Plasticized starch and cellulose whiskers composites

Nanocomposites materials were prepared using a starch/glycerol based matrix and a colloidal suspension of cellulose whiskers as a natural and biodegradable reinforcing phase. The cellulose whiskers used in this study, prepared from tunicin, an animal cellulose, consist of slender parallelepiped rods with lengths ranging from 100 nm to several pm and widths on the order of 10-20 nm. The raw materials were mixed in an autoclave reactor and afterwards they were cast and evaporated under vacuum. The resulting films were characterized using differential scanning calorimetry, water absorption experiments and mechanical analysis in the linear range. High performance composites were obtained from these systems, preserving the natural and biodegradable character of starch. A high reinforcing effect and a thermal stabilization due to the whiskers addition were observed. Favorable interactions between the matrix and the reinforcing phase are also reported. In addition, the composites show a decrease in water sensibility as the cellulose whiskers content increases

When cholesterol is not cholesterol: a note on the enzymatic determination of its concentration in model systems containing vegetable extracts

Abstract Background Experimental evidences demonstrate that vegetable derived extracts inhibit cholesterol absorption in the gastrointestinal tract. To further explore the mechanisms behind, we modeled duodenal contents with several vegetable extracts. Results By employing a widely used cholesterol quantification method based on a cholesterol oxidase-peroxidase coupled reaction we analyzed the effects on cholesterol partition. Evidenced interferences were analyzed by studying specific and unspecific inhibitors of cholesterol oxidase-peroxidase coupled reaction. Cholesterol was also quantified by LC/MS. We found a significant interference of diverse (cocoa and tea-derived) extracts over this method. The interference was strongly dependent on model matrix: while as in phosphate buffered saline, the development of unspecific fluorescence was inhibitable by catalase (but not by heat denaturation), suggesting vegetable extract derived H2O2 production, in bile-containing model systems, this interference also comprised cholesterol-oxidase inhibition. Several strategies, such as cholesterol standard addition and use of suitable blanks containing vegetable extracts were tested. When those failed, the use of a mass-spectrometry based chromatographic assay allowed quantification of cholesterol in models of duodenal contents in the presence of vegetable extracts. Conclusions We propose that the use of cholesterol-oxidase and/or peroxidase based systems for cholesterol analyses in foodstuffs should be accurately monitored, as important interferences in all the components of the enzymatic chain were evident. The use of adequate controls, standard addition and finally, chromatographic analyses solve these issues.</p