摘要:

AbstractCold water soluble polysaccharides (CWX) extracted from taro were tested for their influence on the pasting properties of taro starch and 3 other commercial starches (maize, rice and wheat). Addition of taro CWX resulted in increased peak viscosity with maize and rice starch and a decrease in peak viscosity with wheat starch. Cold paste viscosity was decreased in wheat and taro starch, but not in maize and rice starch. Examination of the effect of pH and salt on changes in maize starch viscosity showed no further variation on addition of taro CWX.

ISSN:0038-9056    

DOI:10.1002/star.19970490702

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA study has been made of the effect of hydrolysis on the structure of three types of starch and their subsequent gelatinisation behaviour. The techniques utilised are simultaneous small and wide angle X‐ray scattering (SAXS and WAXS respectively) using a synchrotron source, and differential scanning calorimetry. By fully fitting the small angle scattering curve to identify the behaviour of the different regions within the starch granule, it is possible to understand how the SAXS peak can get less pronounced upon hydrolysis, while the WAXS peaks get more intense. The breadth of the DSC gelatinisation endotherm also increases with extent of hydrolysis. All three findings can be related to the preferential destruction of the amorphous background region during the hydrolysis proces

ISSN:0038-9056    

DOI:10.1002/star.19970490703

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractIn this work we present a new method which allows to determine the structural changes of starches subjected to a thermal process. Using that method, the initial and final gelatinization temperatures and the amount of energy required to induce the thermal changes can be deduced. The method takes the advantage of the dielectric dissipation of electrical energy in the system consisting of a mixture of starch grains and water enclosed in a specially designed sealed cell. AC electrical power at a fixed voltage and frequency is applied to the material to be studied. The magnitude of the electric current is then monitored as the temperature is raised (by Joule effect) up to temperatures of 120°C. The plots of the electric currentVstemperature in all the samples studied yield two distinct extreme values: the onset and the ending temperatures of the gelatinization of the processed samples. Analyzing the currentVstime plots during the gelatinization of starch, we are able to determine the energy required for the transformation process. The method as such, demonstrates to be a useful technique to determine the basic parameters during starch gelatinization and it is much simpler then those known in the field

ISSN:0038-9056    

DOI:10.1002/star.19970490704

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractDifferential Scanning Calorimetry (DSC) was used to study retrogradation of wheat starch. For storage at 4°C, enthalpy (ΔH) values of retrogradation endotherm (recrystallization) of wheat starch containing various moisture levels (25–80%) slowly continued to increase except in samples with moisture level of 50, 60 and 70%. For storage at 26°C and 32°C, most recrystallization of wheat starch occured within one and two weeks of storage time, while recrystallization with a moisture level of 50% at 26°C occurred for 4 weeks. The peak temperatures of retrogradation endotherm at various moisture levels (25–80%) after 4 weeks of storage time increased largely as the storage temperatures increased from 4 to 32°C. The enthalpy values of retrogradation endotherm after 4 weeks of storage occurred to a greater extent at a lower storage temperature. The glass transition temperature and starch recrystallization have a close relationship. In the recrystallization of wheat starch, the nucleation and propagation rate after 4 weeks of storage can be converted into enthalpy and peak temperature of retrogradation

ISSN:0038-9056    

DOI:10.1002/star.19970490705

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractStarch‐hydrocolloid interactions were studied in concentrated (40% w/w starch) aqueous dispersions by differential scanning calorimetry and dynamic rheometry. At the levels commonly employed in food product formulations (1–2% w/w hydrocolloid on a starch basis), polysaccharides of varying molecular structures (xanthan, β‐glucan, arabinoxylan, guar gum) did not affect the gelatinization temperature of waxy maize and wheat starches. However, the hydrocolloids increased the phase transition temperature range (Tm‐Ti) and the melting enthalpy of starch crystallites, implying a stabilization of the granular structures during heating. There was also an enhancement in the crystallization rate of amylopection on aging gels at 5°C, the effect being more marked with the waxy maize starch gels. The most pronounced effect, however, has been the retardation of gelation kinetics of waxy maize starch by the hydrocolloids. The decrease in storage modulus (G′) development of amylopectin‐hydrocolloid gels was attributed to the interference of intermolecular associations among amylopectin molecules by the polysaccharide, which seems to be a prerequisite for establishment of a continuous network structure. In contrast, wheat starch gel rheology did not seem to be affected by the

ISSN:0038-9056    

DOI:10.1002/star.19970490706

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractTo obtain water resistance in extruded corn starch, additions of polysaccharides konjac and curdlan were examined. Solubility of extrudates increased as the starch moisture content decreased. Solubility of extruded starch with 3% curdlan added was 38% of that of control. On the other hand, in case of addition of konjac, solubility of extrudates was increased regardless of additive amount. Solubility of extrudates was linearly related to expansion ratio, specific volume, swelling power and shear strength. It was suggested that the structure of extrudates with addition of curdlan were tight and more resistant to absorption of water than the control. Solubility of ground extrudates was linearly related to that of intact extrudates. Extrudates with addition of curdlan exhibited rigid surface and internal structures.

ISSN:0038-9056    

DOI:10.1002/star.19970490707

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe kinetics of the maltose hydrolysis by means of free and immobilized in polyacrylamide gel glucoamylase has been investigated. The kinetic constants in theMichaelis‐Menten'sequation have been determined. In the case of immobilized enzyme two different methods have been used, the one giving intrinsic constant values and the other – affected by the diffusion resistances. The obtained kinetic parameters were compared with these determined for free enzyme system.A mathematical model of the process has been constructed. The inhibition effect of the product and the reversibility of the reaction have been taken into account. The model has been solved using already determined kinetics parameters. Very good correlation between calculated and experimental data was fo

ISSN:0038-9056    

DOI:10.1002/star.19970490708

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractGlucoamylase (GA) (EC 3.2.1.3) fromRhizopussp. A‐11 using metalion regulated liquid medium was purified by ammonium sulfate precipitation and column chromatography on CM‐Sephadex C‐50. Since purification was easy, the enzyme was purified about 5.0 fold with a 72.9% yield. The enzyme was proved to be homogeneous as judged by SDS‐PAGE, and has a molecular weight of about 72.4kDa. The enzyme strongly digested against raw starches. Raw cassava, wheat, and corn starch digesting relative specific activities of the purified enzyme were 15, 13, and 15%, respectively, as compared with soluble starch digesting specific activity (21,360 units/mg protein). Raw cassava, wheat, and corn starch adsorption rates were 99,99, and 99%, respectively. This culture produced little acid or neutral protease. According to the high raw starch digesting activity, high raw starch adsorption rate, low protease activity, and high molecular weight of the GA, it may be classified as GA‐I. Most proteins in the culture were GA. These results suggest a considerable advantage for GA production by liquid cu

ISSN:0038-9056    

DOI:10.1002/star.19970490709

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractRecently an improved gas chromatographic method to determine the total and free adipate content of acetylated cross‐linked starches has been developed. Within the auspices of an ISO/TC 93 work group, these protocols were validated in 1993 by an international collaborative study. Statistical evaluation is essential to confirm validation, but the recommended protocols to apply have evolved with time. When the test was first done, the Dutch Normalisation protocol NEN 6303 (1988) based on ISO 5725 (1986) was current. However, in 1994 a revised ISO 5725 was issued, which should now be the preferred version of statistics. A study of the respective protocols shows that they differ in respect to the criteria applied for outlier detection and removal. When making an evaluation with each of the statistical protocols, somewhat different values for reproducibility and repeatability are obtained.Applying the latest version of ISO 5725, the validation of the international collaborative study gave the following results: (1) for the total adipate determination the repeatability (r) and reproducibility (R) are respectively 60 and 120ppm adipic acid, and (2) for the free adipate determination the repeatability (r) and the reproducibility (R) are respectively 10.1 and 55.4ppm adipic aci

ISSN:0038-9056    

DOI:10.1002/star.19970490710

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractIn a conventional method of cyclodextrin production starch is first liquefied by a heating method in the presence or absence of an hydrolizing enzyme before cyclodextrin glucosyl transferase (CGTase) is added to induce synthesis of cyclodextrins. The production of cyclodextrins is carried out at below 60°C within a period of 2–3 days. A novel cyclodextrin glucosyl transferase produced by Novo Nordisk A/S which is characterized as a thermostable enzyme with capacity to liquefied starch was tested. Different starches were simultaneously liquefied and converted by CGTase using various experimental reaction conditions. The investigations indicate the influence of the starch source (potato, wheat, corn, tapioca, waxy maize), of the initial starch concentration (5–25%), of the enzyme dosage (0,1–0,75%) and of reaction time (1–24h) on the ratio of created α‐, β‐ and

ISSN:0038-9056    

DOI:10.1002/star.19970490711

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY