Starch thermogram

DSC can also be used to determine starch retrogradation. After heating potato starch (30% (w/w)) to 180°C, samples are cooled to 5°C. Once the temperature reaches 5°C, the sample is immediately removed from the DSC and stored at low temperature. After a certain number of days, the sample pan is placed into the sample holder of the DSC, and heated from 5 to 180°C at 10°C /min. The instrument is calibrated using indium and an empty pan as a reference. The enthalpy (AH) of phase transitions is measured from the endotherm of DSC thermograms based on the mass of dry solid. Transition temperatures such as onset, peak, and completion temperature are also measured. 

The high lipid content of oat starch is reflected in the high value of the transition enthalpy (AHCX) measured for the amylose-lipid complex (Table 15.4). This transition is reversible, and on a rerun greater AHCX, as well as Tcx (endotherm peak temperature), was found.26 When the oat starch was defatted, the endotherm assigned to the amylose-lipid complex disappeared from the DSC thermogram.26 Extraction at room temperature with 1-propanol water (3 lv/v) did not influence the thermogram of the starch, but if the starch was refluxed in the same solvent, a decrease in AH and a complete elimination of the endotherm ascribed to the amylose-lipid complex occurred.28 For oat starches with a lipid content of 1.1-1.7%, it was possible to... 

C, respectively, compared with those of glucose, glycine, sucrose, maltose, and starch, 31, -71, 62, 87, and > 200 °C, respectively. Mixing the Standard Melanoidin with water rapidly reduced the Tg for 4.4% (w/w, total) water rg=19°C and for 18.3% water Tg = -70 °C. The DSC thermogram also showed sharp endotherm peaks for Solution A and the Standard Melanoidin at 160 and 140 °C, respectively, attributed to the degradation of carbonyl compounds. The temperature at which this peak occurs was also lowered on addition of water 4.4% lowered it to 100 and 24% to 80 °C. 

Figure 4-15 Schematic of DSC Thermograms of Starch Heated in Excess and Limited Water Content At low water content the endotherm shows two peaks M and M2 (Hoseney, 1998).

DSC thermograms obtained during thawing of starch pastes (sucrose not included) (a) without hydrocolloid, (b) with xanthan gum, (c) with guar gum, and (d) with sodium alginate. Upper curves not-annealed samples numbers indicate Tg onset. Lower curves samples annealed at - 4.5°C numbers indicate onset. Curves were not normalized and correspond to different mass samples. 

DSC thermograms of samples frozen and armealed (30 min) at T = - 19°C (a) starch-sucrose-water (b) starch-sucrose-xanthan gum-water (c) starch-sucrose-guar gum-water (d) starch-sucrose-alginate-water. Numbers indicate Tg onset. 

In differential thermal analysis, the starch is intimately mixed with a thermally inert materiaP such as calcined kaolin or alumina the mixture is heated at a uniform rate, and the temperature of the mixture is compared with that of a sample of the pure, inert material heated in the identical manner. Any exothermic or endothermic reaction in the starch causes a positive or negative temperature-difference between the two samples this can be recorded, and appears as a positive or negative peak on the resultant thermogram. Differential thermal analysis can be conducted in different atmospheres, such as air, oxygen, or nitrogen, or under vacuum. 

FIGURE 3.2 DSC thermograms of native and microwaved cereal starches. (From Lewandowicz, G. et al., Carbohydr. Polym., 42, 193, 2000. With permission.)... 

Figure 4.4 DSC thermograms of potato starch-water in sealed pans, recorded at a heating rate of 10 °C/min, with the volume fraction of water varying from 0.28 in the bottom curve to 0.81 in the top curve. Reproduced with permission from ref. [15].

Figure 2.2 DSC thermograms of potato starch obtained at a heating rate of 10 C/min, labelled with volume fraction of water present. (Reprinted with permission from reference 111], Copyright 2013, Wiley.)...

Figure 2.3 DSC thermograms of retrograded waxy corn starch with intermediate water content after initial heating to 120°C and immediate quenching and storage at 5 °Cfor 0, 1, 2, 3, 4, 5, 10, 18 h, 1, 3, 5, 10, 15 and 20 days, respectively (from bottom). (Reprinted with permission from reference 134], Copyright 2013, John Wiley Sons, Ltd.)...

TG/DTG/DSC investigation of the starch-cellulose composite films was performed in order to study their thermal decomposition behavior. Some thermal characteristics of composite materials which contain different cellulose fillers (beech cellulose, beech wood sawdust) were evidenced from thermograms (data presented in Table 7.4). 

Features of the interactions between starch gel and A-300 reflect also in the TSDC thermograms (Figure 1.170). An LTband (T< 170 K) shifts toward higher temperatures and its intensity for water/ starch/A-300 is smaller than that for water alone or A-300 suspension. An HT band (J> 170 K) shifts toward lower temperatures and its intensity grows. The first effect is due to stronger hydrogen... 

FIGURE 5.11 (a) TSDC thermograms of dry initial starch, hydrogel of gelatinized starch (14.2 wt%),... 

Figure 8.2 DSC thermograms of potato starch obtained at a heating rate of 10 °C/ min, labelled with volume fraction of water present. Weight of starch (dry basis), from top to bottom 1.59, 2.05, 3.19, 2.33, 2.62, 2.05, 2.78, 3.99 and 3.30 mg. The intersection of the straight lines drawn in the 0.45 fraction thermogram shows the method of extrapolation to determine T. Molar ratios of water to starch for these experiments, from top to bottom, are 24.8, 10.1, 6.97, 6.12, 4.83, 3.64, 3.27, 2.50 and 2.25. Reproduced with permission from J.W. Donovan, Biopolymers, 1979,18, 263. 1979, Wiley [11]...

Fig. 15.51. DSC thermograms of wheat starch in water (45 55, g/g) I native starch, II gelatinized starch (according to Slade, Levine, 1991)...

Staling of white-bread crumb begins with the formation of crystalline structures in amylopectin. The endotherm peak at 60 °C appears again in the thermogram of stored white bread (Fig. 15.52). A state of order arises which corresponds to that of B starch (cf. 4.4.4.14.2) and binds up to 27% of crystal water, which is withdrawn from amorphous starch and proteins. The crumb loses its elasticity and becomes stale. On storage of white bread, the amount of water that can freeze decreases corresponding to the conversion to non-freezing crystal water (Fig. 15.53). 

Decomposition (melting) of the gel appeared in thermograms in the form of a relatively sharp deviation of the base line towards the endothermic region. The agar-water system behaves itself in a similar way (Figure 23) [4, 73, 138]. The melting temperature of the starch gel coincides with the curve of mutual solubility (coexistence curve) (Figure 20, HNP curve). This is the curve with the upper critical temperature of solubilization (UCTS). 

---