Gel texture and chain structure of amylomaltase-modified starches compared to gelatin

Amylomaltase (AM) (4-α-d-glucanotransferase; E.C. 2.4.1.25) from Thermus thermophilus was used to modify starches from various botanical sources including potato, high amylose potato (HAP), maize, waxy maize, wheat and pea, as well as a chemical oxidized potato starch (Gelamyl 120). Amylopectin chain length distribution, textural properties of gels and molecular weight of 51 enzyme and 7 non-enzyme-modified starches (parent samples) were analyzed. Textural data were compared with the textural properties of gelatin gels. Modifying starch with AM caused broadening of the amylopectin chain length distribution, creating a unimodal distribution. The increase in longer chains was supposedly a combined effect of amylose to amylopectin chain transfer and transfer of cluster units within the amylopectin molecules.Exploratory principal component analysis (PCA) data analysis revealed that the data were composed of two components explaining 94.2% of the total variation. Parent starches formed a cluster separated from that of the AM-modified starches.Extended AM treatments reduced the apparent molecular weight and the gel texture without changing the amylopectin chain length distribution. However, the gel texture was typically increased as compared to the parent starch. AM-modified HAP gels were about twice as hard as gelatin gels at identical concentration, whereas gels of pea starch were comparable to gelatin gels. Modifying Gelamyl 120 and waxy maize with AM did not change the textural properties. Branching enzyme (BE) (1,4-α-d-glucan branching enzyme; EC 2.4.1.18) from Rhodothermus obamensis was used in just one modification and in combination with AM. The combined AM/BE modification of pea starch resulted in starches with shorter amylopectin chains and pastes unable to form gel network even at concentration as high as 12.0% (w/w). The PCA model of all gel texture data gave suggestive evidence for starch structural features being important for generating a gelatin-like texture.     

淀粉对磷酸化的虾蛄肌原纤维蛋白凝胶特性的影响

将马铃薯、木薯和玉米淀粉分别添加到磷酸化的虾蛄肌原纤维蛋白中,探讨在不同淀粉添加量、不同三聚磷酸钠添加量及不同温度下对磷酸化蛋白所形成凝胶特性的影响。结果表明：随着三聚磷酸钠添加量的增加,3 种淀粉形成的复合蛋白凝胶强度和保水性均提高;随着淀粉添加量的增加,马铃薯、木薯淀粉对复合蛋白的凝胶特性有显著影响（P＜0.05）,玉米淀粉对蛋白凝胶特性没有显著影响（P＞0.05）;随着温度的升高,3 种淀粉均能使蛋白的凝胶强度升高,但保水性下降。本研究结果为进一步研究虾蛄中肌原纤维蛋白凝胶特性以及淀粉的利用提供了一定的基础。     

Effect of partial hydrolysis with an immobilized proteinase on thermal gelation properties of beta-lactoglobulin B

We have investigated the influence of partial hydrolysis with an immobilized proteinase from Bacillus licheniformis on the thermal gelation of isolated beta-lactoglobulin B. Gelation behaviour was determined by dynamic rheological measurements (small deformation) and the gels were characterized with respect to microstructure and water-holding properties. A fine-stranded gel with a complex modulus of approximately 2000 Pa was formed from beta-lactoglobulin (50 g/l in 75 mM-Tris-HCl, pH 7.5). Limited hydrolysis prior to thermal gelation resulted in coarser gels with thicker protein strands and larger pores. Gel structure correlated with its permeability, proton mobility and water-holding capacity. Total stiffness gel increased with low degrees of hydrolysis, but decreased after prolonged hydrolysis. Maximal gel stiffness was 1.5-fold that gels made from of unhydrolysed beta-lactoglobulin. This was much lower than the stiffening effect obtained after partial hydrolysis of whey protein isolate, showing that the gel strengthening effect of partial hydrolysis was depedent on the protein composition and/or the hydrolysis and gelatin conditions. A mechanism to explain the observed effects of hydrolysis on gelation and gel properties is presented.     

Morphological,thermal, rheological and noodle‐making properties of potato and corn starch

A comparison between the morphological, thermal, rheological and noodle‐making properties of corn starch and potato starches separated from five different potato cultivars was made. The granule size and shape of all starches differed significantly. Potato starch granules were comparatively larger than corn starch granules, while the transition temperatures were found to be higher for corn starch. Consistency coefficients and flow behaviour indices measured by back extrusion were higher for potato starches than for corn starch. Stickiness of cooked starch pastes was observed to depend upon their consistency coefficient. The gels made from all potato starches showed higher gel strength than those from corn starch. The gel strength of starches from both corn and potato increased during refrigerated storage. The amylose content, swelling power, solubility and light transmittance values of potato starches were significantly higher than those of corn starch. Noodles made from potato starches had higher cooked weight and cooking loss than corn starch noodles. Texture profile analysis revealed that potato starch noodles also had higher hardness and cohesiveness than corn starch noodles. Hardness of cooked noodles from all starches increased and cohesiveness decreased during storage. Noodles made from starches of higher viscosity exhibited higher hardness and cohesiveness. Textural differences among cooked starch noodles appeared to be associated with morphological, thermal and rheological properties of corn starch and potato starches. © 2002 Society of Chemical Industry     

RHEOLOGICAL AND CALORIMETRIC INVESTIGATIONS OF STARCH-FISH PROTEIN SYSTEMS DURING THERMAL PROCESSING2,,3

During the thermal processing of starch-surimi systems, significant rheological changes due to the sol-gel transformation of fish proteins and the gelatinization of starch were observed by rigidity scanning. Differential scanning calorimetry (DSC), produced results which corresponded well with rheological changes. Starch gelatinization in cooked fish-starch gels was studied by DSC. The effects of starches on the textural properties of cooked gels were dependent on their gelatinization characteristics, such as gelatinization temperature, degree of swelling and water uptake of the granules. Gels producing higher failure stress values were obtained after starch gelatinized; however, no significant effect on failure strain was observed by the addition of starch. Pregelatinized starch had detrimental effects on the gelation of fish protein, and more water was absorbed by this starch compared to non-pregelatinized starches. Resulting gels were weaker and less deformable.     

Enzymatic modifications of pea protein and its application in protein-cassava and corn starch gels

The interactions between starch and proteins during processing influence pasting and rheological properties of starch and produce modifications on starch gel structure. Enzymatic modifications have been proposed for overcoming the limitations of using proteins as food ingredients. This work aimed to study the impact of native and enzymatically modified pea proteins on the properties of protein-starch (from cassava or corn) gels. Pea protein isolate (PPI) was incubated with endopeptidase (AL) or microbial transglutaminase (TG). Pasting profile, rheological behaviour and water retention capacity of protein-starch gels were analyzed. Protein (native and enzymatically modified) incorporation increased the viscosity of both corn and cassava starches during gel preparation. However, the hydrolyzed protein reduced drastically the increment of viscosity of protein-starch gels. The addition of PPI led to corn starch network that shifted from an elastic-like nature to a more viscous-like, whereas the opposite effect was observed in cassava gel network. TG- and AL-treated proteins led to a decrease of both G′ and G″ moduli of protein-starch gels, and AL-treated proteins showed the highest decrease on these parameters. Hydrolyzed proteins also favoured the syneresis of the protein-corn starch gel, whereas crosslinked proteins tended to reduce it. Enzymatic modifications of pea proteins affected significantly pasting and rheological properties of protein-starch gels.     

Microalgae biomass interaction in biopolymer gelled systems

Microalgae are an enormous biological resource, representing one of the most promising sources for the development of new food products and applications. Pea protein/κ-carrageenan/starch gels, interesting vegetarian alternatives to dairy desserts, served as model systems to study the addition of microalgal biomass, its effect, and subsequent rheological behaviour. Spirulina and Haematococcus gels presented a markedly different rheological behaviour compared to the control mixed biopolymer gelled system. The present goal is to clarify how these microalgae affect the gelation and interact with each biopolymer present in the complex mixed gel system. Hence, the aim of the present work is to study the effect of Spirulina and Haematococcus microalgal biomass addition on the rheological behaviour of pea protein, κ-carrageenan and starch simple gels, as well as in pea protein/κ-carrageenan and pea protein/starch systems. The gelation process was monitored in-situ through dynamic oscillatory measurements (temperature, time and frequency sweep tests) for a 24 h maturation period, and rheological results were supported with fluorescence optical microscopy observations. The addition of Spirulina and Haematococcus to biopolymer gelled systems induced significant changes in the gels’ rheological behaviour and microstructure. In general, it was observed that the gelling mechanism is ruled by the biopolymers, while microalgae seem to be embedded in the gel network acting as active particle fillers. The addition of Haematococcus resulted in more structured gels in comparison to the control and Spirulina systems. In the case of κ-carrageenan gels, both microalgae induced a large increase in the rheological parameters, which should be related to the high ionic content of microalgal biomass. Spirulina addition on starch systems promoted a decrease in the gels’ rheological parameters. This should be related to the starch gelatinization process, probably by competing for water binding zones during the granules’ hydration process.     

Interactions in bovine serum albumin–calcium alginate gel systems

Young's modulus of heat-denatured gels of calcium alginate and bovine serum albumin (BSA) was determined and compared to the modulus of BSA gels containing sodium alginate and to pure BSA gels. Ionic strength, pH, and calcium concentration were varied. The BSA/Ca-alginate gels were either prepared with -glucono-δ-lactone (GDL) and CaCO₃ to induce alginate gelation before the gelation of BSA, or by soaking heat-denatured BSA/Na-alginate gels in a CaCl₂ solution. BSA/Ca-alginate gels were stronger than BSA/Na-alginate gels at all conditions, and stronger than pure BSA gels up to higher pH values and up to somewhat higher ionic strengths than BSA/Na-alginate gels. The strength of BSA/Ca-alginate gels was highly dependent on the strength of the alginate gel. This was shown by variation of the calcium concentration and by soaking the gels in EDTA, NaCl, and CaCl₂ solutions. When BSA/Na-alginate or BSA/Ca-alginate gels prepared at optimum conditions were soaked in solutions of higher ionic strength or pH, no reduction in gel strength was observed. Consequently, they were much stronger than gels that were prepared directly at high pH or ionic strength. The results may suggest that the alginate network in a BSA/Ca-alginate gel increases the effectiveness of electrostatic BSA-alginate cross-links or entanglements. However, other explanations are also possible.     

Mixed gels of fine-stranded and particulate networks of gelatin and whey proteins

Mixed gels of gelatin and whey protein concentrate were investigated, as well as their pure systems, by tensile tests and by dynamic oscillatory measurements. The systems were studied for homogeneous particulate whey protein gels at pH 5.4 and for inhomogeneous particulate whey protein gels at pH 4.6. The influence on the systems of the Bloom number of the gelatin component has also been investigated. Results of the fracture properties, such as stress and strain at fracture, indicate a transition in rheological properties. Results of the elastic modulus, obtained by tensile measurements, as well as the storage modulus, obtained by dynamic oscillatory measurements, both agree with predictions for phase inversions from the Takayanagi models as modified by Clark, which are in agreement with the fracture properties. The transition points are different for the different mixed gel series but take place between 1 and 3 wt% gelatin and 8 wt% whey protein concentrate, depending on factors such as the microstructure of the whey protein concentrate. Dynamic oscillatory measurements showed that gel formation of whey protein concentrate is unaffected by the presence of gelatin, which is in agreement with light microscopy results. Light microscopy revealed that the mixed gel systems were bicontinuous and that the whey protein network structure was unaffected by the presence of gelatin. It is postulated that the predicted phase inversions of the mixed gels are due to a shift in rheological properties without any phase inversions in the microstructure.     

不同蜡制玉米淀粉对肌原纤维蛋白凝胶特性的影响

将蜡制玉米淀粉、酯化蜡制玉米淀粉和交联酯化蜡制玉米淀粉以添加量分别为0%、2%、4%、6%、8%、10%添加到肌原纤维蛋白中,形成蛋白淀粉复合物,研究3?种淀粉对肌原纤维蛋白凝胶保水性、质构特性、白度值、表面疏水性、流变特性和微观结构的影响。结果表明,相比纯肌原纤维蛋白,淀粉均能显著提高复合凝胶的保水性、硬度和弹性（P＜0.05）,且随添加量的增加而显著增加（P＜0.05）,但在添加量为10%时,各指标上升不显著（P＞0.05）,其中交联酯化蜡制玉米淀粉效果最好;3?种淀粉均能增加复合凝胶的白度值,但交联酯化蜡制玉米淀粉的添加会使复合凝胶的白度值过大（P＜0.05）,对色泽不利;同时,淀粉能显著提高复合蛋白的表面疏水性和凝胶的弹性模量（P＜0.05）,且随着添加量的增加而显著增加（P＜0.05）,与肌原纤维蛋白凝胶相比,复合凝胶结构趋于致密均匀。在实验的3?种淀粉中,除色泽因素外,交联酯化蜡制玉米淀粉提高凝胶性能的效果要优于其他两种淀粉。?     

Rheological Behaviour of Thixotropic Starch and Gelatin Gels

Thixotropic behaviour of starch, gelatin and mixed starch/gelatin gels was investigated by different rheological methods by means of the rotational viscosimeter with coaxial cylinders. Influence of different factors (gel composition, preparation temperature, gel age, homogenization and viscosimeter rotor acceleration) on the coefficients of thixotropy and parameters of the flow equation was considered. The recovery of destructed gels was followed by Doherty-Hurd method, but also a modified method was developed and applied for determination of some specificities in the rheological behaviour of starch and gelatin gels.     

Hydrothermal Modifications of Tropical Tuber Starches. 1. Effect of Heat‐Moisture Treatment on the Physicochemical,Rheological and Gelatinization Characteristics

Cassava, sweet potato and arrowroot starches have been subjected to heat‐moisture treatment (HMT) under different conditions using a response surface design of the variables. A comparative study was performed on the pasting properties, swelling behaviour and the gelatinization properties of the modified starches and also on the rheological and textural properties of their pastes. X‐ray diffraction studies have shown that cassava starch exhibited a slight decrease in crystallinity, whereas sweet potato and arrowroot starches showed an increase in crystallinity after HMT at 120ºC for 14 h with 20% moisture. The swelling volume was reduced and the solubility was enhanced for all three starches after HMT, but both effects were more pronounced in the case of arrowroot starch. The decrease in paste clarity of the starch after HMT was higher in the case of cassava and sweet potato starches. Viscosity studies showed that the peak viscosity of all three starches decreased after HMT, but the paste stability increased as seen from the reduced breakdown ratio and setback viscosity. Studies on rheological properties have shown that storage and loss moduli were higher for the starches heat‐moisture treated at higher moisture and lower temperature levels than the corresponding native starches. Storage of the gel at ‐20ºC resulted in a significant increase in storage modulus for all the three starches. All the textural parameters of the gels were altered after the treatment which depended on the nature of the starch and also the treatment condition.     

Gelatinization and Thermal Properties of Modified Cassava Starches

The thermal properties of seven commercial modified cassava starches, including oxidized, acetylated, cross‐linked, and combined acetylated and cross‐linked starches were studied by differential scanning calorimetry (DSC) in the glassy and rubbery states. Increase in gel hardness in the rubbery state during storage was also monitored, as well as gelatinization behavior. The modified starches were prepared from granular starch and had a degree of substitution in the range 0–0.053. The glass transition temperatures (T_g) of the modified starches were 3–6°C significantly lower than that of the non‐modified starch. The physical aging peak temperatures were also significantly reduced by 2–3°C, compared to the non‐modified starch, while aging enthalpies increased. Starch modifications did not decrease amylopectin retrogradation significantly. During storage, the oxidized starch gel became significantly harder than the non‐modified starch gel, while the hardness of the acetylated and/or cross‐linked starch gels was significantly reduced, which confirmed that acetylation or cross‐linking can decrease hardness, even when the extent of modification is limited. Different modifications controlled different properties of the starch system, with cross‐linking and acetylation influencing the gelatinization behavior and the changes in starch gel texture during storage, respectively.     

Viscoelastic behavior of an agar—gelatin mixture gel as a function of its composition

The stress relaxation behavior of an agar—gelatin mixture gel was analyzed as a function of the stress relaxation behaviors of the component agar and gelatin gels. A six-element model composed of three components of the Maxwell mechanical model was applicable for each stress relaxation behavior. Except for the behavior of the shortest relaxation time, the three elastic moduli of the mixture gel, including the instantaneous elastic modulus, became predictable from the corresponding moduli of the agar and the gelatin gels, taking into account the concentration dependence and using a parallel-series combination model for the elasticity. The viscosities of the mixture gel were also predictable from the corresponding viscosities of the component agar and gelatin gels, except for the behavior of the shortest relaxation time.     

Isothermal gelation of proteins. 1. Urea-induced gelation of whey proteins and their gelling mechanism

The changes in dynamic elastic moduli of whey proteins [whey protein isolates, β-lactoglobulin (B-Lg), α-lactalbumin (A-La) and bovine serum albumin (BSA)] at various concentrations in the presence of 8 molldm³ urea with time were measured at 25°C, because whey protein-urea systems set to gels automatically at room temperature without heating. From the time dependence behavior of elastic moduli for the proteins, the individual proteins were characterized as BSA having good, B-Lg intermediate and A-La poor urea-induced gelation. The disulfide bonds and hydrogen bonds played important roles in the formation the urea-induced gels.     

RELATIONSHIP BETWEEN PHYSICOCHEMICAL PROPERTIES OF STARCHES AND EXPANSION OF FISH CRACKER 'KEROPOK'

The influence of physicochemical properties of starches on expansion of‘keropok’was studied. Swelling power, solubility, and amylose leaching of a starch were dependent on the lipid and protein contents of the starch. The morphology of different starch granules used in‘keropok’gel was observed using scanning electron microscopy. The sizes of swollen starch granules in the gel were quantitatively measured by image analysis. The average length and width of swollen gelatinized sago and tapioca starch granules were significantly higher than that of wheat starch, and consequently, the linear expansion of‘keropok’with wheat starch was lower than those of‘keropok’made with tapioca or sago starches. Linear expansion was positively correlated to swelling power and solubility of the starch. Textural properties of‘keropok’gels with different starches were also measured and found to have correlation with linear expansion of the final products.     

Starch enzymatic hydrolysis,structural, thermal and rheological properties of pigeon pea (Cajanus cajan) and dolichos bean (Dolichos lab-lab) legume starches

Cajanus Cajans and Dolichos lab-lab legume starches from Argentine cultivars were investigated under a technological and nutritional point of view. Their physico-chemical, structural, thermal and the rheological properties of their gels were evaluated. Rice (RS) and potato (PS) starches were included as references. In vitro digestibility from Englyst method was also evaluated. Legume starches had the highest amylose content and the most stable chemical structure. Their rapidly digestible starch and starch digestibility rate index were very low, similar to PS, and fivefold lower than RS. They had a much higher slowly digestible starch content than PS. Legume starches showed the highest gel stability versus heating and stirring and an intermedium pasting temperature between RS and PS. They formed viscoelastic gels at 6% concentration with stronger elastic-like behaviour and higher yield stress than references. Our results indicate these legumes represent an efficient starch source to provide tailor-made properties to food/industrial applications.     

Effects of pressure-shift freezing and conventional freezing on model food gels

Summary Gels of agar, starch, ovalbumin, gelatin and an industrial β-lactoglobulin protein isolate, were frozen conventionally in a −30 °C freezer and by pressure-shift freezing at 200 MPa at −15 °C. Thawing was carried out conventionally at 20 °C and by the application of a pressure of 200 MPa. The microscopic structure and mechanical properties of the thawed gels were compared with those of the initial gels. Microscopic examination showed that pressure-shift freezing produces smaller and more uniform ice crystal damage than conventional freezing at −30 °C. The results also suggest that the freeze-thaw behaviour of food gels can be categorized into two general types: (1) gels which have a reduced gel strength as a result of mechanical damage to the gel microstructure caused by ice crystal formation, and (2) gels which have an enhanced gel strength, as a result of molecular structural changes that take place in the frozen state. Agar and gelatin were found to be typical of type (1) gels, whereas starch, β-lactoglobulin protein isolate and ovalbumin were found to be typical of type (2) gels. In the case of starch, retrogradation during thawing was found to be the most important factor.     

Rheological/textural properties of starch and crude hsian‐tsao leaf gum mixed systems

The Effects of hsian‐tsao leaf gum (HG) on the rheological/textural properties of non‐waxy starches were studied. Pronounced interactions between starch and HG were observed. The rheological properties, including pseudo‐gel viscosity in the rapid visco‐analyser test, storage and loss moduli in the dynamic rheological test, as well as firmness in the texture analyser test, of the mixed gels generally improved with increasing gum concentration to a certain level, then deteriorated with further increase in gum concentration. The critical gum concentration for the development of optimal rheological properties depended on the starch type and concentration. Within the concentration range studied, mixed systems with wheat starch could generally reach the highest pseudo‐gel viscosity, firmness, and storage modulus if the starch/HG ratio was appropriate, followed by those with corn and tapioca starch. Copyright © 2003 Society of Chemical Industry     

The effect of shear on the rheology and structure of heat‐induced whey protein gels

The influence of mechanical shearing on the small deformation properties and microstructure of heat‐induced whey protein gel has been studied. The viscoelastic properties of these gels at different concentrations of 10% and 20% (w/w) exposed to different shear rates of 0, 50, 100, 200 and 500 s^?1 during gelation were measured using dynamic oscillatory rheometry. The structure of both the shear treated and unsheared gels was then investigated using light microscopy. The results showed that the storage modulus of the gels at both concentrations was increased by increasing the shear rate exposure during gelation while the shear‐treated gels were more elastic and showed frequency‐independent behaviour. As the total protein concentration of the gel increased, the viscoelastic properties of the gels also increased significantly and the gels showed greater elasticity. The gels obtained from the higher shear rate exposure were stronger with higher elastic moduli at both protein concentrations. Images of the gels obtained using light microscopy showed that shearing resulted in phase separation and some aggregation in the structure of the gels at both concentrations. However, the shearing rates applied in this study were not enough to cause aggregation breakdown in the gel network.