Physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate

The amino acid composition and physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate (HPI) were evaluated and compared with those of soy protein isolate (SPI). Edestin, a kind of hexameric legumin, was the major protein component. HPI had similar or higher levels of essential amino acids (except lysine), in comparison to those amino acids of SPI. The essential amino acids in HPI (except lysine and sulfur-containing amino acids) are sufficient for the FAO/WHO suggested requirements for 2-5 year old children. The protein solubility (PS) of HPI was lower than that of SPI at pH less than 8.0 but similar at above pH 8.0. HPI contained much higher free sulfhydryl (SH) content than SPI. Differential scanning calorimetry analysis showed that HPI had only one endothermic peak with denaturation temperature (T(d)) of about 95.0 degrees C, attributed to the edestin component. The T(d) of the endotherm was nearly unaffected by 20-40 mM sodium dodecyl sulfate but significantly decreased by 20 mM dithiothreitol (P < 0.05). The emulsifying activity index, emulsion stability index, and water-holding capacity of HPI were much lower than those of SPI, and the fat adsorption capacity was similar. The data suggest that HPI can be used as a valuable source of nutrition for infants and children but has poor functional properties when compared with SPI. The poor functional properties of HPI have been largely attributed to the formation of covalent disulfide bonds between individual proteins and subsequent aggregation at neutral or acidic pH, due to its high free sulfhydryl content from sulfur-containing amino acids.     

Molecular structure, physicochemical characterization, and in vitro degradation of barley protein films

Barley protein films were prepared by thermopressing using glycerol as a plasticizer. The combined effects of heating temperature and amount of plasticizer interacted to determine protein conformation and, subsequently, the properties of the film matrix. The film barrier and mechanical properties were systematically investigated using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), SDS-PAGE, and protein solubility tests. These experiments demonstrated that heat treatment induced barley protein unfolding and then protein aggregation and the formation of covalent disulfide bonds to enhance film strength. Increasing the amount of plasticizer reduced protein denaturation and limited protein interactions, resulting in significantly improved film flexibility at the cost of reduced film moisture barrier property and tensile strength. In vitro degradation experiments demonstrated that barley films were resistant in gastric conditions, yet can still be completely degraded by intestinal enzymes, and they possess low cytotoxicity to Caco-2 cells. The prepared barley films have potential for development as delivery systems for gastric-sensitive bioactive compounds to the intestine for release.     

Solubility, tensile, and color properties of modified soy protein isolate films

Protein solubility (PS) values of different soy protein isolate (SPI) films were determined in water, 0.01 N HCl, 0.01 N NaOH, 4 M urea, and 0.2 M 2-mercaptoethanol. Tensile and color (L, a, and b values) properties of films also were determined. Control films were cast from heated (70 degrees C for 20 min), alkaline (pH 10) aqueous solutions of SPI (5 g/100 mL of water) and glycerin (50% w/w of SPI). Additional films were cast after incorporation of dialdehyde starch (DAS) at 10% w/w of SPI or small amounts of formaldehyde in the film-forming solutions. Also, control film samples were subjected to heat curing (90 degrees C for 24 h), UV radiation (51.8 J/m(2)), or adsorption of formaldehyde vapors. PS of control films was highest (P < 0.05) in 2-mercaptoethanol, confirming the importance of disulfide bonds in SPI film formation. All treatments were effective in reducing (P < 0.05) film PS in all solvents. Both DAS and adsorbed formaldehyde rendered the protein in films practically insoluble in all solvents. Adsorption of formaldehyde vapors and heat curing also substantially increased (P < 0.05) film tensile strength from 8.2 to 15.8 or 14.7 MPa, respectively. However, heat curing decreased (P < 0.05) film elongation at break from 30 to 6%. Most treatments had small but significant (P < 0.05) effects on b color values, with DAS-containing films having the greatest (P < 0. 05) mean b value (most yellowish). Also, DAS-containing, heat-cured, and UV-irradiated films were darker, as evidenced by their lower (P < 0.05) L values, than control films. It was demonstrated that PS of SPI films can be notably modified through chemical or physical treatments prior to or after casting.     

Mechanical properties and water-vapor permeability of soy-protein films affected by calcium salts and glucono-delta-lactone

Edible films were prepared from solutions of soy protein with calcium salts and glucono-delta-lactone (GDL). Calcium salts cross-linking interactions with soy-protein isolate (SPI) could result in the formation of films with rigid three-dimensional structure. GDL contributed to the formation of a homogeneous film structure due to increased protein--solvent attraction. Tensile strength (TS) of calcium sulfate treated SPI film (8.6 MPa) was higher than the TS of calcium chloride treated SPI films (6.4 MPa) and the control SPI film (5.5 MPa). Puncture strength (PS) of calcium sulfate treated SPI film (9.8 MPa) was higher than the PS of calcium chloride treated SPI films (8.5 MPa) and the control SPI film (5.9 MPa). SPI film formulated with GDL had larger elongation at break (39.4%) than that of SPI control film (18.2%). Calcium salts and GDL-treated SPI films had lower water-vapor permeability than the SPI control film.     

硬脂酸-胱氨酸-大豆分离蛋白复合膜的机械特性和吸湿性研究

以硬脂酸作为增塑剂,胱氨酸作为交联剂制备具有一定力学性能和良好抗湿性能的大豆分离蛋白复合膜。将膜放在25℃,相对湿度为50%的干燥器中平衡两天,用质构仪测定膜的抗拉强度(TS),延伸率(E(%))。在水分活度a_w为0.10～0.90的范围内研究了复合膜在25℃的吸湿特性。吸湿速率和吸湿等温线数据分别拟合到Peleg's 方程和GAB(Guggenheim-Anderson-de Boer)模型。结果表明：大豆蛋白复合膜的TS、延伸率E(%)以及吸湿速率随着硬脂酸和胱氨酸的添加比率显著地变化。硬脂酸和胱氨酸的最佳添加比率为40∶60(w/w)(每升蛋白质溶液中加入10 g混合添加剂),此时,大豆蛋白膜的强度比原来提高2倍,并且有最佳的吸湿速率。吸湿数据和GAB 模型有很高的拟合度,拟合系数最高达0.99。     

Preparation and characterization of films from pea protein

The conditions for protein film preparation from an alkaline dispersion of a pea protein isolate were investigated in the presence of polyols as plasticizers. Mechanical and barrier properties of resulting films were studied as a function of protein dispersion conditions, protein and plasticizer concentrations and ratios, chain length of the plasticizer, and pH and composition of the alkaline medium. Neither the mode of protein hydration nor the pea isolate origin had a significant effect on the mechanical properties of pea protein films. However, increasing the plasticizer chain length induced slightly higher surface hydrophobicity but poor mechanical properties. Addition of monoglycerides to film-forming solution allowed a significant improvement of the films during aging. Both tensile strength and surface hydrophobicity increased when ammonium hydroxide was used as protein dispersing agent instead of sodium hydroxide.     

高压微射流压力对大豆蛋白-大豆多糖体系功能性质的影响

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。     

Characterization of biodegradable films obtained from cysteine-mediated polymerized gliadins

This study focuses on the effect exerted by interchain disulfide bonds on the functional properties of films made from gliadins when cross-linked with cysteine. Gliadins were extracted from commercial wheat gluten with 70% aqueous ethanol, and cysteine was added to the film-forming solution to promote cross-linking between protein chains. The formation of interchain disulfide bonds was assessed by SDS-PAGE analysis. Gliadin films treated with cysteine maintain their integrity in water and become less extensible while their tensile strength increases as a consequence of the development of a more rigid network. The glass transition temperature of cross-linked films shifts to slightly higher values. The plasticizing effects of glycerol and moisture are also demonstrated. The mechanical behavior of cysteine-cross-linked gliadin films was compared to that of polymeric glutenins. Cross-linked gliadins displayed tensile strength values similar to those of glutenin films but achieved slightly lower elongation values. Cysteine-cross-linked gliadin films present the advantage that they are ethanol soluble, facilitating film fabrication or their application as a coating for food or for any other film or surface.     

Solution and film properties of sodium caseinate/glycerol and sodium caseinate/polyethylene glycol edible coating systems.

The aim of this study is to determine the effects of plasticizer hydrogen bonding capability and chain length on the molecular structure of sodium caseinate (NaCAS), in NaCAS/glycerol and NaCAS/polyethylene glycol 400 (PEG) systems. Both solution and film phases were investigated. Glycerol and PEG reduced the viscosity of aqueous NaCAS, with the latter having a greater effect. This was explained in terms of protein/plasticizer aggregate size and changes to the conformation of the caseinate chain. In the film phase, glycerol caused more pronounced changes to the film tensile strength compared with PEG. However, the effect of glycerol on film water vapor permeability was smaller. These observations are attributed to the differences in plasticizer size and hydrogen bonding strength that controls the protein-plasticizer and protein-protein interactions in the films. Glass transition calculations from the tensile strength data indicate that the distribution of bonding interactions is more homogeneous in NaCAS/PEG films than in NaCAS/glycerol films.     

Cast Films from Soy Protein Isolates and Fractions

Glycerol-plasticized soy protein films were cast from alkaline aqueous film-forming solutions of laboratory-prepared 7S, 11S, and soy isolate (LSI) fractions and from commercial soy isolate (CSI). Tensile strength (TS), elongation at break (E), water vapor permeability (WVP), total soluble matter (TSM), protein solubility (PS), and Hunter L, a, and b color values of these films were determined. The 11S films had greater TS than 7S films (P < 0.05), while LSI films had greater TS than CSI films (P < 0.05). No significant differences were detected among mean E values and among mean WVP values of all films (P > 0.05). The 7S films had higher TSM and PS values than 11S films (P < 0.05). CSI films were significantly darker (lower L value) and more yellow (greater positive b value) than LSI films (P < 0.05).     

Modification and characterization of biodegradable methylcellulose films with trimethylolpropane trimethacrylate (TMPTMA) by γ radiation: effect of nanocrystalline cellulose

Methylcellulose (MC)-based films were prepared by solution casting from its 1% aqueous suspension containing 0.25% glycerol. Trimethylolpropane trimethacrylate (TMPTMA) monomer (0.1-2% by wt) along with the glycerol was added to the MC suspension. The films were cast and irradiated from a radiation dose varied from 0.1 to 10 kGy. Then the mechanical properties such as tensile strength (TS), tensile modulus (TM), and elongation at break (Eb) and barrier properties of the films were evaluated. The highest TS (47.88 PMa) and TM (1791.50 MPa) of the films were found by using 0.1% monomer at 5 kGy dose. The lowest water vapor permeability (WVP) of the films was found to be 5.57 g·mm/m(2)·day·kPa (at 0.1% monomer and 5 kGy dose), which is 12.14% lower than control MC-based films. Molecular interactions due to incorporation of TMPTMA were supported by FTIR spectroscopy. A band at 1720 cm(-1) was observed due to the addition of TMPTMA in MC-based films, which indicated the typical (C═O) carbonyl stretching. For the further improvement of the mechanical and barrier properties of the film, 0.025-1% nanocrystalline cellulose (NCC) was added to the MC-based suspension containing 1% TMPTMA. Addition of NCC led to a significant improvement in the mechanical and barrier properties. The novelty of this investigation was to graft insoluble monomer using γ radiation with MC-based films and use of biodegradable NCC as the reinforcing agent.     

Partially carboxymethylated feather keratins. 2. Thermal and mechanical properties of films

Free cysteine thiol groups of keratin extracted from chicken feathers were partially carboxymethylated with iodoacetic acid (25-76% cysteine modification). Stable dispersions were used for the preparation of films by solution casting. Glycerol was used as a plasticizer (0.05-0.47 g/g of keratin), and films were stored at a constant relative humidity (20, 30, 50, 70, or 90%). The degree of crystallinity in the films was higher when more cysteine residues were carboxymethylated. The films displayed an optimum in mechanical properties at approximately 50% cysteine carboxymethylation. The tensile strength at this optimum was 25 MPa, the E modulus, 350 MPa, and the elongation at break, 50%. Probably, this optimum was the result of both a decreasing amount of disulfide bonds and an increasing degree of crystallinity for higher degrees of cysteine modification. The influences of a higher amount of glycerol and of different storage conditions on the mechanical properties of films from keratin with a defined degree of cysteine modification were also investigated.     

Physicochemical modifications of high-pressure-treated soybean protein isolates

Changes induced by high pressure (HP) treatment (200-600 MPa) on soybean protein isolates (SPI) at pH 3 (SPI3) and pH 8 (SPI8) were analyzed. Changes in protein solubility, surface hydrophobicity (Ho), and free sulfhydryl content (SH(F)) were determined. Protein aggregation and denaturation and changes in secondary structure were also studied. An increase in protein Ho and aggregation, a reduction of free SH, and a partial unfolding of 7S and 11S fractions were observed in HP-treated SPI8. Changes in secondary structure were also detected, which led to a more disordered structure. HP-treated SPI3 was partially denatured and presented insoluble aggregates. A major molecular unfolding, a decrease of thermal stability, and an increase of protein solubility and Ho were also detected. At 400 and 600 MPa, a decrease of the SH(F) and a total denaturation were observed.     

酸溶剂对葛根淀粉/壳聚糖复合可食膜性能的影响

为了考察壳聚糖酸溶剂对葛根淀粉/壳聚糖复合可食膜抗菌、物理和机械性能的影响,该文选择质量分数为1%的乙酸、乳酸、苹果酸为溶剂,配制质量体积比2g/L的葛根淀粉-壳聚糖复合膜液,以0.5g/L的抗坏血酸为活性添加剂,0.6g/L的丙三醇为增塑剂,0.1g/L的吐温20为表面活性剂,采用流延法制备可食性复合膜。结果表明:复合膜液具有一定的表面活性;酸溶剂未对膜液表面张力产生显著影响。有机酸溶剂种类对复合膜性能影响显著,其中乙酸复合膜的机械强度最大,平均抗拉强度和穿透力分别为5.73MPa和8.63N,水溶性最小,约34%,对抗坏血酸缓释效果最明显;乳酸复合膜的延展性最优,平均断裂伸长率和穿透距离分别为71.5%和6.05mm;苹果酸复合膜的抑菌效果最佳,对大肠杆菌和金黄色葡萄球菌的抑制率分别达到98.9%和81.2%,阻水性最强,透湿系数为4.824.82×10-11g/(m·s·Pa),故可根据不同使用目的选择相应复合膜。研究结果为该类复合包装膜在实际食品上的应用提供理论依据。     

High-pressure homogenization lowers water vapor permeability of soybean protein isolate-beeswax films

Soybean-protein isolate (SPI) has excellent film-forming capacity. However, the water vapor permeability of SPI film is high, which will cause the moisture lose of packaged products. The effect of high-pressure homogenization (HPH) on the water vapor permeability of SPI-beeswax films was evaluated. The HPH was effective at lowering the water vapor permeability of SPI-beeswax films to about 50% of the control. The HPH reduced the particle size of films and made their matrix more compact. The HPH improved the hydrophobicity of SPI-beeswax films. For the first time, we proved that the HPH improved the bound-beeswax content in SPI-beeswax films. The bound beeswax was effective at lowering the water vapor permeability of films rather than the free beeswax in the film matrix. In summary, the HPH lowered water vapor permeability of SPI-beeswax films by reducing their particle size and raising their hydrophobicity and bound-beeswax content.     

辉光放电低温等离子体改性大豆分离蛋白可食膜工艺优化

为制备具有良好性能的可食膜,该文采用大豆分离蛋白(soy protein isolate,SPI)为成膜基材,利用辉光放电等离子体作用对可食膜进行改性,并研究等离子体处理时间、丙三醇质量浓度、pH值对可食膜水蒸气透过系数(water vapor permeability,WVP)、氧气透过率(oxygen permeability,OP)抗拉强度(tensile strength,TS)、断裂伸长率(elongation,E)的影响。利用响应面法对工艺参数进行优化,得到各因素对可食膜性能影响的大小依次为pH值丙三醇质量浓度等离子体处理时间。试验结果表明:丙三醇质量浓度为0.02 g/mL、等离子体处理时间为11.31 min、pH值为11,可食膜性能综合得分S为0.90。此时可食膜的断裂伸长率为273.77%、抗张强度为3.46 MPa、水蒸气透过系数为1.81×10~(-12) g/(cm·s·Pa)、氧气透过率为1.43×10~(-5) cm~3/(m~2·d·Pa)。通过原子力显微镜和接触角测量仪对可食膜表面进行观察,结果表明:经低温等离子体处理的可食膜表面物理结构发生改变,粗糙度增加,水接触角变小,有效提高大豆分离蛋白膜的机械性能和表面润湿性。     

丁香酚对高粱醇溶蛋白可食性膜结构及性能的影响

为开发天然的可降解、可食性包装材料,以高粱醇溶蛋白为原料,采用溶液共混的方法制备可食性丁香酚/高粱醇溶蛋白复合膜,分析不同浓度丁香酚对可食性高粱醇溶蛋白膜物理性能及微观结构的影响并探讨其变化机理。结果表明,添加4%丁香酚可优化蛋白膜的机械性能,提升膜的拉伸强度(TS)和断裂伸长率(EAB);添加丁香酚不影响蛋白膜的水蒸气透过系数(WVP),但略微提高了蛋白膜的溶解度;添加4%丁香酚可增加蛋白膜对紫外光和可见光的吸光度值,即增强膜的光阻隔性能。DSC测量显示,添加丁香酚后降低了高粱醇溶蛋白的玻璃态转变温度(Tg),表明丁香酚提高了丁香酚/高粱醇溶蛋白复合膜的延展性;FTIR分析结果表明,添加丁香酚后使得高粱醇溶蛋白二级结构中的α-螺旋、无规则卷曲转变为β-折叠、β-转角,表明丁香酚有助于提高丁香酚/高粱醇溶蛋白复合膜的机械性能;SEM结果显示,4%丁香酚与高粱醇溶蛋白的相容性良好,制备的复合膜截面光滑紧致。本研究结果为可降解、可食性膜新材料的研究及应用推广提供了理论参考。     

Plasticization of a protein-based film by glycerol: a spectroscopic, mechanical, and thermal study

Kafirin, the seed storage protein of the cereal sorghum, is highly homologous with the maize storage protein zein. The effects of plasticisation of a kafirin film by glycerol in the absence of water were examined by a combination of spectroscopic (NMR and infrared), rheological, and calorimetric methods. The results suggest that at low glycerol levels the glycerol is absorbed onto and possibly into the protein. Increasing the level of glycerol increases the motion of the protein and changes the protein conformation. There are corresponding changes of the mechanical properties of protein films. At 40% (w/w) of glycerol, two glass transition temperatures were observed, one of which corresponded to the glass transition temperature of pure glycerol. This result indicates that at this level of plasticizer there are sufficient glycerol/glycerol interactions occurring to allow a separate glass formation process for glycerol.     

适宜物理-酶联合改性提高酸性条件下大豆分离蛋白乳化性

为提高酸性条件下大豆分离蛋白（soy protein isolates,SPI）的乳化性能,该文研究了物理-酶联合改性对SPI（pH值为4）的乳化性能影响,通过对比确定了物理-酶联合改性,即超声波-酶复合改性和挤压膨化-酶复合改性两种改性方法在酸性条件下的乳化性能效果最好;并通过对改性后 SPI（pH 值为4）进行溶解性、游离巯基、二硫键、粒径、扫描电镜（scanning electron microscope,SEM）和激光共焦扫描显微镜（confocal laser scanning microscopy,CLSM）分析,从蛋白结构变化上进一步揭示了乳化性能提高现象的原因。结果表明：超声波联合植酸酶-酸性蛋白酶改性的 SPI （Uphy-aci-SPI）的乳化活性（emulsifying activity index,EAI）为0.53 m2/g,比未改性SPI（0.18 m2/g）显著提高了196%（P<0.05）,乳化稳定性（emulsifying stability index,ESI）为17 min,比未改性SPI（13.5 min）显著提高了25.9%（P<0.05）;挤压膨化联合菠萝蛋白酶改性的SPI（Ebro-SPI）的EAI为0.46 m2/g,比未改性SPI显著增加了155%（P<0.05）,ESI为17 min,比未改性SPI显著增加了25.9%（P<0.05）。在pH值为4的条件下对物理-酶联合改性的SPI的性质分析发现,物理-酶联合改性的SPI与未改性SPI相比,物理-酶联合改性的SPI的溶解性显著增加（P<0.05）;物理-酶联合改性的SPI的乳状液平均粒径减小,CLSM观察乳状液中油与蛋白溶液稳定共融,改善了油滴之间的空间排斥力。物理-酶联合改性的SPI游离巯基的含量显著增加（P<0.05）,二硫键含量显著降低（P<0.05）。SEM观察物理-酶联合改性的SPI为结构松散、破碎均一的微观结构。由此可见,乳化性能的提高是通过深层改变蛋白的结构来实现的。该研究可为探索提高酸性条件下SPI的乳化性能的方法提供理论依据。     

Solubility and moisture sorption isotherms of whey-protein-based edible films as influenced by lipid and plasticizer incorporation

Plasticized whey-protein and whey-protein emulsion films were produced using sorbitol and glycerol as plasticizers and butterfat and candelilla wax as lipids. Protein, plasticizer, and lipid ratios were optimized to obtain acceptable free-standing flexible films. Water solubility (20 degrees C, 24 h) and moisture sorption isotherms (0.18-0.90 a(w), 25 degrees C) of the films were determined. The experimental moisture sorption isotherm values were fitted using the Guggenheim-Anderson-DeBoer (GAB) model. Solubility and equilibrium moisture contents (EMC) of the films were influenced by plasticizer and lipid incorporation. EMCs of all films increased rapidly at a(w) > or = 0.65. Incorporation of lipids reduced solubilities and EMCs of sorbitol- and glycerol-plasticized films. The effects of plasticizer and lipid type on GAB constants were also determined.