Food Nutrition

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Browsing Food Nutrition by Funder "Deutscher Akademischer Austauschdienst (DAAD)"

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    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 Rohm
    The 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.
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    Long- and Short-Range Structural Changes of Recrystallised Cassava Starch Subjected To In Vitro Digestion
    (Food Hydrocolloids, 2011-05) C. Mutungi; C. Onyango; T. Doert; S. Paasch; S. Thiele; S. Machill; D. Jaros; H. Rohm
    The conformational and structural order of resistant starch type III made from cassava starch was studied. The gelatinized starch was debranched using pullulanase and then recrystallised by annealing, temperature-cycling or heat-moisture treatment. Subsequently, the recrystallised products were subjected to in vitro digestion using porcine pancreatic α-amylase and amyloglucosidase. The undigested and digested products were analyzed for polymer chain distribution, crystallinity, molecular order, structural conformations and thermal stability using high performance anion exchange chromatography, wide angle X-ray diffraction, Fourier transform infrared spectroscopy, 13C CP/MAS nuclear magnetic resonance and differential scanning calorimetry, respectively. Average degree of polymerisation increased from 20 to 22 glucose units upon digestion. Both the undigested and digested starches comprised mixtures of A, B and V crystalline types. Percentage of crystallinities by X-ray diffraction were 40.9%, 50.7% and 56.2% in annealed, temperature-cycled and heat-moisture treated starches, respectively. These values increased to 47.9%, 54.4% and 58.2%, respectively, in the digested products. The ordered fractions in the undigested annealed, temperature-cycled and heat-moisture treated starches were 69.3%, 71.4% and 79.2%, respectively, as determined by 13C CP/MAS nuclear magnetic resonance. However, the disordered phase was indistinct in the digested products although the contents of non-crystalline conformations were significantly (p < 0.01) higher. The melting enthalpies of the digested residues increased by factors of 2.50 in annealed, 2.53 in temperature-cycled and 2.06 in heat-moisture treated starches, suggesting molecular rearrangement in a manner related to the enzyme susceptibility of the initial materials.