Browsing by Author "Onyango C."

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    Crystallinity, Thermal and Morphological Characteristics of Resistant Starch Type III Produced by Hydrothermal Treatment of Debranched Cassava Starch
    (Wiley Online Library, 2009-11-25) Mutundi C.; Rost F.; Onyango C.; Henle D.; Rohm H.
    Cassava starch was debranched using pullulanase and the linear glucans recrystallized by incubation at 60°C or by temperature cycling at 120/60°C, and further subjected to heat-moisture treatment (HMT). Resistant starch (RS III) contents increased from 21.4 g/100 g in the debranched starch (DS) to 67.3 g/100 g in the debranched starch incubated at 60°C (DRS) and 47.8 g/100 g in the debranched starch subjected to temperature cycling (DCS), and further to 84.8 g/100 g and 88.4% g/100 g in HMT-DRS and HMT-DCS, respectively. Total crystallinity varied between 31.4-59.8% and the crystalline type was C in DS and DRS and A in DCS, HMTDRS and HMT-DCS. The melting properties were characterized by broad endotherms, but the exact melting region and enthalpy were dependent on recrystallization method. The main endothermic peaks of DS and DRS occurred at 103.9 and 109.8°C, respectively, whereas DCS exhibited split endotherms at 113.6 and 138.1°C. Heat-moisture treatment broadened the endotherms and increased their enthalpies. Scanning electron micrographs revealed surface topography differences related to size and aggregation of individual crystalline bodies.
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    Structural And Physicochemical Properties And In Vitro Digestibility of Recrystallized Linear Α-D- (1 → 4) Glucans Derived from Mild-Acid-Modified Cassava Starch
    (Food Research Internationa, 2010) Mutungi C.; Onyango C.; Rost F.; Doert T.; Rohm H.; Jaaros D.
    Molecular structure and recrystallization method influence the techno-functional behaviour of recrystallized starch as a functional ingredient in foods. The physicochemical properties of debranched and recrystallized mild-acid-modified cassava starch were studied. Cassava starch was treated with 0.14 mol/L hydrochloric acid for 24, 96 and 216 h at 40 °C prior to debranching with pullulanase. The debranched starches (DS) were recrystallized by annealing (ANN-DS), temperature-cycling (TC-DS) or heat-moisture treatment (HMT-DS) and the particle distribution, crystallinity, thermal properties, solubility, water binding and in vitro digestibility were analyzed. Acid treatment increased the fraction of linear α-d-(1 → 4) glucans comprising 13–30 monomers. Particles comprised loosely to firmly coalesced primary elements forming aggregates of mono- or bi-modal size distribution at ⩽5 μm and ⩾20 μm. The relative crystallinities ranged between 31.1–56.1%. Water binding decreased significantly with acid treatment whereas both solubility and water binding were influenced by the recrystallization method and decreased in the order: DS > ANN-DS > TC-DS > HMT-DS. Major thermal transitions occurred at 80– 130 °C and 130–160 °C, and the in vitro digestibility rates of 6.8–62.8% correlated significantly (p < 0.001) with relative crystallinity and melting enthalpy.