School of Chemical and Bio Engineering

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Browsing School of Chemical and Bio Engineering by Author "Abebe Moges"

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    Characterization of Heat-Moisture Treared Starch from Locally Produced V. Faba for The Improvement of Freeze-Thaw stability of “Siljo” Paste
    (Addis Ababa University, 2011-06) Abebe Moges; Shimelis Admassu (PhD)
    Functional properties of granular and heat moisture treated (HMT) starches isolated from locally grown V. faba CS-20-DK variety were studied for their effect on the freeze-thaw stability of Siljo paste. Faba bean grain was dehulled, milled, sieved and fractionated into, course (>125μm), medium (80-125μm), and fine (< 80μm) size flour particles. Flour fractionates were slurred in a tap water and separated into supernatant and primary starch residue (PSR) using batch centrifuge. Sieving into fine flour particle resulted in higher carbohydrate (79.36%), lower protein, fat, ash, and fiber distribution, and highest starch yield (52.76%) and least nitrogen (0.08%) and ash (0.05%) contents in the total solids of PSR. Starch yield is comparable with 37% yield from horsebean flour obtained by Kawamura et al (1955) method. The starch obtained from fine flour fractionate was subjected into HMT at 19%; 23%; and 27% (d.b) moisture levels, treated in a hot air oven at 1000C for 16hr, and then dried and milled. The effect of temperature on hydration properties and least gellation concentration (LGC) were determined as a measure of water retention capacity of retrograded starch of granular and HMT starch was investigated. Hydrothermal conditioning led to restricted swelling power (SP) and significant increase in water solubility (WS) and water absorption index (WAI) with the level of conditioning moisture. In all investigations highest SP, WS, and WAI of starches in the temperature range of 85-950C suggests that water penetration into the granules can be achieved at elevated temperature. HMT resulted in increase hydrophilic tendency and conversely decreased the hydrophobic tendency. Except HMT19%; LGC of all HMT starches progressively decreased with the increase in conditioning moisture level. Percentage of retrogradation was decreased after HMT. Degree of retrogradation between the 1st and the 4th days starch gels storage was investigated in the range 100-100% (granular); 85-100% (HMT19%); 52-89% (HMT23%); and 48-84% (HMT27%). The effect of partial substitution of HMT starch at various concentrations (9%, 23%, and 38%) on the freeze-thaw stability (% syneresis) of Siljo paste was evaluated. The highest and the least percentage of syneresis were 167% for normal flour and 73% for the 37.5% HMT27% substituted flour. The incorporation of HMT starch resulted in improved resistance of Siljo paste against the re-crystallization process upon cooling. Application of HMT starch is recommended for the production of sauces and soups with a better stability at ambient or refrigerated storage conditions