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1.
In this contribution, we have analyzed the effect of sucrose on dynamic interfacial (dynamic surface pressure and surface dilatational properties) and foaming (foam capacity and foam stability) characteristics of soy globulins (7S and 11S). The protein (at 1 x 10(-3), 1 x 10(-2), 0.1, and 1 wt %) and sucrose (at 0, 0.25, 0.5, and 1.0 M) concentrations in aqueous solution and the pH (at 5 and 7), and ionic strength (at 0.05 and 0.5 M) were analyzed as variables. The temperature was maintained constant at 20 degrees C. We have observed the following. (i) The dynamics of adsorption (presence of a lag period, diffusion, and penetration at the air-water interface) of soy globulins depend on the peculiar molecular features of proteins (7S or 11S soy globulin) and the level of association/dissociation of these proteins by varying the pH and ionic strength, as well as the effect of sucrose in the aqueous phase on the unfolding of the protein. The rate of adsorption increases with the protein concentration in solution, at pH 7 compared to pH 5, at high ionic strength, and in the absence of sucrose. (ii) The surface dilatational properties reflect the fact that soy globulin adsorbed films exhibit viscoelastic behavior. The surface dilatational modulus increases at pH 7 compared to pH 5, but decreases with the addition of sucrose into the aqueous phase. (iii) The rate of adsorption and surface dilatational properties (surface dilatational modulus and phase angle) during adsorption at the air-water interface play an important role in the formation of foams generated from aqueous solutions of soy globulins. (iv) The increased interfacial adsorption (at high surface pressures) and the combined effects of interfacial adsorption and interfacial interactions between adsorbed soy globulin molecules (at high surface dilatational modulus) can explain the higher stability of the foam, with few exceptions.  相似文献   

2.
In this contribution, we have analyzed the effect of different strategies, such as change of pH (5 or 7) or ionic strength (at 0.05 and 0.5 M), and addition of sucrose (at 1 M) and Tween 20 (at 1 x 10(-4) M) on interfacial characteristics (adsorption, structure, dynamics of adsorption, and surface dilatational properties) and foam properties (foam capacity and stability) of soy globulins (7S and 11S at 0.1 wt %). We have observed that (1) the adsorption (presence of a lag period, diffusion, and penetration at the air-water interface) of soy globulins depends on the modification in the 11S/7S ratio and on the level of association/dissociation of these proteins by varying the pH and ionic strength (I), the effect of sucrose on the unfolding of the protein, and the competitive adsorption between protein and Tween 20 in the aqueous phase. The rate of adsorption increases at pH 7, at high ionic strength, and in the presence of sucrose. (2) The surface dilatational properties reflect the fact that soy globulin adsorbed films exhibit viscoelastic behavior but do not have the capacity to form a gel-like elastic film. The surface dilatational modulus increases at pH 7 and at high ionic strength but decreases with the addition of sucrose or Tween 20 into the aqueous phase. (3) The rate of adsorption and surface dilatational properties (surface dilatational modulus and phase angle) during adsorption at the air-water interface plays an important role in the formation of foams generated from aqueous solutions of soy globulins. However, the dynamic surface pressure and dilatational modulus are not enough to explain the stability of the foam.  相似文献   

3.
The effects of enzymatic deamidation by protein-glutaminase (PG) on the functional properties of soy protein isolate (SPI) were studied. Conditions for the deamidation were evaluated by means of response surface methodology (RSM). Optimal conditions based on achieving a high degree of deamidation (DD) with a concurrently low degree of hydrolysis (DH) were 44 °C, enzyme:substrate ratio (E/S) of 40 U/g protein and pH 7.0. Under optimal conditions, both DD and DH increased over time. SDS-PAGE results indicated that lower molecular mass subunits were produced with increasing DD. Far-UV circular dichroism spectra revealed that the α-helix structure decreased with higher DD, while the β-sheet structure increased until 15 min of deamidation (32.9% DD), but then decreased at higher DD. The solubility of deamidated SPI was enhanced under both acidic and neutral conditions. SPI with higher DD showed better emulsifying properties and greater foaming capacity than SPI, while foaming stability was decreased. It is possible to modify and potentially improve the functional properties of SPI by enzymatic deamidation using PG.  相似文献   

4.
Gluten solubility was improved by enzymatic proteolysis at moderate acidic pH level. Reversed‐phase HPLC analysis of gluten hydrolysates with a degree of hydrolysis (DH) in the range of 0–5% showed that both hydrophilic and hydrophobic soluble peptides were released. Emulsifying and foaming properties of hydrolysate dispersions at 3.75 mg/mL decreased with the increasing DH at all pH levels and salt conditions investigated. On the other hand, the soluble fractions separated from those hydrolysate dispersions exhibited good functional properties, independently of the initial DH. The proportion of hydrophilic and hydrophobic peptides in the soluble fractions depended on DH, pH level, and salt concentration. Nevertheless, these soluble fractions were characterized by an excellent capacity to stabilize both oil‐water and air‐water interfaces.  相似文献   

5.
We studied gliadin solubility, surface tension and foam behavior, and the presence of different gliadin types in gliadin aqueous solutions and foams as a function of pH. Gliadin has excellent foaming properties only at neutral and alkaline pH. Its solubility is minimal near neutral pH, while almost complete at acidic and alkaline pH. Surface tensions of gliadin solutions are minimal around neutral pH, higher at alkaline pH, and highest at acidic pH, which corresponds well with their respective foaming properties. Foams at acidic and alkaline pH values are enriched in γ-gliadin, while foams at pH 8.0 have a similar distribution of α- and γ-gliadins. Thus, γ-gliadin predominantly contributes to the foaming properties of gliadin. The poor foaming properties of gliadin at pH 2.0 improve in the presence of 0.25 and 1.0% NaCl. It follows that the presence of positively charged amino acid residues hinders the formation of stable foam at acidic pH.  相似文献   

6.
Soy protein isolate (SPI) was modified by ultrasound pretreatment (200 W, 400 W, 600 W) and controlled papain hydrolysis, and the emulsifying properties of SPIH (SPI hydrolysates) and USPIH (ultrasound pretreated SPIH) were investigated. Analysis of mean droplet sizes and creaming indices of emulsions formed by SPIH and USPIH showed that some USPIH had markedly improved emulsifying capability and emulsion stabilization against creaming during quiescent storage. Compared with control SPI and SPIH-0.58% degree of hydrolysis (DH), USPIH-400W-1.25% (USPIH pretreated under 400W sonication and hydrolyzed to 1.25% DH) was capable of forming a stable fine emulsion (d43=1.79 μm) at a lower concentration (3.0% w/v). A variety of physicochemical and interfacial properties of USPIH-400W products have been investigated in relation to DH and emulsifying properties. SDS-PAGE showed that ultrasound pretreatment could significantly improve the accessibility of some subunits (α-7S and A-11S) in soy proteins to papain hydrolysis, resulting in changes in DH, protein solubility (PS), surface hydrophobicity (H0), and secondary structure for USPIH-400W. Compared with control SPI and SPIH-0.58%, USPIH-400W-1.25% had a higher protein adsorption fraction (Fads) and a lower saturation surface load (Γsat), which is mainly due to its higher PS and random coil content, and may explain its markedly improved emulsifying capability. This study demonstrated that combined ultrasound pretreatment and controlled enzymatic hydrolysis could be an effective method for the functionality modification of globular proteins.  相似文献   

7.
糖接枝处理改善大豆蛋白纤维聚集体泡沫稳定性   总被引：1，自引：3，他引：1  
为了探究糖接枝对大豆蛋白纤维聚集行为和泡沫性质的影响,明确蛋白质结构与功能的关系,该研究以大豆蛋白(soy protein isolation,SPI)和乳糖(lactose)为原料,通过干热法制备糖接枝大豆蛋白(SPI-lactose conjugate,SPI-Lac),以及在酸性条件下加热诱导其形成纤维聚集体(p H值2.0),制备了一种糖接枝大豆蛋白纤维聚集体(SPI-lactose conjugate fibillar aggregates),并考察了糖接枝对大豆蛋白的纤维聚集行为及泡沫性质的影响。研究结果表明:大豆蛋白在酸性条件下(p H值2.0)经加热后会发生水解,同时水解产物不断聚集形成大分子的纤维聚集体。糖接枝导致大豆蛋白的水解速度下降,但荧光光强和粒径的结果表明糖接枝能增强纤维聚集能力。SPI-Lac在中性条件下的溶解度(p H值5.0—7.0)显著高于SPI(P0.05),且不同时间处理的SPI-Lac纤维聚集体均能改善SPI在酸性条件下的溶解度(p H值2.0—5.0)。此外,不同时间处理的SPI-Lac纤维聚集体在酸性条件下的起泡能力均高于SPI纤维聚集体。SPI和SPI-Lac纤维聚集体的形成会导致SPI起泡能力的下降,但是短时间酸热处理形成的纤维聚集体泡沫稳定性得到显著改善。因此,糖接枝结合短时间酸热处理制备的糖接枝大豆蛋白纤维聚集体在中性条件下的泡沫稳定性显著提高(P0.05),是合理有效的蛋白质改性方法。  相似文献   

8.
适宜含水率保持油茶籽贮藏品质   总被引：4，自引：4，他引：0  
为了确定油茶籽贮藏适宜的含水率,研究了在4℃,不同含水率(7%、10%、13%、16%、20%)油茶籽贮藏期间的品质变化。结果表明,较低的含水率能较好保持油茶籽的贮藏特性及营养品质。其中,含水率为7%的油茶籽贮藏效果较好,但与10%处理效果差异不明显(P>0.05)。在整个贮藏期,含水率为7%时油茶籽可溶性蛋白下降了13.05 mg/g,油酸含量下降了2.38%,酸值、过氧化值等品质指标上升速率较慢,同时能较好保持β-谷甾醇和角鲨烯等生物活性成分;其次是10%的含水率处理。而含水率为20%的油茶籽贮藏期间可溶性蛋白下降较快,贮藏结束时为25.47 mg/g,油茶籽劣变严重,所提取的油样品质变差,营养物质含量较少,因此含水率20%的油茶籽不适宜长期贮藏。综合考虑油茶籽品质因素和处理成本,认为控制含水率在10%以下能较好保持油茶籽的贮藏品质。该研究可为科学合理地贮藏油茶籽提供参考。  相似文献   

9.
We evaluated the influence of heat treatment on interfacial properties (adsorption at the oil-water interface and dilatational rheology of interfacial layers) of soy protein isolate. The related structural properties of protein affecting these interfacial behaviors, including protein unfolding and aggregation, surface hydrophobicity, and the state of sulfhydryl group, were also investigated. The structural and interfacial properties of soy protein depended strongly on heating temperature (90 and 120 °C). Heat treatment at 90 °C induced an increase in surface hydrophobicity due to partial unfolding of protein, accompanied by the formation of aggregates linked by disulfide bond, and lower surface pressure at long-term adsorption and similar dynamic interfacial rheology were observed as compared to native protein. Contrastingly, heat treatment at 120 °C led to a higher surface activity of the protein and rapid development of intermolecular interactions in the adsorbed layer, as evidenced by a faster increase of surface pressure and dilatational modulus. The interfacial behaviors of this heated protein may be mainly associated with more flexible conformation and high free sulfhydryl group, even if some exposed hydrophobic groups are involved in the formation of aggregates. These results would be useful to better understand the structure dependence of protein interfacial behaviors and to expand utilization of heat-treated protein in the formulation and production of emulsions.  相似文献   

10.
邵平  孙培龙  孟祥河  姜绍通 《核农学报》2007,21(3):268-272,280
对小麦面筋蛋白进行琥珀酰化和蛋白酶复合改性以提高其溶解性及其他特性。对复合改性面筋蛋白与原面筋蛋白、琥珀酰化面筋蛋白、碱性蛋白酶改性面筋蛋白进行了比较。结果表明:在pH 3~11、水解度4%~12%的范围内,复合改性面筋蛋白的溶解度亦随着水解度的增大而增大,比原面筋蛋白、酰化面筋蛋白、中性蛋白酶和碱性蛋白酶的改性产物都高。起泡性和起泡稳定性则先增加后降低,在水解度4%时具有较佳值,但在各水解度下较单一改性的面筋蛋白产物都要低。添加复合改性面筋蛋白面团黏弹性和面包口感较好,内部结构均匀、细腻。  相似文献   

11.
为提升大豆分离蛋白（soy protein isolate,SPI）的功能性质,该文引入大豆可溶性多糖（soybean soluble polysaccharides,SSPS）,构建大豆分离蛋白-大豆可溶性多糖体系（SPI-SSPS）,研究动态高压微射流（dynamic high-pressure microfluidization,DHPM）处理对SPI-SSPS功能特性的影响。分别采用0,60,100,140和180 MPa的 DHPM压力处理SPI-SSPS,探究不同压力对SPI-SSPS起泡特性、乳化特性、溶解性、粒度分布和表面疏水性的影响。结果表明,DHPM处理能提高SPI的溶解性和起泡特性,且SSPS的存在能显著提高DHPM对SPI功能性质的改善效果（P<0.05）。100和60 MPa的DHPM处理能使SPI-SSPS呈现较高的起泡能力和起泡稳定性,分别为未处理样品的1.2和2.4倍。140 MPa的DHPM处理使SPI-SSPS溶解性较强,为未处理样品的1.8倍。然而,DHPM处理会显著降低SPI-SSPS的乳化特性、粒径和表面疏水性（P<0.05）。随着处理压力的增加,SPI-SSPS的粒度和表面疏水性逐渐降低,在180MPa的DHPM处理下SPI-SSPS具有较小的粒径和较低的荧光强度。综上所述,DHPM结合SSPS改性技术可用于改善SPI的功能性质（如溶解性、起泡性）,促进SPI在食品工业的应用。该文的研究结果可为SPI的功能性质改性提供参考。  相似文献   

12.
Defatted sesame meal ( approximately 40-50% protein content) is very important as a protein source for human consumption due to the presence of sulfur-containing amino acids, mainly methionine. Sesame protein isolate (SPI) is produced from dehulled, defatted sesame meal and used as a starting material to produce protein hydrolysate by papain. Protein solubility at different pH values, emulsifying properties in terms of emulsion activity index (EAI) and emulsion stability index (ESI), foaming properties in terms of foam capacity (FC) and foam stability (FS), and molecular weight distribution of the SPI hydrolysates were investigated. Within 10 min of hydrolysis, the maximum cleavage of peptide bonds occurred as observed from the degree of hydrolysis. Protein hydrolysates have better functional properties than the original SPI. Significant increase in protein solubility, EAI, and ESI were observed. The greatest increase in solubility was observed between pH 5.0 and 7.0. The molecular weight of the hydrolysates was also reduced significantly during hydrolysis. These improved functional properties of different protein hydrolysates would make them useful products, especially in the food, pharmaceutical, and related industries.  相似文献   

13.
In this work we have used different and complementary interfacial techniques (surface film balance, Brewster angle microscopy, and interfacial dilatational rheology) to analyze the static (structure, morphology, reflectivity, miscibility, and interactions) and dynamic characteristics (surface dilatational properties) of beta-casein and monoglyceride (monopalmitin and monoolein) mixed films spread on the air-water interface. The static and dynamic characteristics of the mixed films depend on the interfacial composition and the surface pressure. At higher surface pressures, collapsed beta-casein residues may be displaced from the interface by monoglyceride molecules with important repercussions on the interfacial characteristics of the mixed films. From the frequency dependence of the surface dilatational properties, we have elucidated the relationships between interfacial dilatational rheology and changes in molecular structure, interactions, miscibility, and relaxation phenomena in protein-monoglyceride mixed films.  相似文献   

14.
Suni‐bug (Eurygaster spp.) enzyme was partially purified from bug‐damaged wheat and used to prepare gluten hydrolysates at 3% and 5% degree of hydrolysis (DH). Functional properties of gluten and gluten hydrolysates were determined at 0.2% (w/v) protein concentration and pH 2–10. Gluten solubility after enzymatic hydrolysis increased significantly (P < 0.05) up to 89.1, 89.6, and 95.0% at pH 7, 8, and 10, respectively. Emulsion stability (ES) of gluten hydrolysates improved at neutral and alkaline pH (P < 0.05) and emulsifying capacity (EC) increased significantly (P < 0.05) except at pH 10. Foaming capacity (FC) values of gluten hydrolysates were significantly higher (P < 0.05) at pH 6, 7, 8; foam stability (FS) values of gluten hydrolysates were significantly higher (P < 0.05) at pH 6 and 7. Enzymatic modification of gluten by wheat‐bug enzyme resulted in hydrolysates with higher antioxidant activity compared to gluten. Significant correlations (P < 0.001) were found between solubility and EC, ES, FC, and FS values of gluten and its hydrolysates with 3% and 5% DH.  相似文献   

15.
The baking properties of oats are poor, mainly due to the lack of gluten matrix and hence the surface properties of the aqueous phase are crucial for the gas retention in oat dough. Our aim was to study the composition and foaming properties of the water‐soluble fraction from differently processed oats. A water extract from kilned oats contained nonpolar triglycerides and had poor foaming properties, whereas removing lipids with hexane extraction improved the foaming capacity and foam stability. A water extract from supercritical carbon dioxide extracted oats (CO2‐oats) was free from nonpolar lipids and had good foam stability and excellent foaming capacity. Moreover, oat lipid‐binding proteins, tryptophanins, were highly concentrated in the CO2‐oats‐derived foam and apparently played an important role in the foam structure. Supplementing CO2‐oats extract with small quantities (<0.05%) of nonpolar lipids of oats destructed its foaming properties. In a preliminary baking trial, the addition of the nonpolar lipids to CO2‐oats and wheat‐starch‐based baking recipes resulted in baked goods with reduced volume. The study showed that nonpolar triglycerides were present in the aqueous phase of oat in a quantity that impaired foaming. Moreover, this was the first study showing that tryptophanins, lipid‐binding proteins of oats, were highly concentrated in foams prepared of oats free of water‐extractable nonpolar lipids. In conclusion, tryptophanins can be considered as the foam‐active proteins of oats that prevent the lipid‐induced destabilization of foam structures which could improve the baking properties of oats.  相似文献   

16.
Some nutritional and functional properties of defatted wheat germ protein   总被引：24，自引：0，他引：24  
Defatted wheat germ protein (DWGP) was isolated by alkaline extraction at pH 9.5 and subsequent isoelectric precipitation at pH 4.0, and its nutritional and functional properties were studied. The results showed that the amino acid content of defatted wheat germ was as high as 26.793 g/100 g, and the contents of eight essential amino acids were all relatively high. The isoelectric point of DWGP was 4.0. When pH >6.0, the DWGP had high solubility with a nitrogen solubility index of 70%. The emulsifying activity and emulsifying stability of DWGP were similar to those of bovine serum albumin and a little higher than those of casein. DWGP had good foaming capacity, but its foaming stability (FS) was not very good. However, the FS of DWGP can be improved through physical, chemical, or enzymatic methods. Moreover, DWGP had excellent water retention (WR); especially at pH 8.0 and a temperature of 70 degrees C, the WR of DWGP was the highest at 229.4%. DWGP offers is a potential source of functional protein isolate for possible food applications.  相似文献   

17.
Rice endosperm protein was modified to enhance solubility and emulsifying properties by controlled enzymatic hydrolysis. The optimum degree of hydrolysis (DH) was determined for acid, neutral, and alkaline type proteases. Solubility and emulsifying properties of the hydrolysates were compared and correlated with DH and surface hydrophobicity. DH was positively associated with solubility of resulting protein hydrolysate regardless of the hydrolyzing enzyme, but enzyme specificity and DH interactively determined the emulsifying properties of the protein hydrolysate. The optimum DH was 6–10% for good emulsifying properties of rice protein, depending on enzyme specificity. High hydrophobic and sulfhydryl disulfide (SH-SS) interactions contributed to protein insolubility even at high DH. The exposure of buried hydrophobic regions of protein that accompanied high-temperature enzyme inactivation promoted aggregation and cross-linking of partially hydrolyzed proteins, thus decreasing the solubility and emulsifying properties of the resulting hydrolysate. Due to the highly insoluble nature of rice protein, surface hydrophobicity was not a reliable indicator for predicting protein solubility and emulsifying properties. Solubility and molecular flexibility are the essential factors in achieving good emulsifying properties of rice endosperm protein isolates.  相似文献   

18.
Interfacial and emulsifying properties of potato protein isolate (PPI) have been studied to evaluate its potential application to stabilize oil/water emulsions at two pH values (2 and 8). The amount, type, and solubility of proteins and the size of aggregates have been determined in aqueous dispersion. Air-water and oil-water interfacial properties (adsorption, spreading, and viscoelastic properties) have been determined as a function of concentration and pH using soluble phases of PPI. The behavior of PPI stabilized oil/water emulsions has been then analyzed by droplet size distribution measurements and interfacial concentration. PPI exhibits low solubility over a wide range of pH values, with the presence of submicrometer aggregates. The pH value exerts a negligible effect on interfacial tension (oil-water) or surface pressure (air-water) but displays very important differences in viscoelastic properties of the interfacial films formed between oil and water. In this sense, pH 8 provides a major elastic response at oil-water interfaces as compared to pH 2. In relation with this result, a much higher ability to produce fine and stable emulsions is noticed at pH 8 as compared to pH 2. Consequently, there is an evident relationship between the rheological properties of the oil-water interfacial films and the macroscopic emulsion behavior.  相似文献   

19.
Industrial proteins from agriculture of either animal or vegetable origin, including their peptide derivatives, are of great importance, from the qualitative and quantitative point of view, in food formulations (emulsions and foams). A fundamental understanding of the physical, chemical, and functional properties of these proteins is essential if the performance of proteins in foods is to be improved and if underutilized proteins, such as plant proteins (and their hydrolysates and peptides derivatives), are to be increasingly used in traditional and new processed food products (safe, high-quality, health foods with good nutritional value). In this contribution we have determined the main physicochemical characteristics (solubility, composition, and analysis of amino acids) of a sunflower protein isolate (SPI) and its hydrolysates with low (5.62%), medium (23.5%), and high (46.3%) degrees of hydrolysis. The hydrolysates were obtained by enzymatic treatment with Alcalase 2.4 L for DH 5.62 and 23.5% and with Alcalase 2.4 L and Flavorzyme 1000 MG sequentially for DH 46.3%. The protein concentration dependence on surface pressure (surface pressure isotherm), a measure of the surface activity of the products (SPI and its hydrolysates), was obtained by tensiometry. We have observed that the degree of hydrolysis has an effect on solubility, composition, and content of the amino acids of the SPI and its hydrolysates. The superficial activity and the adsorption efficiency were also affected by the degree of hydrolysis.  相似文献   

20.
In this paper we present surface dynamic properties (interfacial tension and surface dilational properties) of a whey protein isolate with a high content of beta-lactoglobulin (WPI) adsorbed on the oil-water interface as a function of adsorption time. The experiments were performed at constant temperature (20 degrees C), pH (5), and ionic strength (0.05 M). The surface rheological parameters and the interfacial tension were measured as a function of WPI concentration (ranging from 1 x 10(-)(1) to 1 x 10(-)(5)% w/w) and different processing factors (effect of convection and heat treatment). We found that the interfacial pressure, pi, and surface dilational modulus, E, increase and the phase angle, phi, decreases with time, theta, which should be associated with WPI adsorption. These phenomena have been related to diffusion of the protein toward the interface (at short adsorption time) and to the protein unfolding and/or protein-protein interactions (at long-term adsorption) as a function of protein concentration in solution and processing conditions.  相似文献   

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