Glass Transition Of Starch Research Articles

Optimising Starch Transformation in Aquafeed Extrusion for Enhanced Water Stability and Performance

The physical quality of aquafeed pellets is paramount for the health and performance of aquatic species in aquaculture systems. Starch, a small, but necessary component of aquafeed, plays a crucial role in creating durable and water-stable pellets. This paper investigates the complex relationship between starch transformation during extrusion cooking and its influence on water stability. Through a series of experiments involving various extrusion parameters, including three melt moisture levels and three screw speeds, the study reveals that the key to producing water-stable aquafeed lies in optimizing starch gelatinization and minimizing dextrinization. High screw speeds, in conjunction with moderate to high melt moisture levels, facilitate starch gelatinization while avoiding dextrinization, resulting in pellets with superior water stability. Conversely, low melt moisture levels at any screw speed or any melt moisture at low screw speeds lead to poor water stability due to increased dextrinization or suboptimal gelatinization levels. The research also underscores the critical role of the glass transition of starch. Starch in its semi-crystalline state is found to be more susceptible to shear degradation during extrusion. Therefore, rapidly elevating the raw material's temperature above its glass transition temperature is crucial for achieving water-stable aquafeed.

Impact of granule hydration on maize and wheat starch chemical reactivity at the granular and molecular levels

Granular and molecular reaction patterns of maize and wheat starches (normal and waxy genotypes) were investigated in relation to extent of granule hydration (equilibrated at 25, 55, 75, 86 or 100% relative humidity [RH]; moisture range ≈ 10–40 g/100 g starch) within a model reaction system utilizing a fluorescent reagent (5-(4,6-dichlorotriazinyl)aminofluorescein). The greatest incremental increase in granule hydration (49–80%) and overall extent of reaction (30-76-fold) occurred between 86 and 100% RH, likely accentuating the starch glass transition temperature (Tg), which was depressed to room temperature via gradual granule hydration. Under limited hydration conditions (25–86% RH; presumably below Tg), reaction was confined to granule surfaces, whereas under conditions of sufficient hydration/plasticization (100% RH; presumably above Tg), reaction occurred throughout the granule matrix, dramatically increasing reaction of amylose and amylopectin branch chains. For normal starches, amylose was more inert to reaction in low moisture conditions (25–87% RH), indicating either a lesser prevalence at granular surfaces or insufficient hydration to react. Waxy starches exhibited more homogenous granular reaction patterns and greater overall extents of reaction than their respective normal starch counterparts, due to reactivity differences amongst amylose and amylopectin medium and long chains. Findings also provide insights for manipulating granular/molecular reaction locale in “dry” starch modifications.

Glass transition of anhydrous starch by fast scanning calorimetry

By means of fast scanning calorimetry, the glass transition of anhydrous amorphous starch has been measured. With a scanning rate of 2000Ks−1, thermal degradation of starch prior to the glass transition has been inhibited. To certify the glass transition measurement, structural relaxation of the glassy state has been investigated through physical aging as well as the concept of limiting fictive temperature. In both cases, characteristic enthalpy recovery peaks related to the structural relaxation of the glass have been observed. Thermal lag corrections based on the comparison of glass transition temperatures measured by means of differential and fast scanning calorimetry have been proposed. The complementary investigations give an anhydrous amorphous starch glass transition temperature of 312±7°C. This estimation correlates with previous extrapolation performed on hydrated starches.

Impact of Soaking and Drying Conditions on Rice Chalkiness as Revealed by Scanning Electron Microscopy

Chalkiness is one of the most influential factors on head rice yield. Parboiling is known to be an effective way to remove chalkiness and improve head rice yield. However, the steps involved in the removal of chalkiness are still not completely resolved. This study investigated the effects of soaking temperature, soaking duration, and drying conditions on the removal of rice chalkiness. Chalky brown rice kernels were selected and soaked at 25, 65, 70, or 75°C for 3 h. After 1, 2, or 3 h, the rice samples were frozen before drying or immediately dried. Soaking at 25°C did not remove chalkiness and caused no morphological change in starch granules. When the soaking temperature increased from 25 to 65, 70, and 75°C, the chalkiness decreased from 100% to 34.1, 29.7, and 15.9%, respectively. Soaking rice at temperatures above the starch glass transition temperature but below the gelatinization temperature reduced chalkiness owing to rearrangement of starch granules and protein denaturation to fill the void spaces in the chalky area. During soaking, the morphology of starch granules also changed from round to angular in shape. Drying at temperatures above the starch glass transition temperature also facilitated rearrangement of starch granules to further reduce rice chalkiness.

Influence of citric acid on the properties and stability of starch‐polycaprolactone based films

ABSTRACTThe influence of citric acid (CA) on structural and physicochemical properties of blend films based on corn starch and polycaprolactone (PCL) was studied. Films were obtained by melt blending of starch and PCL and compression molding. Phase separation of polymers observed by scanning electron microscope and atomic force microscope was reduced by CA incorporation. CA affected both starch and PCL crystallization as deduced from the X‐ray diffraction patterns and values of melting enthalpy. Glass transition of starch was reduced by PCL incorporation, while this occurred to a greater extent in films containing CA. Obtained results point to enhanced interactions between PCL and starch chains in films with CA, although this only quantitatively benefits the film properties at a low PCL ratio. Compounding starch with small amounts of PCL, using glycerol and CA, can supply films with better functional properties than net starch films. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42220.

Starch transformation in bran-enriched extruded wheat flour

Wheat flour was extruded at different conditions of barrel temperature (120 °C and 180 °C), water content (18% and 22%) and screw speed (400 rpm and 800 rpm) with an increasing concentration of wheat bran fibers (2.8%, 12.6% and 24.4%). In the tested extrusion conditions, starch crystallites were fully dissociated. The estimated starch solubility was influenced by the process conditions and ranged from 24.1% to 63.1%. At same process conditions, the starch solubility was increased only at the highest bran level. The bran concentration influenced the glass transition temperature, melting temperature and sorption isotherm of the unprocessed wheat flour. At the extrusion conditions, it showed that higher bran levels led to a higher amount of free water and a decrease in starch glass transition temperature of up to 13 K. The differences in starch transformation, induced by the concentration of bran, might contribute to the modulation of the expansion properties of bran-containing starchy foams.

Effect of Sucrose on Glass Transition, Gelatinization, and Retrogradation of Wheat Starch

ABSTRACTDifferential scanning calorimetry (DSC) was used to study the effect of sucrose on wheat starch glass transition, gelatinization, and retrogradation. As the ratio of sucrose to starch increased from 0.25:1 to 1:1, the glass transition temperature (Tg, Tg′) and ice melting enthalpy (ΔHice) of wheat starch‐sucrose mixtures (with total moistures of 40–60%) were decreased to a range of −7 to −20°C and increased to a range of 29.4 to 413.4 J/g of starch, respectively, in comparison with wheat starch with no sucrose. The Tg′ of the wheat starch‐sucrose mixtures was sensitive to the amount of added sucrose, and detection was possible only under conditions of excess total moisture of >40%. The peak temperature (Tm) and enthalpy value (ΔHG) for gelatinization of starch‐sucrose systems within the total moisture range of 40–60% were increased with increasing sucrose and were greater at lower total moisture levels. The Tg′ of the starch‐sucrose system increased during storage. In particular, the significant shift in Tg′ ranged between 15 and 18°C for a 1:1 starch‐sucrose system (total moisture 50%) after one week of storage at various temperatures (4, 32, and 40°C). At 40% total moisture, samples with sucrose stored at 4, 32, and 40°C for four weeks had higher retrogradation enthalpy (ΔH) values than a sample with no sucrose. At 50 and 60% total moisture, there were small increases in ΔH values at storage temperature of 4°C, whereas recrystallization of samples with sucrose stored at 32 and 40°C decreased. The peak temperature (Tp), peak width (δT), and enthalpy (ΔH) for the retrogradation endotherm of wheat starch‐sucrose systems (1:0.25, 1:0.5, and 1:1) at the same total moisture and storage temperature showed notable differences with the ratio of added sucrose. In addition, Tp increased at the higher storage temperature, while δT increased at the lower storage temperature. This suggests that the recrystallization of the wheat starch‐sucrose system at various storage temperatures can be interpreted in terms of δT and Tp.

Effect of Crystallinity on the Glass Transition Temperature of Starch.

The glass transition temperature (T(g)) of potato and wheat starches, stored for several periods after gelatinization, was measured by differential scanning calorimetry (DSC), and the relative crystallinity of the starches was measured by X-ray diffractometry. T(g) of stored starches was higher than that of starches without storage, and the T(g) increment of starches gelatinized at 120 degrees C was higher than that of starches gelatinized at 60 degrees C. The water content at which the glass transition of a starch occurs at 25 degrees C was estimated from DSC data, and it increased linearly with relative crystallinity in two groups that differed in the gelatinization method. These results also showed the quantitative relationship between T(g) and retrogradation. In addition, these results suggested that the glass transition of starch could be interpreted in the same way as the glass transition of cross-linked synthetic polymers.

A calorimetric investigation of the influence of sucrose on the gelatinization of starch

The gelatinization of starch in the presence of low levels of water and high levels of sucrose was studied. The gelatinization temperature was found to increase in the presence of sucrose, whereas the gelatinization enthalpy was unaffected. The gelatinization temperature range was not as broad in the presence of sucrose as without sucrose. Furthermore, the shape of the gelatinization endotherm was changed by the addition of sucrose. The double endotherm obtained in limited-water/starch systems was changed into a single endotherm, similar to the endotherm obtained in excess-water/starch systems although at a higher temperature. To obtain this change in the shape of endotherm more sucrose was needed for a waxymaize starch than for maize starch or potato starch. The effect of sucrose, thus, seemed to be both to restrict the gelatinization and to make the gelatinization occur more easily. The first effect (temperature) was related to the discussion in the literature on the glass transition of starch. The second effect (shape of the endotherm) may be due to a lower local viscosity in the presence of sucrose, resulting in a shorter time interval necessary for the transitions to occur.

Annealing and Glass Transition of Starch

AbstractThe enthalpy of the order‐disorder transition of starch increased as the starch hydration period was increased from 1 h to 24 h. This was explained as the exothermic heat of hydration cancelling part of the endothermic heat of melting. Annealing of starch was shown to occur at 3 to 8°K below the Tm of starch. This would suggest that the Tg and Tm of starch does not occur at the same temperature.