温度对于大豆分离蛋白起泡性的影响研究

研究了20～90℃下商业用大豆分离蛋白(SPI)的起泡性。随着溶解温度的升高,5%大豆分离蛋白的溶解性及疏水性逐渐提高,起泡能力逐渐增强,泡沫稳定性则逐渐下降;将不同温度下5%大豆分离蛋白中的可溶性蛋白采用离心方法分离后发现可溶性蛋白的起泡性表现出与5%大豆分离蛋白相反的趋势,尤其在20～40℃的溶解温度下可溶性蛋白的起泡性远远优于大豆分离蛋白的起泡性。研究结果也说明,溶液中高比例可溶性大豆蛋白的存在可能有利于蛋白质泡沫的形成,但不能对泡沫的稳定性起到良好的支撑作用,同时大豆蛋白在溶液中的构象也会影响其起泡性。     

Surface Properties of Heat‐Induced Soluble Soy Protein Aggregates of Different Molecular Masses

Suspensions (2% and 5%, w/v) of soy protein isolate (SPI) were heated at 80, 90, or 100 °C for different time periods to produce soluble aggregates of different molecular sizes to investigate the relationship between particle size and surface properties (emulsions and foams). Soluble aggregates generated in these model systems were characterized by gel permeation chromatography and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Heat treatment increased surface hydrophobicity, induced SPI aggregation via hydrophobic interaction and disulfide bonds, and formed soluble aggregates of different sizes. Heating of 5% SPI always promoted large‐size aggregate (LA; >1000 kDa) formation irrespective of temperature, whereas the aggregate size distribution in 2% SPI was temperature dependent: the LA fraction progressively rose with temperature (80→90→100 °C), corresponding to the attenuation of medium‐size aggregates (MA; 670 to 1000 kDa) initially abundant at 80 °C. Heated SPI with abundant LA (>50%) promoted foam stability. LA also exhibited excellent emulsifying activity and stabilized emulsions by promoting the formation of small oil droplets covered with a thick interfacial protein layer. However, despite a similar influence on emulsion stability, MA enhanced foaming capacity but were less capable of stabilizing emulsions than LA. The functionality variation between heated SPI samples is clearly related to the distribution of aggregates that differ in molecular size and surface activity. The findings may encourage further research to develop functional SPI aggregates for various commercial applications.     

Solubility and Foaming Properties of Phytate-Reduced Soy Protein Isolate

A pilot scale ion exchange process was developed to produce a 75 - 77% phytate-reduced soy protein isolate. The solubility and foaming properties of this isolate were compared to those of control and commercial soy protein isolates as a function of protein concentration (5 and 10%, w/v), pH (3, 6 and 9) and preheat temperature (25, 60 and 80°C). Phytate-reduced soy protein extract exhibited minimum solubility at pH 4.8 - 5.0, compared to 4.2 - 4.5 for control soy extract. Phytate-reduced soy protein isolate was most soluble and functional at pH values below its isoelectric point (pH 3), whereas control and commercial soy isolates were generally most soluble and functional at pH values above their isoelectric point (pH 6 and 9).     

Comparisons of emulsifying properties of Maillard reaction products conjugated by green, red seaweeds and various commercial proteins

Conjugates were prepared with seaweeds and commercial proteins at 60 °C for 24 h. Bradford protein analysis, SDS–polyacrylamide gel electrophoresis, water absorption capacity, oil absorption capacity, foaming capacity and emulsion activity index/emulsion stability index for seaweeds, commercial proteins and their conjugates were examined. Band patterns with molecule weight ranged from 31 kDa to 116 kDa for conjugates disappeared on the SDS–PAGE. Protein contents measured with the Bradford assay were 0.05–0.12 g/g for conjugates, while measurements for commercial proteins were 0.57–0.90 g/g. Red seaweed and its conjugates showed significantly higher water absorption capacities than those found in other samples, and measurements were 13.03–20.00 ml/g. However, oil absorption capacities of conjugates were lower than commercial proteins. At the foaming initial stage, red seaweed conjugates demonstrated higher foaming capacity than those of commercial proteins and red seaweeds. Conjugates showed higher emulsion activity index than those for seaweeds. Nonetheless, seaweed–protein mixtures showed significantly lower emulsion activity index values than those of commercial and conjugates. The highest emulsion stability indexes were conjugated samples of green seaweed–soy protein isolates and green seaweed–soy protein concentrates which values were 0.977 and 0.919, respectively.     

Physicochemical and Functional Properties of Soy Protein Substrates Modified by Low Levels of Protease Hydrolysis

ABSTRACT: Endo-protease treatments achieving low degrees of hydrolysis (DH 2% and 4%) were used to improve functional properties of hexane-extracted soy flour (HESF), extruded-expelled partially defatted soy flour (EESF), ethanol-washed soy protein concentrate (SPC), and soy protein isolate (SPI). These substrates had protein dispersibility indices ranging from 11% to 89%. Functional properties, including solubility profile (pH 3 to 7), emul-sification capacity and stability, foaming capacity and stability, and apparent viscosity were determined and related to surface hydrophobicity and peptide profiles of the hydrolysates. Protein solubilities of all substrates increased as DH increased. Emulsification capacity and hydrophobicity values of the enzyme-modified HESF and EESF decreased after hydrolysis, whereas these values increased for SPC and SPI. Emulsion stability was improved for all 4% DH hydrolysates. Hydrolyzed SPC had lower foaming capacity and stability. For substrates other than SPC, foaming properties were different depending on DH. Hydrolysis significantly decreased the apparent viscosities regardless of substrate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated differences in the molecular weight profiles of the hydrolysates. HESF and EESF, which had high proportions of native-state proteins, showed minor changes in the peptide profile due to hydrolysis compared with SPC and SPI.     

Isoflavone Aglycone Content and the Thermal,Functional, and Structural Properties of Soy Protein Isolates Prepared from Hydrothermally Treated Soybeans

Soybeans were hydrothermally treated at 2 different temperatures (40 °C and 60 °C) and for 4 different hydration times (4, 8, 12, and 16 h) to (i) increase the isoflavone aglycone content in a soy protein isolate and (ii) evaluate the changes in thermal, functional, and structural properties of a soy protein isolate as a function of hydrothermal treatment conditions. Our study is the first to evaluate aglycone content, extraction yield, β‐glucosidase activity, differential scanning calorimetry, protein digestibility, scanning electron microscopy, water absorption capacity (WAC), foaming capacity (FC), and foaming stability of soy protein isolates prepared from hydrothermally treated soybeans. For aglycone enhancement and the extraction yield maintenance of soy protein isolates, the condition of 40 °C for 12 h was the best soybean hydrothermal treatment. The structural rearrangement of proteins that occurred with the hydrothermal treatment most likely promoted the capacity of proteins to bind to aglycone. Moreover, the structure shape and size of soy protein isolates verified by scanning electron microscopy appears to be related to the formation of hydrophobic surfaces and hydrophobic zones at 40 °C and 60 °C, respectively, affecting the protein digestibility, WAC, and FC of soy protein isolates.     

A comparison of the buttermilk solids functional properties to nonfat dried milk,soy protein isolate,dried egg white,and egg yolk powders

Physicochemical (i.e., sulfhydryl group, protein, and total solubility) as well as functional properties (i.e., water-holding and fat-absorption capacity, foaming and emulsification capacity, and stability) of commercial buttermilk solids (BMS) were compared to nonfat dried milk, soy protein isolate, and dried egg yolk and egg white powders on an equivalent protein basis. BMS showed limited functional properties in water-holding capacity (0.75 g water/g protein) and fat-absorption capacity (1.2 g of oil/g of protein), and foaming capacity (0.5 ml of foam/ml of solution) and stability. However, emulsifying capacity and stability of BMS was not significantly different from other dried protein powders. Results indicated that 0.9 g of protein (approximately 0.45%, wt/vol, concentration) from BMS was needed to emulsify a maximum oil concentration of 50% in water at temperatures up to 50 degrees C. Denaturation of protein, quantified by free sulfhydryl groups, was a critical factor affecting the functionality of BMS and all other protein powders tested. The milk fat globule membrane present in BMS did not enhance either emulsifying capacity or stability.     

高固形物浓度对大豆分离蛋白酸性蛋白酶酶解产物功能特性的影响

本文系统研究了提高固形物浓度对酸性蛋白酶酶法改性大豆分离蛋白分子量分布、氮溶解指数、分散稳定性、持水力、乳化性、起泡性和泡沫稳定性的影响。结果表明:大豆分离蛋白经过酸性蛋白酶控制酶解制备的改性大豆分离蛋白,其产物氮溶解指数、起泡性均有明显提高,分散稳定性略有提高;但持水力、乳化性、泡沫稳定性有所降低。在相同水解度下,随着酶解体系中固形物浓度的提高,改性大豆分离蛋白的分散稳定性、持水力、乳化活性均呈上升趋势,酶解产物中分子量小于10 kDa的肽段以及氮溶解指数呈下降趋势。当水解度小于8%时,低浓度酶解产物起泡性高于高浓度酶解产物,而水解度超过8%时,高浓度酶解产物起泡性大体高于低浓度酶解产物。     

Emulsifying Capacity and Emulsion Stability of Soy Proteins Compared with Corn Germ Protein Flour

Both emulsifying capacity (EC) and emulsion stability (ES) increased with increasing concentrations from 0.4% to 0.8% of soy flour (SF), soy concentrate (SC), soy isolate (SI) and corn germ protein flour (CGPF) when studied by response surface methodology. EC and ES increased as pH increased from 6 to 8 in all samples. Increasing incubation temperatures of protein solutions from 20–70°C or from 4–20°C did not affect EC or ES, respectively. SF had the highest EC, followd by SI, SC, and CGPF.     

不同浓度大豆分离蛋白热诱导聚集体的研究

采用体积排阻色谱(SEC-HPLC)和激光光散射(LLS)研究了由醇洗豆粕制备的不同浓度的大豆分离蛋白热诱导聚集体(100℃,15 min)的分子量分布和粒径分布。SEC-HPLC检测结果表明,经热处理的蛋白溶液主要由3部分组成,即聚集体、中间体及未聚集部分;蛋白浓度为1%时,聚集体的百分含量为18.70%;蛋白浓度增加到5%时,聚集体的百分含量增加到54.15%;同时LLS的测定结果表明,蛋白溶液有不均一的粒径分布且体系浓度增加时平均粒径(Rh)由56.5 nm增至144.9 nm。     

Extraction,purification and characterization of globulin from common buckwheat (Fagopyrum esculentum Moench) seeds

Salt-soluble globulin was extracted from common buckwheat (Fagopyrum esculentum Moench) seeds. The protein content of buckwheat globulin (BWG) was over 90%. Anion-exchange chromatography (with stepwise salt gradient elution) was used to obtain two fractions of BWG, corresponding to the basic and acidic polypeptides, respectively, at a ratio of approximately 1:2. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the acidic and basic polypeptides were linked by disulfide bonds. The basic polypeptide has an estimated molecular weight of 23–25 kDa, an isoelectric point in slightly alkaline region (pH 8–9), and showed a high degree of homology with other legumin-like proteins. Disulfide and sulfhydryl contents in BWG were estimated as 36.4 and 3.20 μM/g of protein, respectively. BWG exhibited beneficial functional properties such as high solubility, emulsifying activity and emulsion stability, while the foaming properties were relatively poor. BWG had lower water holding capacity and comparable fat binding capacity when compared to a commercial soy protein product.     

Functional Properties of Guar Proteins

Water and fat absorption, emulsification capacity (E.C.), foaming capacity (F.C.), and foam stability (F.S.) of guar meal and protein isolate have been determined and compared with those of soybean meal and isolate. Guar meal had lower water absorption capacity, similar fat absorption capacity and greater F.S. and E.C. than soybean meal. Guar protein isolate (GPI) had lower water absorption capacity but higher fat absorption capacity than soy protein isolate (SPI). The foaming capacity and emulsification capacity were similar at all pH's except around pH 4. However the foam stability of GPI was greater than that of SPI.     

Characteristics and Functionality Enhancement by Glycosylation of Bitter Melon (Momordica charantia) Seed Protein

Seeds of ripe bitter melon (Momordica charantia) contain approximately 30% protein. However, this protein, which is less functional than soy protein, may have desirable functionalities as a food ingredient after modification. Bitter melon seed protein isolate (BMSPI) was prepared under optimal extraction conditions (defatted meal to 1.3 M NaCl was 1:10 w/v; pH 9.0) and its functional properties were investigated before and after modification by glycosylation. Glycosylation was conducted at varying relative humidities (50%/65%/80%) and temperatures (40 °C/50 °C/60 °C) using a response surface central composite design. Degree of glycosylation (DG) ranged from 39.3 to 52.5%, 61.7 to 70.9%, and 81.2 to 94.8% at 40 °C, 50 °C, and 60 °C, respectively (P values < 0.0001). Denaturation temperatures of all DGs ranged from 111.6 °C to 114.6 °C, while unmodified/native BMSPI had a value of 113.2 °C. Surface hydrophobicity decreased to approximately 60% when the DG was maximal (94.8%). Solubility decreased almost 90% when the DG was maximal in comparison to the native BMSPI (62.0%). Emulsifying activity increased from 0.35 to 0.80 when the DGs were ≥80%, while emulsion stability increased from 63 to 72 min when the DGs were greater than 70%. A similar trend was observed with foaming capacity and foaming stability of the glycosylated proteins. This glycosylated BMSPI with improved emulsifying and foaming properties could be used as an ingredient in food products where such properties are required.     

Characterization of globulin from Phaseolus angularis (red bean)

Phaseolus angularis (red bean) seeds contain about 25% protein (dry basis), almost half of which is globulin. Similar to globulins from other Phaseolus species , 7S vicilin is the major fraction of red bean globulin (RBG), with 11S legumin as a minor component. The amino acid profile of RBG met or exceeded the FAO/WHO standard. Circular dichroism measurements indicate that RBG is a protein rich in α-helical and β-turn structures. RBG exhibited higher protein solubility than Supro 610, a commercial soy protein isolate, especially at acidic pHs, with minimal solubility at around pH 5.0. Compared to Supro 610, RBG had lower water hydration capacity and comparable fat binding capacity, which might be because of its lower surface hydrophobicity. RBG had higher emulsifying activity index and emulsion stability than Supro 610, but with poorer foaming properties.     

Functional properties and chemical composition of fractionated brown and yellow linseed meal (Linum usitatissimum L.)

Considering its high content of protein and dietary fiber, linseed meal is a remarkable source for food ingredient and food additive production. In this study, brown and yellow linseed meal (Linum usitatissimum L.) were fractionated via pH control, to obtain five linseed meal fractions rich in protein and fiber. The fractions were characterized by measuring functional properties, proximate and carbohydrate composition, and lignan contents. Acid soluble protein fractions were characterized by lower emulsification capacities and foaming activities in comparison to a commercial soy protein isolate. Alkaline soluble protein fractions showed emulsification activities comparable to whole egg and relatively high contents of secoisolariciresinol diglucoside (SDG) of 110 mg/g DM and 56.2 mg/g DM, respectively. The good emulsification and foaming activities, as well as the enriched concentration of SDG and therefore high nutritional value, make especially the alkaline soluble protein fraction highly interesting for food ingredient production.     

酶水解制备具有潜在免调节活性大豆肽的研究

由于已有的一些研究报道初步表明带正电荷的小分子肽具有免疫调节作用,本研究分别应用Alcalase、Flavourzyme、Protease A和Peptidase R四种商业酶,单独使用或将它们进行组合,分别以大豆分离蛋白（SPI）、可溶性大豆蛋白（SSP）和不溶性大豆蛋白（InSP）为底物,在不同的酶-底物比、底物浓度、pH和温度条件下进行水解大豆蛋白,测定了水解度、水解产物的分子量分布和带正电荷肽的相对含量.结果表明,Alcalase在相同条件下可以获得较高的水解度和较大的水解蛋白平均分子量;以InSP作为底物的水解产物中带正电荷肽的相对含量最高.水解条件对水解度有较明显的影响,但是平均分子量和正电荷肽相对含量的影响较弱。     

Combined effect of dynamic heat treatment and ionic strength on the properties of whey protein foams – Part II

The aim was to investigate the effect of dynamic thermal treatment in a tubular heat exchanger on the denaturation and foaming properties of whey proteins, such as overrun, foam stability and texture. A 2% w/v WPI solution (pH 7.0), with and without NaCl addition (100 mM), was submitted to heat treatment at 100 °C. The results demonstrated that heat treatment slightly reduced overrun, whereas NaCl and heat treatment improved foam stability, enhanced texture and provided smaller bubble diameters with more homogeneous bubble size distributions in foams. The foaming properties of proteins, especially stability, were shown to depend not only on the amount of protein aggregates, but also on their size. While insoluble aggregates (larger than 1 μm diameter) accelerated drainage, soluble aggregates (about 200 nm diameter) played a key role on the stabilization of gas–liquid interfaces.     

Isolation and characterization of proteins from soymilk residue (okara)

Protein was extracted from okara at pH 9.0 and 80 °C for 30 min, giving a recovery of 53% protein. The extracted protein was isolated by isoelectric precipitation at pH 4.5, and the dried, defatted protein isolates (prepared at 25 and 80 °C) had over 80% protein.

The okara protein isolates have essential amino acid profiles similar to the FAO scoring pattern, and high in vitro protein digestibility, with methionine and cysteine as the limiting amino acids. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed that okara protein isolates had a large quantity of high molecular weight components suggesting protein aggregation. Differential scanning calorimetry and hydrophobicity data suggested extensive protein unfolding in the okara products.

Okara protein isolates had lower solubility than a commercial soy protein isolate at both acidic and alkaline pH, probably due to protein aggregation. Other functional properties, including emulsifying, water and fat binding, and foaming properties, were found to be comparable to the commercial soy isolate.     

Functional Properties of Pork Liver Protein Fractions

The functional (emulsifying, gelling and foaming) properties of liver protein fractions as well as their molecular weight distribution and surface hydrophobicity were investigated and compared to commercial proteins. Two protein fractions were characterized: water soluble (WSLP) and WSLP combined with salt soluble liver proteins (W?+?SSLP). The effect of salt concentrations was also investigated (0, 1.8 and 3.4 % NaCl). Both WSLP and W?+?SSLP displayed good emulsifying properties and foam stability. However, their gelling properties were rather poor. An increase in salt concentration decreased the emulsifying properties of WSLP while the effect on W?+?SSLP was less pronounced. Addition of 1.8 % NaCl increased foaming ability of WSLP and W?+?SSLP while foam stability was not affected. Further increase of NaCl (3.4 %) decreased both foaming ability and foam stability and is probably attributed to refolding of the protein molecules because of the higher level of hydrophobic groups with 3.4 % NaCl. Gel forming ability of WSLP and W?+?SSLP containing 0 % was higher compared to high salt concentrations. However, higher salt concentrations shifted onset gelation temperature of WSLP and W?+?SSLP to lower temperatures probably due to partial unfolding of the proteins as indicated by an increase of the surface hydrophobicity.     

Functional properties of protein hydrolysates from pea (Pisum sativum,L) seeds

The aim of this study was to investigate the effects of partial enzymatic hydrolysis on functional properties of two different pea protein isolates obtained from two pea genotypes, Maja and L1. Papain and commercial protease (Streptomyces griseus protease) were used for protein modification. Solubility, emulsifying and foaming properties were estimated at four different pH values (3.0, 5.0, 7.0 and 8.0). Papain increased solubility of L1 pea protein isolate at pH 3.0, 5.0 and 8.0, emulsifying properties and foaming capacity at all pH values. Otherwise, papain increased solubility of Maja pea protein isolate only at pH 8.0. This pea protein isolate modified with both enzymes formed emulsions with improved stability at lower pH (3.0, 5.0). The commercial protease‐prepared pea protein isolates showed generally low solubility and different emulsifying and foaming properties. Proper selection of enzyme, conditions of hydrolysis and genotypes could result in production of pea protein isolates with desirable functional properties.