Browsing by Author "Calvin Onyango"
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Publication Composition of Polyphenols in Wheat Bread Supplemented with Pleurotus ostreatus Mushroom(2015) Stella W. Ndung’u; Christina A. Otieno,; Calvin Onyango; Fredrick MusiebaPleurotus 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 Debranched Cassava Starch Crystallinity Determination by Raman Spectroscopy: Correlation of Features in Raman Spectra with X-Ray Diffraction And 13C CP/MAS NMR Spectroscopy(Carbohydrate Polymers, 2012-01-04) Christopher Mutungi; Lars Passauer; Calvin Onyango; Doris Jaros; Harald RohmBecause starch crystallinity influences the physical, mechanical, and technological aspects of numerous starch-based products during production and storage, rapid techniques for its assessment are vital. Samples of different levels of crystallinity were obtained by debranching gelatinized cassava starch, followed by subjection to various hydrothermal treatments. The recrystallized products were further subjected to partial hydrolysis with a mixture of α-amylase and glucoamylase prior to freeze–drying. Crystallinities were determined using X-ray diffraction (XRD) and 13C CP/MAS NMR spectroscopy, and correlated with FT-Raman spectra features. XRD crystallinities ranged between 0 and 58%, and agreed with crystalline-phase fractions (R2 = 0.99) derived from the respective 13C CP/MAS NMR spectra. A strong linear correlation was found between crystallinities and integrated areas of the skeletal mode Raman band at 480 cm−1 (R2 = 0.99). With appropriate calibration, FT-Raman spectroscopy is a promising tool for rapid determination of starch crystallinity.Publication Dynamic Moisture Sorption Characteristics of Enzyme-Resistant Recrystallized Cassava Starch(American Chemical Society, 2011-01-24) Christopher Mutungi; Stefan Schuldt; Calvin Onyango; Yvonne Schneider; Doris Jaros; Harald RohmThe interaction of moisture with enzymeresistant recrystallized starch, prepared by heat-moisture treatment of debranched acid-modified or debranched non-acid-modified cassava starch, was investigated in comparison with the native granules. Crystallinities of the powdered products were estimated by X-ray diffraction. Moisture sorption was determined using dynamic vapor sorption analyzer and data fitted to various models. Percent crystallinities of native starch (NS), non-acidmodified recrystallized starch (NAMRS), and acid-modified recrystallized starch (AMRS) were 39.7, 51.9, and 56.1%, respectively. In aw below 0.8, sorption decreased in the order NS > NAMRS > AMRS in line with increasing sample crystallinities but did not follow this crystallinity dependence at higher aw because of condensation and polymer dissolution effects. Adsorbed moisture became internally absorbed in NS but not in NAMRS and AMRS, which might explain the high resistance of the recrystallized starches to digestion because enzyme and starch cannot approach each other over fairly sufficient surface at the molecular level.Publication Effect Of Heat-Moisture-Treated Cassava Starch and Amaranth Malt on The Quality of Sorghum-Cassava Amaranth Bread(African Journal of Food Science, 2013-05-31) Calvin Onyango; Eunice A. Mewa; Anne W. Mutahi; Michael W. OkothGluten-free batter and bread was prepared from modified cassava starch, sorghum and amaranth flour. Heat-moisture treatment (80°C, 18, 24 or 30% moisture content, and 8, 16 or 24 h incubation) of cassava starch increased its crystallinity, onset pasting temperature and water absorption index; and decreased its swelling power, water solubility index and peak viscosity. Heat-moisture treated cassava starch was made into batter with sorghum and amaranth in the ratio of 50:40:10. The other ingredients, weighed on flour-weight-basis, were water (75%), sugar (6.7%), fat (2%), salt (1.7%), and amaranth malt at 0, 1 or 2.5%. The interaction effect (that is, starch modification x amaranth malt) significantly (P ≤ 0.05) affected batter consistency. Breads made from heat-moisture treated starch were softer than those containing native starch. The interaction effect (that is, starch modification x amaranth malt) was significant (P ≤ 0.05) only for the texture profile analysis property of cohesiveness. Further investigation of the effect of heat-moisture treatment showed that the interaction effect (that is, moisture content x incubation time) significantly (P ≤ 0.05) affected only the Texture Profile Analysis properties of hardness and chewiness.Publication Genetic Diversity of Kenyan Native Oyster Mushroom (Pleurotus)(Taylor & Francis Online, 2017-01-20) Ojwang D. Otieno; Calvin Onyango; Justus Mungare Onguso; Lexa G. Matasyoh; Bramwel W. Wanjala; Mark Wamalwa; Jagger J.W. HarveyMembers of the genus Pleurotus, also commonly known as oyster mushroom, are well known for their socioeconomic and biotechnological potentials. Despite being one of the most important edible fungi, the scarce information about the genetic diversity of the species in natural populations has limited their sustainable utilization. A total of 71 isolates of Pleurotus species were collected from three natural populations: 25 isolates were obtained from Kakamega forest, 34 isolates from Arabuko Sokoke forest and 12 isolates from Mount Kenya forest. Amplified fragment length polymorphism (AFLP) was applied to thirteen isolates of locally grown Pleurotus species obtained from laboratory samples using five primer pair combinations. AFLP markers and internal transcribed spacer (ITS) sequences of the ribosomal DNA were used to estimate the genetic diversity and evaluate phylogenetic relationships, respectively, among and within populations. The five primer pair combinations generated 293 polymorphic loci across the 84 isolates. The mean genetic diversity among the populations was 0.25 with the population from Arabuko Sokoke having higher (0.27) diversity estimates compared to Mount Kenya population (0.24). Diversity between the isolates from the natural population (0.25) and commercial cultivars (0.24) did not differ significantly. However, diversity was greater within (89%; P > 0.001) populations than among populations. Homology search analysis against the GenBank database using 16 rDNA ITS sequences randomly selected from the two clades of AFLP dendrogram revealed three mushroom species: P. djamor, P. floridanus and P. sapidus; the three mushrooms form part of the diversity of Pleurotus species in Kenya. The broad diversity within the Kenyan Pleurotus species suggests the possibility of obtaining native strains suitable for commercial cultivation.Publication Modification Of Gluten-Free Sorghum Batter and Bread Using Maize, Potato, Cassava or Rice Starch(LWT - Food Science and Technology, 2011-04) Calvin Onyango; Christopher Mutungi; Günter Unbehend; Meinolf G. LindhauerGluten-free sorghum bread was made from cassava, maize, potato or rice starch and sorghum in the ratios 10:90, 20:80, 30:70, 40:60 and 50:50. The other baking ingredients, on flour-weight-basis, were water (100%), sugar (6.7%), egg white powder (6%), fat (2%), salt (1.7%) and yeast (1.5%). Increasing starch content changed the batters’ consistencies from soft doughs to thin pourable batters. Increasing starch content decreased crumb firmness and chewiness, and increased cohesiveness, springiness and resilience of all breads. Cassava-sorghum and rice-sorghum breads had better crumb properties than maize-sorghum or potato-sorghum breads. Although the crumb properties of all breads declined (i.e. firmness and chewiness increased; cohesiveness, resilience and springiness decreased) on storage, the formulation containing 50% cassava starch retained the best overall texture.Publication Nutrient composition, sensory attributes and starch digestibility of cassava porridge modified with hydrothermally-treated finger millet(Science Direct, 2020) Calvin Onyango; Susan Karenya Luvitaa; Guenter Unbehend; Norbert HaaseABSTRACT Cassava (CAS) porridge has low energy density and is a poor source of several nutrients. Its energy density and nutrient composition is normally improved by blending it with other flours. The aim of this study was to determine the effect of hydrothermally-treated (HTT) finger millet on nutrient composition, sensory attributes and starch digestibility of cassava porridge. Composite flour had higher protein, fibre, lipid and mineral content than cassava flour. The high α-amylase activity of HTT finger millet permitted the quantity of CAS-HTT flour to be raised from 9.5% w/v to 19% w/v without altering the free-flowing drinkable consistency of porridge. Partial substitution of CAS with HTT finger millet had no effect on starch digestibility and tannin content but increased the phytate content of CAS-HTT porridge. Hydrothermally-treated finger millet masked the aroma and colour of cassava resulting in dark-coloured CAS-HTT porridge with a bitter taste.Publication Physico-chemical Properties of Flour, Dough and Bread from Wheat and Hydrothermally-treated Finger Millet(Science Direct, 2020-05) Calvin Onyango; Luvitaa S. K; Guenter Unbehend; Norbert HaaseAbstract Hydrothermally-treated (HTT) finger millet was prepared by tempering the grains twice with water (10:1) followed by incubation at about 25–30°C in a woven polypropylene sack for 10 days. Hydrothermally-treated finger millet was darker and had higher α-amylase activity and lower starch digestibility than native (NAT) grains. The HTT finger millet was composited with wheat flour and used to prepare bread. Composite dough had higher dough stability, dough development time and degree of softening but lower dough energy, extensibility and resistance to extension than WHE dough. The higher specific volume and lower crumb firmness and chewiness of WHE-HTT compared to WHE-NAT bread was attributed to the high α-amylase activity and water absorption capacity of HTT finger millet. Wheat-HTT bread had higher dietary fibre, phytate and phenolic acid content but the same starch and protein digestibility as WHE bread.Publication Rheological Properties of Wheat-Maize Dough and Their Relationship with the Quality of Bread Treated with Ascorbic Acid and Malzperle Classicâ® Bread Improver(African Journal of Food Science, 2015-02-28) Calvin Onyango; Ljiljana Unbehend; Guenter Unbehend; Meinolf G. LindhauerThe aim of this work was to investigate the effect of ascorbic acid and a commercial bread improver on the physical quality of wheat-maize bread, and establish correlations between the physical properties of the bread and rheological properties of the dough. Wheat flour was substituted with 10, 20 or 30% maize flour and the farinograph and extensograph properties of the dough were evaluated. Farinograph water absorption, dough development time, dough stability and farinograph quality number decreased whereas the degree of softening increased with increasing substitution of wheat flour with maize flour. Extensograph dough energy, resistance to extension, extensibility and maximum resistance decreased with increasing substitution of wheat flour with maize flour. Ascorbic acid and commercial bread improver improved bread specific volume and form ratio; decreased crumb firmness, resilience and chewiness; and increased crumb springiness and cohesiveness. Farinograph water absorption and degree of softening; and extensograph energy, extensibility, maximum resistance and ratio number showed the highest number of significant correlations (P ≤ 0.01 or P ≤ 0.05) with the physical properties of wheat-maize bread.Publication Starch and Modified Starch in Bread Making: A Review(African Journal of Food Science, 2016-09-27) Calvin OnyangoStarch 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.