Seymour G. Gilbert

Determination of Potential Migrants from Commercial Amber Polyethylene Terephthalate Bottle Wall

Potential migrants were isolated from commercial polyethylene terephthalate (PET) bottles using Soxhlet extraction. The concentrated extract was then subjected to GC/MS analysis. A total of 19 migrants has been identified. The majority of compounds appeared to be intermediate reaction products or residual monomers of their dehydration and transesterification products. Several processing aids such as fatty acids and commonly used plasticizers were also identified. The amount of seven compounds present in the major portion of exhaustive extract of the PET bottle wall ranged from 800 µg/g polymer to as low as 0.6 µg/g.

Isolation and Identification of Potential Migrants in Gamma-Irradiated Plastic Laminates by Using GC/MS and GC/IR

Potential migrants were isolated by Soxhlet extraction from plastic laminates of PETG/PVDC/PE used to make a single-use injection system. Most of compounds were identified from mass spectra by comparison to reference spectra. However, reference spectra were not available for several major compounds in the Soxhlet extract from irradiated test laminates. Those unknown compounds were identified by using both GC/IR and GC/MS. The change in polymer structure due to irradiation was also monitored by using Fourier transform infrared spectroscopy.

Determination of protein immobilized on solid support by tryptophan content

Abstract The method of Gaitonde and Dovey [ Biochem. J. 117, 907 (1970)] for the determination of tryptophan by reaction with ninhydrin in acid is adapted for the measurement of protein bound to solid support materials, including collagen. DEAE-Sephadex, DEAE-cellulose, polyacrylamide and collodion give negligible background absorbance with the reagent; collagen and activated agarose give some color, but this can be abolished by pretreating the collagen with H 2 O 2 . Collagen, Sephadex and agarose dissolve in the reagent. Levels of lactase (β-galactosidase) and glucoamylase were readily and linearly measured down to 0.2 mg in the presence of 21 mg collagen, and activity and immobilized protein content of lactase-collagen complexes were linearly related.

Control of water in foods during storage

Moisture content and its water activity (aw) are critical parameters affecting the shelf life of most food products. In most cases excessive amounts of water will cause spoilage, while in other cases loss of water will render foods unacceptable. The control of water in foods requires knowledge of their sorption/desorption behavior, critical moisture content, the environmental storage conditions of temperature and relative humidity, packaging parameters including volume to area ratios and permeability. Fast and reliable methods of evaluating the above parameters are needed to predict the storage life of foods. The importance of moisture control in produce as well as in dry products is discussed. Fast methods to evaluate water sorption/desorption behavior of foods are described. A computer program, which integrates all parameters required to predict the water dependent shelf life of foods, including changing conditions during storage, is also reported.

Isolation and identification of oxidation product of 2,6-Di-(tert-butyl)-4-methylphenol from polyethylene film

Abstract2,6-Di-(tert-butyl)-4-methylphenol is a widely used antioxidant in the production of polyethylene. An oxidation product of this antioxidant was isolated from aged polyethylene film and purified by preparative thin layer chromatography. This compound was identified as 3,3′, 5,5′-tetra-bis(tert-butyl)-stilbenequinone with the aid of IR- and mass spectroscopy. The generation of this oxidation product can lead to the discoloration of polyethylene film, and its formation can be catalyzed by contact with carbon black.

Sorption isotherms of acrylonitrile on an acrylonitrile-styrene copolymer

Abstract Inverse Gas Chromatography (IGC) was used to construct sorption isotherms of acrylonitrile (ACN) on an acrylonitrile-styrene copolymer. The absolute value of the isosteric heat of adsorption (at constant uptake) increased with decrease in the amount of ACN adsorbed, indicating a stronger monomer-polymer interaction at the lower monomer concentrations. The Gibbs free energy obtained from the partition coefficients, as calculated from the ratio of monomer concentrations in the stationary and moving phases, was of the same order of magnitude as the values obtained from the specific retention volumes. The absolute value of this energy increased with decrease in monomer concentration and temperature, indicating a more favourable monomer-polymer interaction at the low temperatures and monomer concentrations.

Permeability of turkey eggs from hens with different hatchability rates

Abstract 1. 1. Permeability comparisons were made on egg shell and membranes from Small White turkey hens having average low (66%) and average high (90%) hatchability records after 15 weeks of production. 2. 2. Average permeabilities of egg shells with membranes in the dry state were higher in eggs from hens with a history of low hatchability (26.55 × 10−7 cm3 · mm · STP/sec · cm2 · T), as compared with eggs from hens with a history of high hatchability (23.39 × 10−7 cm3 · mm · STP/sec · cm2 · T). 3. 3. Lower permeability was found for egg membranes in the wet state.

Chemical Modification of Collagen and the Effects on Enzyme-Binding: Mechanistic Considerations

The effect of structural modification on the enzyme-binding capacity of collagen has been studied using beta-galactosidase (E. coli K12) immobilized to collagen membrane by the impregnation procedure. The apparent steady-state activities of the resultant collagen-enzyme complexes were determined as a means of evaluating the enzyme-binding capacity of the modified collagen. In addition, the amount of enzymic protein bound to the collagen support was determined by the tryptophan content of the complex. The tertiary structure of the collage matrix was modified by cross-linking with the difunctional reagent, glutaraldehyde, and by aging in the dry state. Such structural modifications were found to markedly reduce the enzyme (beta-galactosidase) binding capacity of collagen films. The enzyme-binding capacity of the crosslinked collagen membrane was completely restored by proteolytic enzyme treatment of the aged film but only partly so for the glutaraldehyde treated films. Proteolytic enzymes used to treat a dispersion of collagen microfibrils prior to casting into a membrane also resulted in an increase in enzyme-binding. The effect of structural modification of collagen on enzyme-binding and the locus of enzyme attachment are discussed.

Application of a Modified I.G.C. Method in the Study of the Water Sorptional Behavior of Selected Proteins I. Lysozyme-Water Interactions

SUMMARY The water sorptional bahavior of a hydrophilic protein (purified lysozyme) as affected by sample pretreatment (slow freezing, fast freezing, glycosylation and predrying) was studied using a modified pulse inverse gas chromatographic method. Fast-frozen lysozyme showed a slightly higher water adsorption than slow-frozen one, where glycosylated lysozyme adsorbed less compared to the unglycosylated sample. On the other hand, predrying of the substrates caused a relatively significant diminishing on their sorptional behavior because of structural changes (restructuring) occuring during predrying. Data were succesfully fitted to the Guggenheim, Anderson and De Boer (G.A.B.) equation and analysed according to the Zimm-Lundberg cluster theory. Results showed enhanced cluster formation tendency for predried materials as well as for glycosylated lysozyme.