适宜贮藏温度和添加剂提高苹果粉稳定性

为提高喷雾干燥苹果粉的贮藏稳定性和优化贮藏条件,基于水分活度保藏理论和玻璃化转变理论,探讨了温度及添加剂对苹果粉吸附等温线和玻璃化转变温度的影响。采用静态称量法研究了苹果粉在不同温度(5、25和45℃)下的吸附等温线;采用Lewicki、GAB、Smith、Henderson和Peleg模型拟合试验数据,得到描述苹果粉水分吸附特性的数学模型;采用差示扫描量热法测定了添加β-环糊精、麦芽糊精、可溶性淀粉和玉米淀粉的苹果粉在贮藏温度40℃达到水分平衡时的玻璃化转变温度;采用Khalloufi,El-Maslouhi,Ratti方程拟合数据,探讨添加剂对苹果粉临界水分活度和临界平衡干基含水率的影响。结果表明,GAB模型为描述苹果粉水分吸附特性的适宜模型;苹果粉的平衡干基含水率随着水分活度的增加而增加,水分活度小于0.76时随着温度的升高而降低;苹果粉的玻璃化温度随平衡干基含水率的增加而降低,添加β-环糊精的苹果粉玻璃化温度较高,不易结块,有利于提高苹果粉的贮藏稳定性。研究可为苹果粉适宜干燥技术条件和贮藏条件的确立提供参考。     

膨化干燥灰枣粉玻璃化转变及贮藏稳定性

为了综合水分活度及玻璃化转变理论构建状态图,获得灰枣粉的较佳贮藏条件,该文采用静态称量法和差示扫描量热法测定灰枣粉的吸附特性及玻璃化转变温度。结果表明,膨化干燥灰枣粉水分吸附的平衡干基含水率随水分活度的增加而增加,水分吸附等温线呈J型,描述灰枣粉水分吸附特性的适宜模型为GAB模型（R2=0.9968）;灰枣粉的玻璃化转变温度随含水率升高而降低,湿基含水率由0.064 g/g增加到0.175 g/g时,玻璃化转变温度由29.90℃降低到?35.02℃;灰枣粉干基含水率≤0.1223 g/g、贮藏温度≤?0.062°C时其稳定性较好,研究结果为灰枣粉加工、运输等过程中的贮藏条件提供理论参考。     

干制荔枝果肉吸附等温线及热力学性质

为了解干制"乌叶"荔枝果肉含水率与水分活度、贮藏温度之间的复杂关系,并为干制"乌叶"荔枝果肉贮藏条件的确定提供技术依据,运用吸附原理,在水分活度为0.112~0.976范围内,研究了干制"乌叶"荔枝果肉在20、30和40℃时的水分吸附等温线;采用8种模型对试验数据进行拟合,通过比较模型决定系数(R2)和均方根误差确定用于描述干制"乌叶"荔枝果肉吸附等温线的最适模型;通过不同温度下干制"乌叶"荔枝果肉的吸附等温线数据获得净等量吸附热、焓变、熵变和自由能等热力学性质。结果表明,干制"乌叶"荔枝果肉的水分吸附呈Ⅲ型等温线,在相同水分活度时,平衡含水率随温度的升高而下降。Peleg模型用于描述吸附等温线是较适合的,决定系数为R2为0.9950~0.9979,均方根误差为1.9431~2.7102。热力学性质显示,净等量吸附热随含水率的增加而降低,在较高含水率时趋近于0。焓变与净等量吸附热有相同的值,其范围为0.95~186.98 k J/mol。熵变随含水率的增加而降低,并没有表现出对温度的依赖性。自由能随含水率和温度的增加而减小。焓-熵补偿理论适用于干制"乌叶"荔枝果肉中的水分吸附过程,此水分吸附过程是焓驱动的。研究结果为干制"乌叶"荔枝果肉的加工和贮藏稳定性提供理论依据。     

澳洲坚果果仁粉水分解吸-吸附等温线的测定与分析

为给澳洲坚果果仁粉的干燥和贮藏条件的确定提供技术依据,试验测定了其在室温(25℃)下的水分解吸-吸附等温线。采用非线性回归的方法,应用常见的BET、GAB、Halsey、Henderson、Oswin和Smith模型对试验所得解吸-吸附等温线进行拟合分析,以确定最佳拟合模型及其参数。结果表明,其解吸等温线属于国际理论和应用化学联合会分类的第Ⅱ种类型,其吸附等温线属于第Ⅲ种类型,解吸-吸附滞后现象属于H3型;GAB模型是其最佳的解吸等温线拟合方程,Henderson模型是最佳的吸附等温线拟合方程;GAB模型拟合解吸等温线的参数A、B、C分别为8.2439、0.4815、1.3545。Henderson模型拟合吸附等温线的参数A、B分别为0.3006、0.8682。     

玉米淀粉水分吸附等温线的研究及模型建立

为了更好地指导玉米淀粉及其含物制品的干燥、储藏和包装，需要确定温度对玉米淀粉水分吸附特性的影响，及建立一个包含温度和水活度在内的新吸附等温线模型。 根据吸附原理，利用静态调整环境湿度法，测定了玉米淀粉在30℃、45℃和60℃ 3个温度不同水活度下的吸湿和解吸等温线。结果显示玉米淀粉的等温线属于Ⅱ型等温线，在一定的水活度下随着温度的升高吸附能力下降。随着水活度的增加平衡含水率增加，在整个水活度范围内吸附等温线存在一个很明显的滞后作用。用BP神经网络建立了一个新的吸附等温数学模型，分析表明BP神经网络模型不仅包含水活度和温度2个参数而且拟合程度优于其它的数学模型。     

热风-脉动压差闪蒸干燥对苹果片水分及微观结构的影响

该文应用菲克第二定律、采用低场核磁共振及磁共振成像系统(MRI,magnetic resonance imaging)、差示量热扫描、扫描电子显微镜等技术,分析不同预干燥温度对苹果片脉动压差闪蒸干燥过程中水分扩散和微观结构的变化。试验结果显示:随预干燥温度升高,水分扩散速率加快,有效水分扩散系数随温度升高而变大,整体范围在9.84×10-9~7.24×10-8 m2/s;干燥作用引起水分状态由高自由度向低自由度迁移,自由水含量在干燥初期迅速降低,不易流动水含量先增加后降低;MRI结果表明:苹果鲜样水分集中于中心部位,随干燥进行,水分向外扩散并均匀分布于样品中,含水率的降低,导致图像亮度呈现降低趋势,同时样品表现出向中心收缩的现象;脉动压差闪蒸干燥过程中,含水率与玻璃化转变(Tg)和水分活度(aw)之间表现出极显著相关性(R0.90,p0.01),含水率的降低引起Tg升高、aw降低,且Tg与aw之间呈线性相关(R20.81);水分的散失导致微观结构发生变化,细胞破裂形成空腔,脉动瞬间的真空作用促使苹果片多孔海绵状结构进一步形成,赋予其酥脆口感。该试验可以为苹果片在脉动压差闪蒸干燥方面提供理论依据和技术参考。     

复合助剂对低温喷雾干燥蓝靛果粉理化性质的影响

为保证低温喷雾干燥后蓝靛果粉品质,采用黄金分割法研究复合助剂（麦芽糊精、β-环糊精和乳清蛋白）对喷雾干燥蓝靛果粉理化性质的影响,分析低温进风温度（50～90 ℃）对蓝靛果粉花青素保留率、集粉率和含水率的影响规律。结果表明,在麦芽糊精、β-环糊精的质量比例为85.4%、14.6%时,集粉率高达37.96%;随进料溶液中麦芽糊精质量比例增加,蓝靛果粉玻璃化转变温度、水溶性指数、堆积密度、亮度L^*值、红度a^*值和色差值ΔE呈增加趋势,含水率、花青素含量和黄度b^*值呈下降趋势;在麦芽糊精、β-环糊精和乳清蛋白质量比例为72.9%、12.5%、14.6%时,集粉率达到最高（40.11%）;随料液中乳清蛋白质量比例增加,蓝靛果粉含水率、花青素含量呈上升趋势,其玻璃化转变温度、水溶性指数、亮度L^*值、红度a^*值、黄度b^*值和色差值ΔE等指标呈下降趋势;复合助剂显著提高蓝靛果粉集粉率（P<0.05）,对其中的花青素起到较强保护作用,其含水率、水溶性指数、堆积密度等理化指标均接近于最优水平。在低温喷雾干燥研究发现,随进风温度上升,集粉率和含水率呈负相关,在进风温度90 ℃时,集粉率最高的配方中可实现较高花青素保留率（89.94%）。低频核磁共振波谱以及质子密度图像信息分析表明,加入的助剂与蓝靛果果汁中水分通过氢键、静电结合力和疏水作用等分子间作用力,形成稳定性高水合物、增强液滴聚结抵抗力,提高料液玻璃态转换温度,从而实现高集粉率和高花青素保留率的蓝靛果果粉低温喷雾干燥;红外光谱分析表明,复合助剂可在蓝靛果果粉中形成分子间氢键,并对花青素等活性物质进行固定包埋保护。研究结果可为蓝靛果粉喷雾干燥加工生产提供理论支撑和参考依据。     

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。     

冷冻面片动态热机械性能研究

以不同小麦粉为材料制作面片,用动态热机械分析仪(Dynamic Mechanical Thermal Analysis,DMTA)研究面片从20℃至-80℃和从-80℃至20℃的降温和升温过程中动态热机械性能,目的是探求冷冻面制品加工过程中的变化规律,冷冻面制品玻璃化转变温度及其影响因素.结果表明:不同小麦品种面片之间、同一小麦品种不同制粉细度面片之间、同一小麦粉不同加水量面片之间的降温和升温过程中的动态热机械性能均有差异,特别是玻璃化温度Tg′峰差异较大;在降温过程中,粗粉和细粉样品的玻璃化温度Tg′分别为-33.23和-39.90℃;高水分样品有两个连续的玻璃化温度Tg′峰,分别为-41.42和-42.97℃,低水分样品的玻璃化温度Tg′为-33.23℃;在升温过程中,细粉样品普冰143的玻璃化温度Tg′为2.40℃,细粉样品郑农973出现3个玻璃化温度Tg′峰,分别为-7.97、-6.41和10.31℃;粗粉样品的玻璃化温度Tg′为3.62℃,细粉样品有3个玻璃化温度Tg′峰,分别为-7.97、-6.41和10.31℃;高水分和低水分样品的玻璃化温度Tg′分别为-10.14和3.62℃.小麦粉冷冻面制品的冷冻加工温度应为其玻璃化温度,以保证冷冻面制品的质量,而不是现在普遍采用的-18℃.     

肉大鸡颗粒饲料的吸湿解吸平衡模型

为了研究成品饲料的吸湿解吸平衡规律,用GAB模型及其含温度变量的改良模型（mGAB, modified GAB）拟合静态法获得的肉大鸡颗粒料在15、25、35和45℃环境下,在11%至97%平衡相对湿度（即水活度0.11～0.97）范围内的吸湿平衡以及11%～75%（即水活度0.11～0.75）范围内的解吸平衡,得到优异的拟合精度。结果表明：随温度上升,饲料的平衡含水率下降,吸湿和解吸之间存在明显的滞后现象。用BET解吸模型计算的15～45℃范围内单层含水率为6.34%～5.39%（干基）,并且随温度升高线性下降。以水活度0.65为安全贮存的临界点,对应于吸湿和解吸过程, 用改良GAB模型估计4个温度点的安全水分（干基）分别为13.09%和14.71%、12.92%和14.33%、12.74%和14.00%、12.56%和13.66%。研究结果为饲料的贮存和冷却过程规律研究提供了参考。     

Ascorbic acid-containing whey protein film coatings for control of oxidation

A formulation for the whey protein isolate film or coating incorporating ascorbic acid (AA-WPI film or coating) was developed. Tensile and oxygen-barrier properties of the AA-WPI film were measured. Antioxidant effects of the AA-WPI coating on roasted peanuts were studied by comparing the values of peroxide (PO), thiobarbituric acid reactive substance (TBARS), and free-radical-scavenging activity, determined with noncoated peanuts and peanuts coated with WPI with and without ascorbic acid during storage at 21% relative humidity (RH) and 23, 35, and 50 degrees C. The incorporation of AA reduced elongation of WPI films. The oxygen-barrier property of the WPI film was significantly improved by incorporation of AA. The AA-WPI coating retarded lipid oxidation in peanuts significantly at 23, 35, and 50 degrees C. The AA-WPI coated peanuts were more red than noncoated peanuts at all storage temperatures.     

Effect of processing on the displacement of whey proteins: applying the orogenic model to a real system

Atomic force microscopy (AFM) has been used to investigate the displacement of a commercial whey protein system and the behavior as compared to that of beta-lactoglobulin (Mackie, A. R.; Gunning, A. P.; Wilde, P. J.; Morris, V. J. Orogenic displacement of protein from the air-water interface by competitive adsorption. J. Colloid Interface Sci. 1999, 210, 157-166). The whey protein isolate (WPI) was displaced from an air-water interface by the surfactants Tween 20 and Tween 60. Displacement data obtained were compared with data obtained for pure beta-lactoglobulin and have shown that WPI was more resistant to displacement from the air-water interface than native beta-lactoglobulin. This was related to the greater surface elasticity of WPI at higher surface stresses. In the presence of Tween 20, WPI was observed to remain on the interface at surface pressures up to 8 mN/m greater than the surface pressure at which complete displacement of beta-lactoglobulin was observed. Displacement of WPI and beta-lactoglobulin films by the surfactant Tween 60 showed similar results. However, because of the lower surface activity of Tween 60, it was not possible to reach surface tension values similar to those obtained for Tween 20. Despite the lower surface activity of Tween 60, WPI was still observed to be present at the interface at surface pressure values greater than those by which beta-lactoglobulin had been completely displaced.     

Effects of pH and the gel state on the mechanical properties, moisture contents, and glass transition temperatures of whey protein films.

The mechanical properties, moisture contents (MC), and glass transition temperature (T(g)) of whey protein isolate (WPI) films were studied at various pH values using sorbitol (S) as a plasticizer. The films were cast from heated aqueous solutions and dried in a climate chamber at 23 degrees C and 50% relative humidity (RH) for 16 h. The critical gel concentrations (c(g)) for the cooled aqueous solutions were found to be 11.7, 12.1, and 11.3% (w/w) WPI for pH 7, 8, and 9, respectively. The cooling rate influenced the c(g), in that a lower amount of WPI was needed for gelation when a slower cooling rate was applied. Both cooling rates used in this study showed a maximum in the c(g) at pH 8. The influence of the polymer network on the film properties was elucidated by varying the concentration of WPI over and under the c(g). Strain at break (epsilon(b)) showed a maximum at the c(g) for all pH values, thus implying that the most favorable structure regarding the ability of the films to stretch is formed at this concentration. Young's modulus (E) and stress at break (sigma(b)) showed a maximum at c(g) for pH 7 and 8. The MC and epsilon(b) increased when pH increased from 7 to 9, whereas T(g) decreased. Hence, T(g) values were -17, -18, and -21 degrees C for pH 7, 8, and 9, respectively. E and sigma(b) decreased and epsilon(b) and thickness increased when the surrounding RH increased. The thickness of the WPI films also increased with the concentration of WPI.     

Modification of the rheological properties of whey protein isolate through the use of an immobilized microbial transglutaminase

A process was developed in which calcium-independent, microbial transglutaminase (mTgase) was immobilized to controlled-pore glass. Avidin was adsorbed to glass beads that had been derivatized and biotinylated. The enzyme was biotinylated and adsorbed to the avidin affinity matrix. Solutions of 8% whey protein isolate (WPI) were then incubated with the mTgase beads, resulting in limited cross-linking of whey proteins. As incubation time increased, intrinsic viscosity increased, gelation temperature decreased, and stronger, more brittle gels were formed upon heating. This process allowed for recycling of the enzyme, eliminated the requirement for a downstream inactivation step, and permitted control over the extent of cross-linking. The functional properties of several batches of WPI were modified using <10 mg of the same enzyme, illustrating the capacity of immobilized enzymes to be used more frequently in applications of this nature.     

Cross-linking and rheological changes of whey proteins treated with microbial transglutaminase

Modification of the functionality of whey proteins using microbial transglutaminase (TGase) has been the subject of recent studies. However, changes in rheological properties of whey proteins as affected by extensive cross-linking with TGase are not well studied. The factors affecting cross-linking of whey protein isolate (WPI) using both soluble and immobilized TGase were examined, and the rheological properties of the modified proteins were characterized. The enzyme was immobilized on aminopropyl glass beads (CPG-3000) by selective adsorption of the biotinylated enzyme on avidin that had been previously immobilized. WPI (4 and 8% w/w) in deionized water, pH 7.5, containing 10 mM dithiothreitol was cross-linked using enzyme/substrate ratios of 0.12-10 units of activity/g WPI. The reaction was carried out in a jacketed bioreactor for 8 h at 40 degrees C with continuous circulation. The gel point temperature of WPI solutions treated with 0.12 unit of immobilized TGase/g was slightly decreased, but the gel strength was unaffected. However, increasing the enzyme/substrate ratio resulted in extensive cross-linking of WPI that was manifested by increases in apparent viscosity and changes in the gelation properties. For example, using 10 units of soluble TGase/g resulted in extensive cross-linking of alpha-lactalbumin and beta-lactoglobulin in WPI, as evidenced by SDS-PAGE and Western blotting results. Interestingly, the gelling point of WPI solutions increased from 68 to 94 degrees C after a 4-h reaction, and the gel strength was drastically decreased (lower storage modulus, G'). Thus, extensive intra- and interchain cross-linking probably caused formation of polymers that were too large for effective network development. These results suggest that a process could be developed to produce heat-stable whey proteins for various food applications.     

Water sorption properties of extruded zein films

Water interactions in extruded zein films were investigated through moisture sorption isotherms. Sorption isotherms of zein products were affected by composition and structure morphology. Zein powder showed moisture sorption hysteresis, which was not observed in extruded samples. Extruded samples held less moisture than zein powder, while films containing oleic acid showed further reduction in moisture uptake. Brunauer, Emmett, and Teller (BET) and Guggenheim, Anderson, and De Boer (GAB) models fitted well the moisture sorption isotherms of zein products. Monolayer values estimated by BET and GAB models were consistent with predictions based on zein structural models. Water vapor permeability (WVP) of zein films was affected by the relative humidity of testing environment. Higher relative humidity resulted in higher WVP.     

互花米草厌氧发酵渣活性炭处理含镉废水的研究

采用静态吸附法,进行磷酸活化法不同剂料质量比（0.5～3.0）及活化温度（400～700℃）条件下制备的互花米草厌氧发酵渣活性炭对镉的吸附性能研究,考察不同初始浓度条件下活性炭对镉的平衡吸附量,旨在以吸附法治理含镉废水,探索吸附机理、影响因素、除镉吸附剂的最佳制备条件以及活性炭物化性质对镉吸附性能的影响。结果表明,镉的吸附性能与活性炭的制备条件有关,随着活化温度的升高,镉的吸附量逐渐增大,主要是因为高温条件下活性炭表面PO34-充当活性位点,促进镉的吸附。当剂料质量比为1.0,活化温度为700℃时,制备出的活性炭对镉的吸附性能最好,其最大吸附量可达38.91mg·g^-1,远远高于商业活性炭。镉的吸附量随着溶液初始浓度的增加而增大,吸附等温线符合Langmuir方程。溶液pH和活性炭表面化学性质是决定镉吸附量大小的决定性因素,当溶液pH在2～4时,各活性炭对镉的吸附能力随pH的增加而增加。本文为含镉废水的处理提供了一种低价高效的方法。     

Effects of protein and peptide addition on lipid oxidation in powder model system

The effect of protein and peptide addition on the oxidation of eicosapentaenoic acid ethyl ester (EPE) encapsulated by maltodextrin (MD) was investigated. The encapsulated lipid (powder lipid) was prepared in two steps, i.e., mixing of EPE with MD solutions (+/- protein and peptides) to produce emulsions and freeze-drying of the resultant emulsions. EPE oxidation in MD powder progressed more rapidly in the humid state [relative humidity (RH) = 70%] than in the dry state (RH = 10%). The addition of soy protein, soy peptide, and gelatin peptides improved the oxidation stability of EPE encapsulated by MD, and the inhibition of lipid oxidation by the protein and the peptides was more dramatic in the humid state. Especially, the oxidation of EPE was almost perfectly suppressed when the lipid was encapsulated with MD + soy peptide during storage in the humid state for 7 days. Several physical properties such as the lipid particle size of the emulsions, the fraction of nonencapsulated lipids, scanning electron microscopy images of powder lipids, and the mobility of the MD matrix were investigated to find the modification of encapsulation behavior by the addition of the protein and peptides, but no significant change was observed. On the other hand, the protein and peptides exhibited a strong radical scavenging activity in the powder systems as well as in the solution systems. These results suggest that a chemical mechanism such as radical scavenging ability plays an important role in the suppression of EPE oxidation in MD powder by soy proteins, soy peptides, and gelatin peptides.     

Storage stability of microencapsulated cloudberry ( Rubus chamaemorus ) phenolics

Cloudberries ( Rubus chamaemorus ) contain phenolics (mainly ellagitannins), which have recently been related to many valuable bioactivity properties. In general, phenolics are known to react readily with various components, which may create an obstacle in producing stable functional components for food and pharmaceutical purposes. In this study, the aim was to improve the storage stability of cloudberry phenolic extract by microencapsulation. The phenolic-rich cloudberry extract was encapsulated in maltodextrins DE5-8 and DE18.5 by freeze-drying. Water sorption properties and glass transition temperatures (T(g)) of microcapsules and maltodextrins were determined. Microcapsules together with unencapsulated cloudberry extract were stored at different relative vapor pressures (0, 33, and 66% RVP) at 25 degrees C for 64 days, and storage stability was evaluated by analyzing phenolic content and antioxidant activity. Compared to maltodextrin DE18.5, maltodextrin DE5-8 had not only higher encapsulation yield and efficiency but also offered better protection for phenolics during storage. Without encapsulation the storage stability of cloudberry phenolics was weaker with higher storage RVP. Microencapsulation improved the storage stability of cloudberry phenolics. The physical state of microcapsules did not have a significant role in the stability of cloudberry phenolics because phenolic losses were observed also in amorphous glassy materials. The antioxidant activity of the microencapsulated cloudberry extract remained the same or even improved slightly during storage, which may be related to the changes in phenolic profiles.