The effect of concentration and botanical source on the gelation and retrogradation of starch

The changes in shear modulus of pea, wheat, maize and potato starch gels with time, at concentrations between 10 and 40% w/w, were followed. In this range, the cooling of gelatinised dispersions of starch resulted in turbid, elastic gels. The initial rate of development of stiffness of the gels followed the order: pea>maize>wheat>potato, and was related to the amount of amylose solubilised during gelatinisation. The initial gelation was not reversed on heating to 100° C. There was also a long-term increase in gel stiffness, which was thermally reversible. This long-term increase, linked to a crystallisation involving amylopectin, followed the order: pea>potato>maize>wheat. With increasing starch concentration this latter process becomes more important.     

Rheological Properties of Mixed Gels using Waxy and Non‐waxy Wheat Starch

Mixed starches with an amylose content of 5, 10, 18, 20, 23, and 25% were prepared by blending starches isolated from waxy and non‐waxy wheat at different ratios. The dynamic viscoelasticity of mixed 30% and 40% starch gels was measured using a rheometer with parallel plate geometry. The change in storage shear modulus (G′) over time at 5 °C was measured, and the rate constant of G′ development was estimated. As the proportion of waxy starch in the mixture increased, starch gels showed lower G′ and higher frequency dependence during 48 h storage at 5 °C. Since the amylopectin of waxy starch granules was solubilized more easily in hot water than that of non‐waxy starch granules, mixed starch containing more waxy starch was more highly solubilized and formed weaker gels. G′ of 30% and 40% starch gels increased steadily during 48 h. 30% starch gel of waxy, non‐waxy and mixed starches showed a slow increase in G′. For 40% starch gels, mixed starch containing more waxy starch showed rapidly developed G′ and had a higher rate constant of starch retrogradation. Waxy starch greatly influenced the rheological properties of mixed starch gels and its proportion in the mixture played a major role in starch gel properties.     

Effect of storage temperature on the ageing of concentrated wheat starch gels

Flour Milling and Baking Research Association, Chorleywood, Rickmansworth, Herts. Using differential thermal analysis (d.t.a.) the progress of ageing of concentrated wheat starch gels stored at temperatures from?1° to 43° has been investigated. A very close relationship has been found between the ageing of starch gels as measured by d.t.a. and the staling of bread as measured by crumb firmness at storage temperatures of?1°, 10° and 21° but some differences have been found at 32° and 43°. The results at ?1°, 10° and 21 ° provide very strong confirmatory evidence that starch crystallisation is the chief factor in the firming of bread. At elevated storage temperatures (32° and 43°) the róle of starch crystallisation in the firming of bread apparently gradually diminishes. Analysis of the results indicates that the mechanism of crystallisation of the starch, instantaneous nucleation followed by rod-like growth of crystals, is the same over the whole range of storage temperatures ?1° to 43°. Evidence is also presented to show that there is a possibility that at higher storage temperatures a more symmetrically perfect crystal structure is being formed.     

Untersuchungen über die Retrogradation der Stärke in konzentrierten Weizenstärkegelen. Teil 1. Herstellung konzentrierter Gele,Einfluß der Stärkekonzentration und Herstellungsbedingungen auf die Retrogradation der Stärke

Investigations on the Retrogradation in Concentrated Wheat Starch Gels. Part 1. Preparation of Concentrated Gels, Influence of the Starch Concentration and Conditions of Preparation on the Starch Retrogradation . A method for the preparation of homogenous, concentrated wheat starch gels is described. The influence of the starch concentration and conditions of gel preparation has been investigated by determination of gel strength (Avrami-analysis) and solubilized starch. An increase in starch concentration from 40 to 55% caused a corresponding increase in gel strength of the fresh gels, an enhanced increase in gel strength during storage and a reduction of soluble starch. The time of heating during gel preparation had little influence on retrogradation. The influence of the temperature of heating (130° and 100°C) was dependent on the starch concentration: with 40 and 50% gels a strong increase in water soluble starch is observed with the higher temperature, whereas the gel strength is increased with the 50% gels only. The amylose content in the gel extracts shows that both starch fractions take place in retrogradation. The water binding capacity of the insoluble starch is decreased during storage demonstrating that the retrogradation also occurs in the insoluble starch and significantly contributes to the increase in gel strength. Retrogradation in concentrated starch gels therefore proceeds inside and on the surface of the swollen starch granules as well as in the solubilized starch leached out during the heating process.     

Isolation and Characterization of Adzuki Bean (Vigna angularis cv Takara) Starch

Starch was isolated from Minnesota-grown adzuki beans (Vigna angularis, cv Takara). The relatively low yield (21.5%) may be characteristic of the isolation method [and may well represent the practical limits for starch recovery for this extraction procedure]. Starch granules were oval to kidney shaped, with mean size 32 μm (range 15-45 μm). SEM micrographs revealed presence of deep surface fissures. Gelatinization temperature range was 64-66-68°C and amylose content was 28.8%. Gardner color values were L = 92.5, a = 0.0, b = 5.6. Starch showed low swelling power and solubility in water. Brabender viscosity patterns showed neither peaks nor breakdown of hot paste. Starch formed stable gels at 5% and higher concentrations; gel strength was similar to that of corn and wheat starch gels, but was definitely stronger than that of potato starch. Retrogradation was greater than in corn or wheat starch gels.     

Morphology of starch in surimi gels

 The purpose of this work was to study the changes undergone by starch during heat-induced surimi gel preparation either with or without added egg white, and their effects on the structure of gels using light and scanning electron microscopy. Gels were made from SA-grade Alaska pollack (Theragra chalcogramma) surimi with: (1) salt (3%, w/w); (2) salt and waxy corn starch (3% and 5%, respectively w/w); or (3) salt, waxy corn starch and egg white (3%, 5% and 5%, respectively, w/w). Final moisture was adjusted to 73% or 83%. The gels were prepared by prior setting (40°C, 30 min, followed by 90°C, 30 min) or cooking (90°C, 30 min). The prepared gel was frozen and stored at –20°C (±1°C) until analysis. Samples were observed by light and scanning electron microscopy. The results show that the starch granules alter according to the processing conditions, with the predominance of crystalline or amorphous morphology depending upon the availability of heat and water. Large cavities formed in the protein gel matrix during setting can trap water; as a result, water availability is limited for starch to swell and gelatinize even in the high-moisture gel. Received: 13 March 1997     

Effect of Hydrothermal Treatment on Formation and Structural Characteristics of Slowly Digestible Non‐pasted Granular Sweet Potato Starch

The formation and structural characteristics of slowly digestible non‐pasted granular starch in sweet potato starch were investigated under various hydrothermal treatment conditions. The moisture content of the sweet potato starch was adjusted to 20, 50 or 90%, and the starch was heated at 40, 55 or 100°C for 12 h in a dry oven. The relative crystallinity of the hydrothermally treated samples was decreased with increasing temperature, and the X‐ray diffraction patterns of the samples were altered from C_b‐type to A‐type. Microscopic observations did not reveal any changes in the starch granules of any samples except those with moisture contents of 50 and 90% that were heated at 100°C. When gelatinization parameters were examined, samples with moisture contents of 50 and 90% that were heated at 55°C and samples of all moisture contents that were heated at 100°C had peak temperatures higher than that of raw starch but gelatinization enthalpies lower than that of raw starch. The swelling factor of the samples heated at 40°C did not change significantly, whereas that of samples heated at 55 and 100°C was decreased at increased moisture levels. The sweet potato starch with 50% moisture content that was heated at 55°C had the highest content of granular slowly digestible starch, about 200% that of raw starch, although our study did not involve further hydrothermal treatment conditions. Further study is required to complete a process for more efficient production of heat stable and slowly digestible starch.     

Retrogradation of Rice Starches Studied by Differential Scanning Calorimetry and Influence of Sugars, NaCl and Lipids

In waxy and nonwaxy rice starch gels the retrogradation process was a function of time. The enthalpy for rice starch gel with high amylose content was higher than those for low amylose content or for waxy starch samples. In all rice starch gels, samples stored under 25°C had lower enthalpy and higher endothermic onset temperature. In presence of sucrose, extent of retrogradation increased, while in presence of NaCl, it decreased. Effects of maltose, glucose and lipids were dependent on rice starch gel and storage temperature.     

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.     

Characterisation of amylose and amylopectin with various moisture contents after frying process: effect of starch–lipid complex formation

Frying is commonly used to process starchy foods. This work explored the interactions of amylose (AM) and amylopectin (AP) with lipids during frying. Maize-derived AM and AP that were adjusted to various moisture contents were fried at 180 °C. The significant effects of moisture content and formation of starch–lipid complexes were confirmed. Rheological analysis indicated that the elasticity of the fried AM paste decreased. This change was observed in AM but not in AP. Viscoelasticity decreased as the initial starch moisture content was increased. The presence of a V-type structure was confirmed by XRD. In general, relative crystallinity decreased as moisture content was increased. On the other hand, the increasement of starch–lipid complex could elevated the degree of crystallisation. AM was more likely than AP to undergo complexation with lipids during frying. Increasing the moisture content of starch within 20%~60% promoted the formation of starch–lipid complexes.     

Physicochemical Properties of Casein‐Starch Interaction Obtained by Extrusion Process

Extruded samples of starch‐casein blends were processed by using a single‐screw extruder. The independent variables in the process were temperature (126–194°C), moisture content (18–29%) and starch‐casein blend (5–95%). These independent variables affected significantly the physicochemical and textural properties of the biopolymers. The highest values for expansion (EXP) and water absorption index (WAI) were found when a higher starch proportion was present in the blends, at 126°C barrel temperature and moisture content higher than 25%. By increasing the barrel temperature, from 126°C to 194°C, the water solubility index (WSI) and color parameter were increased. Initial viscosity (IV) and viscosity at 90°C (V90) were mainly affected by the barrel temperature at 194°C. However, the viscosity at 50°C (V50) was affected neither by the different extrusion variables nor by the biopolymer proportion in the blends. Compression force (CF) was strongly dependent on moisture content and casein proportion in the blend. The higher CF values were found at starch concentrations around 50% and 25% moisture content, for higher or lower values than these the obtained extruded products were softer and consequently had lower CF values.     

Sardine Surimi Gels as Affected by Salt Concentration, Blending, Heat Treatment and Moisture

The effects of simultaneous modification of salt concentration, blending time, moisture content and heat treatment at different setting and cooking temperatures and time on characteristics of sardine (Surdina pilchardus) surimi gels was examined using a randomized incomplete block design. Maximum gel strength (GS) was obtained at highest salt concentrations and 78% moisture. Pre-setting was required to achieve acceptable gel quality. Highest GS values were found in gels set for 30–60 min at 35°C prior to heating at 90°C for 40 min. However, GS decreased after prolonged heating at 90°C. Gels set at 25, 35 and 40°C for 90 min had lower GS values when heated at 90°C for 40 min but were stable during further heating.     

OSCILLATORY PROBE RHEOMETRY AS A TOOL FOR DETERMINING THE RHEOLOGICAL PROPERTIES OF STARCH-WATER SYSTEMS 1

An oscillatory probe rheometer was effective at measuring the viscosity of starch pastes and the viscoelastic properties of starch gels. Because low shear strains were applied, the integrity of the gel was not disrupted during the testing. As the starch concentration of the systems increased, the complex modulus (G*) and storage modulus (G′) increased. At 20°C, the strength of the resulting gels, as measured by log G′, was a linear function of starch concentration. Loss tangent values (G″/G′) could be used to determine the approximate temperature at which the sol became a gel. As the starch concentration of the systems increased, the temperature of the sol to gel transformation increased from approximately 35°C (5% starch) to 60°C (10% starch).     

Crystallisation and moisture sorption properties of selected Australian unifloral honeys

The sorption properties of yapunyah (Eucalyptus ochropholia) and yellow box (Eucalyptus melliodora) honeys (Australian unifloral honeys) were investigated in a controlled relative humidity (RH) environment at 30 °C for 71 days. The original water activity of the honeys affected the sorption properties. These two honeys absorbed moisture at and above 67.9% RH and desorbed moisture at and below 51.4% RH. The crystallisation behaviour of tea tree (Melaleuca quinquenervia) and yapunyah honeys was studied during storage at 13 and 23 °C. The degree of crystallisation was monitored by measuring the absorbance at 660 and 665 nm using a spectrophotometer. The heat‐treated honeys did not show any sign of crystallisation after 5 months, whereas a seeding with precrystallised honey induced crystallisation of the same honeys. This crystallisation was more rapid at 13 than at 23 °C. Copyright © 2003 Society of Chemical Industry     

X-ray Diffraction Pattern and Functional Properties of <Emphasis Type="Italic">Dioscorea hispida</Emphasis> Dennst Starch Hydrothermally Modified at Different Temperatures

Starch from Thai yam Dioscorea hispida Dennst was hydrothermally modified at its original moisture content (∼13%, w/w) and 90 °C to 130 °C for 10 h. X-ray diffraction analysis of the modified starch showed that the crystallographic pattern of the starch was altered from type B in native starch to type C in the starch modified at 90 °C and to type A in those modified at 100–130 °C. Along with the change in crystallographic pattern, decreases in granule swelling, starch solubility, and amylose leaching were observed. Up to the modification temperature of 100 °C, a reduction in the estimated degree of crystallinity and an increase in peak viscosity were noted. Seven percent starch gel of all modified starches, except for that modified at 130 °C, showed higher complex moduli over 0.001 to 10 Hz in dynamic shear test when compared with 7% native starch gel.     

Comparison of the Thermostability of Red Hake and Alaska Pollock Surimi during Processing

Thermostability of red hake (Vrophycis chuss) mince and its temperature-dependent gel-forming properties were determined while using Alaska pollock (Theragra chalcogrumma) for comparison. Fish mince and surimi were subjected to various washwater, chopping and setting/ cooking temperatures, cooking times at varying salt concentrations and moisture levels. The optimal temperatures for washing and chopping were 15°C and 12°C for red hake and 10°C and 4°C for pollock, respectively. All treatments significantly affected gel properties. For red hake gels, 77% moisture, 2.0% salt, and a 40°C preheat-setting temperature produced the most cohesive gel. Gels of both red hake and pollock gradually became less cohesive with extended cooking time. The results suggest that red hake is more thermally stable than pollock.     

Thermal Conductivities of Starch Gels at High Temperatures Influenced by Moisture

Thermal conductivities (k) of gelatinized starch gels and of starch gels with dissolved sucrose were determined at 80 to 120°C and at 39.6 to 75% moisture by a line heat source probe method. A special made sample holder prevented moisture evaporation during determination. Regression equations relating k to temperature and moisture were developed through stepwise regression analysis. Reliability of the developed equations was verified through experiments. The maximum error for regressed k values was 0.0085 W/mK.     

Enhancement of Resistant Starch (RS3) in Amylomaize,Barley, Field Pea and Lentil Starches

Native starches isolated from amylomaize. Glacier high amylose barley, field peas and lentils contained 3–5% (w/w) resistant starch (RS3). Retrograded gels that were prepared from these starches had higher RS3 (6–9%) contents. The effects of gel concentration (% starch), storage temperature and time on the RS3 content of the retrograded gels were investigated; the optimum RS3 content was determined in gels prepared at = 10% (w/v) starch concentration and stored under = 20°C for = 5 days. Annealing of the retrograded starch gels by heating and cooling cycles, further enhanced RS3 content to 9–19%; the effect of annealing temperature and number of heat-cool cycles on the RS3 content of the annealed gel were studied. The hydrolysis of retrograded starch gels by pulanase enzyme or acid (2.2 N HCl), prior to annealing, enhanced the RS3 formation during annealing; the enzyme or acid treatment increased RS3 content of the annealed gel to 15–24% or 17–24%, respectively. The potential molecular mechanism that is responsible for the RS3 increase is discussed.     

GPC Profile Change of Potato Starch with Extrusion Processing

Native potato starch (moisture content 15%) was treated by twin screw extruder under four operating conditions with varying barrel temperatures (110°C–230°C). These modified starch samples were compared to native and drum-dried starch. Starch sample solution for gel chromatography was prepared by the three methods (acidic, alkaline, and neutral methods). They were subjected to gel chromatography on Toyopearl HW-75, and some difference was found among the three gel chromatographic patterns obtained from the same starch solution. This discrepancy among GPC patterns suggests formation of some types of anhydro-bonds between chains of amylopectin and or amylose in the extrusion process. Elevating barrel temperature increases degree of depolymerization. The size of fragments formed with the treatment is bigger than that of oligosaccharides but smaller than that of amylose.     

HIGH TEMPERATURE DRYING CHARACTERISTICS AND MOISTURE ADSORPTION ISOTHERMS OF BLACK PLUM (VITEX DONIANA) SYRUP AND SYRUP-STARCH

Modified sweeteners were formulated from mixtures of Black plum syrup and phosphorylated corn starch concentrations of 20, 30, and 40% (w/w). Each mixture was coated on an aluminium plate at 1 mm thickness, dehydrated at 60°, 70°, 80° and 90°C, and evaluated for drying and moisture sorption characteristics. Results showed that the mixtures exhibited falling rate drying characteristics. The rate of dehydration increased in the order 20% > 30% > 40% starch at constant temperature. The incremental choice of 10% starch and drying temperature except at 70° and 80°C had significant effect (p < 0.05) on drying rate. The moisture isotherm curves of the pre-dried mixtures were sigmoid in shape. Their monolayer values or upper critical moisture contents necessary for shelf-stability were significantly different from each other for the samples pre-dried at 60°C. The effect of drying temperatures on equilibrium moisture content was only significant at 90°C (p < 0.05).