Effects of genotype and growing locations on properties of wheat starch gels

This study examines the contributions of genotype and the effects of growing location and storage to variability in the strength, syneresis and in vitro enzyme digestibility of wheat (Triticum aestivum L.) starch gels. The study involved starch that was extracted from five wheat varieties grown in four locations. Length of storage at 4 °C after hydrothermal treatment of the starch accounted for 30–50% of the variance in the three gel properties. Genotype contributed significantly to variability in syneresis and enzyme digestibility of the starch gels, indicating a degree of heritability of these characteristics in the wheat varieties studied. Gel strength was strongly influenced by effects from the growing location. Syneresis and enzyme‐resistant starch were negatively correlated with granule size and swelling power of native starch. Syneresis was also correlated negatively with pasting viscosities of starch granules, and positively with amylose content and pasting temperature. Gel strength was correlated positively with relative crystallinity and negatively with the breakdown of peak viscosity. Length of storage had a major influence on gel strength, syneresis and in vitro enzyme digestibility, although genotype contributed significantly to variability in syneresis and enzyme‐digestibility. Growing conditions were a significant influence on gel strength.     

Changes in rheological properties of hydroxypropyl potato starch pastes during freeze—thaw treatments. III. Effect of cooking conditions and concentration of the starch paste

The effects of different cooking conditions and concentrations on the freeze-thaw stability of hydroxypropyl potato starch (molar substitution 0·125) paste were investigated by dynamic rheological measurements and syneresis determination. The cooking conditions of the starch were chosen by taking the starch pastes at peak consistency (SP/Peak), at half breakdown consistency (SP/HB), after being held at 95°C for 15 min (SP/95°C) and after the whole pasting cycle (SP/25°C) in the Brabender Amylograph. The concentration effect was studied with the starch pastes after a whole pasting cycle at 35, 50 and 65 g kg^?1. Depending on cooking conditions and concentration, the rheological responses in changes of complex modulus (G*) and phase angle () of the starch pastes, with regard to the number of freeze-thaw cycles, differed considerably. This indicated that the starch pastes had undergone various structural changes during freeze-thaw treatments. With an increased extent of pasting, and with an increased starch concentration, the rheological responses indicative of the destabilisation process of the starch pastes were, in general, delayed. The number of freeze-thaw cycles required for the appearance of a peak in G*, related to the first syneresis, was one, two, five and six for SP/Peak, SP/HB, SP/95°C and SP/25°C, respectively. For the starch pastes at 35, 50 and 65 g kg^?1, it was four, six and seven cycles, respectively. Based on these rheological data, it was suggested that the amount of inter-mingled amylose and amylopectin in the dispersion of hydroxypropyl starch paste is the main controlling factor, which plays a critical role in the rheological response as well as in the syneresis.     

Individual and sequential effects of stirring,smoothing, and cooling on the rheological properties of nonfat yogurts stirred with a technical scale unit

Few studies have considered the impact of unit operations during stirred yogurt manufacture because their operational sequence is difficult to replicate at the laboratory scale. The aim of this study was to investigate the individual and sequential effects of stirring in the yogurt vat, smoothing, and cooling on the rheological properties of yogurts, using a technical scale unit simulating some industrial conditions. The yogurts were prepared from a milk mixture that was standardized to contain 14% total solids, 0% fat, and 4% protein, and then homogenized, heated (94.5°C, 5 min), and inoculated at 41°C with the same thermophilic lactic starter. The operating parameters under investigation were 2 stirring durations in the yogurt vat (5 or 10 min), 2 cooling systems (plate or tubular heat exchanger), and 2 smoothing temperatures (38°C for smoothing before cooling; 20°C for smoothing after cooling). Sampling valves were installed at critical points on the technical scale unit so that the effect of each operation on the properties of stirred yogurt could be quantified individually. Syneresis, apparent viscosity, firmness, and consistency were analyzed after 1 d of storage at 4°C. In general, as the yogurts moved through the technical scale unit, the properties of the yogurts (evaluated after 1 d) changed: viscosity increased but syneresis, firmness, and consistency decreased. The individual effects of the operations showed that smoothing and cooling, compared with stirring duration, made the greatest contribution in terms of modifying yogurt properties. The stirring parameters (5 or 10 min) had similar effects on the yogurts. The use of a plate heat exchanger promoted a decrease in syneresis, whereas a tubular heat exchanger had a greater effect in terms of increasing firmness and consistency. The type of cooling system had no effect on stirred yogurt viscosity. Smoothing at 38°C had a greater effect on the increase in firmness, whereas smoothing at 20°C contributed more to a decrease in syneresis and increases in viscosity and consistency. This study confirms that each unit operation has a defined effect on the rheological properties of a nonfat stirred yogurt, which also depends on the operation sequence.     

How do different cooling temperatures affect the characteristics of set-type yoghurt gel?

The impact of cooling temperatures on gel characteristics of set-type yoghurts was investigated through 28 days of storage. Yoghurt samples were cooled at four different temperatures (−10 °C, −5 °C, 0 °C, 4 °C) after incubation until the central temperature of yoghurt cups reached 4 °C. Cooling temperature and storage period were determined as significant factors affecting the yoghurt gel characteristics (p < 0.05). Yoghurts cooled at 0 °C clearly differed from the other yoghurts in terms of gel firmness and consistency. Confocal images of yoghurts cooled at 0 °C showed more homogeneous protein matrix than the other samples. Microbial counts and the acidity of the yoghurt samples increased with storage period. Textural parameters, water holding capacity and susceptibility to syneresis increased until 14th day of storage and then decreased. Sensory analysis of yoghurt samples confirmed the results obtained by microbiological and textural measurements.     

Physicochemical Characteristics of Pigeonpea and Mung Bean Starches and Their Noodle Quality

This study compared the properties of pigeonpea and mung bean starches and noodles made from each. No large differences in size and shape of respective starch granules were observed. The degree of syneresis of pigeonpea starch was nearly three times that of mung bean starch. Swelling power of pigeonpea starch was considerably lower at 60°C and 70°C but it did not differ markedly at 80° and 90°C. The Brabender . viscosity patterns of 6% starch pastes of pigeonpea and mung bean indicated no pasting peak during heating to 95°C; neither showed breakdown of the hot paste. Sensory tests indicated that pigeonpea starch of dhal (decorticated dry split cotyledons) was as good for noodle preparation as mung bean dhal starch.     

Influence of heating conditions and starch on the storage modulus of Russet Burbank and Yukon Gold potatoes

The storage modulus of Russet Burbank (RB) and Yukon Gold (YG) potato discs (13.3 mm × 4.5 mm) was measured continuously during heating in water at temperatures ranging from 40 to 80 °C for 120 min using a dynamic mechanical analyser with a heating stage. The starch content of YG potatoes was higher than that of RB potatoes, but the raw starch granule size distribution of both varieties was similar. RB samples had the highest storage modulus values (25% higher than raw tissue) when heated in 60 °C water for 35 min. Image analysis revealed that the perimeters of starch granules in the potato samples increased by about 50% during heating for 30 min at 60 °C. Heating temperature and time and starch content influenced the storage modulus. © 2001 Society of Chemical Industry     

Characterization of the Pasting,Flow and Rheological Properties of Native and Phosphorylated Rice Starches

Phosphorylation of rice starch and its effects on the physiochemical properties of the starch were investigated. Phosphorylation was conducted using the oven heating method by heating mixtures of rice starch and monosodium dihydrogenphosphate at 120‐150°C for 0.5‐2 h, and the pasting, flow and rheological properties of the resulting starch phosphates were analyzed. Phosphorylation with substitution degrees of up to 0.12 was achieved by raising the reaction temperature to 140°C, but further increase in the temperature to 150°C caused a marked reduction in the degree of substitution. Phosphorylation resulted in significant declines in pasting temperature and setback, but increases in peak viscosity and breakdown. Suspensions of rice native starch and starch phosphates were shown to be non‐Newtonian, pseudoplastic fluids, exhibiting typical shear thinning. They also exhibited yield stress, the magnitude of which increased with the degree of phosphate substitution. Dynamic testing showed that phosphorylation resulted in a decrease in the temperature at which storage and loss moduli (G′ and G″) reached a peak during heating and a reduction in G′ during cooling. These results appeared to indicate that phosphorylation improved the shear stability of rice starch pastes and enhanced swelling of starch granules, but impeded starch retrogradation.     

The Non-reversibility of Pregelatinization Swelling of Wheat Starch A-granules in Saline Conditions

Undamaged A-granule wheat starches, prepared from two cultivars with contrasted pasting characteristics, exhibited differences in the extent of pregelatinization thermal swelling in dilute saline similar to their differences in hot pasting peak viscosity. The granule volume increase from 20°C, determined by a pulse height channelyser linked to a Coulter Counter, was about 1 % up to 40° and about 15% up to 50°C. The swelling was not reversed on cooling from either 40° or 50°C.     

Freezing and Thawing Conditions Affect the Gel Stability of Different Varieties of Rice Flour

The freeze‐thaw stabilities of three different rice flour gels (amylose rice flour with 28% amylose, Jasmine rice flour with 18% amylose and waxy rice flour with 5% amylose) were studied by first freezing at –18 °C for 22 h and subsequent thawing in a water bath at 30 °C, 60 °C and 90 °C, or by boiling in a microwave oven. The freeze‐thaw stability was determined for five cycles. Starch gels thawed at higher temperature exhibited a lower syneresis value (percent of water separation) than those thawed at lower temperature. Amylose rice flour gels gave the highest syneresis values (especially at the first cycle). The Jasmine rice flour gels gave a higher syneresis value than the waxy rice flour gel. Except for freezing by storage at –18 °C and thawing at 30 °C, there was no separation of water at any cycle when waxy rice flour gel was thawed at any temperature, irrespectively of the freezing methods used. Cryogenic Quick Freezing (CQF) followed by storage at –18 °C and then thawing (by boiling or by incubation at any other temperatures) gave lower syneresis values than all comparable samples frozen by storage at –18 °C. The order of syneresis values for the three types of rice flour was waxy rice flour < Jasmine rice flour < amylose rice flour. The syneresis values and the appearance of starch gels, which had gone through the freeze‐ thaw process, suggested that the order of freeze‐thaw stability of gels for the three types of rice flour was waxy > Jasmine > amylose rice flour.     

Rheological and microstructural characterization of double cream cheese

Firmness at 5 °C, dynamic viscoelastic moduli (G' G) and capillary extrusion profiles at 20 °C, were obtained on double cream cheese after the different steps of processing (curd obtention, mixing at 70 °C and 500 r.p.m. with heat-denatured WPC, heating at 85 °C, homogenizing at 20 MPa (1st stage) and 5 MPa (2nd stage) and cooling to 20 °C and 13 °C) and storage 7–9 days at 5 °C. It was found that double cream cheese became firmer and more elastic after heating and homogenization, although it became softer and more viscous after mixing and cooling. Transmission Electron Microscopy (TEM) and cryo-Scanning Electron Microscopy (SEM) micrographs showed that rheology results could be related to aggregation (during heating and homogenization) and disruption (during cooling) of milk fat globule/casein complexes. Dispersion of homogenization clusters after cooling, and aggregation of milk fat globules during storage caused double cream cheese structural instability to appear. It was suggested that the heterogeneity of capillary extrusion profiles could be quantified through application of fractal concepts and Fourier analysis and related to structure and texture of double cream cheese.     

The effect of starch isolation method on physical and functional properties of Portuguese nut starches. II. Q. rotundifolia Lam. and Q. suber Lam. acorns starches

A new starch was isolated from fruits of two acorn species, Quercus rotundifolia and Quercus suber by alkaline (A3S) and enzymatic (ENZ) methods and physical and functional properties were studied. The isolation method induced changes in most of those properties in the isolated starches, mainly in resistant starch content, syneresis, pasting, thermal and rheological properties. Isolated acorn starches presented high amylose content (53–59%) and resistant starch content (30.8–41.4%). Acorn starches showed limited and similar solubility values and swelling power values, showing a gradual increase from 60 °C to 90 °C. The pasting temperatures ranged from 67.5 to 72.0 °C and pastes did not present breakdown, which is suggestive of a high paste stability of acorn starches during heating. At ambient temperature the turbidity and syneresis values were low, but when held at freezing temperatures the syneresis significantly increased. Thermal analysis revealed that the acorn starches easily undergo transition phenomena as shown by the low T_o and enthalpy values (4.1–4.3 J/g), these effects were more evident in starches isolated by ENZ method. Pastes are more elastic than viscous and form strong gels after cooling. Q. suber starch was shown to be more sensitive to the effect of isolation method. Generally, starch isolated by enzymatic method presented less interesting functional properties, since this isolation procedure greater affected the raw structure of starches.     

Long-term stability of waxy maize starch/xanthan gum mixtures prepared at a temperature within the gelatinization range

The retrogradation behavior of waxy maize starch pastes with added xanthan gum was investigated. The pastes were prepared with or without added xanthan gum at two starch concentrations (5:100 and 7:100), at two temperatures within the gelatinization range (70 °C or 72 °C) and at acid or neutral pH. The evolution of the macrostructure (texture, flow behavior and syneresis), microstructure (oscillation rheology) and molecular aggregation (pulsed-field NMR) of the pastes was followed up in an 8 week period during cold storage (7 °C). Heating temperature was found to have a profound effect on the long-term stability of the pastes. Pastes prepared at 70 °C behaved as flocculated dispersions of largely intact, swollen granules which resulted in stable structural properties during the preservation period. At 72 °C, a higher degree of gelatinization and degradation was observed, resulting in structurally unstable systems due to association and crystallization of amylopectin. Especially for these systems, xanthan gum was found to enhance the gelation process, probably due to phase separation. Although xanthan gum may restrict the granule disruption during preparation, this beneficial effect on the freshly prepared pastes did not result in an improved stability during storage.     

Effect of Aqueous Ethanol Cationization on Functional Properties of Normal and Waxy Starches

Cationic starch ethers of normal and waxy corn, normal and waxy barley and normal pea starch were prepared by an aqueous alcoholic process for evaluation of their functional properties as compared to the native starch controls. The native starches exhibited a wide range in average granule size (10–21 μm diameter), amylose content (0–34%) and swelling power (13–31). Cationization to degrees of substitution (DS) of 0.030–0.035 with 3-chloro-2-hydroxypropyltrimethylammonium chloride resulted in marked increases in swelling power of all starches, with little corresponding increases in starch solubility. Cationization also decreased the onset of endothermic transitions and pasting temperatures quite substantially, and promoted the development of sharp peak viscosities in the amylographs of all normal and waxy starches, including that of pea starch. Final cold viscosities of the cationic starches exhibited positive setbacks, and the cooked starch gels, after storage for 7 days at 4°C and −15°C, showed no syneresis. All cationic starches except for waxy corn were more susceptible to α-amylase hydrolysis than native control starches. The general improvement in functional properties, especially in the waxy corn, waxy barley and pea starches, due to the aqueous alcoholic-alkaline cationization process would greatly enhance their industrial applications.     

Corn Starch-Xanthan Gum Interaction and Its Effect on the Stability During Storage of Frozen Gelatinized Suspension

The knowledge of starch pastes behavior during frozen storage becomes necessary to understand more complex systems (e.g. sauces, dressings and desserts) The effect of sub-zero storage on the quality attributes of corn starch pastes (10% w/w) with and without xanthan gum (0.3% w/w) was analyzed. Pastes were frozen at different rates (0.3 to 270cm/h) and stored at −5, −10 and −20°C. Exudate production (syneresis) and rheological behavior were studied by means of capillary suction and rotational viscometry respectively. Ice recrystallization was analyzed by indirect microscopic observations using isothermal freeze fixation and amylopectin retrogradation by differential scanning calorimetry (DSC). Samples stored at −5°C (glass transition temperature) or higher temperatures were under the rubbery state evidenced by starch recrystallization. This state favored molecular mobility leading to deteriorative changes (like spongy structure formation related to amylose retrogradation). At lower storage temperatures (−10 and −20°C) under the glassy state, starch retrogradation was not detected and deteriorative changes can be related to ice recrystallization. The addition of xanthan gum minimized amylose retrogradation, syneresis and rheological changes, however, its presence did not prevent ice recrystallization nor amylopectin retrogradation.     

Studies on Rye Starch Properties and Modification. Part II: Swelling and Solubility Behaviour of Rye Starch Granules

Rye starch shows the typical inhibited swelling behaviour of triticeae starches with an onset of swelling at rather low temperature (50–55°C). Swollen rye starch granules exist as individuals even after swelling at 100°C. The total dispersion of rye starch needs temperatures above 120°C with pressure cooking. On heating of the rye starch suspension preferentially amylose is leached. Defatting of rye starch exhibits no influence on swelling power but results in higher solubility and in increased amylose leaching. The drying procedures applied here resulted in stronger assoziation of the polymer molecules in the starch granule leading to higher swelling temperatures and a reduced solubility. Shiftings of the crystalline/ amorphous-ratio of the starch granules as caused by different drying procedures, had no influence on the results of swelling power investigation but the highest swelling enthalpy as well as Brabender viscosity were exhibited by a sample dried at room temperature. It is proved to be possible to change the swelling behaviour of rye starch to “potato starch type” by slight chemical modification like succination.     

Heat-moisture treatment effects on sweetpotato starches differing in amylose content

Sweetpotato starch from two genotypes, Taiwan (15.2% amylose) and 93-006 (28.5% amylose), were exposed to heat-moisture treatment (HMT) of 25% moisture at 110°C for various exposure times at ‘as-is’ (pH 6.5–6.7) and alkaline pH (pH 10) conditions. In both starch samples at ‘as-is’ pH, there was a shift from a Type A pasting profile (characterized by a high to moderate pasting peak, major breakdown after holding time at 95°C and low cold paste viscosity) to a Type C pasting profile (characterized by lack of a pasting peak and no breakdown, with high cold paste viscosity in 93-006; and a slight breakdown in Taiwan). With HMT at pH 10, the pasting peak viscosity was increased and low hot paste viscosities and high cold paste viscosities were observed. Under both pH conditions after HMT, there were marked increases in gelatinization temperatures and broadening of the DSC gelatinization endotherms, and considerable decreases in swelling volume and solubilities. Gel textures of HMT starch samples appeared to be related to amylose content. Taiwan starch gel had a marked increase in hardness and adhesiveness, while that of 93-006 did not show significant differences in hardness after HMT. Both starch samples showed a marked reduction in resilience, indicating a shift from a long stringy nature to short paste consistency. Starch gels exposed to HMT under alkaline conditions showed a high degree of syneresis.     

Starch Properties of New Sweet Potato Lines Having Low Pasting Temperature

Some new sweet potato lines were developed from progenies of a new cultivar, Quick Sweet, having a low pasting temperature. Starch granules from these lines demonstrated an abnormal morphology characterized by cracking into fragments. Starch and amylose contents were different among these lines. Pasting temperatures of these lines determined by the Rapid Visco Analyser were 53.8 to 66.6°C, i.e. 10 to 20°C lower than that of the control. Peak viscosities of some lines were similar to that of the control. Starch retrogradation, evaluated by percentage of leaked water and hardness of starch gels after cold storage, revealed that the control starch retrograded during storage for two to six weeks, but the starches of some lines retrograded much more slowly than the control starch and exhibited excellent cold storage stability. The pasting temperature had significant positive correlations with the percentage of leaked water and the hardness. These results indicate that Quick Sweet is a useful breeding material for improving pasting and retrogradation properties in sweet potato starch.     

Effects of exopolysaccharide-producing strains of Streptococcus thermophilus on technological and rheological properties of set-type yoghurt

This study investigated the effects of two Streptococcus thermophilus strains, ST 285 and ST 1275, on selected technological and rheological characteristics of set-type yoghurt. The strains were selected for their capability to produce distinctly different exopolysaccharides (EPS) and were thus coded as capsular (ST 285) or ropy-capsular (ST 1275). The culture performance and physico-chemical properties of yoghurt were assessed in relation to different fermentation temperatures (30, 37 or 42 °C) and prolonged storage (up to 30 days) at low temperature (4 °C). ST 1275 showed faster growth and acidification rates, resulting in yoghurt with lower syneresis and higher-flow behaviour index, than ST 285. EPS production appeared to be growth associated with the maximum given at growth temperatures of 37 and 42 °C for ST 285 and ST 1275, respectively; however, EPS concentration declined considerably during storage. Prolonged cold storage increased several rheological characteristics of yoghurt including G′, consistency index and hysteresis loop area. A weak correlation between EPS concentration and textural properties of yoghurt was observed.     

Thermal Transitions of Actomyosin and Surimi Prepared from Atlantic Croaker as Studied by Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) was used to investigate thermal transitions of fish mince (surimi) and actomyosin from croaker. Three endothermic peaks were observed in DSC thermograms of surimi. After addition of salt, transition temperatures shifted to lower temperatures. Preheating samples containing 3% salt at various temperatures showed that 40°C heating caused the first peak to disappear, and preheating at temperatures higher than 50°C caused virtual disappearance of all transition peaks. Low temperature storage (4°C) of samples caused no significant change in thermograms of salted or unsalted surimi over a 5-day storage period. Evidence suggests that changes of fish protein during low temperature “setting” are different from those occurring during high temperature “setting.”     

Critical evaluation of viscometrically determined pasting temperatures in barley malt

Modern varieties of malting barley allow mashing to proceed efficiently to enable saccharification and other biochemical processes. A prerequisite for starch hydrolysis is the disruption of starch granule structure by exceeding a grain specific pasting temperature. For grains, several viscometric methods based on the Rapid‐Visco‐Analyser were developed to determine variations in the pasting temperature reproducibly. Absolute pasting temperatures, as they are necessary to optimize the isothermal mashing process, cannot be determined owing to constructional and data evaluation related limitations. The aim of this research is to investigate and compensate for temperature deviations caused by standard data evaluation and lagging heat transfer from the heating unit into the sample. Accordingly, an improved determination of the pasting onset and a formula to compensate for temperature lags were developed. The optimized data leads to more accurate and reduced pasting temperatures compared with the standard method. The heat transfer was reproducibly quantified (Δϑ : 2.9–5.8°C) and integrated into a compensation formula (R ² = 0.99). It was found that the lag is strongly dependent on the actual sensor temperature but independent of the unpasted sample's initial viscosity. The results were applied on viscometric analyses (n  = 161) to calculate the intrinsic pasting temperatures of barley malt. The determined temperature range is considerably lower than anticipated (56.7–60.5°C). Winter barley exhibits significantly lower pasting temperatures. The outcome of this work can be used to improve the accuracy of prospective analysis and to correct already existing viscometric raw data. Copyright © 2017 The Institute of Brewing & Distilling