Functional properties of films based on soy protein isolate and gelatin processed by compression molding

Soy protein isolate (SPI) based films, blended with gelatin and plasticized with glycerol at pH 10, were prepared by compression molding with the aim to obtain environmentally friendly materials for packaging applications. Different contents and types of gelatin were incorporated into SPI-based mixtures to improve mechanical properties. All films obtained were flexible and transparent. Films with 15% of bovine gelatin showed higher tensile strength and similar elongation at break compared with the ones without gelatin. Moreover, contact angle measurements showed that the addition of gelatin decreased the hidrophilicity of the films, while UV barrier properties were maintained. The effect of gelatin addition has been explained using Fourier transform infrared (FTIR) and the changes observed in the intensity of the bands corresponding to the amide group showed that gelatin interacts with SPI, which was confirmed by the decrease of total soluble matter.     

Thermal and mechanical properties of soy protein films processed at different pH by compression

Glycerol-plasticized soy protein isolate (SPI) based films were prepared by compression with the aim to obtain environmentally friendly materials for packaging applications. Previously to the hot-pressed step, the protein was dispersed in water, the pH was fixed to values higher, lower and at the isoelectric point of SPI (pH = 4.6), and the dispersion was freeze-dried. The effect of pH on physico-chemical properties has been explained using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermo-gravimetric analysis (TGA). The changes observed by FTIR in the intensity of the bands corresponding to the amide group showed that pH affected protein–glycerol interactions. Apart from pH effect, heat and pressure also affected the grade of denaturation of SPI shown by the disappearance of the DSC peak corresponding to 7S globulin. Mechanical properties were also evaluated and related to pH and storage time. Both tensile strength and elongation at break are higher at basic pHs, when the unfolding of protein seems to be optimum in order to interact with the plasticizer. Mechanical properties remained invariable after having been stored under specific conditions for two months. Preparation of SPI-based biofilms processed at different pHs by compression is an innovative study in this field, in which the most employed technique to prepare films has been casting.     

Effect of concentration,ionic strength and freeze-drying on the heat-induced aggregation of soy proteins

The effects of protein concentration, ionic strength, and lyophilization on heat-induced aggregation of soy proteins were analyzed by SDS-PAGE, SEC-HPLC and laser light scattering (LLS). SDS-PAGE profile suggested that the aggregates were formed via non-covalent forces and/or disulfide bonds. At ionic strength of zero, SEC-HPLC revealed that the samples were composed of three major fractions: aggregates, intermediate fractions and non-aggregated molecules. Furthermore, the relative proportion of the aggregate fraction increased as protein concentration increased. Similarly, LLS indicated that the average hydrodynamic radius (R_h) increased at higher protein concentration. In sample with an ionic strength of zero, the intermediate fraction decreased after freeze-drying with a concomitant increase of the aggregate fraction. When the sample was heated at elevated ionic strength, the SEC-HPLC and LLS profiles changed substantially, the intermediate fractions decreased, and lyophilization had effect on the fraction of aggregates. These experiments suggest novel strategies for producing soy protein aggregates with controlled properties.     

Effect of ionic strength on the heat-induced soy protein aggregation and the phase separation of soy protein aggregate/dextran mixtures

The effects of ionic strength on heat-induced aggregation of soy protein and phase separation of different soy protein aggregates with dextran were investigated. The increase of ionic strength accelerated protein aggregation as shown by an increase in turbidity, aggregate fraction and particle size of salt-induced aggregates (SA). Adding salt (NaCl) to the aggregates formed at the ionic strength of zero (non-salt aggregates, non-SA), the increase of aggregate size was also found. Zeta potential results evidenced the charge screening effects of NaCl. The results of phase diagrams indicated that the compatibility of mixtures at higher ionic strength was lower than those at lower ionic strength, and SA was more incompatible with dextran than non-SA. The effects of the increase of aggregate size on the phase separation outweighed the ionic strength, which indicated that the depletion interaction also played an important role in the phase separation of soy protein aggregates and dextran. CLSM (Confocal Laser Scanning Microscopy) and rheological observations provided additional information of the microstructures of the mixtures.     

Thermal stability of soy protein isolate and hydrolysate ingredients

The objective of this study was to characterize the effects of pH, protein concentration and calcium supplementation on thermal stability, at 140 °C, of soy protein isolate (SPI) and soy protein hydrolysate (SPH) ingredients. Increasing pH between 6.4 and 7.5 led to significantly (p < 0.05) higher mean heat coagulation times (HCTs) at 140 °C, for all soy protein ingredients at 1.8, and 3.6% (w/v) protein. Increasing protein concentration from 1.8 to 7.2% (w/v) led to shorter HCTs for protein dispersions. Calcium supplementation up to 850 mg/L, except in the case of supplementation of SPI 1 with calcium citrate (CaCit), decreased HCT for soy protein ingredient dispersions, at pH 6.4 – 7.5. No significant differences (p < 0.05) were found in mean HCT for dispersions supplemented with calcium chloride (CaCl₂) and those supplemented with CaCit at 450, 650 and 850 mg/L Ca²⁺, in the pH range 6.4–7.5.     

Thermal behavior of emulsions manufactured with soy protein ingredients

The conformation, denaturation and aggregation behavior of proteins are important factors which dictate their ingredient functions and applications in formulated food products. The effect of variation in pre-treatment temperature (70–90 °C × 30 s), pH (6.4–7.5) and calcium supplementation (450 and 850 mg/L) on heat coagulation time (HCT at 140 °C) of model emulsions (3.6% (w/v) protein) stabilized with soy protein isolate (SPI) and soy protein hydrolysate (SPH) ingredients was determined. Generally, HCT of emulsions was not significantly affected by alteration of constituent pre-heating temperatures. Model emulsions displayed higher HCTs with increasing pH and lower levels of intrinsic ash content. At both supplementation levels, calcium addition led to decreased HCTs. Supplementation with chloride salts caused a greater decrease in HCT compared to supplementation with citrate salts. Furthermore, soy protein hydrolysis was associated with lower emulsion thermal stability. Results demonstrate that modification of ingredient and manufacturing parameters may be a useful approach for enhancing thermal stability properties of soy protein stabilized emulsions.     

Long time exposure to soy/isoflavone-rich diet enhances testicular and prostate health in Long-Evans rats

Soy isoflavone consumption appears to be beneficial for several health parameters. We report the influence of (lifelong exposure to) a high soy/isoflavone (High-Iso) compared to a low soy/isoflavone (Low-Iso) diet on body weight (BW), white adipose tissue (WAT) deposition, prostate weight (PW), testicular weight (TW), and testosterone levels in young adult male Long-Evans rats. WAT deposition and the WAT/BW ratios were significantly less in High-Iso vs. the Low-Iso fed animals. TW and TW/BW ratios were significantly greater in High-Iso vs. Low-Iso fed animals. Sertoli cell area, seminiferous tubule lumens and seminiferous tubule areas were significantly greater in High-Iso vs. Low-Iso animals. These data suggest that consumption of a soy diet high in isoflavone/polyphenolic molecules from conception appear to be beneficial in decreasing PW and WAT deposition while increasing TW, Sertoli cell area and seminiferous tubule volume.     

Microencapsulation properties of protein isolates from three selected Phaseolus legumes in comparison with soy protein isolate

The spray-drying microencapsulation properties of protein isolates from three selected Phaseolus legumes (kidney, red and mung beans; KPI, RPI and MPI), at a specific concentration (6 g/100 mL) and oil/protein ratio (1:1, w/w) were compared with soy protein isolate (SPI). The oil retention efficiency (RE), redispersion and dissolution behavior, as well as microstructure of the spray-dried powders were characterized. The influence of storage at 75% relative humidity for 7 days on these characteristics was also evaluated. The results indicated that the microencapsulation properties (except RE in the KPI case) of the three protein isolates were considerably poorer than SPI, though their emulsifying ability was even superior. The microencapsulating properties of these protein isolates were largely associated with their interfacial properties, especially the interfacial protein concentration. Among the three protein isolates, the spray-dried powders with KPI exhibited highest RE but least redispersion and/or dissolution behavior. The storage resulted in a severe loss of RE and ability to be redispersed and/or dissoluted, with much higher extent observed for the KPI powder. These results suggest that appropriate modifications, especially in interfacial properties, should be conducted on these proteins to warrant their application as wall materials in spray-drying microencapsulation.     

Effect of soy protein supplementation on the quality of ripening Cheddar-type cheese

The impact of soy protein isolate on the proteolysis and organoleptic properties of Cheddar-type cheese during ripening was studied. Cheese was prepared from cow's milk (control) and cow's milk plus soy protein isolate by using a starter culture of Streptococcus thermophilus and Lactobacillus delbrueckii subsp . bulgaricus, and then ripened at 12  ±  1°C for 3 and 5 months. The molecular weight range and peptide fraction in the cheeses were determined by high-performance liquid chromatography (HPLC), and the microstructure was observed by scanning electron microscopy (SEM). Sensory evaluation was used to compare the flavour, body, texture and appearance of the cheeses. The results show that the molecular weight range (9924–9966  Da) in the control cheese was larger than that (6954–6957   Da) in the soy protein-treated cheese and the microstructure in the latter was less compact than in the control cheese. In the sensory evaluation, higher scores were given for some experimental cheese than the control cheese. After 5 months of ripening, the organoleptic properties of the cheese had markedly improved and no bitter off-flavour was detected in the treated cheeses. It was concluded that soy protein could be used to improve the quality of cheese and the addition of 5% soy protein isolate could be recommended for improving the flavour and texture of Cheddar-type soy supplemented cheese.     

大豆降胆固醇活性肽的初步分离纯化

研究了大豆降胆固醇活性肽的初步分离纯化,用Alcalase碱性蛋白酶水解大豆分离蛋白得到的酶水解物经过大孔吸附树脂脱盐,并用不同浓度的乙醇以疏水性大小洗脱,得出浓度为75%的乙醇洗脱物具有最高的降胆固醇活性,将此洗脱物再经过SephadexG15凝胶过滤色谱进行分子量分级,得到了部分纯化的大豆降胆固醇肽,其最高降胆固醇活性肽是分子量大多在1000以下的小肽,抑制率为81.26%。     

离子强度对大豆分离蛋白结构及表面疏水性的影响

旨在采用生物化学和光谱学方法及手段,从蛋白质分子空间构象和溶液性质角度,探讨离子强度对大豆分离蛋白结构及表面疏水性的影响机制。研究表明:大豆分离蛋白表面疏水性在等电点两侧呈现显著下降趋势,而随着离子强度的增大大豆分离蛋白表现出\     

Volatile aroma components of soy protein isolate and acid-hydrolysed vegetable protein

The volatile aroma components of soy protein isolate (SPI) and acid-hydrolysed vegetable protein (aHVP) were compared by gas chromatography–mass spectrometry (GC–MS) and gas chromatography olfactometry (GCO). Major differences were found between the two soy-based products. Aliphatic aldehydes and ketones were mainly found in SPI, whereas pyrazines and sulphur-containing compounds were dominant in aHVP. Analyses of the non-volatile components showed that SPI was mainly protein (82.5%) with some lipid (3.5%), whereas aHVP contained no protein, only free amino acids (18.4%) and a trace quantity of lipid (0.4%). Polyunsaturates (47.8%), followed by saturates (24.9%) and monounsaturates (14.8%) dominated the fatty acid profile of the SPI lipid fraction. Both SPI and aHVP had a free fatty acid content <0.1%. Sensory analyses of aqueous suspensions of SPI and aHVP demonstrated significant differences in the odours of the two products. Compounds responsible for some of these differences were identified by GCO and GC–MS analyses of aqueous suspensions. The possible role of SPI and aHVP in the development of aroma in extrudates containing these soy products is discussed.     

Effect of processing,fermentation, and aging treatment to content and profile of phenolic compounds in soybean seed,soy curd and soy paste

This study reports the effect of processing, fermentation, and aging treatment on the content and profile of 43 phenolic compounds in soybean seeds, soy curd (tofu), and soy paste (ChungGukJang, CGJ). Mean content of phenolic compounds was ranked as soybean seed = CGJ aged for 3 days (CGJ-3D) = CGJ aged for 6 days (CGJ-6D) > tofu (P < 0.0001). Low percent recovery (47.1%) of phenolic compounds in tofu was due to heating (boiling), leaching in water, filtering, coagulation, and whey exclusion during tofu making. Aging period did not affect the mean contents of 43 phenolic compounds in the CGJ, whereas it affected the phenolic acids contents in the CGJ (P < 0.01). Benzoic, ferulic, chlorogenic, gentisic, protocatechuic, or β-Resorculic acid was major phenolic compounds in soybean seeds, tofu, CGJ-3D, or CGJ-6D. Especially, the CGJ-3D contained large amounts of isoflavone aglucons and phenolic acids compared to soybean seeds or tofu.     

Cross-linked soy protein as material for biodegradable films: Synthesis, characterization and biodegradation

The modification of soy protein isolate (SPI) with different amounts of a naturally occurring cross-linking agent (genipin, Gen) and glycerol used as plasticizer was carried out in this work. The films yielded were cast from heated and alkaline aqueous solution of SPI, glycerol and Gen and then dried in an oven. Total soluble matter, water vapor permeability and mechanical properties were improved by adding small amounts of Gen. These properties were not significantly affected (P ? 0.05) by additions exceeding 2.5% (w/w of SPI). The opacity and cross-linking degree were linearly increased with the addition of Gen, whereas the swelling ratios in water were decreased. All the films were submitted to degradation under indoor soil burial conditions and the weight loss of the films was measured at different times. This study revealed that the film biodegradation time can be controlled or modified from at least 14 to 33 days. The tests performed showed the potential of Gen to improve the SPI film properties, in which the possibility of employing such new films as biodegradable food packaging was raised.     

Microwave improvement of soy protein isolate–saccharide graft reactions

Soy protein isolate (SPI) was mixed with lactose, maltose, dextran or soluble starch (SS) and heated (temperature ?90 °C) by microwave irradiation. Compared to the classical heating, the microwave heating (MH) speeded up the graft reactions of SPI with sugars. From the results calculated, the rate constants of free amino groups in the grafts of SPI with lactose, maltose, dextran and SS by MH were, respectively, 6, 7, 57 and 12.3 times of those by classical heating. After heating by microwave, the lysine and arginine decreased and from, the FTIR spectroscopy of SPI and its grafts by MH, the absorbance of –C–O stretching and –OH deformation vibrations (1050–1150 cm⁻¹) and free –OH form (3643–3630 cm⁻¹) in SPI grafts increased compared to SPI. The temporal development of the graft reactions of SPI with sugars by MH was also shown by SDS–PAGE.     

Soybean isoflavones: Efficacy of extraction conditions and effect of food type on extractability

Soy isoflavones are phytochemicals of intense interest due to their association with a variety of health protective effects. Analytical techniques to identify and quantify these compounds vary in accuracy, reproducibility and sensitivity. In this study, solvent extraction efficiencies, and the effect of replicate extractions, and sonication on the isoflavone content of two soy products (high and low protein content) were evaluated. The later study was conducted to determine the effect of protein content on isoflavone extractability. Repeated extractions (up to five sequential extractions) of soy meal sample increased the total concentration of isoflavones by 74%, 69% and 65%, using acetonitrile–HCl, methanol and ethanol. The increment for soy protein isolate was 147%, 103% and 105%, respectively. Sonication of both samples in the three solvents for 15 min extracted as much isoflavones as the total of the five sequential extractions. These results strongly indicates that, a one step extraction without sonication can markedly under-estimate the concentration of isoflavones in foods, and that protein content of foods may have a marked impact on isoflavone extractability.     

Mechanical and thermal properties of soy protein films processed by casting and compression

Soy protein isolate (SPI) based films are environmentally friendly because they are biodegradable and come from renewable sources but they are brittle. Different ratios of plasticizer were incorporated into SPI-based films to improve mechanical properties. Glycerol has a plasticizing effect on the films in the range of 30–40%. Apart from the plasticizer, the processing method employed to prepare films also influenced on the mechanical properties. Films processed by compression showed much better mechanical properties, higher tensile strength and elongation at break, than the ones processed by casting. Analysis of the thermal properties revealed that denaturation temperatures of the two main globulin fractions present in SPI were influenced by the moisture content of the sample but not by the processing method employed.     

Complexation of curcumin with soy protein isolate and its implications on solubility and stability of curcumin

Curcumin, a natural polyphenolic food colourant, suffers a low bioavailability because of its low solubility and instability in aqueous solutions. Our study demonstrates that the food derived soy protein isolate (SPI) can form a complex with the curcumin. Fluorescence spectroscopy of the SPI–curcumin complex revealed that the complex is formed through hydrophobic interactions. Moreover, curcumin molecules quench the intrinsic fluorescence of SPI upon binding. Upon complexation, curcumin showed increased water solubility. Stability studies by UV spectroscopy showed that >80% of the curcumin was stable in the SPI–curcumin complex when dissolved in water, simulated gastric and intestinal fluids for 12 h, which would provide sufficient time for intestinal absorption. SPI–curcumin complex exhibits enhanced antioxidant activity and is capable of forming foam and emulsion, indicating its possible utilisation in food product formulation. This study suggests that SPI, being an edible protein, could be used as a material to encapsulate water-insoluble bioactive compounds in functional foods.     

pH及离子强度对燕麦分离蛋白功能特性及亚基特性的影响

以燕麦籽粒为原料提取燕麦分离蛋白(OPI),研究不同pH及盐离子强度下燕麦分离蛋白溶解性、起泡性、乳化活性及亚基特性。结果表明:①燕麦分离蛋白在pH 5.0～6.0时溶解度最低,起泡性最低,泡沫稳定性最高,在碱性条件下乳化性及乳化稳定性较高;pH 2.0,3.0的酸性条件造成了可溶性燕麦分离蛋白肽链的部分水解,形成了相对分子质量为31.0～43.0kDa的亚基条带,碱性条件下无明显区别。②NaCl浓度为0.05mol/L时溶解度最低,在0.6～0.9mol/L时,起泡性、泡沫稳定性及乳化性均较高;溶解度最低时,可溶性蛋白主要是由相对分子质量为43.0kDa的亚基组成,NaCl的加入,造成了可溶性燕麦分离蛋白肽链的断裂,形成了相对分子质量分别为43.0,66.2kDa的多肽链。