Browsing by Author "Henle Thomas"

Now showing 1 - 6 of 6
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    Determination of Optimum Conditions for Enzymatic Debranching of Cassava Starch and Synthesis of Resistant Starch Type III using Central Composite Rotatable Design
    (WILEY ONLINE LIBRARY, 2009-07-13) Christopher Mutungi; Onyango Calvin; Jaros Doris; Henle Thomas; Rohm Harald
    Cassava starch was debranched by treatment with isoamylase and pullulanase and the yield of resistant starch type III (RS III) optimized with respect to starch solids concentration (7.5-15%, w/v), incubation time (8-24 h) and enzyme concentration using central composite rotatable design. Higher concentrations of pullulanase (10-35 U/g starch) compared to isoamylase (30–90 mU/g starch) were required to give a similar degree of starch hydrolysis within the experimental domain. A clear debranching end-point was identifiable by following the reducing value, blue value and β-hydrolysis limit of cassava starches debranched using isoamylase. It was difficult to define a debranching endpoint of pullulanase treatment by these parameters due to contaminating α-D-(1→4) activity. The yield of RS III was significantly higher in isoamylolysates and increased steadily with increasing degree of hydrolysis to peak at 57.3%. Purification of the debranched material further increased the RS III yield to 64.1%. Prolonged (24 h) hydrolysis of cassava starch with high concentration of pullulanase (35 U/g) gave lower RS III contents in the purified (34.2%) and unpurified (36.2%) hydrolysates compared to 49.5 and 62.4%, respectively, at moderate pullulanase concentration (22.5 U/g) and incubation time (16 h).
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    Digestibility and Antinutrient Properties of Acidified and Extruded Maize–Finger Millet Blend in the Production of Uji
    (ScienceDirect, 2004) Onyango Calvin; Noetzold Horst; Ziems Annette; Hofmann Thea; Bley Thomas; Henle Thomas
    Lactic and citric acids were used as alternatives to backslop fermentation in the manufacture of extruded uji (a thin porridge from eastern Africa). Acidity of the blends was reduced by fermentation or progressively lowered with 0.1, 0.5 and 1.0 mol/l lactic or citric acids before extrusion. The absence of ethanol soluble starch in the extrudates indicated that extrusion solubilizes starch without formation of maltodextrins. In vitro starch digestibility increased from 20 mg maltose/g starch in the raw blend to about 200 mg/g after extrusion. Extrusion reduced total dietary fibre by 39–68%, redistributed soluble to insoluble fibre ratios and had a negligible effect on the formation of resistant starch (less than 1 g/100 g). In vitro protein digestibility increased after fermentation or acid treatment followed by extrusion. Nitrogen solubility index decreased by 40–50% when the unfermented, lactic or citric acid treated blends were extruded, but increased by 20% when the blend was fermented before extrusion. Amino acid analysis showed that histidine, lysine and arginine contents were lowest in the fermented-extruded blends. Tannin content decreased from 1677 mg/100 g in the raw blend to between 551 and 1093 mg/100 g in the extrudates whereas phytate content remained unaffected by extrusion (248–286 )
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    Effect of Extrusion Variables on Fermented Maize–Finger Millet Blend in the Production Of Uji
    (ScienceDirect, 2004) Onyango Calvin; Henle Thomas; Ziems Anette; Thea Hofmann; Thomas Bley
    The effects of screw speed, feed moisture, glucose, fructose, sucrose and maltose on extrusion of lactic fermented and dried maize–finger millet blend was investigated. Fermentation caused a reduction in sectional expansion index, flour bulk density and water absorption index (WAI) but increased specific volume, water solubility index and darkened the extrudates. Increase in feed moisture (13–25%) reduced sectional expansion index, specific volume and yellowness but increased extrudate moisture content, bulk density and darkness of the extrudates. Increasing screw speed (158–242 rpm) had a negative correlation only with specific volume and lightness (P<0.05). An increase in the content of any of the sugars reduced extrudate moisture content, sectional expansion index, WAI and specific volume but increased bulk density and water solubility index. Extrudates treated with monosaccharides were darker than extrudates treated with disaccharides.
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    Influence of Incubation Temperature and Time on Resistant Starch Type III Formation From Autoclaved and Acid-Hydrolysed Cassava Starch
    (SciencDirect, 2006-11-24) Onyango Calvin; Bley Thomas; Annette Jacob; Henle Thomas; Rohm Harald
    Raw cassava starch, having 74.94 and 0.44 g/100 g resistant starch type II and III (RS II and RS III), respectively, was autoclaved at 121 °C in water, 1, 10 or 100 mmol/L lactic acid. The formation of RS III was evaluated in relation to variable incubation temperature (−20 to 100 °C), incubation time (6–48 h) and autoclaving time (15–90 min). Negligible to low quantities of RS III (0.59–2.42 g/100 g) were formed from autoclaved starch suspended in 100 mmol/L lactic acid, whereas intermediate to high quantities (2.68–9.97 g/100 g) were formed from autoclaved starch suspended in water, 1 or 10 mmol/L lactic acid, except for treatments with water or 10 mmol/L lactic acid incubated at 100 °C for 6 h (1.74 g/100 g). Autoclaving times corresponding to maximum RS III contents were 15 and 45 min for water and 10 mmol/L lactic acid, respectively. Whereas, the RS III fractions from cassava starch suspended in water had melt transitions between 158 and 175 °C with low endothermic enthalpies (0.2–1.6 J/g), the thermal transitions of the acidtreated samples were indistinct.
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    Production of High Energy Density Fermented Uji using a Commercial Alpha-Amylase orby Single-Screw Extrusion
    (ScienceDirect, 2003) Onyango Calvin; Henle Thomas; Hofmann Thea; Bley Thomas
    The effects of alpha-amylase and extrusion on the viscosity and energy density of uji, a spontaneously fermented thin porridge from different combinations of maize, finger millet, sorghum and cassava, were investigated. Fermentation alone was not able to reduce the viscosity of uji, but addition of 0.1–2.1 ml/100 ml alpha-amylase to the fermented slurry or extrusion of the fermented and dried flour at 150–180°C and a screw speed of 200 rpm reduced the viscosity of 20 g/100 ml uji from 6000–7000 to 1000–2000 cP, measured at 40°C and a shear rate of 50 s−1. The amount of flour required to make uji could thus be increased by a factor of 2.0–2.5 and consequently it was possible to produce uji with acceptable energy densities (0.6–0.8 kcal/g) for child feeding.
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    Proximate Composition and Digestibility of Fermented and Extruded Uji From Maize– Finger Millet Blend
    (LWT - Food Science and Technology, 2004) Onyango Calvin; Noetzold Horst; Bley Thomas; Henle Thomas
    The proximate composition, amino acid profile and in vitro starch and protein digestibilities of raw; fermented; fermented and cooked; unfermented and extruded; and fermented and extruded maize–finger millet blend was studied. Aspartic acid, glycine,cystine, methionine, tyrosine and lysine increased after fermentation, while contents of all other amino acids showed no significant changes. Greater losses of amino acids occurred when the fermented blend was extruded than when cooked. Fermentation improved protein and starch digestibilities, whereas cooking or extruding the fermented blend reduced the digestibilities. Extruding the unfermented blend increased protein and starch digestibilities and reduced nitrogen solubility index by 50%. Raw flour had 0.41 g/100 g water-soluble starch which declined to 0.05 g/100 g on fermentation but increased to 20–34 g/100 g after extrusion