Authors:J. Silverio, E. Svensson, Ann-Charlotte Eliasson, and G. Olofsson
In the present study, isothermal microcalorimetry was introduced as a tool to investigate properties of starch retrogradation during the first 24 h. The study was made on purified amylose and amylopectin from corn, as well as on native starches, such as wheat, potato, maize, waxy maize and amylomaize, differing in their amylose content. The results were obtained in the form ofP-t traces (thermal powervs. time), and integration of these traces gave a net exothermic enthalpy of reaction, caused by the crystallization of amylose and amylopectin. TheP-t traces reflected the quantities of amylose and amylopectin in the starch studied. Depending on the amylose content and the botanical source of the starch, the rate of crystallization of amylose was high and predominated over that of amylopectin during the first 5–10 h. The contribution from amylose crystallization to the measured exothermic enthalpy was very substantial during this period. After ∼10 h, amylose crystallized at a lower constant rate. During the first 24 h, amylopectin crystallized at a low steady rate. The exothermic enthalpies obtained by the isothermal microcalorimetric investigations during the first 24 h of retrogradation were generally low in relation to the endothermic melting enthalpies observed by differential scanning calorimetry (DSC) measurements after 24 h of storage. The discrepancies in enthalpy values between the two methods are discussed in relation to phase separation and the endothermic effects owing to the decrease in polymer-water interactions when polymer-rich regions in the starch gel separate. Besides the exothermic enthalpies obtained, theP-t traces also made it possible to study the initial gelation properties of amylose from different botanical sources. The present study further demonstrated that isothermal microcalorimetry can provide a possible way to investigate the antistaling effect of certain polar lipids, such as sodium dodecylsulphate (SDS) and 1-monolauroyl-rac-glycerol (GML), when added to starches of different botanical origin. The net exothermic heat of reaction for starch retrogradation during the first 24 h was decreased when GML or SDS was added to the starch gels. The recordedP-t traces also showed how the effect of the added lipid influenced different periods during the first 24 h of starch retrogradation, and that the effect depended mainly on the amylose content, the botanical source of the starch, and the type of lipid used. When GML or SDS was added to waxy maize, the isothermal microcalorimetric studies clearly indicated some interaction between amylopectin and the polar lipids. These results concerning the action of anti-staling agents are further discussed in relation to the helical inclusion complexes formed between amylose-polar lipid and amylopectin-polar lipid.
The degradation of cellulose and starch samples in air and nitrogen has been investigated by thermal analysis techniques.
The techniques employed were differential thermal analysis, rising temperature and temperature jump thermogravimetry. Rate
data were obtained from these experiments and Arrhenius parameters calculated from these values. This data was used to determine
the mechanism by which the cellulose and starch samples degraded. The Arrhenius parameters were also calculated. The behavior
of starch and cellulose upon thermal analysis were compared and are reported.Eact for corn starch was found to be 474 kJ mol−1 and for a cellulose 242 kJ mol−1.
Authors:L. Lacerda, M. da Silva Carvalho Filho, I. Demiate, G. Bannach, M. Ionashiro, and E. Schnitzler
Corn starch, partially hydrolyzed by fungal α-amylase was investigated by using thermal analysis, microscopy and X-ray diffraction.
After enzymatic treatment lower degradation onset temperatures were observed. DSC analysis showed almost similar range of
gelatinization temperature, however, the enthalpies of gelatinization increased for the partially hydrolyzed starch granules.
According to the X-ray diffraction analysis, stronger cereal pattern peaks were recognized after enzymatic digestion. The
results suggested that the hydrolysis was more pronounced in the amorphous part of the starch granules.
Authors:F. Santos de Souza, A. Gomes Barreto, and R. Macêdo
The present work proposes evaluation of the gelatinization processes of starch by means of DSC coupled with a photovisual
system. The use of DSC, TG and DTA for a fast and efficient evaluation of the starch is suggested. The DSC curves of starch
gels with water contents of 20, 30, 40 and 50% (mass/v) exhibited different phase transitions, corresponding to the gelatinization
processes at the different water contents for the different lots. The DSC-photovisual system confirmed calorimetric behaviour
differences between the starch lots studied.
Authors:V. T. Huang, L. Haynes, H. Levine, and L. Slade
Dielectric Spectroscopy (DS) and Thermomechanical Analysis (TMA) were used to identity the glass transition temperature (Tg) of native wheat starch, vital wheat gluten and a commercial bread, in response to changes in moisture content. An open-ended coaxial probe technique was used to measure the permittivity or dielectric constant (ɛ′) and the loss factor (ɛ″) as functions of moisture, for 2.45 GHz frequency, at constant density and temperature. Plots of ɛ′ and ɛ″ as functions of moisture content showed dramatic changes in mobility-based dielectric properties, which occur upon transition from the glassy solid to the rubbery liquid state. The modified TMA method can measure the change in viscoelastic properties aroundTg. This study further confirms that synthetic polymer science principles can be applied to food systems.