Optimization of microfibrillated cellulose isolation from cocoa pod husk via mild oxalic acid hydrolysis: A response surface methodology approach.

Theobroma cacao L. species, cultivated worldwide for its valuable beans, generates up to 72% weight of the fruit as waste. The lack of reutilization technologies in the cocoa agroindustry has hindered the exploitation of valuable bio-components applicable to the generation of high value added bioproducts. One such bioproduct is microfibrillated cellulose (MFC), a biopolymer that stands out for its desirable mechanical properties and biocompatibility in biomedical, packing, 3D printing, and construction applications. In this study, we isolated microfibrillated cellulose (MFC) from cocoa pod husk (CPH) via oxalic acid hydrolysis combined with a steam explosion. MFC isolation started with the Solid/Liquid extraction via Soxhlet, followed by mild citric acid hydrolysis, diluted alkaline hydrolysis, and bleaching pre-treatments. A Response Surface Methodology (RSM) was used to optimize the hydrolysis reaction at levels between 110 and 125 °C, 30-90 min at 5-10% (w/v) oxalic acid concentration. The cellulose-rich fraction was characterized by Fourier-Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) analyses. Characterization analyses revealed a cellulose-rich polymer with fibers ranging from 6 to 10 µm, a maximum thermal degradation temperature of 350 °C, and a crystallinity index of 63.4% (peak height method) and 29.0% (amorphous subtraction method). The optimized hydrolysis conditions were 125 °C, 30 min, at 5% w/v oxalic acid: with a 75.7% yield. These results compare with MFC obtained through highly concentrated inorganic acid hydrolysis from different biomass sources. Thus, we show a reliable and greener alternative chemical treatment for the obtention of MFC.

Structure and sequence based functional annotation of Zika virus NS2b protein: Computational insights.

While Zika virus (ZIKV) outbreaks are a growing concern for global health, a deep understanding about the virus is lacking. Here we report a contribution to the basic science on the virus- a detailed computational analysis of the non structural protein NS2b. This protein acts as a cofactor for the NS3 protease (NS3Pro) domain that is important on the viral life cycle, and is an interesting target for drug development. We found that ZIKV NS2b cofactor is highly similar to other virus within the Flavivirus genus, especially to West Nile Virus, suggesting that it is completely necessary for the protease complex activity. Furthermore, the ZIKV NS2b has an important role to the function and stability of the ZIKV NS3 protease domain even when presents a low conservation score. In addition, ZIKV NS2b is mostly rigid, which could imply a non dynamic nature in substrate recognition. Finally, by performing a computational alanine scanning mutagenesis, we found that residues Gly 52 and Asp 83 in the NS2b could be important in substrate recognition.