Thermomechanical Behavior of Concentrated Starch‐Water Preparations

Abstract

Cereal Chem. 74(5):581-588The rheological behavior of concentrated starch preparations from various origins was studied by dynamic mechanical thermal analysis (DMTA). Four types of starch were used: wheat, potato, normal, and waxy corn adjusted to moisture contents in the 42-49% (w/w) range. The thermal treatments of the starch-water mixtures consisted of heating to 85°C and cooling to room temperature, both at a rate of 1°C/min. During heating, the storage modulus (E´) appearance was first characterized by an increase with a maximum at ≈70°C (or potato starch at 63°C) followed by a decrease to 85°C. During cooling, storage modulus increased steadily down to room temperature. The magnitude of these variations depended on the starch type. Despite some differences, all the loss tangent curves showed a decrease during heating from 60-70°C to 85°C, followed by a plateau during cooling. To propose an interpretation for the DMTA results, we measured, by laser-light diffraction, the influence of heating (up to the maximum E´ peak) on the distribution of the granule sizes of the different starches. Moreover, differential scanning calorimetry (DSC) was used to measure the temperature range where the melting of starches ordered regions occurred. Partial melting enthalpies were plotted against temperature. The hypothesis of a relationship between swelling and an increase in rigidity during heating seemed to be confirmed by laser-light diffraction, whereas DSC indicated the decrease in rigidity was caused predominantly by order-disorder transitions. During cooling, amylose gelation plays a major role in the rigidity increase, but a contribution of amylopectin is not excluded.

Efeito do tamanho dos grânulos nas características estruturais e físico-químicas do amido de trigo

“…Grânulos com diâmetro >10 μm e formato lenticular são considerados tipo A, enquanto os que 27 . Para todas as cultivares analisadas, foi observada maior porcentagem de grânulos com diâmetro ≤10 μm.…”

“…O amido de trigo possui distribuição bimodal em relação ao tamanho, com grânulos tipo A que apresentam diâmetro >10 μm e formato lenticular, e grânulos tipo B com diâmetro ≤10 μm e formato esférico 24,27 .…”

Influence of water on potato starch-lipid interactions. An electron spin resonance (ESR) probe study

“…This decrease was not observed with waxy starch (without amylose) and was thus attributed to the onset of amylose solubilisation and subsequent increase in the accessibility of water to starch sites during heating. 40 Then, during the gelatinisation process 41,42 (ie above approximately 65°C), D rot of the water-soluble probe was also observed to increase, probably as a consequence of the swelling and overall increase in the molecular mobility resulting from the disappearance of organised structures.…”

Thermal relaxation and mechanical relaxation of rice gel

“…An endothermic peak is observed in stage 1, whose onset and peak temperatures are 70 ℃ and 81 ℃ respectively (Fig.2). This is attributed to the melting of the starch crystallites and the occurrence of gelatinization of starch [18] . The difference in gelatinization temperature may be influenced by starch purity, amylose to amylopectin ratio, crystalline to amorphous ratio, and molecular structure of amylopectin, and so on [6,19] .…”