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.     

Physicochemical properties of soya bean protein gel prepared by microbial transglutaminase in the presence of okara

The influences of okara on the gelling and secondary protein structure of soya protein isolate (SPI) were investigated. Okara was ultra‐refined by high‐pressure homogenisation. The resulting particle sizes and microscopic morphologies were determined using a laser particle size analyser and a confocal laser scanning microscope, respectively. After okara homogenisation, surface area average particle size (D₃₂) decreased from 49.68 to 23.29 μm and volume average particle size (D₄₃) decreased from 118.94 to 55.08 μm. Dynamic rheological measurements showed that the storage (G′) and loss (G′′) moduli of SPI gelled in the presence of okara were mostly higher than those of SPI gels alone and were increased as the okara amounts increased. Linear law analysis revealed that SPI–okara gels were weak gels and frequency independent. Fourier transform infrared spectroscopy showed that okara and transglutaminase influenced the prevalence of α‐helices, β‐turns, β‐sheet and random coils.     

Effects of Soy Protein on Physical and Rheological Properties of Wheat Starch

It is necessary to understand the interaction phenomena between proteins and polysaccharides for the development of starch‐based products with better physical and sensory properties. A simplified model system was chosen to study the influence of soy protein on physical and rheological properties of wheat starch and the possible interactions between them. Thermal and pasting behaviors of the slurries and texture properties, water retention capacity and ultra structure of soy protein‐wheat starch gels were analyzed. While soy protein isolate increased the viscosity of starch suspension during and after heating, gels with soy protein presented a weaker structure than wheat starch gels. Results suggested association between leached out material and swollen granule surface of starch with soy protein. Scanning electron microscopy reflected these changes in the gel ultrastructure.     

Physicochemical Properties of Waxy and Normal Maize Starches Irradiated at Various pH and Salt Concentrations

Waxy and normal maize starches of various pH values and salt contents were prepared, irradiated with gamma rays (5–20 kGy) and their molecular structure, pasting viscosity and rheological properties determined. Average molar mass and size of both waxy and normal maize starches decreased considerably by irradiation from >338.0×10⁶ to <39.4×10⁶ g/mol and from >237.5 to <125.2 nm, respectively. Adjustments of pH had little influence on the average molar mass and size of irradiated starch, whereas incorporation of salt greatly reduced the molar mass and size of irradiated waxy and normal maize starches. As the pH increased from 4 to 8, the pasting viscosity of the irradiated starches decreased from 1032 to 279 mPa s in waxy and from 699 to 381 mPa s in normal starches. Pasting viscosity of both irradiated waxy and normal starch decreased from 689 to 358 mPa s and from 327 to 184 mPa s as the salt concentration increased from 1 to 5%. The G′ of gels, determined during cooling from 90 to 10°C or storage for 8 h, decreased in irradiated waxy and normal starches by pre‐conditioning at pH 8 and in irradiated waxy starches by pre‐conditioning at 5% NaCl. With 5% NaCl, G′ of irradiated normal maize starch during cooling increased up to the irradiation level of 10 kGy, and increased during storage for 8 h at all levels of irradiation. Incorporated salt prior to irradiation appears to induce incremental modifications in the molecular structure, rheological and retrogradation properties of starch by boosting the degradation of molecules.     

Effect of grinding on the structure of pea protein isolate and the rheological properties of its acid-induced gels

The purpose of this study was to expand the application range of pea protein isolates by improving the rheological properties of their acid-induced gels. A pea protein isolate was ground for different durations, and changes in the structure and properties of its gels were studied. Furthermore, the influence mechanism of grinding on gelation was revealed. The results showed that grinding slightly changed the secondary structure of the pea protein isolate and had a great impact on its tertiary structure. Compared with the unground pea protein isolate, the solubility of the ground pea protein isolate increased from 45.89% to 69.84%, and the water-holding capacity of the gels increased from 52.04% to 94.67% at 7.5 min of grinding. After grinding for 15 min, the particle size of the pea protein isolate decreased from 1292.4 to 945.7 nm, and the polydispersity index decreased from 0.387 to 0.321. Rheological measurements showed that the storage modulus (G′), viscosity and recovery of protein gel samples improved after grinding. Thus, grinding enhanced the potential of protein gels for new applications.     

核桃蛋白对大米淀粉凝胶化及凝胶特性的影响

研究不同核桃蛋白添加量下大米淀粉的糊化特性、流变特性、热特性及凝胶质构和水分子状态.结果表明,核桃蛋白以浓度依赖的方式降低了大米淀粉糊的黏度和相变焓值,而使糊化温度升高,当核桃蛋白添加质量分数达12％时,峰值黏度、谷值黏度、最终黏度分别降低了 30.77％、12.35％和14.65％,糊化温度升高了 8.89％;所有样...     

Rheological,thermal and microstructural properties of whey protein isolate‐modified cassava starch mixed gels at different pH values

The objective of this study was to investigate the rheological, thermal and microstructural properties of whey protein isolate (WPI)‐hydroxypropylated cassava starch (HPCS) gels and WPI‐cross‐linked cassava starch (CLCS) gels at different pH values (5.75, 7.00 and 9.00). The rheological results showed that the WPI‐modified starch gels had greater storage modulus (G?) values than the WPI‐native cassava starch gels at pH 5.75 and 7.00. Differential scanning calorimetry curves suggested that the phase transition order of the WPI and modified starch changed as the pH increased. Scanning electron microscopy images showed that the addition of HPCS and CLCS contributed to the formation of a compact microstructure at pH 5.75 and 7.00. A comprehensive analysis showed that the gelling properties of the WPI‐modified starch were affected by the difference between the WPI denaturation temperature and modified starch gelatinisation temperature and by the granular properties of the modified starch during gelatinisation. These results may contribute to the application of WPI‐modified starch mixtures in food preparation.     

Effects of cornstarch on the gel properties of black bean protein isolate

The effects of common starch (CS) and high amylopectin starch (HAS) from corn on the properties of heat induced black bean protein isolate (BBPI) gels prepared by heating at 95°C for 30 min were investigated by using dynamic oscillatory rheometer, texture analyzer, and scanning electron microscopy (SEM). Compared with BBPI alone, the presence of cornstarch (1–4%, wt/vol) could improve storage modulus (G′) and textural properties of BBPI (10%, wt/vol) gels. The mixed system of BBPI and 4% (wt/vol) HAS exhibited the highest G′ and formed the gel faster and more easily, which resulted in firmer and more elastic gel than BBPI‐CS at all starch concentrations. It was possible that HAS had lower pasting temperature and higher viscosity than CS, which was beneficial to the formation of BBPI gel network and strengthened the stability of network structure. Moreover, it might also be related to the synergistic effect between protein and starch. The CS and HAS existed in the BBPI gel network could bind water, leading to the increase in the water‐holding capacity (WHC) of mixed gels, especially 4% (wt/vol) HAS, which was related to homogeneous and compact microstructure with small pores.     

Effect of Amaranthus and buckwheat proteins on the rheological properties of maize starch

The relationship between pasting properties (determined with a Rapid Visco-Analyser) of maize starch and the texture of the resulting gel was examined after addition of Amaranthus and buckwheat proteins. An increase in the peak viscosity due to the addition of protein concentrates was observed, and a lesser increase from the addition of protein hydrolysates. The increase in starch pasting viscosity was related to protein solubility, and could be attributed to the starch granule stabilizing action of proteins. The interactions between starch and proteins were further investigated using oscillation and creep/recovery rheological tests. Generally, the proteins weakened starch gel structure, shown by the lower elastic modulus (G′) and higher phase degree (δ) compared to gels without any proteins added. The same results were obtained from creep/recovery experiments. It seemed that, since native proteins interact more with the granules, they act as a barrier to the release of amylose molecules; hence the resulting gels became weak. If desired, such effects could be lessened by partially hydrolyzing the proteins. ©     

Effect of soy protein substitution for sodium caseinate on the transglutaminate-induced cold and thermal gelation of myofibrillar protein

The influence of soy protein isolate (SPI) substitution for sodium caseinate (SC) on the properties of cold-set (4 °C) and heat-induced gels of pork myofibrillar protein (MP) incubated with microbial transglutaminase (TG) was investigated. The strength of cold-set MP–SC gels (formed in 0.45 M, NaCl, 50 mM phosphate buffer, pH 6.25) increased with time of TG incubation, but those gels with more than 66% SPI substituted for SC had a >26% reduced strength (P < 0.05). Upon cooking, both incubated and non-incubated protein sols were quickly transformed into highly elastic gels, showing up to 6000 Pa in storage modulus (G′) at the final temperature (72 °C). However, no differences (P < 0.05) in G′ were observed between heated samples with SPI and SC. Myosin heavy chain, casein and soy proteins gradually disappeared with TG incubation, contributing to MP gel network formation. Both cold-set and heat-induced gels had a compact protein matrix, attributable to protein cross-linking by TG.     

Physical properties of emulsion gels formulated with sonicated soy protein isolate

This study aimed to determine the effect of high-intensity ultrasound (HIU) on physical properties of soy protein isolate dispersions (SPI) and their addition to emulsion gels (EG) containing soybean oil (SBO), inulin (IN) and carrageenan (CAR). Sonicated and non-sonicated SPI dispersions were mixed with CAR, IN and SBO and heated at 90 °C for 30 min to gel the emulsion. An increase in solubility and oil binding capacity was observed in sonicated SPI dispersions (S-SPI) compared to the non-sonicated ones. HIU changed the molecular weight of SPI and decreased apparent viscosity in the dispersions. The use of S-SPI in the EG reduced the droplet size and increased the hardness and G′ values. The use of S-SPI allowed a reduction of 75% of carrageenan in the EG without affecting the hardness of the gel. The results suggest that HIU can be used to improve rheological properties of functional EG.     

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.     

Using high-pressure homogenization as a potential method to pretreat soybean protein isolate: Effect on conformation changes and rheological properties of its acid-induced gel

This study evaluated the conformational changes and rheological properties of acid-induced gels of insoluble soybean protein isolate (SPI) pretreated with high-pressure homogenization (HPH) under different pressure and cycles. Results showed that HPH pretreatment destroyed the spatial structure of the insoluble SPI, significantly decreased the particle size of the SPI dispersion, and increased the SH content. Through the characterization of its acid-induced gelation product, the best ability to withstand small strains (< 3%) of gel was found in a single HPH cycle under 100 MPa. The SPI gels with a relatively compact structure transformed from strain stiffening to strain softening with the strain increased, and it provided satisfactory stability to withstand large-amplitude oscillatory shear in three-time HPH cycles under 100 MPa. Meanwhile, SPI gels exhibited a more chaos spatial topology network after HPH pretreatment through fractal analysis, and the gels eventually exhibited “soft gel” and shear-thinning behavior with HPH pretreatment. This provides an evidence for the beneficial effect of HPH on the structural homogenization and subsequent gel formation stability of protein gels, and explores its potential applications in the food industry.     

超声协同大豆分离蛋白对米粉和米面包品质的影响及机制研究

目的 探究超声协同大豆分离蛋白(soybean isolate protein, SPI)对米粉以及米面包品质的影响。方法 以碎米为主要原料，5个梯度（0%、3%、6%、9%、12%，以碎米粉质量计）的大豆分离蛋白(soybean isolate protein, SPI)为辅料，比较超声协同5个梯度SPI对混合粉热机械学特性、糊化特性、流变特性以及米面包比容、损耗率、感官评价的影响。结果 与未进行超声处理的样品相比，超声协同SPI处理的米粉的吸水率从64.90±0.00增加至94.80±0.00，其混合粉的峰值黏度从2704.00±47.76降低至1567.00±116.73，表明超声使淀粉部分支链断裂，生成大量短直链淀粉，导致分子量下降，相互作用减弱；超声处理后的样品G′曲线呈现出先增加后降低的趋势，G''曲线随着SPI含量的增加呈现出逐渐降低的趋势。当SPI添加量为9%时，米面包的比容达到最大值，为0.86±0.08，感官评分从50.05±3.75增加至86.27±2.28分；当SPI添加量达到12%时，米面包的损耗率达到最低。结论 综上所述，采用9% SPI的方法制备米面包，可以有效的改善米面包品质，本研究为米面包在食品领域的应用提供了理论基础。     

Influence of selected hydrocolloids on triticale starch rheological properties

The aim of the study was to define the influence of selected nonstarch polysaccharides (guar gum, xanthan gum and arabic gum) on several rheological properties of triticale starch pastes/gels, at constant polysaccharide concentration (6.5 g/100 g). These included pasting characteristics, flow curves at 50 °C and mechanical spectra at 25 °C. It was found that the presence of a gum in a system modified the rheological properties of triticale starch gels/pastes, depending on the type and concentration of the gums. In the case of guar and xanthan gums, higher pasting viscosity was observed and the shear stress was increased compared with native starch. The presence of guar gum reduced the degree of thixotropy hysteresis, negative values for this being found for systems with xanthan in spite of their shear‐thinning behaviour. Systems containing arabic gum displayed lower values of pasting and flow viscosity. The type and concentration of gums added to the polysaccharide influenced the viscoelastic properties of the gels.     

Physicochemical and Gelatinization Properties of Starches Separated from Various Rice Cultivars

Morphological, viscoelastic, hydration, pasting, and thermal properties of starches separated from 10 different rice cultivars were investigated. Upon gelatinization, the G′ values of the rice starch pastes ranged from 37.4 to 2057 Pa at 25 °C, and remarkably, the magnitude depended on the starch varieties. The rheological behavior during gelatinization upon heating brought out differences in onset in G′ and degree of steepness. The cultivar with high amylose content (Goami) showed the lowest critical strain (γ_c), whereas the cultivars with low amylose content (Boseokchal and Shinseonchal) possessed the highest γ_c. The amylose content in rice starches affected their pasting properties; the sample possessing the highest amylose content showed the highest final viscosity and setback value, whereas waxy starch samples displayed low final viscosity and setback value. The onset gelatinization temperatures of the starches from 10 rice cultivars ranged between 57.9 and 64.4 °C. The amylose content was fairly correlated to hydration and pasting properties of rice starches but did not correlate well with viscoelastic and thermal characteristics. The combined analysis of hydration, pasting, viscoelastic, and thermal data of the rice starches is useful in fully understanding their behavior and in addressing the processability for food applications.     

Rheological and calorimetric properties of corn‐, wheat‐, and cassava‐ starches and soybean protein concentrate composites

The effect of soy protein concentrate (SPC) on the rheological and calorimetric properties of corn, wheat, and cassava starches was assessed. SPC increased T_o values and decreased the ΔH of all tested starches, which could be related to lower availability of water for starch gelatinization and/or to the interactions between SPC and amorphous regions of starch granules. SPC and sugar addition modified the viscosity parameters (obtained through a rapid visco‐analyser) of starch pastes, which was attributed to an increase in solid content and to the interaction of proteins with the starch dispersed phase. Frequency sweeps were carried out with a rheometer on gels containing starch, SPC, and sucrose. SPC raised storage and loss modulus, producing more consistent starch gels. Besides, penetration tests showed that SPC steadily increased starch gel firmness. Scanning electron micrographs showed that protein concentrate produced gels with closer structures. Summarizing, the starch and SPC in the gels obtained were expected to be arranged in a two‐phase system. Results showed that it is possible to achieve different textures for starch dessert formulations.     

Heat‐induced gels of soy protein and κ‐carrageenan at different pH values

Heat‐induced (90 °C/30 min) gelling of soy protein isolate (SPI) and κ‐carrageenan (κ‐CR) systems at pH values of 6.7 and 5.7 was evaluated. κ‐CR addition, increase in protein concentration and reduction in pH led to decreases in the initial gel structure forming temperature. Self‐supporting gels were not formed at concentrations of 8% (w/w) SPI or at concentrations below 0.3% (w/w) κ‐CR, but an increase in the concentration of SPI and κ‐CR led to an increase in the stress at rupture without influencing the deformability. Gel properties were a consequence of a simultaneous process of gelling and phase separation during heating. The non‐linear parameter of the Blatz, Sharda and Tschoegl (BST) rheological model allowed for the evaluation of the structural characteristics that in general corresponded to strain hardening behaviour. Strain weakening behaviour was observed at high biopolymer concentrations and at pH 6.7, which was associated with accentuated phase separation and a more discontinuous gel network.     

In vitro and In vivo studies on intragastric soya protein–polysaccharide gels in a beverage matrix

Intragastric gelation is a mechanism whereby a consumed liquid food gels under the acidic gastric condition. It was hypothesised that intragastric gelation would result in satiety due to delayed gastric emptying. Three treatment beverages that is soya protein isolate (SPI) with λ‐carrageenan (SPI‐LC; high viscosity, gelling), guar gum (SPI‐GG; high viscosity) and no polysaccharide (SPI; low viscosity) were given to twenty participants in a randomised 3 × 3 double‐blind within‐subject crossover design trial and asked to rate their hunger and fullness scores (visual analogue scale; VAS) before and up to 60 min after consumption of the beverage. Results show that there were no significant effects on hunger, fullness and energy intake after consuming the SPI‐LC (gelling) beverage compared to the SPI‐GG beverage, but did evoke weak satiety signals up to 20 min after consumption when compared to the control (low‐viscosity) SPI beverage. Therefore, intragastric gelation does not result in satiety in this study.     

Rheological properties and permeability of soy protein-stabilised emulsion gels made by acidification with glucono-δ-lactone

BACKGROUND: Soy protein, an important efficient emulsifier, is widely used by the food industry for incorporation into milk, yogurts, ice cream, salad dressings, dessert products, etc. The objective of this study was to investigate the rheological and physical properties of soy protein‐stabilised emulsion gels as affected by protein concentration and gelation temperature. RESULTS: The rheological properties and permeability were determined using oscillatory rheometry, permeability and whey separation. The modulus (G′ and G″), fracture stress and fracture strain of acid‐induced emulsion gels after 20 h of glucono‐δ‐lactone addition depended strongly on soy protein concentration and gelation temperature. At increasing soy protein concentrations, acid‐induced emulsion gels had shorter gelation times but higher storage moduli (G′), fracture stresses and strains. Increasing gelation temperature decreased the gelation time, G′, fracture stresses and strains. Permeability and whey separation were significantly affected by the protein concentration and the gelation temperature. A significant positive correlation was observed between whey separation and permeability coefficient in emulsion gels formed at different temperatures. CONCLUSION: The rheological properties and permeability of soy protein‐stabilised emulsion gels were significantly influenced by protein concentration and gelation temperature. Copyright © 2011 Society of Chemical Industry