Alfred R. Fratzke

Purification and characterization of a xylobiose- and xylose-producing endo-xylanase from Aspergillus niger

Abstract A xylanase from a commercial Aspergillus niger pentoglycanase was purified to homogeneity by column chromatography on Ultrogel AcA 54, SP-Sephadex, Sephadex G-50, and SP-Sephadex. The enzyme hydrolyzed xylotriose slowly to xylose and xylobiose, and xylotetraose and higher xylo-oligosaccharides rapidly to mixtures of smaller xylo-oligosaccharides, with xylobiose and xylose being the preponderant final products. The anomeric configuration of the products was inverted, in contrast to the behavior of most other carbohydrases that initially produce mixtures of oligosaccharides. This enzyme is a glycoprotein having an amino acid composition high in acidic residues. Its molecular weight is 20,800 and its isoelectric point is at pH 6.7. Optimal pH values for activity and stability are between 4 and 6 and, in a 20-min assay, maximal activity is attained at 55°.

Degradation studies of novel degradable starch-polyethylene plastics containing oxidized polyethylene and prooxidant

Linear low-density polyethylene films were prepared that contained native corn starch (7, 14, or 28%), low or high molecular weight oxidized polyethylene (15%), and a prooxidant mixture (18% POLYCLEAN II) that contains manganese and vegetable oil. For each mixture all components were first mixed at high temperatures in a twin-screw extruder and pelletized. The pellets were cast into films using a single-screw extruder. Oxidized-polyethylene addition did not impair the transparency and thickness of the films and did not reduce the percentage elongation, whereas significant reductions in film mechanical properties were observed. Thermal and photodegradation properties of each film were evaluated by 70°C forced-air oven treatment (20 days), by high-temperature, high-humidity treatment in a steam chamber (20 days), and by exposure to ultraviolet light (365 nm; 4 weeks). Changes in the mechanical properties of the films were determined by an Instron Universal Test Machine; in the carbonyl index, Fourier transform infrared spectroscopy; and in molecular weight, by high-temperature gel-permeation chromatography (HT-GPC). The addition of oxidized polyethylene, especially high molecular weight oxidized polyethylene, and up to 14% starch to the films significantly increased the rate of thermal and photodegradation.

Chemical Method for the Determination of Starch in Polyethylene

Abstract A chemical/spectrophotometric procedure has been developed that allows the determination of starch and some modified starches (as glucosyl residues) in polyethylene films and pellets. The method uses samples containing up to 60 mg polyethylene and determines the anhydrous starch content of samples possessing starch loads in the range typically encountered with degradable plastics (5–40%). The method consists of dissolution of the polyethylene component into decahydronapthalene (decalin) at 150[ddot]C followed by solubilization with partial hydrolysis of the starch component in 1M HCl at 100[ddot]C. An aliquot of the resulting starch hydrolyzate is analyzed for total carbohydrate using the phenol-sulfuric acid method. The method has been tested on two sets of specially prepared starch-polyethylene films as well as on several commercial products.

Enzymatic Production of Sugars from Hemicellulose

For many years there has been an intense research effort to unlock the secrets of the enzymatic hydrolysis of cellulose. More recently the breakdown of lignin by enzymes has drawn interest. Comparatively neglected has been the enzymatic hydrolysis of the third major component of cellulosic materials, hemicellulose. Yet no breakdown of native cellulose is likely to be economically feasible without incorporating a means to hydrolyze the hemicelluloses that may comprise up to 30% of the total dry weight.