Monitoring Freeze-Drying by Low Resolution Pulse NMR: Determination of Sublimation Endpoint

An NMR method was developed for detection of the sublimation period endpoint during the freeze-drying of potato pieces. Longitudinal (T₁ and transverse (T₂) relaxation times were estimated using rapid NMR methods. Samples were immediately examined to determine presence of a frozen core. The plot of T₁ vs T₂ showed an abrupt increase at a point corresponding to the complete elimination of the frozen core. Similar Tj vs T₂ curves were observed when monitoring freeze-drying of a single potato piece inside the NMR probe-head. The detection of an anomalous freeze-drying is possible by monitoring the T₁ the T₂ or the free induction decay signal.     

真空冷冻干燥紫甘薯叶的工艺研究

为了对采后紫甘薯叶进行充分的开发利用,提高农副产品的附加值及利用率,研究了紫甘薯叶真空冷冻干燥的最佳工艺参数。以冻干后紫甘薯叶的含水量为指标,利用正交试验对冻干过程的3个阶段进行了分析。并以色差变化为指标,采用正交试验研究了紫甘薯叶的最佳护色条件。研究表明:紫甘薯叶真空冷冻干燥最佳工艺过程为:预冻3h,升华干燥8h,解析干燥2h;最佳护色条件为:护色剂ZnCl2、质量浓度500mg/L、温度70℃、时间30s。     

Unique Hydration Behavior of Potato Starch as Determined by Deuterium Nuclear Magnetic Resonance

Deuterium Nuclear Magentic Resonance (NMR) measurements at 4.7 Tesla revealed a unique hydration behavior of potato starch that involved the presence of a tightly bound water population with anisotropic motions within the potato starch granule, even in the presence of excess, bulk water in potato starch slurries. Well-defined powder patterns with residual deuterium quadrupole splittings of about 1 kHz were also observed at 20°C for raw potato tubers. Three other water populations, a weakly bound, a surface-trapped, and a bulk water population, were also present up to 60% starch and were in fast exchange with each other at room temperature, resulting in a broadened, single Lorentzian ²H NMR peak. These three water populations were absent below 35% moisture content in potato starch, but not in corn starch. The unique hydration properties of potato starch might be important for novel processing methodology.     

NMR IMAGING, CALORIMETRIC, and MATHEMATICAL MODELING STUDIES of FOOD FREEZING

Nuclear magnetic resonance imaging (MRI), calorimetry, and temperature measurements were used to monitor cylindrical potato sections frozen at -11C and -42C. MRI showed the advance of the nonsymmetric freezing zone and loss of signal intensity as liquid water turned to ice. Differential calorimetry was used to follow heat removal during transient freezing. Measured times to 95% enthalpy change were 24 min (-42C) and 49 min (-11C), as compared to modeled values of 29 min (-42C) and 100 min (-11C). Times to 95% change in the NMR signal, integrated over the area of the image, were 21 min (-42C) and 56 min (-11C). Changes in NMR signal intensity could be correlated with the amount of unfrozen water remaining after a steady-state had been reached. At -42C, NMR indicated 25% unfrozen water remaining as compared to 26% by calorimetry, and 22% by modeling. At -11C, NMR measured 67% unfrozen water remaining as compared to 48% by calorimetry, and 25% by equilibrium modeling.     

Étude,par diffraction des rayons X,de I'influence de la cryodessiccation sur la structure cristalline de I'amidon

Examination on the Influence of Freeze-Drying on Crystalline Starch Structure by Means of X-Ray Diffractometry. The influence of freeze-drying on the crystalline structure of various starches (potato, wheat, maize, waxy maize, manioca, arrow-root) and wheat amylose has been examined by means of X-ray diffractometric diagrams. Only the crystalline structure of potato starch is altered by the treatment. A change in structure becomes apparent only, if freeze-drying is done slowly and if the water content of starch is above 25%, related to d. s. However, a restoration of the original structure of starch is possible, by moistening under certain conditions as described in the text. An explanation for the observations is proposed by means of a new hypothesis on structure organization of starch granules as well as the part of water as a determining factor for organization.     

不同干燥方式对紫薯全粉品质的影响

紫甘薯具有很高的营养价值,紫薯全粉的开发研究有利于其加工的扩大化和优质化。以紫薯为原料,通过鼓风干燥、真空冷冻干燥、真空干燥三种干燥方法对紫薯全粉的制备进行研究,探讨三种方式对于紫薯全粉基本化学成分、色差、碘蓝值、持水性和持油性、总花青素含量等品质的影响。通过对比实验得出结论,真空冷冻干燥对于紫薯全粉的基本化学成分、色差、碘蓝值、持水性和持油性、总花青素含量等品质的综合影响最小,真空干燥紧随其后。因此,为了保持紫薯全粉的完整性,同时考虑生产成本,在加工紫薯全粉过程中以真空干燥方法为最佳。     

Comparison of the consistencies of cooked mashed potato prepared from seven varieties of potatoes

Potato protein concentrates (PPC) were isolated from potato juice of seven studied varieties by thermal coagulation of 6.0–6.2 pH juices at 90–95 °C, followed by freeze-drying. Three levels of PPC were added to cooked mashed potato to raise the protein contents to 3, 4 and 5%, along with three levels of dry potato to obtain similar dry matter contents in mashed potatoes after the additions. The consistency of cooked mashed potato was measured objectively by a “back extrusion cell” connected to an Instron 1140 texturometer. Studied varieties differed in their consistencies of cooked mashed potato which increased with the dry matter content and increased after applying additives: (PPC and dry cooked potato). In spite of the similar dry matter contents the hardness of cooked mashed potato was higher when the PPC was used as an additive than with the dry potato addition.     

两种干燥方式对马铃薯全粉营养品质和加工特性的影响

以新鲜"云薯304"切片后,采用漂烫冻干、不漂烫冻干、漂烫烘干和不漂烫烘干四种工艺条件制备干片,再经研磨粉碎制成半生的马铃薯全粉,研究不同工艺条件下全粉的营养品质和加工特性。结果表明:采用漂烫冻干工艺,马铃薯全粉的颜色与鲜马铃薯颜色最接近,制备的马铃薯全粉还原糖含量最低,为0.15%;蛋白质含量(9.01%)、总淀粉含量(69.12%)、直链淀粉含量(31.60%)与其他三种工艺处理无显著差异;从加工特性上看马铃薯全粉的持水力(5.27 g水/g全粉)和持油力(1.55 g油/g全粉)、透光率(83.43%)和各个温度下的膨胀度(50℃:9.32 g/g;60℃:11.98 g/g;70℃:13.11 g/g;80℃:15.35 g/g;90℃:12.50 g/g)均最高,都显著高于其他三种工艺(P<0.05);且凝胶流程最短,为10.96 mm。因此,可认为漂烫冻干是制备马铃薯全粉的最优工艺。     

土豆冷冻干燥工艺的试验研究

本文对土豆冷冻干燥过程进行了深入研究，测得了土豆的共晶点和共熔点，对土豆的预处理工艺进行了试验研究，通过对土豆冻干试验因素的分析，得到了土豆的最佳冷冻干燥工艺。     

土豆泠冻干燥工艺的试验研究

本文对土豆冷冻干燥过程进行了深入研究,测得了土豆的共晶点和共熔点,对土豆的预处理工艺进行了试验研究,通过对土豆冻干试验因素的分析,得到了土豆的最佳冷冻干燥工艺.     

Chemical characterization and functional properties of a potato protein concentrate prepared by large-scale expanded bed adsorption chromatography

Native potato proteins consisting mainly of patatin and protease inhibitors were isolated from industrial potato fruit water by expanded bed adsorption (EBA) chromatography. The EBA-refined proteins were dried by different methods and the effect of drying-conditions on solubility, extent of denaturation, rheology and emulsifying properties was investigated. Drying methods include spray drying at varying outlet temperatures, vacuum freeze drying, fluid-bed and atmospherical freeze drying. Solubilities measured in the range pH 4-6 showed that the higher solubility was at pH 6 of around 65%, except for spray drying using an outlet temperature of 165 °C, which showed low solubility for all pH values. Spray drying at 90 °C and atmospheric freeze-drying emerged as the least deleterious methods with respect to retaining esterase and protease inhibitor activities, comparable to the vacuum freeze drying. The values obtained for the complex modulus suggest that potato protein is not a good gel former even when the protein was vacuum freeze dried. Emulsions prepared with xanthan as stabilizer were more stable at pH 6 compared to pH 4 judged from oil particle sizes. This study showed that potato proteins obtained under gentle isolation and drying conditions will provide interesting functional properties for potential application in food systems.     

冻融循环下抗冻多肽对冷冻马铃薯面团的品质保护及作用机理

通过将抗冻多肽添加到马铃薯面团中,研究在冻融循环条件下抗冻多肽对冷冻马铃薯面团品质的保护作用。在冻融循环条件下测定抗冻多肽（tilapia scale antifreeze peptides,TSAPP）对冷冻马铃薯面团的比容、发酵性能、失水率、淀粉糊化度、质构特性、水分分布与迁移等的影响及作用机理。结果表明：添加1% TSAPP使马铃薯面团比容增大、发酵时间缩短、淀粉糊化程度高、失水率降低;质构分析显示,与空白对照组相比,1% TSAPP组的马铃薯馒头硬度、咀嚼性和胶黏性分别下降了29.96%、26.99%、28.30%;核磁共振分析显示,TSAPP可以影响冷冻马铃薯面团中的水分状态使深层结合水含量增加,半结合水含量减少;TSAPP还能抑制水分流失,提高马铃薯面团的持水力。结论：抗冻多肽可作为冷冻马铃薯面团产品的低温保护剂。     

不同干燥方法对甘薯茎叶粉物化特性的影响

本试验研究了3种干燥方法(热风干燥、真空冷冻干燥及喷雾干燥)对五个品种甘薯茎叶粉(宁紫1号、徐053601、廊薯7-12、福薯2号和冀薯65)物化特性的影响,并采用主成分分析筛选甘薯茎叶粉物化品质评价指标。结果表明:不同干燥方法对甘薯茎叶粉的堆积密度、吸水指数、持油性和溶胀能力有显著性影响。经热风干燥的甘薯茎叶粉堆积密度最高,在0.54~0.67 g/cm3范围内;喷雾干燥后的甘薯茎叶粉吸水指数和持油性显著高于其他两种干燥方法,分别在13.73~17.40 g/g和3.0~5.0 g/g范围内,但溶胀能力显著低于另外两种干燥方法,仅为0.58~3.64 m L/g。主成分分析筛选出甘薯茎叶粉的物化品质评价指标分别为持油性、乳化活性、乳化稳定性和吸水指数;根据主成分分析结果筛选出最适宜制粉的甘薯茎叶品种为徐053601。综合考虑3种干燥方法对甘薯茎叶粉物化品质方面的影响,确定喷雾干燥为甘薯茎叶粉的最佳干燥方法。     

不同干燥方式对甘薯叶理化特性和抗氧化能力的影响

目的 探究三种不同干燥方式(微波干燥、热风干燥、冷冻干燥)对甘薯叶物化特性的影响。方法 以新鲜甘薯叶为原料,探究三种不同干燥方式对甘薯叶基本成分(水分、蛋白质、总膳食纤维、粗脂肪、可溶性糖、总酚、总黄酮和绿原酸含量)、物化特性(色度、微观结构、胆固醇吸附能力、持水力、持油力和葡萄糖吸附能力)和抗氧化活性(DPPH.清除率、ABTS法自由基抑制率、总还原力和.OH清除能力)以及酚类物质的组成等影响。结果 不同干燥方式对甘薯叶基本成分的影响中,利用热风干燥的甘薯叶水分含量最高,为7.96 g/100 g;冷冻干燥含水量最低,为7.29 g/100 g;冷冻干燥的蛋白质含量、粗脂肪、总酚、总黄酮以及绿原酸含量最高,分别为31.39 g/100 g、3.43 g/100 g、50.73 mg CAE/g DW、18.49 mg RE/g DW、7.05 mg/g DW;热风干燥的总纤维含量最高,为28.8 g/100 g。不同干燥方式对甘薯叶理化指标的影响中,利用冷冻干燥的甘薯叶色泽品质明显优于热风干燥和微波干燥;热风干燥的胆固醇吸附能力和持油力最强,分别为0.23 mg/mL,1.54 g/g;冷冻干燥的持水力和葡萄糖吸附能力最优,分别为7.33 g/g和12.00 mmol/g。抗氧化性上,不同方法测定的抗氧化能力都表现为冷冻干燥＞微波干燥＞热风干燥,冷冻干燥的总还原力、DPPH.清除能力、.OH清除能力、ABTS+^{清除率分别高达}83.34、41.28、9.17、27.21 mg Vc/g。结论 冷冻干燥最适合用来对甘薯叶进行干燥处理。     

NMR studies of changes in subcellular water compartmentation in parenchyma apple tissue during drying and freezing

The potential of Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) for non-invasively monitoring the subcellular and intercellular redistribution of water in cellular tissue during drying and freezing processes is assessed and it is concluded that despite exciting advances in NMR micro-imaging and NMR microscopy, nonspatially resolved NMR relaxation and diffusion techniques still provide the best probes of subcellular water compartmentation in tissue. The power of the NMR relaxation technique is illustrated by using the changes in the distribution of NMR water proton transverse relaxation times to monitor the subcellular compartmentation of water and ice during the drying and freezing of parenchyma apple tissue. The NMR drying data are analysed with a numerical model of the cell and show that mild air-drying in a fluidized bed results in loss of water from the vacuolar compartment, but not from the cytoplasm or cell wall regions. The loss of vacuolar water is associated with overall shrinkage of the cell and only a slight increase in air space. During freezing the vacuolar compartment is found to be the first to freeze, with the cytoplasmic and cell wall compartments only freezing at much lower temperatures. Freeze-drying apple tissue gives much lower water contents than fluidized bed drying, but the NMR data confirms that it destroys membrane integrity and causes cell wall collapse.     

Short communication: Effects of vacuum freeze-drying on inactivation of Cronobacter sakazakii ATCC29544 in liquid media with different initial inoculum levels

Vacuum freeze-drying is an important food-processing technology for valid retention of nutrients and bioactive compounds. Cronobacter sakazakii has been reported to be associated with severe infections in neonates through consumption of contaminated powdered infant formula. In this study, effects of vacuum freeze-drying treatment for 12, 24, and 36 h on inactivation of C. sakazakii with different initial inoculum levels in sterile water, tryptic soy broth (TSB), skim milk, and whole milk were determined. Results indicated that the lethality rate of C. sakazakii in each sample increased with the extension of vacuum freeze-drying time. With initial inoculum levels of 10² and 10³ cfu/mL, the survival of C. sakazakii in different liquid media was significantly affected by vacuum freeze-drying for 12, 24, and 36 h. In addition, the lethality rates of C. sakazakii in whole milk, skim milk, and TSB was significantly reduced compared with those in sterile water. Furthermore, whole milk showed the strongest protective role for C. sakazakii cells, followed by skim milk and TSB medium. Using the scanning electron microscope, the intracellular damage and obvious distortion of C. sakazakii cells were observed after vacuum freeze-drying for 24 and 36 h compared with the untreated sample, and the injured cells increased with the extension of vacuum-drying time. We concluded that inactivation of vacuum freeze-drying on C. sakazakii cells is related to the food matrix, and a combination with other methods for inactivating C. sakazakii is required for ensuring microbial safety of powdered infant formula.     

红薯叶复合面条热泵-热风联合干燥特性及干燥模型建立

将红薯叶粉添加到复合面条中,基于响应面法对红薯叶复合面条的热泵-热风联合干燥特性进行探究,运用低场核磁技术分析干燥过程复合面条内部水分迁移的质热传递规律,建立红薯叶复合面条联合干燥过程的数学模型.结果表明:随着热泵干燥温度的升高、转换点含水量的增大、热风干燥温度的升高,干燥所需能耗降低,有效水分扩散系数增大,煮制吸水率...     

Freezing of potato tissue pre-treated by pulsed electric fields

The effects of pulsed electric fields (PEF) pre-treatment on the freezing, freeze-drying and rehydration behavior of potato were studied. Potato samples (26 mm diameter, 10 mm high) were treated by PEF (400 V/cm) for various durations between 10⁻⁴ and 0.3 s. The degree of tissue damage was quantified by the change in electrical conductivity. PEF treated and untreated samples were either frozen in an air-blast freezer with air at −35 °C and 2 m/s velocity or freeze-dried at 0 °C and 0.04 mbar pressure and then rehydrated in water at 25 °C. The freezing times for PEF pre-treated samples reduced as the PEF-induced tissue damage increased. Scanning electron microscope images of the air-blast frozen and then freeze-dried samples showed increased deformation of cells and larger intercellular spaces (frozen samples only) for the PEF pre-treated samples. However, PEF pre-treatment improved the rate of freeze-drying and improved the quality and rehydration of the samples.     

NaCl-induced changes in structure and water mobility in potato tissue as determined by CLSM and LF-NMR

This study for the first time reports the combined use of low-field nuclear magnetic resonance (LF-NMR) and confocal laser scanning microscopy (CLSM) in the study of the effects of salting on low and high dry matter (DM) potato tissue. The simultaneous use of CLSM and NMR resulted in important information in relation to the interpretation of the origin of the NMR water populations. Salting caused the raw potato cells to loose weight, which in the microscopic images was observed as loss of turgor pressure still further away from the edges of the samples with increased salting time. The total water loss after salting was lowest for high DM potatoes. The LF-NMR analyses revealed that this could be ascribed to a faster T₂ relaxation time of the cytoplasmatic and extracellular water and thus to water being more restricted in high DM potatoes. In addition, a tendency to a faster T₂ relaxation time was observed for both low and high DM potatoes with increasing salting time, which reveals a salt-induced restriction of the cytoplasmatic and extracellular water population. The paper illustrates the aptitude of NMR and CLSM to determine and elucidate structural changes and associated changes in water mobility in potato tissue.     

Structural changes and shrinkage of potato during frying

Summary Light microscopy was used to study changes in cell size, blister formation and crust evolution during potato frying. Frying experiments with both French fries and crisps of different thickness (1–5 mm) were performed at temperatures of 140 and 180 °C. Thickness, volume and density changes were also measured. The formation of crust in French fries starts after the potato surface reached approximately 103 °C, and then the crust thickness increased linearly with the square root of frying time, this increase being faster at 180 °C. The potato volume decreased during frying, although in the late stages the volume may increase because of oil uptake and cell separation caused by entrapped water vapour. Shrinkage was adequately described by the Weibull model with a residual value, with shrinkage rate increasing with temperature and decreasing with potato thickness. The residual volume was not affected by temperature (65% for French fries and 59–30 for crisps, depending on thickness). Volume appeared to decrease mainly as the result of water loss, except for very low water content, and thus potato density changes were very small.