The Influence of Gratering, Fermentation and Variety on the Physio-Chemical Quality of Cassava Starch

The study was conducted to determine the influence of gratering and fermentation parameters on the physicochemical quality of starch obtained from two cassava varieties in Sierra Leone (i.e., SLICASS 11 and SLICASS 6). Fresh cassava roots harvested from the Department of Agricultural Engineering were peeled, washed and grated before fermentation and starch extraction. Fermentation was carried out under separate aerobic and anaerobic conditions for a period of Seven days. Physicochemical analyses were conducted at the Postharvest Food and Bioprocess Engineering Laboratory of the Department of Agricultural and Bio-System Engineering, Njala University to determine the solubility, water absorption capacity and swelling power of starch extracts obtained from various experimental treatments. Fermentation method and duration had significant effects on the solubility, water absorption capacity (WAC) and swelling power (SP) of starch extracts. Maximum solubility and WAC were recorded on the fifth day, for both cassava varieties tested, with apparent significant difference resulting from the two gratering bands (i.e., with 1.5-inch nail hole and 4-inch nail hole sizes, respectively). While swelling power increased consistently with temperature for starch obtained from SLICASS-11 variety, an irregular pattern was observed for SLICASS-6 variety. A multiple correlation analysis proposes a significant and weak correlation between temperature, WAC (+0.150) and swelling power (+0.048). Also multiple correlation analyses suggest a significant correlation between fermentation period, the functional properties of starch extracts obtained from both fermentation methods and cassava varieties (i.e., solubility (−0.226), water absorption capacity (+0.301) and swelling power (+0.329)).

First-principles study of He trapping in η-Fe_2C

The distribution of He in η-Fe2C has been studied by first-principles calculations.The formation energies of interstitial He and substitutional He（replacing Fe） are 3.76 eV and 3.49 eV,respectively,which are remarkably smaller than those in bcc Fe,indicating that He is more soluble in η-Fe2C than in bcc Fe.The binding potencies of both a substitutionalinterstitial He pair（1.28 eV） and a substitutional-substitutional He pair（0.76 eV） are significantly weaker than those in bcc Fe.The binding energy between the two He atoms in an interstitial-interstitial He pair（0.31 eV） is the same as that in bcc Fe,but the diffusion barrier of interstitial He（0.35 eV） is much larger than that in bcc Fe,suggesting that it is more difficult for the interstitial He atom to agglomerate in η-Fe2C than in bcc Fe.Thus,self-trapping of He in η-Fe2C is less powerful than that in bcc Fe.As a consequence,small and dense η-Fe2C particles in ferritic steels might serve as scattered trapping centers for He,slow down He bubble growth at the initial stage,and make the steel more swelling resistant.