低酯果胶和乳清分离蛋白复合凝胶性质的研究

本实验研究混合体系pH 值、NaCl 浓度和CaCl2 浓度对低酯果胶与乳清蛋白复合凝胶的硬度和持水能力的影响。响应面分析结果表明,pH 值、NaCl 浓度和CaCl2 浓度对凝胶性质有显著影响。低酯果胶和乳清分离蛋白复合凝胶的最佳条件为pH6、NaCl 浓度0.2mol/L、CaCl2 浓度10mmol/L,在此条件下制得的复合凝胶强度接近200g,持水能力接近75%。     

柠檬酸钠辅助谷氨酰胺转移酶对牦牛乳凝胶特性的研究

为了解决牦牛酸奶在贮藏和运输过程中易出现凝胶破碎和乳清析出等质构缺陷。本实验主要研究了柠檬酸三钠(TSC)对经谷氨酰胺转移酶(MTGase)处理的脱脂牦牛乳形成凝胶的持水力、硬度和流变特性的影响。将不同浓度的柠檬酸三钠(0、10、30和50mmol/L)加入到牦牛乳中,分散均匀后重新调整pH至6.55～6.65,然后加入MTGase以促进牦牛乳酪蛋白的共价交联反应。将上述分散体系用1.4%(w/v)D-葡萄糖酸-δ-内酯(GDL)于42℃下酸化4～5 h。结果表明,当TSC的浓度分别为0、10、30和50 mmol/L时,牦牛乳酪蛋白胶束形成的颗粒直径分别为300、110、70、30 nm。在0～30 mmol/L范围内,随着TSC浓度的增加,经过MTGase处理后的牦牛乳形成的酸凝胶的硬度、持水力和屈服应力呈显著的增加趋势,超过30 mmol/L,凝胶的硬度、持水力和屈服应力逐渐降低。总体而言,TSC能够将牦牛乳酪蛋白胶束分解成较小的颗粒,在MTGsae存在的条件,能显著改善牦牛乳酸凝胶的质构缺陷。     

阿魏酸异辛酯抑制酪氨酸酶活性的动力学研究

在30℃,pH=6.8的Na2HPO4-NaH2PO4缓冲体系中,采用酶动力学方法研究阿魏酸异辛酯对酪氨酸酶单酚酶和二酚酶活力的抑制动力学。实验结果表明,阿魏酸异辛酯对酪氨酸酶单酚酶和二酚酶活性均有良好抑制作用,对单酚酶和二酚酶活力的相对抑制率达到50%的阿魏酸异辛酯浓度(IC50)约分别为0.24 mmol/L和0.45 mmol/L,比熊果苷抑制二酚酶活性的IC50值5.3 mmol/L小得多。阿魏酸异辛酯能明显延长单酚酶的迟滞时间,0.4 mmol/L阿魏酸异辛酯能使迟滞时间由1.1 min延长至3.6 min。Lineweaver-Burk图显示阿魏酸异辛酯对二酚酶的抑制作用表现为竞争性抑制,抑制常数(K)I为0.20 mmol/L。     

糖醇对结冷胶凝胶质构的影响

利用物性分析仪研究赤藓糖醇、木糖醇、乳糖醇对结冷胶凝胶质构的影响。结果表明：3 种糖醇都能使结冷胶凝胶强度和硬度降低,且都随糖醇质量浓度的增加而降低,3 种糖醇的影响力为乳糖醇>木糖醇>赤藓糖醇,但对结冷胶凝胶脆性的影响不显著。其次,15 g/100 mL的复合糖醇对结冷胶凝胶质构的影响皆小于相同质量浓度的单一糖醇对质构的影响,复合糖醇间不存在正协同作用。最后,在以K+为成胶离子时（40～400 mmol/L）,乳糖醇对结冷胶凝胶质构有影响;在以Ca2+为成胶离子时,只在低浓度时（2～10 mmol/L）,乳糖醇对结冷胶凝胶质构影响明显,当Ca2+浓度升高时（10～50 mmol/L）,乳糖醇对结冷胶凝胶质构几乎不产生影响。     

脂肪醇琥珀酸单酯磺酸钠润湿性能的研究

对癸醇、十二醇、十四醇、十六醇、十八醇琥珀酸单酯磺酸钠盐的润湿性能进行了系统研究．用帆布沉降法测定了这５种产品在不同浓度、不同温度、不同硬水中的润湿性能．实验结果表明：十二醇、十四醇琥珀酸单酯磺酸钠盐均具有较好的润湿性能     

金属离子对大豆蛋白凝胶形成的影响

用大豆分离蛋白模拟传统豆腐的凝胶形成过程,研究了金属离子对大豆蛋白凝胶形成过程及质构特性的影响.结果表明,Na+在0～0.050mol/L时,随着浓度的增大,凝胶形成时间缩短,在0.0500～075mol/L时,凝胶形成时间延长.Ca2+的浓度在0-6.0mmol/L之间时,随着浓度的增大.凝胶形成时间明显减少.Mg2+的浓度在0～0.030mol/L范围内,随着浓度的增大,凝胶形成时间缩短.总的来说,随着金属离子浓度的增加,阴离子对蛋白质构象的影响导致凝胶特性的变化变得复杂.     

离子强度和温度对乳清蛋白凝胶的影响

本实验主要研究凝胶温度和CaCl2 浓度对乳清蛋白冷凝胶的影响。结果表明：较低的凝胶温度和增加CaCl2浓度能够致使乳清蛋白形成清亮的凝胶;在0、10、20℃凝胶温度条件下,增加CaCl2 浓度使得凝胶硬度有所增加;乳清蛋白凝胶的持水性在凝胶温度为0、10℃,CaCl2 浓度为20、40mmol/L 时受到影响;除了0℃ 和20mmol/LCaCl2 条件下,低温能够使乳清蛋白形成较高的凝胶硬度和持水性。凝胶温度和CaCl2 浓度是影响乳清蛋白冷凝胶的关键因素。     

杜仲凝胶软糖的制备工艺优化

为了制备一种外观晶莹、富有弹性而质地软糯具有杜仲独特风味的凝胶保健软糖,以杜仲粉末为主要原料、以明胶和木薯淀粉为复配凝胶剂、以麦芽糖醇为甜味剂、以柠檬酸为酸味剂,运用单因素及正交试验进行配方优化,通过感官评定和质构分析,得出杜仲凝胶软糖最佳工艺配方为:明胶与木薯淀粉的配比为5∶1、杜仲水提取液为150 g/L、麦芽糖醇的添加量为200 g/L、糖度为80%、柠檬酸添加量为0.5 g/L。制成的凝胶软糖表面光滑有色泽,弹性适口,甜酸适中,质量稳定,感官、质构和微生物指标均符合国家标准。杜仲软糖提取物对DPPH自由基、羟自由基具有清除作用,清除作用与试验浓度之间存在较好的线性量效关系,其中,最大试验浓度下（100 mg/mL）羟自由基清除率可达81.5%±2.1%,最大试验浓度下（100 mg/mL） DPPH自由基清除率可达51.5%±1.0%。     

金属离子对大豆蛋白凝胶形成的影响

用大豆分离蛋白模拟传统豆腐的凝胶形成过程,研究了金属离子对大豆蛋白凝胶形成过程及质构特性的影响。结果表明,Na+在0～0.050mol/L时,随着浓度的增大,凝胶形成时间缩短,在0.050～0.075mol/L时,凝胶形成时间延长。Ca2+的浓度在0～6.0mmol/L之间时,随着浓度的增大,凝胶形成时间明显减少。Mg2+的浓度在0～0.030mol/L范围内,随着浓度的增大,凝胶形成时间缩短。总的来说,随着金属离子浓度的增加,阴离子对蛋白质构象的影响导致凝胶特性的变化变得复杂。      

CaCl2和NaCl诱导对大豆分离蛋白纳米纤维冷凝胶的影响

蛋白质自组装形成的纳米纤维因独特的功能和生物学特性而引起人们的关注。本文通过加入CaCl2和NaCl诱导大豆分离蛋白（SPI）纤维溶液制得冷凝胶,研究不同蛋白浓度及离子浓度对凝胶性质的影响。流变学测量结合Percolation模型拟合结果表明：冷凝胶的临界渗滤浓度（cp）比纤维热凝胶方法低,CaCl2和NaCl浓度分别为30 mmol/L和150 mmol/L时cp最小。形成的冷凝胶表现为各向同性渗流和均匀的网络。SPI浓度越大,冷凝胶储存模量G′、凝胶硬度越大,凝胶持水性越好,形成凝胶所需的盐浓度越低。在低离子强度下（CaCl2浓度<50 mmol/L,NaCl浓度<150 mmol/L）,离子强度越大,G′、凝胶硬度和持水性越大。盐浓度进一步增加时,G′、凝胶硬度和持水性下降。在冷固性凝胶中,同等离子强度的条件下,NaCl诱导凝胶的cp值均高于加入CaCl2的cp,说明多价阳离子形成盐桥是形成凝胶网络的主要驱动力。     

柠檬酸-反相微胶团法提取虾壳中甲壳素的研究

以虾壳为原料,采用柠檬酸反向微胶团法研究出一种新型的制备甲壳素的方法。首先用食品级的柠檬酸结合超声波辅助萃取技术脱除虾壳中的无机盐,再用微胶团萃取技术脱除虾壳中的蛋白质,再用30%的双氧水脱色,从而制得甲壳素。在单因素实验的基础上,通过响应面设计,得到柠檬酸反相微胶团法提取虾壳中甲壳素的最优条件。并将该法与酸碱法和酶法制备甲壳素产率进行了对比。结果表明,最优条件为:40 m L反相微胶团中虾壳的原料添加量为0.62 g、KCl浓度为0.15 mol/L、萃取时间为116 min,产率为47.32%。柠檬酸反相微胶团法甲壳素产率极显著低于传统的酸碱法,但极显著高于酶法。该方法可行,可为甲壳素生产工艺的改进提供理论基础。      

Effects of milk pH alteration on casein micelle size and gelation properties of milk

The effects of changes in pH above and below the natural pH of milk (ca 6.6) on the casein micelle size and the gelation properties of the pH adjusted and restored samples were investigated. The size of casein micelles increased at pH 7.0 and 7.5, then started to decrease above pH 8.5. It is postulated that at pH below 8.5 the casein micelles swell, while elevated pH causes their dissociation. Conversely, the size of casein micelles decreased on acidification to pH 5.5 and increased when the pH dropped below 5.5, due to the shrinkage of casein micelles at lower pH before their aggregation at pH below 5.5. In response to neutralising treated milk back to normal milk pH of 6.6, it was found that the casein micelle size of treated milk with a narrow range of pH change between 6.0 and 7.0 was reversible, while beyond this range the structure of casein micelles became irreversible. The restoration of casein micelle size was followed by the restoration of some parameters such as soluble calcium, ethanol stability, and milk whiteness. Acid-induced gelation did not change the elastic modulus, while rennet-induced gelation was affected by initial milk pH. In reference to the size of reversible range elastic modulus (G’) of acid or rennet gels made from restored milk, the sizes were similar to control milk after 6 h of gelation.     

Micellar Transition State in Casein Between pH 5.5 and 5.0

pH-induced changes in casein micelles during direct acidification and bacterial fermentation of reconstituted skim milk at 20°C were monitored by scanning electron microscopy (SEM) in combination with biochemical and rheological methods. For SEM casein micelle observations, an original method of milk sample preparation with porous inorganic membranes was developed. Micrographs suggested that different stages of micellar association were related to pH and that between pH 5.5 and 5.0 casein micelles coalesced. Correlations between microstructural and biochemical changes in casein micelles, and rheological behavior of milk or gel, help to explain the different steps leading to the final protein network of the acid milk gel.     

Interactive effects of casein micelle size and calcium and citrate content on rennet‐induced coagulation in bovine milk

Interactive effects of casein micelle size and milk calcium and citrate content on rennet‐induced coagulation were investigated. Milk samples containing small (SM) and large (LM) micelles, obtained from individual Holstein cows, were modified by addition of calcium and/or citrate and milk coagulation properties were evaluated in a full factorial design. The results showed that LM milk had a higher relative proportion of casein, coagulated faster, and resulted in a stronger gel than SM milk. Addition of calcium slightly decreased casein micelle size, while addition of citrate slightly increased micelle size. Calcium addition resulted in a shorter coagulation time and the strongest gels, while citrate addition increased the coagulation time and resulted in the weakest gels. Addition of calcium and citrate in combination resulted in intermediate coagulation properties. The interactive effect of micelle size and citrate was significant for gel strength. Microstructural differences between the milk gels were consistent with the rheological properties, for example, the micrographs revealed that a more homogeneous network was formed when calcium was added, resulting in a stronger gel. A more inhomogeneous network structure was formed when citrate was added, resulting in a weaker gel. Thus, variations in casein micelle size and in calcium and citrate content influence rennet‐induced coagulation in bovine milk. The calcium and citrate contents in Swedish milk have changed over time, whereby calcium content has increased and citrate content has decreased. In practical cheese making, calcium is added to cheese milk, most likely altering the role of inherent citrate and possibly influencing casein micelle size. The observed interaction effect between casein micelle size and citrate in this study, suggests that larger micelles with moderate citrate level will result in firmer gels, whereas a higher citrate content reduced gel strength more in case of large than SM. Since firmer gels are likely to retain more protein and fat than less firmer gels, this interaction effect could have implications in practical cheese production.     

氧化强度对肌原纤维蛋白结构及凝胶性能的影响

采用模拟氧化体系（10 μmol/L FeCl3,100 μmol/L抗坏血酸,0、0.5、1、3、5、10 mmol/L H2O2）,研究不同氧化程度对猪肌原纤维蛋白（myofibrillar protein,MP）结构及凝胶性质的影响。结果表明：随H2O2浓度升高,蛋白羰基含量上升,总巯基含量、自由氨基含量及内源荧光强度下降,十二烷基硫酸钠-聚丙烯酰胺凝胶电泳表明氧化诱导二硫键的形成引起蛋白质交联聚集加剧,进而导致蛋白表面疏水性和溶解度降低;当H2O2浓度小于1.0 mmol/L时,MP热诱导凝胶性能无明显变化,当H2O2浓度大于1.0 mmol/L时,热诱导凝胶蒸煮损失显著增强（P＜0.05）,凝胶强度明显降低（P＜0.05）,但凝胶白度无明显变化。总体来说,H2O2浓度越高蛋白氧化程度越严重,凝胶强度越低。     

儿茶素对肌原纤维蛋白氧化、结构及凝胶特性的影响

采用羟自由基氧化体系（10 μmol/L FeCl3、100 μmol/L VC和1 mmol/L H2O2）研究不同添加量儿茶素（10、50、100、150 μmol/g）对肌原纤维蛋白氧化、结构及凝胶特性的影响,同时以未氧化和氧化后未添加儿茶素（0 μmol/g）肌原纤维蛋白作为对照组,对肌原纤维蛋白羰基含量、总巯基含量、表面疏水性、溶解度、粒径分布、凝胶强度、凝胶保水性及肌原纤维蛋白流变特性进行测定,并观察凝胶微观结构。结果表明：添加儿茶素能减少羰基化合物的产生,但添加量过高会促进肌原纤维蛋白氧化;与未氧化和未添加儿茶素组相比,添加儿茶素降低了肌原纤维蛋白表面疏水性;随着儿茶素添加量增加,肌原纤维蛋白巯基含量逐渐降低,溶解度显著降低,粒径逐渐增大,凝胶强度和保水性逐渐下降,凝胶微观结构更加疏松多孔,蛋白胶束聚集,中、高添加量（50、100、150 μmol/g）儿茶素使得肌原纤维蛋白失去典型的流变曲线。中、高添加量儿茶素与肌原纤维蛋白发生共价交联,并导致肌原纤维蛋白发生疏水性聚集,最终削弱了肌原纤维蛋白的凝胶特性。     

界面组成对乳化颗粒填充乳清蛋白凝胶强度及持水性的影响

考察了p H（3、7）、氯化钠浓度（50、200mmol/L）以及热处理（90℃、30min）对不同乳化剂（乳清分离蛋白、Tween20、Tween20+马铃薯蛋白水解物）制备O/W乳状液分层稳定性的影响。并以凝胶持水性和凝胶强度为指标,考察了p H和氯化钠浓度对上述不同界面组成的乳化颗粒填充乳清蛋白热诱导凝胶性质的影响。结果表明,以乳状液为溶剂制备的凝胶持水性与凝胶强度高于以水为溶剂制备的凝胶。加入一定量的氯化钠有助于乳状液凝胶持水性与凝胶强度的增加。研究表明,p H和盐浓度对乳状液填充凝胶强度均有影响,乳状液性质对乳状液填充凝胶强度和持水性有一定影响。      

羟自由基氧化对草鱼肌原纤维蛋白结构和凝胶性质的影响

以草鱼肉为研究对象,采用芬顿反应体系(H_2O_2浓度分别为0.1、1.0、5.0、10.0 mmol/L)产生不同浓度·OH对其肌原纤维蛋白进行模拟氧化,研究·OH氧化对草鱼肌原纤维蛋白结构及凝胶性质的影响。结果表明,氧化使肌原纤维蛋白羰基含量显著增加(P0.05),当氧化剂H_2O_2的浓度为10.0 mmol/L时,羰基含量比对照组增加了111.35%;随着H_2O_2浓度的提高,肌原纤维蛋白总巯基、活性巯基、游离氨基含量显著下降(P0.05);二聚酪氨酸水平和表面疏水性显著增加(P0.05)。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分析表明氧化使蛋白质分子间发生交联和聚集,产生了分子质量大于200 ku的蛋白聚集体。可见,·OH氧化使草鱼肌原纤维蛋白中巯基、酪氨酸、色氨酸等氨基酸残基发生了显著氧化修饰,蛋白质分子产生了交联和聚集,蛋白质构象发生了显著变化。此外,氧化可进一步影响肌原纤维蛋白的凝胶性质,使其凝胶网络结构变疏松、凝胶孔隙增大,凝胶中部分不易流动水转变为自由水,最终导致凝胶强度和凝胶持水性显著降低。     

大豆磷脂酰乙醇胺-聚乙二醇单甲醚2000的制备及其性能研究

以聚乙二醇单甲醚2000为原料,先将其氧化为聚乙二醇单甲醚2000羧基衍生物,再制备成高活性的聚乙二醇单甲醚2000酰氯,与磷脂反应制备了大豆磷脂酰乙醇胺-聚乙二醇单甲醚2000(MPEG2000-SPE)。产物结构经1HNMR和IR进行了表征。质量比为m(大豆粉末磷脂)∶m(羧基化聚乙二醇单甲醚)=3∶1,产物收率为85.2%;通过TEM观察了产物在水中形成胶束的大小,通过荧光探针技术研究了产物的临界胶束浓度用以表征产物的热力学稳定性,通过乳化力来表征产物的动力学稳定性,试验表明,产物在水溶液中形成的胶束粒径为30~80 nm,临界胶束浓度为2×10-6mol/L,形成胶束的热力学稳定性优于小分子胶束,产物的动力学稳定性优于大豆粉末磷脂。     

Kinetics of heat-induced interactions among whey proteins and casein micelles in sheep skim milk and aggregation of the casein micelles

The interactions among the proteins in sheep skim milk (SSM) during heat treatments (67.5–90°C for 0.5–30 min) were characterized by the kinetics of the denaturation of the whey proteins and of the association of the denatured whey proteins with casein micelles, and changes in the size and structure of casein micelles. The relationship between the size of the casein micelles and the association of whey proteins with the casein micelles is discussed. The level of denaturation and association with the casein micelles for β-lactoglobulin (β-LG) and α-lactalbumin (α-LA) increased with increasing heating temperature and time; the rates of denaturation and association with the casein micelles were markedly higher for β-LG than for α-LA in the temperature range 80 to 90°C; the Arrhenius critical temperature was 80°C for the denaturation of both β-LG and α-LA. The casein micelle size increased by 7 to 120 nm, depending on the heating temperature and the holding time. For instance, the micelle size (about 293 nm) of SSM heated at 90°C for 30 min increased by about 70% compared with that (about 174.6 nm) of unheated SSM. The casein micelle size increased slowly by a maximum of about 65 nm until the level of association of the denatured whey proteins with casein micelles reached 95%, and then increased markedly by a maximum of about 120 nm when the association level was greater than about 95%. The marked increases in casein micelle size in heated SSM were due to aggregation of the casein micelles. Aggregation of the casein micelles and association of whey protein with the micelles occurred simultaneously in SSM during heating.