Ann-Charlotte Eliasson

The influence of amylose and amylopectin characteristics on gelatinization and retrogradation properties of different starches

Physico-chemical properties of starch from wheat, rye, barley (waxy, high-amylose and normal-amylose), waxy maize, pea and potato (normal-amylose and high-amylopectin) were studied. Emphasis was given to the amylose (total, apparent and lipid-complexed) and amylopectin characteristics as well as to the gelatinization and retrogradation properties measured using differential scanning calorimetry. The total amylose content varied from ca. 1 % for waxy maize to 37% for high-amylose barley. The amylopectin characteristics were determined by high-performance size-exclusion chromatography after debranching with isoamylase. The weight-average degree of polymerization (DPw) was 26, 33 and 27 for the A-, B-, and C-type starches, respectively. In general, the potato starches exhibited the highest retrogradation enthalpies and the cereal starches the lowest, while the pea starch showed an intermediate retrogradation enthalpy. The data were analysed by principal component analysis (PCA). The DPw showed positive correlation to the melting interval, the peak minimum, the offset temperatures of the retrogradation-related endotherm as well as to the gelatinization and retrogradation enthalpies. However, the high-amylose barley retrograded to a greater extent than the other cereal starches, despite low DPw (24). The amylose content was negatively correlated to the onset and the peak minimum temperatures of gelatinization.

Physical properties of amylose-monoglyceride complexes

Complexes of amylose with monoglycerides differing in fatty acid chain length and unsaturation were prepared. The thermal stabilities of these complexes were measured by differential scanning calorimetry, and it was found that the thermal stability increased with increasing chain length and decreased with increasing unsaturation. The resistances of the complexes with respect to enzymic hydrolysis by bacterial a-amylase and amyloglucosidase changed in the same way, i.e. the complexes with long saturated monoglycerides were more resistant to enzymic breakdown than were the complexes with shorter chain or more unsaturated monoglycerides.

Retrogradation of amylopectin and the effects of amylose and added surfactants/emulsifiers

Abstract The retrogradation of mixtures with different amylopectin/amylose ratios and 50% (w/w) water content was followed by differential scanning calorimetry. The effect of the addition of surfactants/emulsifiers (sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB) and monoglycerides) was investigated. The results showed that the relationship beween the melting enthalpy of recrystallized amylopectin and the proportion of amylopectin was not linear. Mixtures with less than 50% amylopectin showed a higher melting enthalpy than expected. The effect of surfactants/emulsifiers on that relationship was to decrease the retrogradation of all the mixtures, but they had their greatest effect on 100%-amylopectin samples and least effect on mixtures with 50% amylopectin. Thermograms obtained for 100% amylopectin with added surfactants/emulsifiers showed transitions above 100°C, thus indicating the formation of a complex between amylopectin and the surfactants/emulsifiers. This was supported by X-ray diffraction analysis, as amylopectin samples with added SDS and CTAB showed a mixture of B- and V-patterns. This complex formation between amylopectin and surfactants/emulsifiers can explain the large reducing effect of the addition of surfactants/emulsifiers on retrogradation of 100% amylopectin samples, and partly the retrogradation of other mixtures.

Interactions between starch and lipids studied by DSC

Abstract Differential scanning calorimetry is a valuable method for obtaining information about starch—lipid interactions. The transition of the amylose—lipid complex and the influence of lipids on starch gelatinization and retrogradation have been studied. The thermal transition of the amylose—lipid complex depends on monoacyl chain length and the polar head of the lipid, on the water content and on the type of starch, i.e. when amylose is present in the form of starch granules. Different polymorphic forms of the amylose—lipid complex exist. Food processing, e.g. extrusion cooking and drum drying, might lead to very different types of complexes. Chemical modification of the starch also affects the thermal properties of the amylose—lipid complex. Indirect evidence is given for the formation of an amylopectin—lipid complex. This evidence includes the decrease in gelatinization enthalpy for a waxy maize starch in the presence of lipids, and the reduced retrogradation of waxy maize starch in the presence of lipids. The influence of the lipid on the complex formation is shown. It is stated that not only the monoacyl chain length and the polar head but also the phase behaviour of the lipid influence the properties of the complex. The lamellar liquid-crystalline phase is much more effective for complex formation than, for example, the cubic phase.

Cereals in breadmaking: a molecular colloidal approach

Basic concepts of surface and colloid chemistry physicochemical behaviour of the components of wheat flour interactions between components components in other cereals flour dough bread.

Crystalline changes in native wheat and potato starches at intermediate water levels during gelatinization

Abstract Changes in the crystallinity of cereal and tuber starches were investigated with WAXS (wide-angle X-ray scattering) under realistic water and temperature conditions during gelatinization. Due to experimental factors the water starch ratios 43, 51 and 58% ( w w ) for the wheat starch samples, and 49, 56 and 64% for the potato starch samples were chosen for the examinations. The results of the X-ray investigation are compared with DSC data and indicate a two-stage process. The crystalline properties are strongly affected by the amount of water available during gelatinization, and the present study demonstrates that the subcell of cereal starches is more stable to water than the subcell of tuber starches.

Differential scanning calorimetry studies on wheat starch—gluten mixtures: I. Effect of gluten on the gelatinization of wheat starch

The influence of gluten on wheat starch gelatinization was studied by using differential scanning calorimetry (DSC). The presence of gluten decreased the starch gelatinization enthalpy and increased the gelatinization temperature. The values obtained in the presence of gluten were compared with those of starch—water mixtures and the amount of water associated with the gluten during the heating was calculated. The results indicated that water was transferred from gluten to starch throughout the heating period.

Studies on α-amylase degradation of retrograded starch gels from waxy maize and high-amylopectin potato

Abstract Gelatinized starch gels of waxy maize and high-amylopectin potato were subjected to different time–temperature conditions, aiming at producing extensive amounts of retrograded amylopectin. The purpose was to investigate the impact of amylopectin retrogradation on the resistant starch formation and on the rate of starch digestion with porcine pancreatic α-amylase. Dried non-cycled gelatinized starch gels were used for comparison. Although differential scanning calorimetry measurements indicated higher amounts of retrograded material in the dried temperature-cycled gels no enzyme resistant starch was detected in any of these samples. However, all cycled starch gels were less-readily degraded by the enzyme than the non-cycled gels. The chain length distribution in the α-amylolysates was studied by high performance anion exchange chromatography after debranching with isoamylase. The main products of hydrolysis were low molecular weight carbohydrates with a degree of polymerization of 1–9 and various branched dextrins. The chain distribution was uniform in the hydrolysates at the different stages of hydrolysis and independent of storage conditions, indicating that the mode of enzyme action remained unaffected by retrogradation. The waxy maize and high-amylopectin potato starches responded similarly to temperature cycling. It was concluded that temperature cycling resulted in a slower hydrolysis of the amylopectin, a phenomena that could be exploited when developing starchy foods with improved nutritional characteristics.

Influence of drum-drying and twin-screw extrusion cooking on wheat carbohydrates, II, effect of lipids on physical properties, degradation and complex formation of starch in wheat flour

Wheat flour was drum-dried or extruded with and without addition of 2% soya soil or 1% linoleic acid, otherwise maintaining similar processing conditions. The starches in the six resulting products were characterised in terms of their water solubilities, pasting properties, molecular weight distributions and in vitro digestibilities. Starchlipid interactions were investigated by measuring the efficiency of fat extraction, the amount of complexed starch calculated from iodine-binding capacities and the thermal behaviour of the flour in differential scanning calorimetry. All drum-dried flours exhibited less starch breakdown and higher initial Brabender viscosities than extruded flours. Lipid addition decreased viscosity and water solubility. The extent of starch breakdown was unaffected by linoleic acid but, surprisingly, increased upon addition of soya oil. Starches from all samples were equally available to glucoamylase, but pancreatic α-amylase digested drum-dried, and especially extruded, flours more slowly than an autoclaved control. Linoleic acid, but not soya oil, further decreased α-amylolysis rates. An additional autoclaving increased digestion rates and abolished differences between the two processes. A close relationship existed between the degree of α-amylolysis and the amount of complexed starch.

Gelatinization and retrogradation of potato (Solanum tuberosum) starch in situ as assessed by differential scanning calorimetry (DSC)

The thermal behavior of potato starch in situ has been studied and compared to properties of isolated starch. Gelatinization and retrogradation properties were studied by differential scanning calorimetry. One early and three late varieties with different degree of mealiness were examined. The early variety (Solanum tuberosum var. Rocket) had lower dry matter content and lower starch gelatinization temperature than the later varieties (var. Asterix, Bintje and King Edward). Samples from distinct parts of the potato tuber were analysed to compare the tissue zones. The starch in the water-rich pith appeared to gelatinize at a higher temperature than in samples from the outer parts of the tuber. This was seen for isolated starch as well as for starch in situ; however, the differences were more pronounced in situ. To investigate the influence of tuber size, samples were taken from stem end storage parenchyma. No influence of tuber size on the starch gelatinization properties was detected by the method used. Retrogradation properties were also studied for stem end storage parenchyma. Melting temperatures of recrystallized amylopectin did not differ between varieties, though there were small differences in rate of recrystallization as measured by changes in melting transition enthalpy with time.