脱乙酰化反应条件对壳聚糖性能的影响

本文研究了甲壳素在脱乙酰化反应时不同反应条件,如碱浓度、反应时间、反应温度和处理方法对壳聚糖性能,如分子量、脱乙酰化度的影响,探讨了分子主链降解反应与脱乙酰化反应之间的关系。结果表明:随着碱浓度和反应时间的增加,壳聚糖脱乙酰化度提高,而分子量降低;脱乙酰化越高,主链降解程度增加;反应温度升高,脱乙酰化反应速度加快;而采用短时重复多次反应的处理方法,则可增加壳聚糖的脱乙酰化度,并减少主链降解程度。     

低取代度乙酰化大米淀粉的性质研究

以大米淀粉为原料,乙酸酐为酯化剂,制备了5种取代度分别为0.056、0.079、0.091、0.098和0.124的乙酰化淀粉。结果表明乙酰化大米淀粉的透明度随着取代度的增大而增加。大米淀粉经酯化后,凝沉性明显减弱,不易回生。乙酰化大米淀粉的溶解度和膨润力随温度的升高而增加,且明显高于原大米淀粉;糊化温度显著降低,衰减值也降低。乙酰化大米淀粉凝胶的硬度比原淀粉明显降低,弹性和内聚性变化不大。通过乙酰化处理,大米淀粉的功能性质得到明显改善。     

不同木薯淀粉对冻融魔芋葡甘聚糖凝胶特性的比较分析

为探究不同木薯淀粉对冻融魔芋葡甘聚糖凝胶的影响,采用木薯淀粉（cassava starch,CS）、木薯醋酸酯淀粉（starch acetate,SA）、木薯乙酰化二淀粉己二酸酯淀粉（acetylated di-starch adipate,ADA）、木薯乙酰化二淀粉磷酸酯淀粉（acetylated di-starch phosphate starch,ADP）四种市售淀粉代替37.5%魔芋葡甘聚糖（konjac glucomannan,KGM）,制备冻融脱乙酰KGM/淀粉复合凝胶。通过质构仪、傅里叶红外光谱仪、热重分析仪、冷场扫描电镜分析其凝胶特性的变化。结果表明,4种木薯淀粉可以改善冻融KGM凝胶的凝胶特性,但不同木薯淀粉间存在差异,KGM/ADP凝胶表现出最优的保水性和热稳定性,与KGM凝胶相比,其析水率从29.75%下降至8.71%,持水率从73.68%提高至87.42%,硬度从274.36 g下降至176.33 g,弹性、内聚性及回复性无显著差异;不同木薯淀粉均未影响葡甘聚糖的脱乙酰行为和结晶形态,但ADP可以改变冻融KGM凝胶微观形貌,提高其抗脱水收缩能力。综合分析,ADP代替部分魔芋葡甘聚糖改善冻融KGM凝胶特性效果最佳,为其在魔芋凝胶食品的应用提供指导。     

高浓度魔芋葡苷聚糖与大豆分离蛋白混合凝胶质地特性研究

研究了不同处理条件和试剂对高浓度魔芋葡苷聚糖与大豆分离蛋白混合凝胶质构特性的影响，并进行了凝胶的扫描电子显微镜观察。结果表明，KGM与SPI混合物在体系pH值为9、温度90℃下加热40min时，其形成的凝胶强度和弹性较好。凝胶微观结构的扫描图片分析表明，高浓度下KGM与SPI混合物在水溶液和碱性条件下均能形成较好的凝胶网络结构，而且不同配比和不同处理样品所形成的凝胶体的微观结构差异较大。     

甘蓝提取物对魔芋葡甘聚糖凝胶流变特性的影响

为探究天然甘蓝提取物（red cabbage extract，RCE）对魔芋葡甘聚糖（konjac glucomannan，KGM）凝胶流变特性的影响，将不同浓度的RCE添加到KGM溶胶中，通过旋转流变仪考察KGM/RCE复合体系的静态与动态流变特性，利用扫描电镜与傅里叶变换红外光谱对其复合凝胶微观结构进行表征。结果表明：KGM/RCE复合凝胶均呈现剪切稀化现象，复合体系的表观黏度随着RCE添加量的增加而降低。动态黏弹性结果表明，储能模量（G′）与损耗模量（G″）均表现出较强的频率依赖性，且RCE添加后，两者数值均下降，表明RCE对凝胶体系中分子的缠绕起阻碍作用。此外，随着RCE添加量的增加，G′与G″的交叉点沿低频方向偏移，可知体系分子间氢键作用加强，使得KGM分子链在移动过程中受到更大阻力，松弛时间延长，导致G′与G″的交点向低频方向移动，凝胶呈现出弹性特征。傅里叶变换红外光谱与扫描电镜结果显示，随着RCE含量的增加，RCE的增塑作用加强，大分子链间的聚集作用被削弱，复合凝胶网络结构稳定性下降从而对复合凝胶的流变学特性起消极作用。     

气相色谱法测定魔芋食品中葡甘聚糖及淀粉含量

建立了魔芋食品及魔芋粉中葡甘聚糖和淀粉含量的测定方法.样品酸水解,水解液中加入肌醇作为内标,浓缩干燥后,进行肟化反应与乙酰化反应.糖腈乙酰酯衍生物进行GC分析,内标法定量.结果表明,KGM单糖成分经衍生化能得到较好的色谱分析结果,采用肌醇作为内标定-量分析,校正了分析过程系统误差,能准确测定葡萄糖和甘露糖的含量,以KGM分子中甘露糖和葡萄糖残基的摩尔比,及甘露糖和葡萄糖含量分别计算出葡甘聚糖和淀粉的含量.葡甘聚糖的测定结果排除了淀粉等其他糖类的干扰,结果准确可靠.     

羧基化纤维素纳米晶须对魔芋葡甘聚糖复合凝胶性能的影响

为改善魔芋葡甘聚糖(KGM)凝胶的黏弹性、凝胶强度以及在高温下的热性能,在1.5 g KGM中分别加入0.2、0.5、0.8、1.0 g的羧基化纤维素纳米晶须(CCNC),制得CCNC/KGM复合水凝胶并做空白对照。利用流变仪分析不同配比下的CCNC/KGM的流体行为,对CCNC/KGM水凝胶的微观结构、特征官能团进行表征,并分析其热重情况。结果表明,CCNC添加量为0.8 g以内,CCNC/KGM复合凝胶体系黏度逐渐加大。扫描电镜结果显示,CCNC的添加量在0.8 g时,CCNC与KGM协同所形成的凝胶网状结构空隙丰富,且在熔融状态出现后,此复配比下的凝胶质量损失较纯KGM水凝胶降低了近50%,在高温中表现出更好的热性能,并保留了一定的凝胶特性;因此CCNC和KGM质量比约为0.8:1.5时,水凝胶的黏弹性、凝胶强度以及高温下的热性能均达到最优,凝胶特性凸显。     

大豆分离蛋白及其与魔芋葡苷聚糖凝胶化作用的动态粘弹性研究

利用动态流变仪研究了胶凝时间、温度、频率及应变等因素对大豆分离蛋白及其与魔芋葡苷聚糖相互作用的动态粘弹性影响。实验结果表明：在高浓度下大豆分离蛋白与魔芋葡苷聚糖所形成的凝胶大都呈现出储存模量G’〉损耗模量G”，表明凝胶动态模量中弹性的贡献已超过了粘性，溶液发生了凝胶化，并形成了三维交联的网络结构。碱性凝固剂的加入提高了凝胶的粘弹性。当频率在一定范围内变化时，未加碱样品其凝胶粘弹性在低频区可用频率依赖性来表征，而在高频区，加碱和未加碱样品其凝胶粘弹性不随频率变化而变化，都保持G’大于G”。     

大豆蛋白稳定乳液油凝胶的制备及其在肉糜中的应用

以大豆蛋白为稳定剂,葵花籽油为油相,通过高速剪切乳化技术制备乳液油凝胶,研究载油量、大豆蛋白浓度和热处理时间对乳液油凝胶的影响,并将乳液油凝胶应用于肉糜中替代动物脂肪。结果表明：大豆蛋白颗粒可以承载体积分数达70%的油相,且在大豆蛋白浓度超过1%的条件下,能形成稳定的乳液油凝胶,其粒径随着大豆蛋白浓度的增加而略微变小。乳液油凝胶经80 ℃热处理后,粒径大小随加热时间基本不变,显示良好的热稳定性。流变分析表明乳液油凝胶的黏度随剪切速率升高而下降,不同加热时间下的储能模量均比损耗模量高,表明乳液形成了弹性的类凝胶网络,且加热处理45 min 的乳液油凝胶黏弹性最为突出。肉糜经高温蒸煮后,肉糜蒸煮得率随乳液油凝胶替代比例的升高而提高,当乳液油凝胶完全替代猪油脂时,油脂和水分的渗出率明显降低。     

基于高精度3D打印的三文鱼植物基替代物研究

目的 基于高精度3D打印技术研究三文鱼植物基替代物。方法 以豌豆分离蛋白(pea protein isolate, PPI)、魔芋胶(konjac gum, KGM)和天然胡萝卜粉为原辅料, 进行精准3D复合打印生产模拟三文鱼色泽、质构的植物基替代物。考察不同物料比例对油墨可打印性的影响; 选取有代表性的油墨配方, 对其流变特性、水分分布情况、微观结构进行表征。结果 PPI和KGM浓度的升高都增强了体系与水结合的能力, 且PPI浓度过高时(20%, m:m)影响了KGM与水结合形成稳定凝胶的能力。PPI15KGM5配方可形成致密的网格结构, 增强了体系的稳定性, 拥有良好的剪切恢复特性, 有利于3D打印; 而PPI20KGM3配方具有更好的机械性能和结构强度, 但是由于PPI浓度过高影响KGM形成稳定凝胶结构, 其剪切恢复特性较差。流变学参数η、τy、G''、屈服应变及剪切恢复特性对油墨3D打印过程影响显著。结论 通过调整3D打印精细化程度(350和500 μm)和模型填充度, 生产了具有差异化质构的高蛋白含量(15%, m:m)产品。其中, 部分产品的粘性 和弹性与真实三文鱼类似, 这为开发3D打印生产植物基替代物提供了新的视角。     

Morphology and gelation properties of konjac glucomannan: Effect of microwave processing

Gelation behaviors of konjac glucomannan (KGM) samples processed via microwave or water bath heating were studied. The microwave-heated gels had significantly better viscoelasticity and stronger KGM molecular chain interactions than water-bath-heated gels. Scanning electron microscopy analysis of the KGM gels revealed a concentrated, uniform network microstructure for the microwave-heated gels and a dense layered structure for the water-bath-heated gels. Microwave heating promotes hydrogen bonding while preserving the molecular chain. Hence, it can be used to improve the gelation properties and micromorphology of KGM without damaging its structure.     

On the gelation of Vicia faba protein in dependence on the acetylation degree

Using the method of mathematical planning of experiments and taking the shear modulus of the gels as an equivalent of the gelation degree, the conditions of the thermal denaturation at the maximum shear modulus were found to be T_D ≈? 100 °C and t_D ≈? 60 min for the non-acetylated Vicia faba protein and T_D ≈? 100 °C and t_D ≈? 40 min for the acetylated Vicia faba protein. On these conditions the dependence of the shear modulus (G) on the protein concentration (C) is expressed by exponential functions G = α C4.3 and G = α C5.0, respectively. By an increasing acetylation of the Vicia faba protein the shear modulus, the thickness of the many-line chains, and the net density of gels are increased; the same is valid for the shear modulus and the masking of disulfide groups by an increasing concentration of non-acetylated and acetylated Vicia faba proteins.     

魔芋葡甘聚糖/表面脱乙酰甲壳素纳米纤维复合凝胶的制备及流变性能

研究魔芋葡甘聚糖（konjac glucomannan,KGM）与不同质量分数的表面脱乙酰甲壳素纳米纤维（surface deacetylated chitin nanofiber,S-ChNF）制成的复合凝胶的微观结构及性能变化。结果表明,KGM/S-ChNF复合凝胶均呈现剪切稀化现象,符合幂定律模型,是一种假塑性流体;且随着S-ChNF添加量的增加,凝胶的黏度增加,剪切应力降低,稠度系数由23.174 Pa·sn增大至29.950 Pa·sn,而流动指数则由0.436 63降低至0.413 08,表明其假塑性能提高。动态黏弹性分析表明,储能模量和损耗模量均表现出对角频率的依赖性,且随着S-ChNF添加量的增加,两者呈现上升趋势。此外,交叉点由6.77 s－1向低角频率方向移动至3.77 s－1,表明分子间氢键作用力增强,增大了KGM分子链移动的阻力,松弛时间变长,凝胶倾向于呈现弹性特征。傅里叶变换红外光谱、扫描电子显微镜及热重分析结果显示,随着S-ChNF含量的增加复合体系内分子间相互作用增强,形成具有稳定网络结构的体系,从而改善复合凝胶的流变性特并且提高了复合凝胶的热稳定性。     

κ -Carrageenan—Protein Interactions: Effect of Proteins on Polysaccharide Gelling and Textural Properties

Gelation and melting processes of kappa-carrageenan (κ-C) in the presence of beta-lactoglobulin (β-lg), native and denatured soy protein (NSP and DSP) isolates were investigated by dynamic rheological techniques, apparent viscosity measurements and DSC. In the presence of proteins, large increases in gelation temperatures and storage moduli of the mixed gels compared to single κ-C gel were observed. Differences between the proteins in the first steps of the gelation process were revealed by apparent viscosity measurements. Although little changes in melting temperatures were observed in the presence of proteins by dynamic rheology, the DSC analysis showed a large increase in these temperatures. Synergistic effects were also observed on textural properties and water absorption of the gels. The addition of proteins increased gel hardness, cohesiveness, gumminess, springiness and reduced syneresis. These results might be due to excluded volume effects that increased the effective concentration of the hydrocolloid and electrostatic interactions between both biopolymers in solution. The different behaviours observed with the three proteins would be related to their water absorption capacity, molecular size, flexibility and superficial charge under the experimental conditions described.     

Effects of konjac glucomannan on heat-induced changes of physicochemical and structural properties of surimi gels

This work demonstrated the protective effects of konjac glucomannan (KGM) on the physicochemical and structural properties of surimi gels subjected to 120 °C. The T₂ relaxation of LF-NMR which was used to detect water mobility, changed more obviously with the addition of deacetylated KGM than with the native, which indirectly implied that deacetylated KGM more pronouncedly influenced the protein structure. Hydrophobic interaction, ionic, hydrogen, and disulfide bonds, were sheltered by deacetylated KGM to greater extent than by native KGM. Raman spectra showed that the reduction of the main random-coil secondary protein structure at 120 °C was more significantly mitigated by deacetylated KGM. The interactions between protein and native or deacetylated KGM were investigated by X-ray diffraction, finding that protein and polysaccharide complexes might be formed. The microstructure of the mixed gels, determined by confocal laser scanning microscopy, demonstrated native and deacetylated KGM helped protein aggregation recover to uniform distribution.     

VISCOELASTIC BEHAVIOUR OF AMYLOSE-FATTY ACID GELS

Rheological measurements were used to study the gelation of amylose in O.01M KOH (pH 12) in the presence of fatty acid potassium salts. Creep compliance-time experiments indicated that addition of the fatty acids caused considerable changes in the rigidity of the amylose gels. The effect was dependent on fatty acid concentration, molecular conformation and lipid acyl chain length. Dynamic measurements on aged amylose-potassium stearate gels showed that the development of rigidity modulus was rapid and dependent on the fatty acid concentration.     

Physicochemical properties of acetylated starches from some Indian kidney bean (Phaseolus vulgaris L.) cultivars

Starches separated from four kidney bean cultivars were modified by acetylation to reduce retrogradation and increase gel stability and compared with respective native starches (data of native starch reported by Wani et al., 2010 ). Acetylation was carried out by treating starches with 0.04 and 0.08 g of acetic anhydride per gram of starch dry weight basis (dwb) at 25 °C and pH between 8.0 and 8.5. The extent of acetylation increased proportionally with the concentration of acetic anhydride used. The pasting curves of 10.7% starch determined by Rapid Visco Analyzer at 160 rpm showed that acetylation decreased the setback viscosity values by 0.64–34.58% and pasting temperature by 4.4–9.2 °C when compared with the native starch. Differential scanning calorimetry observations also revealed significant (P ≤ 0.05) decrease in gelatinisation temperature of acetylated starches than the corresponding native starches. Hardness of starch gels varied between 14.3 and 44.0 g, which was significantly (P ≤ 0.05) lower than the corresponding native starch gels.     

CHARACTERISATION OF A COMMERCIAL SOY ISOLATE BY PHYSICAL TECHNIQUES

The mechanical features of a partially denatured commercial soy isolate (PP 500E) have been explored for comparison with data available on the gelation characteristics of native globular proteins and to improve the understanding of its textural properties as a structuring ingredient in the production of low fat products. The soy sample was reconstituted at 30C and networks were developed either during cooling to 5C or on heating to 90C (complete denaturation of the protein) followed by cooling to 5C. Throughout the course of experimentation, dynamic oscillatory (time, temperature, frequency and strain sweeps) and creep testing (in aqueous or urea solutions) measurements were recorded. Reduction in the thermal energy of the system causes a monotonic increase in storage modulus (G′) whereas the temperature rise results in equilibrium G′ values well below the elastic response observed at 30C. The absence of a positive thermal transition, observed in the gelation of native globular proteins, indicates a different mechanism for structure formation in commercial soy isolates. Application of the cascade treatment to the concentration dependence of the storage modulus argues that the heated and cooled networks possess a higher degree of bond permanency than their cooled-only counterparts. Mechanical spectra in combination with the pattern of network breakage at high deformations suggests that disulphide bonds participate in the network formed by totally denatured soy protein (heated and cooled samples). Inclusion of urea in the aqueous preparations destabilises the predominantly physical forces of attraction in the unheated gels. By contrast, the heated and cooled samples achieve an equilibrium deformation whose storage modulus can be employed in the constitutive equation of rubber elasticity theory. On that basis the number of disulphide bridges per molecule was found to vary between 2.0 and 2.03. This result is consistent with the “string of beads” model proposed for the three-dimensional structure of globular protein gels, where a dendric network is built by the occasional cross-linking of corpuscular strands.     

COAGULATION AND GELATION OF SOY PROTEIN ISOLATES INDUCED BY MICROBIAL TRANSGLUTAMINASE

The reaction process and corresponding mechanism of coagulation and gelation of native soy protein isolates (SPIs) induced by microbial transglutaminase (MTGase) were investigated. The protein constituents of SPIs, including a majority of subunits of β‐conglycinin and acidic subunits of glycinin, could be polymerized by MTGase to form high weight molecular (WM) biopolymers. Both the coagulation and gelation reactions of native SPI solutions induced by MTGase were dependent upon the initial protein substrate concentration ([C] ₀ ). In the coagulating reactions, the turbidity of SPI solutions continually increased with increasing [C] ₀ in the range from 0.25 to 3.0%. As for the gelation reactions, with the concentration increasing from 3 to 8% (w/v), the onset time of gelation of native SPIs induced by 0.8 units/mL of MTGase at 37C shortened by ∼5‐fold, and the storage modulus (G′) of finally formed gels (after 4 h) increased from ∼1 to 1300 Pa. Both the coagulation and gelation reactions of SPI solutions were promoted remarkably by increasing the enzyme concentration. Sodium Dodecyl Sulfate‐Polyacrylamide Gel Electrophoresis analysis showed that the protein constituents of MTGase‐induced aggregates of SPI (2% w/v) were mainly composed of basic subunits of glycinin and some of newly cross‐linked high MW biopolymers. The solubility analysis of protein constituents indicated that the covalent cross‐linkage, hydrophobic and H bindings and disulfide bonds were mainly involved in the coagulation of SPI induced by MTGase.     

Properties of retrograded and acetylated starch preparations Part 2. Dynamics of saccharification with amyloglucosidase and rheological properties of resulting pastes and gels

Various procedures have been used to produce preparations of retrograded starch, by subjecting it to acetylation with methods used in the food industry. The resultant starch preparations were evaluated for their degree of acetylation through titration, swelling power and solubility in water at 80 °C, and saccharification dynamics as affected by amyloglucosidase. Rheological properties of pastes and gels of native starch and modified starch preparations were characterized with the use of a sweep temperature test as a dependency of the storage modulus (G′) and loss modulus (G″) on temperature. In addition, flow curves of pastes were plotted and mechanical spectra of gels of the preparations examined were determined. These modifications had a significant effect on the preparations produced. Retrograded and acetylated starch preparations were characterized by greater solubility in water and greater swelling power, and were less susceptible to amyloglucosidase than the non-acetylated preparations. Rheological properties of the pastes and gels were affected by the methods of their production. Acetylation was found to significantly affect a decrease in the storage modulus value during heating. Pastes of the native starch and modified starch preparations were characterized by the non-Newtonian flow, shear thinning with a tendency to yield stress. In turn, the mechanical spectra demonstrated that - in the concentration applied - both native starch and modified starch preparation were forming weak gels.