Development of antimicrobial oxidized cellulose film for active food packaging.

Foodborne diseases caused by bacteria have aroused ongoing concerns for food safety. Most existing packaging plastics bring pollution and potential toxicity. Here antimicrobial dialdehyde cellophane (DACP) was developed by periodate oxidation. The structure, mechanical properties, optical properties, and barrier properties of DACP were characterized. The antimicrobial activity of DACP against four Gram-positive bacteria was studied. The packaging effect of DACP for food with high water content was evaluated, including strawberry and tofu. The antimicrobial activity of DACP improved with increased aldehyde content. Compared with the polyethylene film and cellophane, our DACP exhibited excellent antimicrobial effect and extended the shelf life of food significantly, which shows promising prospects in food packaging.

TEMPO-oxidized cellulose nanofibril film from nano-structured bacterial cellulose derived from the recently developed thermotolerant Komagataeibacter xylinus C30 and Komagataeibacter oboediens R37-9 strains.

Bacterial cellulose (BC), prepared from two recently developed thermotolerant bacterial strains (Komagataeibacter xylinus C30 and Komagataeibacter oboediens R37-9), were used as a raw material to synthesize nanofibril films. Field-emission scanning electron microscope (FE-SEM) observations confirmed the ultrafine nano-structure of BC pellicle (BCP) with average fibril widths between 50 and 60 nm. The BC was directly oxidized in a TEMPO/NaBr/NaClO system at pH of 10 for 2 h. TEMPO-oxidized bacterial cellulose nanofibrils (TOBCN) were obtained by a mild mechanical treatment and the TOBCN films were prepared through heat-drying. The oxidation yielded a recovery ratio between 70 and 80% by weight with an increase in the carboxylate content of 0.9-1.0 mmol g -1. Nanofibrillation yields were more than 90% and the resulting high aspect ratio TOBCNs were ~6 nm in average width with >800 nm in lengths, when observed under transmission electron microscope (TEM). TOBCN film of K. xylinus C30 exhibited high transparency (79%), tensile strength (142 MPa), Young's modulus (7.13 GPa), elongation around failure (3.89%), and work of fracture (2.29 MJ m-3), when compared to the TOBCN films of K. oboediens R37-9 at 23 °C and 50% RH. Coefficients of thermal expansion of both the TOBCN films were low at around 6 ppm K-1.

Oxidized cellulose esters: I. Preparation and characterization of oxidized cellulose acetates--a new class of biodegradable polymers.

Oxidized cellulose acetates (OCA), with a degree of substitution (DS) value ranging between 1.1 and 2.3 and a free carboxylic acid group content of 20% (w/w), have been prepared by reacting oxidized cellulose (OC, COOH content 20% w/w) with a mixture of acetic acid and acetic anhydride in the presence of sulfuric acid as a catalyst. The DS of OCA, in general, increased with increasing reaction temperature, reaction time, and concentration of acetic anhydride in the reaction mixture. The yield of OCA, in contrast, increased with increasing concentration of acetic anhydride and decreased with increasing reaction time and temperature. The intrinsic viscosity of OCA varied between 0.100 and 0.275, depending on the reaction conditions used during its preparation. In general, an increase in reaction temperature and the use of a prolonged reaction time decreased the intrinsic viscosity of OCA. No correlation was found between DS and intrinsic viscosity of OCA. The apparent pKa of OCA is 3.7-3.9. The new OCA polymers are practically insoluble in water and slowly dissolve in pH 7.4 phosphate buffer solution. They are, however, soluble in a range of organic solvents (e.g. ethyl acetate, acetone, acetone/water, chloroform/methylene chloride, dimethylsulfoxide, dimethylformamide, and/or chloroform/methanol).

Cellulolytic fungi isolated from an alluvial soil in a semi-arid area of the northeast of Brazil

Fungos foram isolados de um solo aluvial numa zona semi-árida (caatinga) do Estado de Pernambuco, em área sem vegetaçäo, anteriormente coberta por espécies de caatinga. O solo foi caracterizado como álico quartzo-arenoso com níveis relativamente altos de Al+++ e pH ácido. Durante a estaçäo seca a umidade do solo é muito baixa e a temperatura na superfície pode chegar a 70oC. Um dos métodos para determinar a retençäo de água pelo solo inclui o uso de um disco de papel de filtro colocado sobre um suporte, dentro de um recipiente plástico contendo solo úmido. Fungos do solo que crescem e destroem o papel de filtro foram isolados e identificados. A capacidade dessas espécies para atacar o papel indica a sua atividade celulolítica. Duas das espécies isoladas (Curvularia brachyspora e Penicillium pinophilum constituem novas referências para o Estado de Pernambuco