温度对浓缩乳蛋白复水过程的影响机制

充分复水溶解形成真溶液或均匀乳浊液是浓缩乳蛋白(MPC)应用的基础。通过考察不同温度条件下MPC复水过程中各主要成分的溶解行为变化,分析温度对MPC复水过程的影响。结果表明:温度通过影响粉粒中酪蛋白胶束成分的溶解速度而影响MPC复水速率。在25~45℃范围内,随温度提高,复水溶解速率显著增加;45~55℃下MPC在1 h内可完成复水,此时复水速率随温度变化差异不明显。复水过程中溶解相和非溶解相组成变化分析表明,MPC颗粒中乳糖和乳清蛋白成分容易分散溶解,而酪蛋白及其结合的钙、镁、磷溶解缓慢,是限制MPC复水溶解的主要因素。提高复水温度不能减少MPC不溶性成分含量。     

pH值与温度对乳粉复水性的影响

用乳粉代替鲜乳生产酸奶的过程中,乳粉复水性对酸奶的质构有很大影响。为考察乳粉复水性,研究了pH值和温度对乳粉复水性的影响。以乳粉黏度、粒径和溶解度等为考察指标,获得了乳粉复水的最佳的pH值和温度条件。结果表明,脱脂乳粉的复水性优于全脂乳粉,温度对乳粉的黏度、粒径和溶解度影响差异显著,通过寻优分析确定了工业乳粉复水性的最佳条件:pH值为6.8,温度55℃,此条件能够显著提高工业乳粉的复水性。     

复水条件对脱水香椿品质的影响

本文研究了不同复水条件处理后脱水香椿的香气成分、色泽、复水比、亚硝酸盐溶出率及维生素C保存率的变化。结果表明:复水温度40℃时,能较好地保护脱水香椿特征香气和萜烯类及含硫化合物等主要香气成分;随复水时间延长,脱水香椿L*降低,复水温度对其无显著影响;复水过程中a*先降低后升高,30 min时a*降至最低即颜色的绿值最大,b*亦较低,且复水温度40℃条件下a*和b*均最小;于复水温度40℃、料液比1:60(g/m L)条件下复水30-40 min,此时复水比及亚硝酸盐溶出率均较高;复水初期维生素C保存率大大降低,20 min后趋于平缓。适度降低复水温度和缩短复水时间有利于保护复水香椿的色泽、香气及营养素,并能保证其安全性。该研究为科学合理利用我国特色资源香椿提供技术依据。     

超声波处理对麻竹笋干复水特性的影响及动力学模型

为研究超声波处理对麻竹笋干复水特性的影响,在不同超声波功率(100、200、300、400、500 W)和超声温度(50、70、90℃)条件下,考察麻竹笋干复水比和复水速率的变化,并分别用Weibull模型、单项扩散模型和Page模型对麻竹笋干复水过程进行动力学拟合。结果表明,超声波功率和温度对麻竹笋干的复水均有较大的影响。随着温度的上升以及超声功率的增大,麻竹笋干的复水比和复水速率均增大。并且,随着超声处理时间的增加,复水比不断增大,复水速率逐渐降低并趋于恒定。当温度为90℃、超声波功率为500 W、超声波处理时间为120 min时复水比达到最大,且远远大于未经超声处理的笋干复水比。在3种动力学模型中,Page模型的实测值和预测值拟合程度最好(R~2 0. 99),能更好地用于描述麻竹笋干复水的过程。     

喷雾干燥温度对牦牛乳粉溶解特性的影响

为探讨喷雾干燥温度对牦牛乳粉溶解特性的影响,分析了在进风温度（出口温度）分别为130（56）、150 （64）、170（73）、190（81）、210（90）℃条件下喷雾干燥牦牛乳粉样品的溶解特性参数,并通过相关性分析对其进行聚类分析。结果表明：喷雾干燥温度对牦牛乳粉的溶解特具有显著影响（P＜0.05）,170（73）℃下喷雾干燥牦牛乳粉样品具有较高的水合能力、堆积密度、溶解度,较小的休止角和分散时间,具有较好的溶解特性,优于在其他温度下干燥牦牛乳粉的溶解特性;牦牛乳粉溶解特性参数间具有较好的相关性,聚类分析可实现对不同喷雾干燥温度条件下牦牛乳粉溶解特性的区分,为对喷雾干燥温度的评价提供参考。     

薇菜干复水工艺研究

选择不同的复水方式对二级薇菜干进行复水研究,以复水温度、复水时间和料液比为自变量,复水比和感官评分为评价指标,设计正交试验,研究各自变量交互作用及其对薇菜品质的影响。试验结果表明,在热-冷-热的复水方式下薇菜干最佳的复水工艺为:复水温度60℃,复水时间1 h,料液比1︰20(g/m L)。     

恒温及变温复水方式对脱水薇菜品质及复水动力学的影响

为探究复水方式对薇菜品质及复水动力学的影响,论文研究了恒温复水与变温复水条件下薇菜复水率、质构特性以及营养物质含量变化,并利用Weibull模型对复水过程进行拟合。结果表明:在恒温复水方式下,随温度升高,薇菜的水分含量升高,硬度、弹性、咀嚼性、还原糖、可溶性蛋白、总酚含量均降低,而抗氧化性先升高而后降低;在变温复水方式下,随温度升高,薇菜的水分含量与抗氧化性增大,硬度、弹性、咀嚼性、还原糖、可溶性蛋白、总酚含量均略有降低;变温复水方式下薇菜的品质高于恒温复水。Weibull模型能较好地模拟不同复水方式下薇菜复水过程。     

人造米复水过程水分传递特性的研究

对人造米复水过程中水分传递特性进行了研究，结果表明：含水量和温度对扩散系数有显著影响；在复水过程中，扩散系数随含水量增加而增大；与温度呈指数上升趋势，一定温度下的活化能与含水量呈正相关。     

气体射流冲击干燥猕猴桃片的复水动力学特性及数学模型

为了研究不同干燥条件和复水温度对猕猴桃片复水动力学的影响,实验监测了不同条件干燥猕猴桃片在相同复水温度下的吸湿曲线,并采用不同复水温度(30、50、70℃)对干制猕猴桃进行复水。此外,采用Peleg、Weibull、Proposed三个经典模型对干燥猕猴桃片的复水动力学进行拟合及验证。结果表明,干燥风温、风速以及喷嘴高度对产品的复水特性均有影响;复水速率随着风温、风速的增加和喷嘴高度的降低而增加。不同复水温度下,复水温度越高复水速率越快。Peleg、Weibull和Proposed模型均能有效描述猕猴桃干片的复水过程,其中Weibull模型具有最好的拟合度,其预测值与实验值呈良好的一致性,更适合于描述猕猴桃干片的复水动力学。     

海藻酸钠/丝素蛋白复合水凝胶的制备及性能研究

将海藻酸钠与丝素蛋白共混制备海藻酸钠/丝素蛋白水凝胶,探讨水凝胶成形过程及不同参数对水凝胶凝胶时间的影响及药物在海藻酸钠/丝素蛋白水凝胶中的缓释情况。试验表明:氯化钙/甲酸溶剂体系溶解脱胶蚕丝可以获得纳米原纤结构的再生丝素溶液,在凝胶过程中,复合水凝胶的凝胶时间随海藻酸钠的含量增加而延长,丝素蛋白/海藻酸钠比例为50/50时,凝胶时间需要89 min;当凝胶温度由15℃升至55℃时,凝胶时间由150 min缩短到55 min,因此可以通过调整海藻酸钠的比例、凝胶温度来调节复合水凝胶的凝胶时间;载药复合水凝胶释药曲线表明,药物释放过程呈先快后慢规律。     

Studies on the rehydration of carrots

The effects of different anions and of solution pH on the degree of rehydration of dehydrated carrots were measured by changes in tissue volume. The carrots had significantly greater rehydrated volumes when rehydrated in distilled water than in any of the salt solutions while the carrots in salt solutions containing citrate^3- had significantly lower rehydrated volumes than in the other salt solutions. This effect may be due to a steric hindrance to the penetration of the anions into the plant cells. In general, at pH values 2 and 12 the carrots rehydrated to a maximum extent. Probably the greater hydration in the solutions of extreme pH is due to their greater ability, in particular those with a pH of 12, to hydrolyse the hemicelluloses and the pectinates in the cell walls of the carrots.     

Structural properties of dehydrated products during rehydration

The following structural properties of dehydrated apple, banana, carrot and potato were examined during rehydration: true density, apparent density, porosity and specific volume. Samples were dehydrated using five different drying methods: conventional, vacuum, freeze, microwave and osmotic; after which they were rehydrated in an air dryer at 50 °C and 80% air humidity. Structural properties were examined during rehydration to various moisture contents, ranging from 0.01 to 3.5 kg kg^–1 (dry basis). The dehydrated products did not recover their structural properties after rehydration as a result of structural damage that occurred during drying and the hysteresis phenomenon which took place during rehydration. Porosity of the rehydrated products was higher during rehydration than during dehydration. A generalized structural model was used to describe the structural properties, and of the four parameters that were incorporated, only the shrinkage coefficient, which represents volume expansion, changed on rehydration.     

Viscoelastic behaviour of dehydrated products during rehydration

Viscoelastic behaviour of dehydrated products during rehydration of apple, banana, carrot and potato was examined under uniaxial compression tests. Samples were dehydrated with four different drying methods: conventional, vacuum, freeze and osmotic-freeze drying and after that they were rehydrated in an air dryer at 50°C and 80% air humidity. Compression tests were performed during rehydration for various moisture contents, ranging from 0.01 to 1.5 kg/kg dry basis. The viscoelastic behaviour of dehydrated products during rehydration were examined comparing the values of the four parameters incorporated into the stress–strain model, during rehydration with those of dehydrated products. The four examined parameters: maximum stress, maximum strain, elastic parameter and viscoelastic exponent seem to show a hysteresis phenomenon. It can be concluded that dehydrated product do not keep their viscoelastic behaviour after rehydration due to structural damages that occur during drying. More specifically, freeze dried materials present the highest hysteresis after rehydration, losing their elasticity and becoming more viscous. Osmotic pretreatment seems to help freeze dried materials to keep their elastic nature, probably due to solids gain. Air and vacuum dried materials showed the smallest hysteresis tendency, keeping their viscoelastic characteristics during rehydration close to those of dried materials.     

Drying and rehydration behaviors of green bell peppers

In this study, the drying behaviors of green bell peppers were examined in convection dryer. The study was carried out for 3 drying temperatures (55, 65, and 75°C) and for pre-treated samples with ethyl oleate solution against control samples. The pre-treated samples dried faster than the control ones. Drying time decreased with an increase of drying temperature. Rehydration ratio of the pre-treated samples was higher than control samples. Moisture transfer from green bell peppers was described by applying the Fick’s diffusion model and the effective moisture diffusivity (D _eff ) was calculated. The D _eff values for pre-treated and control samples varied between 0.705 and 2.618×10⁻⁹ m²/sec. Activation energy values for moisture diffusion ranged from 41.67 and 52.99 kJ/mol. Drying data was fitted to 4 thin-layer drying models, namely, Lewis, Henderson and Pabis, logarithmic, and Page. The best model, which best represented the green bell peppers drying, was logarithmic.     

Modelling of the rehydration process of brocolli florets

The aim was to study the rehydration kinetics of branched bodies such as broccoli florets, at different temperatures, and to this end a diffusional model was used considering the product structure as a sum of different sized cylinders. The rehydration rate was observed to increase with water temperature. The equilibrium moisture content of the product linearly decreased as the water temperature increased (r=0.95). A close fit between the model and the experimental data was obtained when the effective diffusion coefficient (D_eff) and equilibrium moisture content (W_e) were identified at each temperature (average explained %var=99.65). The temperature influence on D_eff was interpreted by the Arrhenius relationship, with an activation energy of 89.73 kJ/mol.     

青菜脱水工艺复水的研究

研究青菜干制品饱满度及干制品的复水性能。在烫漂3min后，浸入15％糊清＋15％蔗糖＋10％盐溶液30min，关在含水量70％时给予30－40kgf力1min的挤压，可显著提高青菜干制品复水率，与对照相比，可提高85％。     

改善真空冷冻干燥豌豆复水性的工艺研究

研究了漂烫和碱处理并用的方式提高豌豆种皮通透性,以及在漂烫水种添加海藻糖的工艺抑制豌豆淀粉老化,对冻干豌豆复水性的影响。试验结果表明,最佳碱处理方案为3%碱液在90℃条件下处理70s,可以有效解决真空冷冻干燥豌豆复水性差的问题;在漂烫水中添加5%的海藻糖,可有效解决糊化后的淀粉在冷冻脱水过程中发生老化,使得可溶性的α-淀粉比例缩小,增强复水性。     

非油炸方便面复水性的改善研究

探讨了干燥温度对非油炸方便面复水性的影响,研究了变性淀粉、复合磷酸盐、单甘酯和瓜尔豆胶在改善复水性中的作用。实验结果表明,最佳干燥工艺条件为105℃、30min,当添加变性淀粉6%、复合磷酸盐0.2%、单甘酯0.1%、瓜尔豆胶0.3%时,可以做出复水性好、口感佳的方便面。     

Normalized Weibull distribution for modeling rehydration of food particulates

Dehydrated food particulates have a rapidly growing market, and their reconstitution is essential in meeting consumers' expectations. Optimal reconstitution properties can be achieved by controlling the drying process and the rehydration conditions. Fundamentals of transport phenomena, particularly diffusion, external resistance and relaxation are some of the mechanisms governing water uptake during rehydration. The Weibull distribution is applied in many biological systems, and was found valuable in the modeling of the rehydration process. Simulation and experimental data showed that the traditional Weibull distribution should be normalized to account for product geometry, thickness and final water content. The Weibull -shape parameter varied with geometry and the mechanism of water uptake. The derived values for spheres, cylinders and slabs were for diffusion: 0.67, 0.72 and 0.81 respectively; for internal resistance: 1.00, 0.98 and 0.97 respectively; and for relaxation: 1.21, 1.32 and 1.60 respectively. The Weibull distribution provides an insight into the rehydration phenomena that govern water uptake by foods containing particulates during rehydration, and could be used for differentiating between diffusion, external resistance and relaxation processes.     

Effect of porosity on rehydration of dry food particulates

Rehydration of food particulates is a complex phenomenon affected by numerous factors that typically include pre‐drying treatments, mode of dehydration, structure, composition and medium viscosity. Freeze drying (FD), air drying (AD) and their combinations, were utilized to produce an array of porosities, ranging from very high to very low values for FD and AD carrots, respectively. Bulk porosity correlated significantly with open, but not with closed, porosity. Bulk and open porosities decreased with AD time. Scanning electron micrographs of the FD samples verified their organized and more open structure in comparison with the AD carrots. Rehydration ratio increased with bulk and open porosity, and was not affected by the closed porosity. The effective moisture diffusivity, derived from fitting the normalized Weibull distribution, increased with bulk and open porosity and was about two orders of magnitude higher for the FD, than for the AD, carrots. The Weibull shape parameter, β, was inversely related to porosity. Its values indicated that water uptake of only the AD carrots followed a Fickian diffusion. A critical porosity value above which water mechanism changed from a Fickian diffusion to imbibition into a porous medium is suggested. Copyright © 2004 Society of Chemical Industry