A c i d precipitation of casein has also been carried out by dissolution of C 0 in skim milk 8. The use of C 0 as a precipitant is attractive because it eliminates the formation of ionic byproducts from mineral acids. The precipitate was washed with distilled water to remove whey proteins, lactose and unbound minerals. The calcium content of casein precipitated in this way was higher than that precipitated using mineral acids. Increased solubility was observed in both cases for films containing glycerol. The increased solubility for the films containing G L Y appears to be due to the presence of the plasticizer, because both film have the same protein content.
The solubility of plasticized C0 -casein films is comparable to that of plasticized zein films made from corn zein, a prolamine, which is soluble in aqueous alcohol mixtures. Water vapor permeability WVP values for C0 -casein films are lower than those for the calcium caseinate films Table 3.
The lower R H for the calcium caseinate films, at comparable thickness to the C0 -casein films, is attributed to greater absorption of water by the protein resulting in swelling of the film. Both types of films showed an increase in W V P values with increasing film thickness which is characteristic of hydrophilic films due to swelling. Such differences in the properties of the two types of films are indicative of structural dissimilarities. Water Solubility of CQ. Whey Protein Whey proteins can be isolated after precipitation of casein from skim-milk.
The effects of heat treatment, protein concentration, and p H on plasticized films were examined. Heat was essential to form intermolecular covalent bonds and intact films 9.
The pure whey protein films, however, were too brittle and required plasticizer, which significantly increased their W V P values Table IV. A t comparable concentrations and relative humidity conditions, sorbitol plasticized whey protein films had lower W V P values than glycerol plasticized films.
Despite many attempts by researchers to make hydrophilic films more hydrophobic, the W V P values for synthetic films are still orders of magnitude lower. Comparisons of oxygen permeability, however, showed that hydrophilic milk protein films are less permeable than synthetic packaging materials 4. Covalent crosslinking of whey protein films with transglutaminase results in very strong films. One should be aware that the effectiveness of this crosslinked coating depends on the acidity and the proteolytic activity of the surface to be coated Table I V.
Classification of corn proteins into albumins, globulins, prolamines and glutelins traditionally has been based on solubility The most interesting property of zein for use as an industrial protein is its ability to form a tough, glossy, and grease-proof coating. It can be cured with various aldehydes to form an essentially insoluble product. Less than half of the protein in the meal, however, is recovered at low temperatures, after the supernate is decanted.
Their molecular weights can readily be estimated by sodium dodecyl sulfate capillary electrophoresis SDS-CE by comparing their migration time to a calibration plot of molecular weight standard proteins. These proteins associate through disulfide linkages, since only the monomer plus a small amount of dimer was present after reduction with 2-mercaptoethanol Figure lb.
Zein films containing no plasticizer had the lowest W V P values Table 5. Films prepared in acetone had lower W V P values than those prepared in ethanol. Incorporation of plasticizer into zein films significantly reduced water vapor barrier properties resulting in an almost doubling in W V P values Table 5.
In addition, W V P values, and the corresponding variation between zein films with the same plasticizer composition, decreased with increasing poly propylene glycol PPG concentrations Figure 2. Incorporation of cross-linking agents into zein films resulted in approximately a fold increase in tensile strength values Table V.
Sodium dodecyl sulfate capillary electrophoresis of zein: unreduced a and reduced b. Dickey et al.
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The precipitated product was scraped from the bottom and walls of the evaporation vessel and dried in a lyophilizer. Except for zein isolate 3, W V P values for the isolates and commercial zein were the same. Cellulose , 6 , — Laine, J. Gurnagul, N. Coefficient of friction of paper.
Surface characterization of cellulose fibers by XPS and inverse gas chromatography. Cellulose , 2 , — Dielectric discharge: A concatenated approach to fiber modification. Sakata, I. Improvement of ply-bond strength of paperboard by corona treatment. Borcia, G. Dielectric barrier discharge for surface treatment: Application to selected polymers in film and fiber form.
Bukovsky, V. The influence of secondary chromophores on the light induced oxidation of paper. Part II: The influence of oxidation of paper. Restaurator , 24 , — Corona-induced graft polymerization of ethyl acrylate onto cellulose film. Bataille, P.
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Copolymerization of styrene on to cellulose activated by corona. Graft polymerization of styrene onto cellulose by corona discharge. Preprints , 32 , — Grafting of acrylamide onto lignocellulosic fibers via dielectric-barrier discharge. Dielectric-barrier discharge treatment: A palmary approach to fiber modification. Surface modification of cellulose. Corona induced bonding of synthetic polymers to wood. Kemppi, A. Studies on adhesion between paper and low-density polyethylene. Paperi ja Puu , 78 , — Adhesion between paper and low density polyethylene.
The influence of starch. Paperi ja Puu , 79 , — The influence of fillers. Oxidative activation of wood surfaces for glue bonding. Forest Products J. Berkes, J.
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Xerox Corp. Process for obtaining a very high transfer efficiency from intermediate to paper. United States Patent. Impact of dielectric-barrier discharge on bonding.
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Enhanced wet-tensile paper properties via dielectric-barrier discharge treatment. Holzforschung , 59 , 65— Nishimura, J.
Improvement of paperboard mechanical properties by corona-discharge treatment. Tappi J. Wet-stiffening of TMP and kraft fibers via dielectric-barrier discharge treatment. Young, R. Cold plasma modification of lignocellulosic material. Denes, A. Hexamethyldisiloxaneplasma coating of wood surfaces for creating water repellent characteristics. Holzforschung , 53 , — Dielectric-barrier discharge treatments at atmospheric pressure for wood surface modification. Holz als Roh-und Werkstoff , 61 , — Tappi useful method Atlanta, GA, 54—56, Ragauskas 1 1. Het is echter in een enkel geval mogelijk dat door omstandigheden de bezorging vertraagd is.
Bezorgopties We bieden verschillende opties aan voor het bezorgen of ophalen van je bestelling. Welke opties voor jouw bestelling beschikbaar zijn, zie je bij het afronden van de bestelling. Schrijf een review. E-mail deze pagina. Auteur: Scholz American Chemical Society. Uitgever: American Chemical Society. Samenvatting This book is part two of a 3-volume series on polymers from renewable resources.
source url The entire set focuses on gathering contributions from the leading workers in specific areas of research pertaining to this field, such as agroproteins, modification of natural polymers, and environmentally benign synthesis and processing. Each book is an up-to-the-minute guide on a wide range of the studies in this emerging field from polysaccharides to polyesters, biostable polymers to the regulatory issues that are critical to the development of new commercial biodegradable products.
Recensie s It is very pleasing to read a book that delivers a lot of exciting new results and comprehensive reviews and stimulates ideas in many promising areas of understanding and application of biopolymers, particularly of biopolyesters and biocatalysts.