Pulsed electric field treatment of carrots before drying and rehydration

BACKGROUND: In this study the effects of pulsed electric field (PEF) pretreatment were evaluated during drying and rehydration of carrots. Carrots pretreated with an electric field intensity of 1 kV cm^?1 (capacitance 0.5 µF, 20 pulses) or 1.5 kV cm^?1 (capacitance 1 µF, 20 pulses) as well as blanched (100 °C, 3 min) carrots were used for the study. Following pretreatment, samples were oven dried at 70 °C and then rehydrated in distilled water (1:30 w/v) at room temperature (24 ± 1 °C). RESULTS: PEF pretreatment increased the drying rate of carrots. However, the rehydration rate of PEF‐pretreated carrots was lower than that of blanched carrots. There were no colour differences between PEF‐pretreated and blanched carrots before drying and after rehydration. In terms of texture, PEF‐pretreated carrots were firmer than blanched carrots. PEF pretreatment reduced the activity of peroxidase by 30–50%, while blanching completely inactivated the enzyme (>95%). CONCLUSIONS: Overall, the results suggest that PEF could be an effective pretreatment during drying and rehydration of carrots. Copyright © 2009 Society of Chemical Industry     

预处理方式对胡萝卜变温压差膨化干燥品质的影响

探讨麦芽糖浆浓度、冷冻处理和水分含量3种胡萝卜预处理方式对胡萝卜变温压差膨化产品品质的影响。结果表明:用40%麦芽糖浆液煮沸处理20 min,在-18℃下冷冻处理24 h,胡萝卜的水分含量控制为40%,在膨化工艺为膨化温度110℃,停止时间5 min,干燥温度80℃,干燥时间150 min的条件下制备的膨化产品品质色泽亮丽、口感酥脆。     

基于热风干燥条件下新疆红枣的质构特性

以新疆主栽制干品种骏枣、灰枣和哈密大枣为研究对象,探讨热风干燥条件下各品种间的基本营养成分与质构特性。并通过DPS和SPSS软件分析了这3种红枣间不同指标的差异,结果表明:3个品种总糖含量均≥59%,除还原糖含量外,其它各营养成分差异不显著（p>0.05）;3个品种间的主要质构指标:硬度、回复性、内聚性、弹性、胶粘性、咀嚼性,存在显著性差异（p<0.05）;糖、水分与质构特性有明显的相关性,即:红枣中水分与弹性负相关R=-0.934、还原糖与咀嚼性呈正相关R=0.989,通过质构指标的主成分分析得出,红枣的质构特性构成主要在第一和第二主成分上,其中在第一主成分中胶粘性、硬度和咀嚼性三个指数所占权重系数分别为0.935、0.886和0.885,第二主成分中,弹性权重比较大为0.975,由此得出胶粘性、硬度、咀嚼性、弹性四种指标可基本评价红枣的质构特性。      

胡萝卜的气体射流冲击烫漂与干燥试验研究

以胡萝卜为研究对象,研究气体射流冲击的烫漂湿度及干燥条件对胡萝卜复水特性和色泽的影响。结果表明,烫漂湿度和干燥温度对复水率的影响较大,胡萝卜的复水率在较高的烫漂湿度时较高,但随温度的升高而降低。烫漂湿度对色差值的影响最大,其次是干燥温度,干燥风速对色差值的影响不大。烫漂湿度越大,复水后色泽越佳。     

Optimisation of convective drying of carrots using selected processing and quality indicators

The effect of drying temperature (40–65 °C) and air rate (2–6 m s^?1) on the formation of Maillard reaction indicators and vitamins content of carrots dehydrated by convection has been investigated. The range of assayed processing conditions, based on a previous central composite face design (CCD), led to moderate changes in the studied parameters, even under the most severe conditions. In addition, the drying kinetic of the process was studied taking into account the experimental quantitation of shrinkage, which allowed the determination of a first drying period with a constant rate of water evaporation per unit of exchange surface. The slope of the first drying period, the moisture loss during the first hour of drying and the level of quality parameters (Maillard reaction indicators and vitamins) were correlated with processing conditions with high accuracy. For the prototype here used, the optima temperature and air rate to maximise the desirability function (0.77) were 46 °C and 4.9 m s^?1.     

Physicochemical,textural and viscoelastic properties of palm diacylglycerol bakery shortening during storage

BACKGROUND: Diacylglycerol (DAG), which has health‐enhancing properties, is sometimes added to bakery shortening to produce baked products with enhanced physical functionality. Nevertheless, the quantity present is often too little to exert any positive healthful effects. This research aimed to produce bakery shortenings containing significant amounts of palm diacyglycerol (PDG). Physicochemical, textural and viscoelastic properties of the PDG bakery shortenings during 3 months storage were evaluated and compared with those of commercial bakery shortening (CS). RESULTS: PDG bakery shortenings (DS55, DS64 and DS73) had less significant increments in slip melting point (SMP), solid fat content (SFC) and hardness during storage as compared to CS. Unlike CS, melting behaviour and viscoelastic properties of PDG bakery shortenings remained unchanged during storage. As for polymorphic transformation, CS contained only β crystals after 8 weeks of storage. PDG bakery shortenings managed to retard polymorphic transformation for up to 10 weeks of storage in DS55 and 12 weeks of storage in DS64 and DS73. CONCLUSION: PDG bakery shortenings had similar if not better storage stability as compared to CS. This is mainly due to the ability of DAG to retard polymorphic transformation from β′ to β crystals. Thus, incorporation of DAG improved physical functionality of bakery shortening. Copyright © 2010 Society of Chemical Industry     

响应面分析热风微波耦合干燥胡萝卜片的形变

为减少干燥过程中的能耗,提高产品体积保留率,提出微波热风耦合干燥方法,运用响应面分析法对影响因素进行优化,提出干燥收缩数学模型,优化参数结果为微波功率密度1.9 w/g,热风温度65℃,胡萝卜片厚度5 mm为最佳组合参数,该参数下体积保留率提高10%,同时干燥能耗是传统热风干燥的21.27%.     

Effects of process parameters on quality changes of shrimp during drying in a jet-spouted bed dryer

ABSTRACT:  The objective of the present study was to investigate the effects of various parameters, that is, concentration of salt solution (2%, 3%, 4%[w/v]), boiling time (3, 5, 7 min), drying air temperature (80, 100, 120 °C), and size of shrimp, on the kinetics of drying and various quality attributes of shrimp, namely, shrinkage, rehydration ability, texture, colors, and microstructure, during drying in a jet-spouted bed dryer. In addition, the effects of these processing parameters on the sensory attributes of dried shrimp were also investigated. Small shrimp (350 to 360 shrimp/kg) and large shrimp (150 to 160 shrimp/kg) were boiled and then dried until their moisture content was around 25% (d.b.). It was found that the degree of color changes, toughness, and shrinkage of shrimp increased while the rehydration ability decreased with an increase in the concentration of salt solution and boiling time. Size of shrimp and drying temperature significantly affected all quality attributes of dried shrimp. The conditions that gave the highest hedonic scores of sensory evaluation for small dried shrimp are the concentration of salt solution of 2% (w/v), boiling time of 7 min, and drying air temperature of 120 °C. On the other hand, the conditions that gave the highest hedonic scores of sensory evaluation for large dried shrimp are the concentration of salt solution of 4% (w/v), boiling time of 7 min, and drying air temperature of 100 °C. The quality attributes of dried shrimp measured by instruments correlated well with the sensory attributes, especially the color of dried shrimp.     

不同干燥方法对胡萝卜粉品质特性的影响

通过对热风干燥、真空干燥、微波干燥及微波-真空干燥4种方法制的胡萝卜粉的粉体特性指标的分析及对比研究,对4种加工工艺生产的胡萝卜粉的品质特性进行了评价,微波-真空干燥制成胡萝卜粉不仅品质好,而且干燥时间短,是一种较好的胡萝卜粉制备方法。     

Physical properties of goat milk powder with soy lecithin added before spray drying

In this study, physical characteristics of goat milk powder produced with the addition of soy lecithin at levels of 0 (control), 0.4, 0.8 and 1.0 g lecithin/100 g of total solids in concentrated milk before the spray drying process were investigated. Goat milk was pasteurised, concentrated at 40% of total solids, spray dried and packed in plastic bags under vaccum conditions. Lecithin addition decreased the wetting time of milk powders, although no influence was observed on dispersibility, water sorption, water activity and particle size distribution of the powders. Powders with higher levels of lecithin showed significantly lower brightness, with a greater intensity of yellow colour. It was concluded that lecithin addition before spray drying process at the minimal proportion in concentrated milk of 0.4 g lecithin/100 g of total solids in concentrated milk is useful for achieving more rapid wetting time of goat milk powder.     

Physicochemical and functional properties of chitosans affected by sun drying time during decoloration

The typical production of chitosan from crustacean shell consists of demineralization, deproteinization, decoloration, and deacetylation. Selected physicochemical and functional properties of chitosans as affected by various decoloration times (4, 5, 6, 7 or 8 h) using sun drying were evaluated. Moisture content (6.67-6.89 g/100 g), degree of deacetylation (81.91-82.73%), and color L^∗ value (78.32-79.43) of chitosans were not affected by sun drying time. However, color a^∗ and b^∗ values decreased when sun drying time was over 4 h. The viscosity of chitosan solution (0.5 g/100 mL acetic acid) decreased gradually with increasing sun drying time, with a more pronounced effect observed at 8 h of sun drying. There was no change in water-binding capacity (WBC) of chitosans decolorized by sun drying between 4 and 6 h; however, further increase in sun drying time from 6 to 7 or 8 h increased WBC of chitosans. DPPH radical scavenging activity of chitosans increased with increasing sun drying time. This study demonstrated that white-colored chitosans could be produced by an alternative decoloration step using sun drying for 4 h following the deacetylation step. However, increasing sun drying time to 7 h produced chitosan with increased WBC and DPPH radical scavenging activity.     

鸡肉火腿肠贮藏期间应力松弛特性及质地评价

研究鸡肉火腿肠贮藏期间应力松弛特性、TPA质地参数变化规律.结果表明:贮藏时间对阻尼体黏滞系数η影响不显著,对其余3个松弛参数影响均极显著;在10℃和5℃条件下,贮藏温度对4个松弛参数影响均不显著.贮藏时间对硬度和耐咀性有较为显著的影响,对内聚性和弹性影响不显著;贮藏温度对4个TPA质地参数的影响是不显著的.在整个贮藏过程中,鸡肉火腿肠的质地没有发生较大的变化,仍保持较好的食用品质.经高温处理,鸡肉火腿肠松弛特性显著降低,其质地变得更加柔软、易嚼.     

微波真空干燥胡萝卜片过程中收缩变形的数学模型研究

研究胡萝卜片微波真空干燥过程中物料的收缩变形,利用正交试验,得出各因素对胡萝卜片干燥变形的影响程度大小及因素之间的相互影响关系,通过数学回归,得到胡萝卜片微波真空干燥过程收缩变形的数学模型方程,并对方程的显著性检验以及参数进行了综合优化,提出了胡萝卜收缩变形较小的微波真空干燥工艺参数的最佳组合.     

An improved viscoelastic model for tufted carpet yarn

To overcome the problem that the existing mathematical model cannot characterize the viscoelastic properties of tufted carpet yarn completely and accurately, an improved viscoelastic model is built using the semi-empirical method. Using the test data of creep and stress relaxation, the parameters of the improved model are determined. Through the evaluation of fitting effect, the optimal mechanical model to characterize the viscoelastic properties of tufted carpet yarn is obtained. The results show that compared with the standard linear model, the improved model is more suitable to characterize viscoelastic mechanical properties of tufted carpet yarns, such as the creep and stress relaxation properties, which provides a solid theoretical foundation for analysis of vibration characteristics and dynamic tension control of tufted carpet yarn.     

太阳能蒸汽热风干燥系统的设计与研究

研制一套太阳能干燥系统,采用真空集热管对水加热,产生水蒸气,并转换成热风,实现对农产品的干燥作业。以胡萝卜作为样品进行干燥机的干燥性能试验,结果表明:当太阳辐射值达到750 W/m2以上时,蒸汽可以稳定工作5～7h;干燥室内高温工作段温度可以稳定在55℃左右,低温工作段温度可以稳定在40℃左右。干燥后的胡萝卜脱水率为82.3%～86.5%,干燥效果良好。     

Stress and crack prediction during drying of Japanese noodle (udon)

The distribution of stress during drying of fresh Japanese noodle (udon) was investigated by mathematically modelling the changes in shrinkage and other mechanical properties, this allowed crack formation to be predicted. It was observed that the shrinkage coefficients were nearly the same in all three directions with changing moisture content, and the degree of shrinkage was independent of the temperature. The Young's modulus, yield stress and fracture stress could be expressed as exponential functions of moisture content. Changes in stress distribution during drying were calculated by coupling the moisture transfer equation with the constitutive equation using a finite element method. The calculated stress distribution indicated that a rapid drying rate causes extensive internal tensile stress in udon. The scheme used in the present study was found to effectively represent the potential for crack formation along the central axis, this was shown to be consistent with the actual cracking pattern.     

Physical and mechanical properties of chitosan films as affected by drying methods and addition of antimicrobial agent

Incorporation of an antimicrobial agent into a biopolymer matrix not only affects the antimicrobial property, but also the physical, mechanical and barrier properties of the resulted films. In addition to the effect of antimicrobial agent different drying methods that are used to prepare the films should also be considered. The aim of this study was to investigate the combined effects of drying methods, namely, hot air drying and low-pressure superheated steam drying (LPSSD), and addition of a natural antimicrobial agent, namely, galangal extract, at concentrations of 0%, 0.6%, 0.9%, 1.2% and 1.5% (w/w film forming solution) on selected physical properties (thickness, moisture content, color and opacity), mechanical properties (tensile strength and percent elongation), barrier properties (water vapor and oxygen permeabilities), degree of crystallinity and degree of swelling of antimicrobial films prepared from chitosan. X-ray diffraction (XRD) analysis, Fourier-transform infrared (FTIR) spectroscopy as well as dynamic mechanical analysis (DMA) were also performed and their results used to explain the observed combined effects. The combined effects were noted to have a statistically insignificant influence on the moisture content, thickness and water vapor permeability of the films. On the other hand, the combined effects had a statistically significant influence on the color, degree of crystallinity, degree of swelling, tensile strength, percent elongation and oxygen permeability of the films. Only the galangal extract concentration had a statistically significant influence on the film opacity. The DMA patterns and FTIR spectra confirmed the formation of crosslinkage interactions between the galangal extract and chitosan matrix.     

Changes of microwave structure/dielectric properties during microwave freeze‐drying process banana chips

This experimental study investigated the trend of structure and dielectric properties during microwave freeze‐drying process banana chips. The mass of banana samples was 160 g, the microwave power set as 2 W g^?1 and the highest drying temperature set as 55 °C. The whole drying process can be finished within 6 h. A network analyser and light microscope were used to determine the dielectric properties and structure. The dielectric properties, ε′ (from 20.80 to 1.20) and ε′′ (from 7.74 to 0.15), and the size of cell get smaller as the drying process continues, especially during the 3–4 h drying, which is the end of primary drying stage and the beginning of secondary drying stage. The trend of dielectric properties and microstructure of samples during drying can be an exact indication of drying stage of MFD.