超高压时间对胶原明胶化及成品明胶品质的影响

以1%(w/v)HCl溶液为传压介质,研究不同时间(0~45min)的超高压(300MPa)处理对胶原的热稳定性及成品明胶的分子量分布、凝胶强度、流变学特性等的影响,以分析超高压时间在胶原明胶化过程中的作用及其对明胶品质的影响。结果显示:经5~45min的超高压处理的明胶化胶原的热稳定性高于传统酸处理组,但是低于未处理组(超高压时间为0min);结合前期工艺研究结果,可以发现超高压处理组胶原的热稳定性较低、明胶提取率较高,说明超高压处理能够破坏链间氢键、松散胶原三螺旋结构,有利于胶原明胶化;且超高压组明胶的亚基组分(α、β)得到很好的保留,而传统酸法明胶亚基组分相对含量很低(小于10%),超高压明胶中高分子量组分(亚基组分)使超高压明胶组明胶具有较好的胶凝特性和粘弹性能。     

兔皮胶原快速明胶化分子机制

通过YASARA软件对酸诱导兔皮胶原蛋白明胶化过程进行动力学模拟,解析兔皮胶原快速明胶化的分子机制。均方根偏差结果表明,酸处理使胶原蛋白分子的非螺旋区亚基组分分离,但对其中单个亚基的构象影响较小。酸处理初期,兔皮胶原三螺旋区的氢键在短时间内被迅速破坏,模拟50 ns后,氢键数量保持相对稳定,与实际研究结果一致。三螺旋结构在酸处理初期伴随着氢键的破坏并向其他二级结构转化,随着模拟时间的延长,α-螺旋与β-折叠相对含量之和呈先增加后减少趋势。当α-螺旋和β-折叠相对含量之和达到最大时,明胶化程度最佳。     

胶原明胶化过程中分子结构的变化

本试验以猪皮胶原为原料,研究胶原明胶化过程微观结构的变化规律。研究表明,8 h的酸处理诱导下,胶原明胶化程度较高,热水提胶后明胶得率可达83.98%,随着酸处理时间进一步延长,明胶得率显著下降;差示量热扫描(DSC)、红外光谱(FTIR)和圆二色谱(CD)研究表明,随酸处理的进行,胶原的三螺旋结构逐渐松散,维系三螺旋结构稳定的价键逐渐被破坏,酸处理8 h后,胶原三螺旋结构被过度破坏,是导致明胶得率降低的主要原因。聚丙烯酰胺凝胶电泳(SDS-PAGE)分析显示,在酸处理的过程中,胶原肽链的降解始终存在,且明胶化胶原中所保留的亚基量直接影响明胶中亚基含量。因此,在明胶化过程中必须在肽链降解和三螺旋结构松散之间寻找平衡点,以获得高得率和高品质明胶。     

大目金枪鱼皮胶原明胶化过程中酸碱浓度对明胶理化性质的影响

以大目金枪鱼皮为原料,考察了碱溶液浓度和酸溶液浓度对胶原明胶化的影响,研究表明,碱液质量分数为0.8%,酸溶液质量分数为2.0%时,明胶得率和凝胶强度均较优;傅里叶转换红外光谱(Fourier transform infrared spectroscopy,FTIR)结果表明,碱处理打破了胶原原有的氢键平衡,使三螺旋结构松散;不同质量分数的酸处理使得胶原原有的结构被破坏,三螺旋结构有所展开,二级结构向无序化转变,这些变化使热提胶过程中亚基更易释放;明胶化胶原的电镜扫描结果显示,碱处理可以对胶原蛋白的结构造成轻微的降解,继续进行酸处理过后,明胶化胶原降解程度明显,逐渐成无规则卷曲状,比较各处理组明胶化胶原表面结构状态后发现,碱处理质量分数为0.8%和酸处理质量分数为2.0%时,胶原表观破坏更明显,与得率结果一致;明胶电泳分析表明,碱处理质量分数较低时,明胶中高分子组分含量较低,而小分子组分含量较高于其他组,随着碱处理质量分数增加,明胶中α链含量增大,碱浓度至2.3%时,明胶中β链含量增高因而α链含量相对降低,导致凝胶强度降低。酸处理组中,质量分数在0.5%~1.5%范围内,酸处理质量分数在1.5%时,明胶中高分子质量组分较多,此时明胶凝胶强度最大。当酸处理质量分数高于2.0%后,所得明胶中的小分子组分含量逐渐增大,在酸处理质量分数达到2.5%后,明胶电泳条带中小分子组分的含量明显增加,造成凝胶强度逐渐降低。     

胶原明胶化程度快速评价体系构建分析与展望

明胶得率和凝胶强度是传统胶原明胶化程度评价的主要指标,但其值测得必须要完成胶原蛋白明胶化和热力提胶两个过程。热力提胶后明胶得率和凝胶强度与明胶化过程中胶原蛋白微观结构的变化密切相关,因此直接根据明胶化的胶原特征结构来评价其明胶化,可以大幅度节约研究时间和成本。本文根据传统酸碱法、酶法、超高压法诱导胶原明胶化过程中的微观结构的变化规律,结合明胶化胶原特征结构及其评价的主要指标的关系,对基于特征分子结构的胶原明胶化评价方法的构建进行了可行性分析和展望。     

超声处理对猪皮明胶特性的影响

对猪皮明胶溶液进行超声处理,重点研究了超声波预处理对猪皮明胶特性及结构变化的影响。结果表明,在超声功率200～600 W,超声时间1～20 min,超声处理可以改善明胶的凝胶特性和流变学特性,相比而言400 W处理10 min效果最优,说明适度超声处理更利于明胶凝胶和流变学特性的改善。在实验所选超声条件下,所产生的空化效应和机械效应等作用改变了明胶构象,使明胶中N—H参与的氢键有所增加,亚基组分展开,但并未造成明胶亚基组分明显降解,有利于明胶凝胶过程中更多的类三螺旋结构形成。     

酸预处理时间对鲢鱼皮明胶理化性质的影响

本文探究了酸预处理时间对鲢鱼皮明胶理化性质的影响。结果发现,当酸预处理时间从10 min增加到80 min,鲢鱼皮的结构变得疏松,在热水浸提中β肽链等胶原高分子组分易发生降解,提取的明胶其羟脯氨酸含量从61个残基下降到43个残基/1000个氨基酸。不管酸预处理时间多长,提取的鲢鱼皮明胶其等电点均在p H 9.2附近,但长时间的酸处理会使明胶的黏度、凝胶性能和成膜性能下降。当酸预处理时间为10 min时,制备的明胶凝胶强度、膜的抗拉伸强度和断裂延伸率分别为242.67 g、28.24 MPa和65.52%。根据圆二色光谱扫描的结果,发现酸预处理时间对明胶二级结构没有明显的影响,但酸预处理时间越长,提取的明胶在干燥过程中越不易复性形成三股螺旋结构,结果导致成膜性能下降。     

超声辅助提取兔皮胶原蛋白及其理化特性

以兔皮为原料,研究超声波在酶法提取胶原蛋白中的应用。结果表明,超声辅助制得的胶原蛋白的提取率为(83.69±0.51)%,与传统酶法相比提高了25%。聚丙烯酰氨凝胶电泳结果表明,超声处理制得的兔皮胶原蛋白主要由α1,α2和β亚基组成,并未造成亚基的降解;紫外光谱表明,超声处理后的胶原蛋白的特征吸收波长为217nm,说明其较好地保持了I型胶原蛋白的特征;傅立叶变换红外光谱表明,经过超声处理后的胶原蛋白分子中的氢键遭到部分破坏,但其三螺旋结构仍保持完整;差示扫描量热仪结果表明,超声法制得的兔皮胶原蛋白的热变性温度和热焓值均略低于传统兔皮胶原,相对而言仍具有较高的热稳定性。     

不同热处理条件下大豆蛋白体外模拟消化产物结构和分子质量分布

采用胃蛋白酶对热处理后的大豆分离蛋白(SPI)进行体外模拟消化,对消化产物的亚基组成、蛋白质二级结构和分子质量分布进行研究。随着热处理温度和时间的增加,水解度先升高后降低,说明适当的热处理条件促进胃蛋白酶对SPI的消化降解。热处理能够改变SPI体外消化模式,使11S亚基消化程度降低,同时使不易消化降解的7S亚基组分被消化降解,形成分子质量低于17 ku或更低分子质量的组分。热处理主要使消化产物二级结构中α-螺旋含量增加,β-折叠含量降低,且SPI消化产物的分子质量分布也发生改变。随着热处理温度的升高,α-螺旋含量先增加后降低,β-折叠含量先降低后增加,而热处理时间对二级结构无显著影响。高温或长时间热处理使SPI消化产物在分子质量大于100 ku和3~10 ku范围内分布增多,在分子质量10~100 ku和小于3 ku范围内分布减少。     

预处理对酶解过程中胶原ACE抑制肽释放的影响

本文探究了酸、碱、热、超声、超高压五种预处理方式对胶原蛋白制备ACE抑制肽的影响。胶原蛋白经预处理后采用碱性蛋白酶酶解制备水解液,对水解液的水解度、ACE抑制率和分子量分布情况进行测定,结果显示碱和超声处理组水解液的水解度、ACE抑制率均高于未处理组,表明这两种预处理方式可能利于胶原三螺旋区位点的暴露;DSC和红外分析预处理后的胶原蛋白结构显示,碱处理改变了胶原蛋白构象特点,影响非共价键的平衡,胶原三螺旋区域的位点被充分暴露,但保持了亚基的完整性,超声处理破坏了胶原螺旋区的共价交联,暴露出更多疏水性位点,利于碱性蛋白酶酶解;而酸、热和超高压处理主要影响胶原非螺旋区,无法在酶解过程中促进胶原ACE抑制活性肽段的释放。     

Effects of acid concentration and the UHP pretreatment on the gelatinisation of collagen and the properties of extracted gelatins

An ultra‐high‐pressure (UHP) transmission medium with HCl was applied as a pretreatment to extract gelatin. The effects of the acid concentration (0–1% (w/v)) on the gelatinisation of collagen and the properties of gelatin were investigated. An increase in the acid concentration decreased the thermostability of collagen and increased the yield of gelatin (from 64% increased to 80%). The content of the subunit components in the pretreated collagen and the gelatin declined slightly as the acid concentration was increased, resulted in slight decrease (P > 0.05) in the gel strength (from 435 g decreased to 408 g). The analysis of Fourier transform infrared spectroscopy (FTIR) spectra showed that the triple‐helical structure, secondary structures of the collagen and covalent cross‐linking in the collagenous fibres were damaged gradually as the acid concentration was increased. The scanning electron microscopy (SEM) images showed that the smooth surface of collagen was partly disrupted with microvoids after UHP/1% HCl pretreatment, which may be related to the damage on the covalent cross‐linking.     

Effects of Annealing on ultra-high pressure induced gelatinization of corn starch

Ultra-high pressure (UHP) can induce starch gelatinization at the room temperature, while the change of starch architecture could affect the gelatinization process. This work evaluated the effects of annealing on UHP induced starch gelatinization. Native and annealed corn starches were subjected to UHP treatment (300–600 MPa) for 15 min at room temperature. The scanning electron microscopy, confocal laser scanning microscopy, differential scanning calorimetry and X-ray diffraction analysis showed that UHP treatment partially disrupted the ordered structures of native and annealed starches, which made starch gelatinized gradually and a transformation in crystal type from type A to type B. However, compared with native starch, annealing (C3 and C24) delayed the internal and external structure destruction of starch granules, as well as induced a slower decrease in ΔH and relative crystallinity as increasing pressure. Therefore, the suitable UHP treatment can increase the pressure resistance of starch, or delay the UHP gelatinization process.     

兔皮明胶提取工艺优化

以兔皮为原料,研究稀盐酸短时诱导兔皮制备明胶的工艺。以明胶提取率和凝胶强度为评价指标,对兔皮明胶制备工艺中的盐酸质量分数、盐酸处理时间、提胶pH值、提胶温度4 个因素进行了优化,在此基础上通过正交试验确定最佳工艺为盐酸质量分数1%、盐酸处理时间10 min、提胶温度65 ℃、提胶pH 4。在此工艺条件下明胶提取率高达（86.85±1.71）%,凝胶强度为（481.43±16.89）g。明胶基本性质符合GB 6783-2013《食品添加剂：明胶》要求。     

稻米淀粉期化进程研究

对不同初始粒径的稻米淀粉的糊化进程进行了研究。结果表明,淀粉的糊化具有上升,平缓和回落三个除段,在糊化温度以下（60℃）,淀粉颗粒仅存在吸水膨胀,糊化度曲线平坦,糊化温度以上,随加热温度和的升高,淀粉的糊化速度和糊化程度迅速增高,明显开成糊化过程的三阶段,较小的初始粒径会加快糊化进程,增大回落程度,但对糊化程度影响不大,加热温度对糊化特性的影响较淀粉的初始粒径大。     

Gelatinization of waxy starches under high pressure as influenced by pH and osmolarity: Gelatinization kinetics, final structure and pasting properties

We investigated the influence of pH and osmolarity on the high-pressure-induced gelatinization of waxy corn and waxy rice starches in salt solutions, and the properties of the resulting gels. Gelatinization kinetics, the gel swelling power of starches, their structure and their rheological properties were studied for starch suspensions treated at 500 MPa. Gelatinization took place mostly in the first 15 min of the pressure treatment and both the gelatinization speed and the maximal level of gelatinized starch decreased with increasing osmolarity. pH had a minor influence on gelatinization kinetics differing from one starch to another. The resulting gels appeared as a mix of a gel and starch granules with a higher proportion of native granules with increasing osmolarity. Gel strength and swelling were positively correlated to their proportion of gelatinized starch. Thus, gels with different structures and gelatinization levels can be obtained under pressure depending on pH and osmolarity.     

Chemical Composition and Structure of Granule Periphery and Envelope Remnant of Rice Starches as Revealed by Chemical Surface Gelatinization

In this work the contribution of molecular structures to the swelling behavior of rice starches was investigated. Rice starches with different amylose contents (0 ‐ 23.4 %) were gelatinized to various degrees (approximately 10, 20, and 50 %) with 13 M aqueous LiCl, and the surface‐gelatinized starch and ungelatinized remaining granules were separated and characterized. The native starches were heated at 85 or 95°C for 30 min in excess water, and the granule envelope remnants were recovered by centrifugation for further characterization. The remaining granules after surface removal exhibited a lower gelatinization temperature and enthalpy, and swelled to a greater extent upon heating than the native counterpart. The amylopectin molecules in granule envelope remnants obtained at 95°C had larger M_w (weight‐average molar mass) and R_z (z‐average gyration radius) than those in remnants obtained at 85°C. The chemical composition and structure of granule envelope remnants obtained at 85°C were different from those obtained at 95°C for the same rice starch cultivar. The results imply that starch periphery may not be responsible for maintaining starch granule integrity during gelatinization and swelling. It is proposed that the composition and structure of the granule envelope remnant that maintains granule integrity are not constant but dynamic. The formation of a semi‐permeable membrane‐like surface structure during gelatinization and swelling is proposed to be a result of molecule entanglement after gelatinization.     

超高压提取木瓜中齐墩果酸的研究

研究了采用超高压提取木瓜中齐墩果酸的最佳工艺条件,并且同回流提取和超声提取方法进行了比较。在单因素实验的基础上,采用正交实验法对木瓜中齐墩果酸的超高压提取工艺进行优选,选用L_9(3~4)进行正交实验,以齐墩果酸的得率为指标,考察粉碎度、超高压压力、保压时间、固液比(g:mL)对齐墩果酸得率的影响。得到的最佳工艺条件为:粉碎度80目、超高压压力350MPa,超高压时间4min,固液比(g;mL)1:20。齐墩果酸的提取得率可达2.72%,同回流提取和超声提取方法相比,超高压提取方法得率高,提取时间短,是提取木瓜中齐墩果酸的适宜方法。     

超声波、超高压对白鲢鱼肌肉脂肪氧合酶构象及酶活力的影响

本研究采用超声波、超高压对白鲢鱼肌肉中的脂肪氧合酶（lipoxygenase,LOX）进行处理,通过测定 LOX活力、圆二色谱、荧光光谱变化,考察超声波、超高压处理对白鲢鱼肌肉LOX构象及活力的影响。实验结 果表明：随着超声波功率的增加、超声时间的延长,LOX分子内α-螺旋和β-折叠含量降低,荧光强度不断增强, 说明其二级结构和三级结构明显发生变化,使LOX活力不断降低,最适超声条件为300 W、3 h,此时酶活力降低 66.07%;随着超高压压力的增加、超高压时间的延长,LOX分子内α-螺旋和β-折叠含量降低,荧光强度不断减弱, 说明LOX分子二级结构和三级结构发生显著变化,LOX活力迅速降低,最适超高压条件为300 MPa、20 min,此时 酶活力降低93.10%。     

高直链玉米淀粉的糊化特性研究

目的研究水浴加热、微波加热和高压加热方法对高直链玉米淀粉糊化性能的影响,为高直链淀粉的进一步开发和应用提供理论基础。方法以高直链玉米淀粉为原料,在过量水分存在条件下,分别采用水浴加热、微波加热和高压加热制备高直链玉米淀粉糊,分别研究不同温度和微波功率下,高直链玉米淀粉糊碘兰值和酶解力随糊化时间增加的变化规律。结果水浴加热、微波加热和高压加热糊化过程中高直链玉米淀粉的碘兰值和酶解力均随时间的延长呈上升趋势,微波加热高直链玉米淀粉糊的碘兰值和酶解力低于高压加热但高于水浴加热,微波加热淀粉的糊化速度大于水浴加热和高压加热。结论高压加热淀粉糊化效果好,淀粉的糊化程度高,是使高直链淀粉完全糊化的较好方法。