to simulate the drying process but this approach can only describe the flow variable in one defined directionalong the domain and therefore, cannot effectively reveal information on air flow patterns which is considered crucial foroptimization process. Three dimensional approach that provides a more realistic simulation of the drying process is necessary foroptimization of the performance of the dryer. The aim of this study was to develop a mathematical model for predicting thetemperature and air velocity distribution in hybrid solar biomass dryer. The model consists of the full set of partial differentialequations that describe the conservation of mass, momentum and heat inside the dryer. The standard model was used to describeturbulence in addition to the governing conservation equations. Simulation was done using ANSYS CFX which is a general purposeComputational Fluid Dynamics (CFD) package. The simulated airflow pattern and temperature distribution on the horizontal andvertical planes in the drying chamber was analyzed and the result revealed spatial homogeneity of drying air condition. The modelwas validated experimentally and the results showed a reasonable agreement between the experimental and simulated results witha small variation of about 0.7 0 C. This indicate that the model prediction was reasonably accurate.Publication Quality of Porridge from Sub-Saharan Africa Evaluated Using Instrumental Techniques and Descriptive Sensory Lexicon - Part 1: Thick (Stiff) Porridge(African Journal of Food Science, 2018-04-30) Onyango, Calvin; Wanjala, George W.The sensory attributes of thick porridges made from different composite flours in neutral, citric acid or sodium bicarbonate media was identified using instrumental methods and modified quantitative descriptive analysis. The results showed that composite flours with high cassava concentrations had lower pasting temperatures but higher peak, breakdown, final and setback viscosities than the cerealrich flours. The onset pasting temperatures of alkali-treated slurries were higher (p < 0.05) than for the neutral- or acid-treated slurries. Acid-treated slurries had higher (p < 0.05) peak viscosities than neutralor alkali-treated slurries. Acid-treated slurries had higher (p < 0.05) breakdown viscosities as compared to the neutral slurries. The toughness and work of shear of thick porridge ranged between 0.21 - 0.58 kg and 0.83 - 5.95 kg·mm, respectively. Thick porridge cooked in alkaline media was significantly darker (p < 0.05) than that made in neutral or acid media. Principal component analysis identified four major principal components (PCs) that accounted for 87.6% of the total variance in the sensory attribute data. The principal component scores indicated that the location of each porridge along each of the four scales corresponded with attributes associated with sodium bicarbonate aroma and taste (PC1); cassava aroma and hardness (PC2); colour of thick porridge (PC3); and finger millet/sorghum aroma (PC4). Thick porridges targeting specific consumer groups in sub-Saharan Africa can be developed by appropriate choice of flours and pH thereby forming the basis for commercial production of thick porridges for different population categories in sub-Saharan Africa with diverse sensory expectations of the product.Publication Quality of Porridge from Sub-Saharan Africa Evaluated Using Instrumental Techniques and Descriptive Sensory Lexicon. Part 2: Thin Porridge(African Journal of Food Science, 2018-05-31) Onyango, Calvin; Wanjala, George W.Thin porridge is a popular nourishment drink for adults and complementary food for children in sub-Saharan Africa. It is made from straight (unblended) or composite flours of maize, sorghum, finger millet and cassava in neutral or chemically-acidified media, or after spontaneous fermentation of the flours. The objective of this study was to determine the impact of type of composite flour and pH on the sensory quality of thin porridges. Instrumental methods and modified quantitative descriptive analysis were used to identify the main sensory attributes of thin porridges made from different composite flours in neutral or acidic media or after spontaneous fermentation. The results of the study indicated that irrespective of the pH, cerealbased composite flours had higher onset pasting temperatures; and lower peak, breakdown, final and setback viscosities than cassava-cereal flours. Thin porridges formulated from cereal-based composite flours tended to have lower firmness, consistencies, cohesiveness and indices of viscosity than those made from cassava-cereal flours. The colour of thin porridges depends on the botanical origin of the composite flours, their ratios and whether the pH was adjusted using citric acid or by spontaneous fermentation. Principal component analysis identified three major principal components (PCs) that accounted for 83.7% of the total variance in the sensory attribute data. The principal component scores indicated that the location of the thin porridges on each of the three scales corresponded with cassava aroma (PC1), finger millet/maize aroma (PC2), and colour and fermented aroma (PC3). This study has shown that thin porridges with different sensory profiles can be produced in sub-Saharan Africa for different population groups.Publication Starch and Modified Starch in Bread Making: A Review(African Journal of Food Science, 2016-12-31) Onyango, CalvinStarch is an important source of energy in human nutrition. It is also widely used as a processing aid in several food and non-food industries. Starch in wheat flour contributes to the development of optimal bread crumb and crust texture. It is also responsible for physical deterioration of bread quality through staling. Starch is mainly extracted from starch-rich plants such as cereals, root and tuber crops and legume seeds. It can be modified using chemical, physical or enzymatic techniques to obtain modified starch. Traditional plant breeding or genetic modification can also be used to produce starches with modified functionalities. Modified starches are essential food processing aids because of their enhanced functional properties. The aim of this paper is to review the role of starch in bread making and subsequently elucidate the influence of modified starch on the quality of wheat bread.