Modulation of mycobiota associated with rice stored in bamboo reinforced concrete silo- molecular identification and phenotypic characterization

The present study was undertaken to investigate the fungal load and community composition on milled rice stored in the form of paddy in bamboo reinforced concrete (BRC) silo for 12 months. The storage period was divided into Phase 1 and 2, corresponding to the first and last six months of storage, respectively. Ten strains of fungi with maximum frequencies were identified throughout the storage duration by molecular (Internal transcribed spacer sequences) and phenotypic (culture method and scanning electron microscopy) characterization. The fungal load remained unchanged during Phase 1 but increased progressively during Phase 2, which could be a direct effect of the changes in grain water activity (0.47–0.63) and storage temperature (25–35°C). Among the isolated fungal strains, Alternaria padwickii was the most predominant species in the rice samples during Phase 1 while Phase 2 was highlighted by the maximum frequency of Aspergillus flavus. Other species encountered and isolated from the rice grains include Curvularia spp., Rhizomucor spp., Pencillicum spp., Hypoxylon spp. and Aspergillus spp. Though undetectable in Phase 1, total aflatoxin content at the end of storage period was found to be 0.42 μg/kg grain, indicating the presence of the Aspergillus spp. in Phase 2. Rapid and accurate identification of fungal species is critical for formulating efficient strategies in management of fungal contamination in a storage system. Storage of rough rice in BRC silo has been shown to be highly effective in mitigating the growth and proliferation of fungi under tropical conditions.     

Structural and mechanical characterization of κ/ι-hybrid carrageenan gels in potassium salt using Fourier Transform rheology

The mechanical and structural properties of κ/ι-hybrid carrageenan gels obtained at various concentrations in the presence of 0.1 m KCl were studied with Fourier Transform rheology (FTR) and cryoSEM imaging. FTR data show that gels formed at concentration below 1.25 wt% exhibit a strain hardening behavior. The strain hardening is characterized by a quadratic increase of the scaled third harmonic with the strain and a third harmonic phase angle of zero degree. Both features are weakly depending on the concentration and conform to predictions from a strain hardening model devised for fractal colloidal gels. However, the phase angle of the third harmonic reveals that κ/ι-hybrid carrageenan gels obtained at higher concentrations show shear thinning behavior. Colloidal gel models used to extract structural information from the concentration scaling of gel equilibrium shear modulus G₀ and the strain dependence of FTR parameters suggest that κ/ι-hybrid carrageenan gels are built from aggregating rod-like strands (with fractal dimension x = 1.13) which essentially stretch under increasing strain. The mechanically relevant structural parameters fairly match the gel fractal dimension (d = 1.66) obtained from the cryoSEM analysis.