摘要:

AbstractNine starches from different plants were studied in the semidilute concentration regime. The amylose content varied between 0% (waxy starch) and 76%. The applied concentration range of 5 to 30% (w/v) corresponds to typical concentrations used for thickeners in food and non‐food industries. With the exception of the amylose rich starches the maximum concentration was at least 4 times larger than the overlap concentration. Up to a certain concentration a common master curve was found for all starches but at high concentrations this master curve was superimposed by association and aggregation phenomena. The aggregation is promoted by the presence of amylose. The onset of aggregation is shifted to lower concentrations when the amylose content in the starches was high. The aggregation proceeds in time. It could be followed by dynamic light scattering and quantitatively be evaluated. The time dependent ageing of the solutions and the finally formed gels gave evidence for a liquid‐solid phase separation that is kinetically hampered by the presence of the branched amylopec

ISSN:0038-9056    

DOI:10.1002/star.19970490602

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractMit dem Ziel der Veränderung funktioneller Eigenschaften einer Weizenstärke wurden die Möglichkeiten zur hydrothermisch‐enzymatischen Modifizierung bei Wasserüberschuß (Temperung) unter weitestgehender Erhaltung der granulären Struktur der Stärke überprüft. Da Weizenstärke wegen der niedrigen Quellungstemperatur unter den üblichen Temperungsbedingungen (T=50°C) nur geringfügig verändert werden kann, wurde zum Abbau des bei höherer Temperungstemperatur irreversibel gequollenen Stärkekornanteils Bakterien‐α‐Amylase eingesetzt. Das hierbei entstehende Saccharid‐Spektrum, das zu ca. 50% aus Maltose gebildet wird, vermag die Matrix der Weizenstärke selbst bei größeren Temperungstemperaturen (54°C) zu schützen. Das Verkleisterungs‐ und Gelbildungsverhalten wird aber in charakteristischer Weise verändert, und zwar insbesondere durch starke Steigerung der Heißkonsistenz bei 95°C. Nachfolgend bricht die erzielte Konsistenz wiederum stark zusammen und liegt unter Abkühlung unter den entsprechenden Daten der Ausgangsstärke. Für die Ausbeute an getemperter Stärke ist bei höherer Temperatur die Reaktionszeit maßgeblich. Um die Schutzfunktion der gebildeten Saccharide, insbesondere der Maltose in größerer Konzentration aufzuzeigen, wurde in Maltosesirupen variabler Konzentration (6, 12, 25%) getempert. Bis zu 12% und einer Reaktionstemperatur von 50°C konnte der Konsistenzverlauf um 300 bis 500‐BE angehoben werden; bei 54°C blieb die Modifizierung begrenzt. In 25%igem Maltosesirup konnte allerdings auch bei 54°C erfolgreich getempert werden. Die Ausbeuteverluste waren erwartungsgemäß klein (<10%). Bei der Anwendung eines gestuften Temperatur‐Zeit‐Programms in Gegenwart von α‐Amylase bzw. 25% Maltosesirup traten die jeweils erwarteten Konsistenzverschiebungen auf, allerdings in begrenzterem Umfang. Markant waren schließlich

ISSN:0038-9056    

DOI:10.1002/star.19970490603

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractIn view of utilizing the commercial enzyme Maltogenase for the production of maltose syrup in a continuous membrane reactor, some kinetic properties of this enzyme were investigated. Preliminary tests were conducted usingZulkowskysoluble starch as substrate. At pH 5.0 and 60°C, theMichaelisandMentenkinetic constants Vmaxand KMwere respectively 2.47mmol of maltose equivalents·min−1·dm−3and 9.64g of Zulkowsky soluble starch·dm−3. Initial hydrolysis velocity was reduced at high starch concentrations and in the presence of maltose. When liquefied cassava starch (≈60 to 340g·dm−3) was used as substrate, hydrolysis kinetics was modelled by analyzing whole progress curves. A simple empirical modell was established and allowed satisfactory descriptions of the experimental data for the formation of maltose over time at large enzyme/su

ISSN:0038-9056    

DOI:10.1002/star.19970490604

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractStarch and oxidized starches of different molecular sises were carboxymethylated under identical conditions. The degree of substitution (DS) of the so obtained. CMS samples increases by decreasing the molecular sise of starch which, indeed, is a manifestation of higher extents of oxidation. The latter was effected using different sodium hypochlorite concentrations and the extent of oxidation was expressed as chlorine consumption. Pastes of these CMS samples exhibit pseudoplastic behaviour and their apparent viscosity decreases as the extent of oxidation increases, when used as thickeners in printing polyester fabric with disperse dyes, these pastes bring about prints the colour strength (K/S) of which are comparable with these for conventional thickeners, namely commercial CMS and sodium alginate. Mixing of sodium alginate with the prepared CMS samples increases the efficiency of the latter to act as the thickening agent. The highest K/S is obtained with CMS derived from starch oxidized using 1.25g active chlorine/1. Mean while, the colour fastness properties of the prints towards rubbing, washing and perspiration are nearly equal to those fabrics printed using the conventional thickeners such as sodium alginate or commercial CMS.

ISSN:0038-9056    

DOI:10.1002/star.19970490605

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAmino acids of differing hydrophobicity were tested as plasticizers in starch‐glycerol (4:1 weight ratio) blends and were compared to the more conventional plasticizers, urea, sucrose and ammonium chloride. In mechanical tests (tensile strength and percent elongation) on extruded ribbons containing up to 20 weight percent plasticizer, glycine and isoleucine hydrochloride were found to be extremely poor plasticizers. However, lysine behaved similarly to sucrose. Proline compared favorably to urea. Moreover, at concentrations of 23 and 29 weight percent, proline was superior to urea in its ability to increase the percent elongation of the starch‐glycerol mixture. The glass transition temperature (Tg) for the standard starch‐glycerol samples was 40°C, as determined by differential scanning calorimetry. Added lysine hydrochloride, sucrose, proline and urea effected the Tgsimilarly. At 5 weight percent all Tg's increased, while at 20 weight percent they dropped to room temperature or below. Isoleucine, at low or high concentration, yielded a Tgof 60°C, consistent with very brittle material. Biodegradation experiments were conducted on selected formulations by monitoring CO2evolution after inoculation withAspergillus niger. Little CO2accumulated from the standard starch‐glycerol mixture or sucrose plasticized blends, likely due to a lack of combined nitrogen. In contrast, proline and urea‐plasticized blends were rapidly

ISSN:0038-9056    

DOI:10.1002/star.19970490606

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractCyclodextrin glycosyltransferases (CGTases) catalyse the cyclisation of starch dextrins to cyclodextrins and concomitantly show amylolytic activity which is commonly determined by the starch‐iodine assay. In the present study it was found that cyclodextrins interfere with this assay. Adding cyclodextrins in concentrations ranging from 0.01mMto 0.6mMto starch‐iodine complex solution resulted in a significant decrease in absorbance at 600nm due to α‐ and β‐cyclodextrin competing with starch in the iodine complex formation. The largest reduction was caused by α‐cyclodextrin. Therefore, the use of the starch‐iodine assay will result in an overestimation of the amylolytic activity of CGTases – particularly when the enzyme has a high α‐cyclodextrin production activity. In contrast, determination of the amylolytic activity by measurement of released reducing sugars with CuSO4/bicinchonate was not disturb

ISSN:0038-9056    

DOI:10.1002/star.19970490607

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

ISSN:0038-9056    

DOI:10.1002/star.19970490608

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

ISSN:0038-9056    

DOI:10.1002/star.19970490609

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

ISSN:0038-9056    

DOI:10.1002/star.19970490610

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

ISSN:0038-9056    

DOI:10.1002/star.19970490612

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY