Effect of glycosylation on the mechanical properties of edible soy protein packaging film

In this paper, we explore the glycosylation conditions (glucomannan content, reaction time, temperature and humidity) to probe the relationship between glycosylation and mechanical properties of soy protein isolate (SPI) film. The mechanical properties were characterized by studying the tensile strength (TS) and elongation at break (EB). Furthermore, degree of glycosylation, free glucomannan content, surface hydrophobicity, sulfhydryl groups content, lysine and arginine content of glycosylation soy protein with different reaction time were investigated to certify the significant effect of glycosylation on mechanical properties of soy protein film. What is more, the comparison of TS and EB, contact angle values and water vapor permeability of glycosylation SPI (GSPI), SPI and mixture of SPI and glucomannan films showed the excellence of GSPI. At the end, the analysis of scanning electron microscope was applied to reveal the effect of glycosylation on the structure of films. These results suggested that glycosylation with glucomannan is an ideal method to enhance the mechanical properties of soy protein isolate film.     

Effect of processing parameters on the properties of transglutaminase-treated soy protein isolate films

The effects of processing parameters, including the applied amount of microbial transglutaminase (MTGase), the pH of film-forming solution, air-drying temperature, as well as the additional pre-incubation, on the properties of MTGase-treated soy protein isolate (SPI) films were investigated. The treatment with low concentration of MTGase (4–10 units per gram of SPI, U g^− 1) significantly increased the tensile strength (TS) values of SPI films, while high concentration of MTGase (over 20 U g^− 1) resulted in significant decrease in the TS values (P ≤ 0.05). The elongation at break (EB) values of corresponding films gradually decreased, and the contact angle values persistently increased with the enzyme concentration. At alkaline pH range, the TS and EB values of MTGase-treated SPI films were significantly higher than that at pH 7.0 (P ≤ 0.05). Meanwhile, the contact angle values significantly decreased with increasing pH from 7.0 to 10.0 (P ≤ 0.05). The TS, EB and contact angle values of MTGase-treated films gradually but insignificantly decreased with increasing the air-drying temperature from 18 to 50 °C (P > 0.05). The properties of MTGase-treated films were also affected by the additional pre-incubation of film-forming solutions with MTGase before casting. Furthermore, the aggregation of SPI or its components induced by MTGase has been proved to mainly account for the influence of processing parameters on the properties of SPI films (MTGase-treated). Thus, low concentration of enzyme, alkaline pH range and low air-drying temperature, at which conditions the MTGase-induced aggregation of SPI in film-forming solutions could be in some extent inhibited or delayed, might facilitate the improvement of the properties of SPI films by MTGase, especially the mechanical and surface hydrophobic properties.Industrial relevanceThe development of biodegradable protein film has attracted a lot of attention worldwide. The enzymatic cross-linking induced by transglutaminase has been confirmed to improve mechanical and surface hydrophobic properties of cast films from most of food proteins, including soy proteins. Results of this study show that, the improvement of properties of cast films of soy proteins by transglutaminase treatment is largely dependent upon many processing parameters, e.g., enzyme concentration, the pH of film-forming solution and temperature.     

增塑剂对大豆蛋白可食膜特性的影响

研究了增塑剂对大豆分离蛋白膜(热法成膜和酶法成膜)成膜特性的影响。增塑剂的种类(甘油、山梨醇或甘油山梨醇的等量混合物)对大豆分离蛋白膜的性能有明显影响。无论是否添加谷氨酰胺转移酶(TGase)，以山梨醇为增塑剂的膜都具有最高的抗拉强度、表面疏水性和总可溶性物量，最低的断裂伸长率、水分含量和透光率。TGase处理SPI(4U／g．蛋白)，可显著改善蛋白膜的抗拉强度和表面疏水性，抗拉强度和表面疏水性分别比对照膜增加10％～20％和17％～56％(P≤0.05)；同时也明显降低了(P≤0.05)膜的断裂伸长率、水分含量、总可溶性物量及透光率。     

冷冻保藏对大豆分离蛋白膜机械性能的影响

用大豆分离蛋白(SPI)制备可食性包装膜时,在成膜溶液中分别添加单甘酯、葡萄糖制成大豆分离蛋白膜,将其分别在室温下(RH65%)保存2d以上和在冷冻保藏7d后测定机械性能,发现添加这些物质后制得的膜的机械性能均受到影响:含单甘酯的膜的抗拉强度(TS)增加超过25%,断裂伸长率(E)变化不大;而含葡萄糖的膜TS增加了35%以上,E增加了55%以上。冷冻对各种SPI膜的机械性能有不同影响,对含葡萄糖的SPI膜的抗拉强度影响很大,TS下降达50%,对其他SPI膜的影响不太大,这意味着不含葡萄糖的SPI膜可用于冷冻食品包装。     

Modulation of mechanical and surface hydrophobic properties of food protein films by transglutaminase treatment

The effects of microbial transglutaminase (MTGase) treatment on the mechanical and hydrophobic properties of cast films from various food proteins were investigated. SDS–PAGE analyses confirmed that the MTGase treatment led to the formation of insoluble film network for most of food proteins. This enzymatic treatment significantly (P < 0.05) increased tensile strength (TS) values of cast films of all food proteins by 13–33% (except whey proteins). Meanwhile, the influence on the elongation at break (EB) values was mainly dependent upon the molecular nature of proteins. For most of food proteins, both increases in TS and EB values of films were obtained after the MTGase treatment. Furthermore, the surface hydrophobicity of most of protein films was also significantly improved. These results suggest that the enzymatic treatment by MTGase could be used as an effective technique to improve mechanical and surface hydrophobic properties of protein films.     

谷氨酰胺转移酶对大豆分离蛋白膜性能的影响

研究注模前酶作用时间对谷氨酰胺转移酶(TGase)改性大豆分离蛋白(SPI)膜性能的影响。在注模之前,将TGase(8U/g SPI)加入到成膜溶液中,分别在磁力搅拌下作用0、30、60、120min,然后注模成膜。利用质构仪检测蛋白膜的机械性能,结合哈克流变仪的动态黏弹实验及SDS-PAGE 实验进一步分析。注模前适度的酶作用(≤60min)在一定程度上有利于TGase 改性的SPI 膜机械强度的提高,特别是抗拉强度(TS)值;但是,时间不宜过长,因为注模前的酶作用也会诱导SPI 蛋白组分的聚沉反应,从而降低成膜溶液中可溶解蛋白的含量。结果表明,TGase改性SPI 膜时,一方面会诱导蛋白交联;另一方面,交联过多又会导致沉淀;在利用TGase 提高SPI 膜的机械性能时如何把握两者之间的关系,在交联的同时抑制酶促聚沉非常重要。     

Physicochemical, functional and structural properties of vicilin-rich protein isolates from three Phaseolus legumes: Effect of heat treatment

The physicochemical, functional and structural properties of vicilin-rich protein isolates from kidney, red and mung beans (KPI, RPI and MPI) were investigated, and the influences of heating (at 95 °C for 30 min) were also evaluated and compared. In the untreated samples, the thermal stability, free SH contents and surface hydrophobicity were different. The differences seemed to be closely related to the differences in extent of aggregation and/or tertiary and secondary conformational structures among proteins. The heating resulted in extensive denaturation of the protein, significant decreases in free SH groups and increases in surface hydrophobicity, but to a varying extent, depending on the type of protein isolates. The protein solubility and emulsifying activities were significantly improved by the heating. The tertiary and secondary structures of these proteins were also to a various extent affected. The conformational structures of proteins in RPI were most flexible, and susceptible to the heating, while the proteins in KPI were most heat-stable in structures. The results clearly indicated close relationships between functional properties of these vicilin-rich protein isolates and their conformational structures.     

Mechanical and barrier properties of biodegradable soy protein isolate-based films coated with polylactic acid

Polylactic acid (PLA)-coated soy protein isolate (SPI) films were prepared by dipping SPI film into PLA solution. The effects of coating on improvements in mechanical and water barrier properties of the film were tested by measuring selected film properties such as tensile strength (TS), elongation at break (E), water vapor permeability (WVP), and water solubility (WS). TS of SPI films increased from 2.8±0.3 up to 17.4±2.1 MPa, depending on the PLA concentration of the coating solution, without sacrificing the film's extensibility. In contrast, the extensibility of SPI film coated with solution containing more than 2 g PLA/100 ml solvent, increased. WVP of PLA-coated SPI films decreased from 20 to 60 fold, depending on the concentration of PLA coating solution. Water resistance of SPI films was greatly improved as demonstrated by the dramatic decrease in WS for PLA-coated films. The improvement in water barrier properties was mainly attributed to the hydrophobicity of PLA.     

Edible films made from membrane processed soy protein concentrates

Edible films were prepared from membrane processed soy protein concentrate (MSC) at various film forming solution pHs, and their mechanical, barrier, and physical properties were compared with soy protein isolate (SPI) films. As the film solution pH increased from 7 to 10, the resulted MSC films were more transparent, yellowish, and had lower oxygen permeabilities. However, tensile strength (TS), modulus of elasticity (ME) and water vapor permeabilities of MSC films were not affected by film solution pHs. The values of MSC films prepared at pH 7 were not significantly (P>0.05) different from those of SPI films prepared at alkaline solutions (pH 8-10). The uniform TS and ME values of MSC film over the wide film solution pH ranges were attributed to the higher solubility of MSC at pH 7. For the films formed at neutral film solutions (pH 7.0), MSC films showed significantly (P<0.05) higher elongation value, film solubility, and transparency compared to SPI films.     

Structure-modifying alkaline and acidic pH-shifting processes promote film formation of soy proteins

The effect of pH-shifting, a process that induces the molten globule state in proteins, on the film-forming potential of soy protein isolate (SPI) at different temperatures was investigated. Partial unfolding at pH 1.5 or 12, followed by refolding at pH 7.0, was performed to alter the protein structure. Glycerin-plasticised films were prepared from pH-treated SPI at ambient temperature (20 °C), or by heating at 50, 60, 70, or 80 °C (30 min). Tensile strength (TS), elongation at break (EAB), water vapour permeability (WVP), protein solubility (pH 3–7), and non-participating proteins of films were analysed, and the film microstructures were examined. The pH₁₂-treated SPI spontaneously formed a transparent, slightly yellowish film at 20 °C, which had the greatest EAB, while pH_1.5-treated and native SPIs required preheating at 50 and 70 °C, respectively, to form a film. Heating generally decreased solubility and WVP but increased TS. Films formed from both pH₁₂- and pH_1.5-treated SPIs were more elastic (up to 2-fold greater in EAB, P < 0.05) than the film formed from untreated SPI despite slightly reduced TS and WVP. Electrophoresis revealed disulphide bonds between A and B subunits of glycinin being a dominant force in pH₁₂- and pH_1.5-treated SPI films, while noncovalent forces were abundant in untreated SPI films. The pH₁₂-treated SPI film consisted of more interactive protein strands than other SPI films, which seemed to explain its superior elastic properties.     

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.     

十二烷基磺酸钠(SDS)在大豆分离蛋白基可食性膜中应用

该文报道研究十二烷基磺酸钠应用于以甘油作为增塑剂的大豆蛋白基可食性膜后对其物理性质影响。研究结果表明:当SDS添加量为40%(十二烷基磺酸钠质量/大豆分离蛋白质量)时,薄膜抗拉强度(TS)值显著(p<0.05)减少43%,最大断裂伸长率(E)值显著(p<0.05)增加至少5%,水分含量(MC)值显著减少(p<0.05),总可溶性物质含量(TSM)值显著增加(p<0.05);当SDS添加量>10%时,WVP值下降50%;SDS添加量为20%、30%、40%时,膜颜色值为显著+b (p<0.05),即黄色值增加。     

热处理和碱处理对可食性大豆分离蛋白膜性能的影响

研究了热处理和碱处理对可食性大豆分离蛋白(SPI)膜性能的影响。对成膜液进行适当的加热和调节pH可以提高SPI膜的抗拉强度(TS)和伸长率(E),降低水蒸气透过系数(WVP)。调节成膜液的pH到9,在70℃加热20min,所得到的膜机械性能和阻湿性能最好。     

微波处理对植物蛋白基可食膜特性改善效果的研究

通过微波处理以谷朊粉（WG）、大豆分离蛋白（SPI）为主要成膜原料的可食保鲜膜，研究其对可食膜特性的改善作用，结果表明微波处理能有效改良三种膜的机械性能、感官性能及通透性，特别是对WG／SPI膜的改良效果最好。利用扫描电子显微镜对微波处理前后蛋白膜的微结构进行研究，微波处理对膜的微结构有明显的改善作用，可使膜表面更光滑平整，使膜的横截面更均匀、规则、致密，其中对WG／SPI膜的改善效果最明显。经微波处理后WG膜、SPI膜、WG／SPI膜的横截面微结构接近。微波处理后膜的结构改善效果与膜的外观、机械性能、通透性的改善效果一致。     

Sorption Characteristics of Soy Protein Films and their Relation to Mechanical Properties

Effects of plasticizers (glycerol, sorbitol, and 1:1 mixture of glycerol and sorbitol) on moisture sorption characteristics of hydrophilic soy protein isolate (SPI) films were investigated at three levels of plasticizer concentration (0.3, 0.5, and 0.7 g plasticizer/g SPI). The combined effects of relative humidity and plasticizer on mechanical properties of soy protein films were also examined. Moisture affinities of soy protein films were affected by hydrophilicity of plasticizer and its concentration. Under given RH conditions, films with higher glycerol ratio absorbed more moisture with higher initial adsorption rate, and films with higher plasticizer contents exhibited higher equilibrium moisture contents. Monolayer moisture contents of SPI films increased as glycerol ratio in a plasticizer mixture and plasticizer concentration increased. Plasticizer and absorbed water loosened the film synergistically, resulting in higher elongation but lower tensile strength. RH effects on mechanical properties of SPI films were varied with plasticizers and their concentration. Films of lower glycerol contents were more sensitive to RH variation as compared to the higher glycerol samples, whereas sorbitol concentration affected the RH region where a sharp decrease in TS value occurred.     

改性纳米TiO2-大豆分离蛋白抑菌保鲜膜的制备及其性能

选取表面改性的纳米TiO2制备大豆分离蛋白（soy protein isolate,SPI）膜,以复合膜的抗拉强度、断裂伸长率、水蒸气透过率、透光性、透氧性、透二氧化碳性为评价指标,通过单因素试验和正交试验优化制膜最佳工艺。结果表明,复合膜的最佳成膜工艺条件为SPI添加量4.5?g/100?mL、改性TiO2添加量2.0?g/100?mL、甘油添加量1.5?g/100?mL,其接触角为115.3°。傅里叶变换红外光谱仪实验结果表明,改性纳米TiO2-SPI复合膜与纳米TiO2-SPI复合膜、普通SPI膜在4 000～600 cm－1波数范围内呈现出相似的红外光谱,且由扫描电子显微镜以及原子力显微镜扫描结果可以看出,与纳米TiO2-SPI复合膜及普通SPI膜相比,改性纳米TiO2-SPI复合膜表面更为致密平整,表面性能表现更佳,改性纳米TiO2-SPI复合膜的结构性质要优于纳米TiO2-SPI复合膜及普通SPI膜。当改性TiO2添加量为2?g/100?mL、365?nm波长紫外灯照射6?h时,复合膜对大肠杆菌和李斯特菌的抑菌性能最强,抑菌率达到91.14%和92.81%。改性纳米TiO2-SPI复合膜具有一定的机械性能和良好的抑菌性能,在食品包装应用方面具有巨大潜力。     

Thermal aggregation,amino acid composition and in vitro digestibility of vicilin-rich protein isolates from three Phaseolus legumes: A comparative study

The heat-induced aggregation and the in vitro digestibility of vicilin-rich protein isolates from three Phaseolus legumes, including kidney bean, red bean and mung bean were investigated and compared, and their amino acid composition and free sulfhydryl (SH) group contents also evaluated. The results showed that the extent in the heat-induced aggregation varied with the type of the protein isolates, and the formation of new disulphide bonds (at the expense of free SH contents) was involved in the formation of the aggregates. The protein isolates with higher levels of hydrophobic and uncharged polar amino acids, and lower basic amino acid contents exhibited lower extent of their heat-induced aggregation. The in vitro pepsin plus trypsin digestibility was different for various native protein isolates. The digestibility was to a varying extent affected by the heat treatment. The influences of heating on the digestibility of these proteins were closely related to the extent of their heat-induced aggregation. The results suggest that the improvement of nutritional property of those vicilin-rich protein isolates by heat treatment is largely dependent upon their amino acid composition as well as the extent of heat-induced aggregation.     

淀粉醛强化大豆分离蛋白/槲皮素复合膜制备及性能研究

目的 探究淀粉醛(dialdehyde starch,DAS)对大豆分离蛋白(soy protein isolate,SPI)/槲皮素(quercetin,QR)复合膜特性的影响。方法 以青稞淀粉为原料,通过高碘酸钠氧化制备了DAS,以SPI为基质,以DAS和QR为添加物,以拉伸强度、水分阻隔性能、抗氧化性能为指标进行单因素试验,通过响应面优化试验筛选出DAS强化的SPI/QR复合膜最佳制备条件后,对复合膜的微观结构进行表征,并对其物理学性能进行测试。结果 DAS强化的SPI/QR复合膜最佳制备条件为每100 mL蒸馏水中添加SPI 6.00 g、pH为8、DAS 5%、QR 4%、DES 25%(DAS、QR、DES以SPI质量计)。在此条件下,薄膜的拉伸强度为(7.37±0.39) MPa、水蒸气透过系数为(3.54±0.29)×10^-11 g/(m·s·Pa)、抗氧化活性为(70.88±0.40)%。结构表征结果表明, DAS的添加使得该复合膜分子间形成了共价亚胺键,表面结构及横断面结构更加致密。此外,该复合膜具有较好的热稳定性、紫外阻隔性、疏水性。结论 D...     

Water Vapor Permeability and Mechanical Properties of Soy Protein Isolate Edible Films Composed of Different Plasticizer Combinations

Water barrier and mechanical properties were measured for soy protein isolate (SPI) films plasticized with glycerol (GLY) and 1 of the plasticizers (propylene glycol [PG], polyethylene glycol [PEG], sorbitol [SOR], or sucrose [SUC]) at a ratio of 25:75, 50:50, 75:25, and 0:100. Plasticizer type as well as the plasticizer ratio in the GLY: plasticizer mixtures affected the film water barrier and mechanical properties. An addition of as little as 25% of a less hygroscopic plasticizer in the mixture induced significant reduction in water vapor permeability (WVP) of SPI films. However, at least 50% of the mixture needs to be GLY to show significant improvement in tensile strength (TS). From our experimental design, 50:50 GLY:SOR was the recommended combination because of its comparatively low WVP value and relatively high flexibility and strength. Incompatibility of GLY:PEG plasticizer mixture in SPI film was observed by surface migration of PEG from the film matrix.     

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.