Mass transfer kinetics and mathematical modelling of the osmotic dehydration of orange‐fleshed honeydew melon in corn syrup and sucrose solutions

A simple mathematical model to predict dehydration and impregnation process during osmotic dehydration of orange‐fleshed honeydew in sucrose and corn syrup solutions was proposed. Results showed low dispersion and a good fitting capability for WL and SG kinetics. Diffusivity values for WL ranged from 0.96 × 10^?10 to 2.22 × 10^?10 and 1.04 × 10^?10 to 3.10 × 10^?10 m² s^?1 in corn syrup and sucrose solutions, respectively. For SG, the obtained range was 0.72 × 10^?10 to 2.35 × 10^?10 and 0.71 × 10^?10 to 2.46 × 10^?10 m² s^?1 in corn syrup and sucrose solutions, respectively. The half‐life of dehydration rates (t_1/2) was from 30.9 to 71.2 min and from 19.4 to 57.5 min in corn syrup and sucrose solutions, respectively. Diffusivities values obtained according to the proposed model were close to the ones observed from diffusive model; t_1/2 was a promising criterion for the process time definition.     

Mass transfer kinetics during osmotic dehydration of pomegranate arils

The mass transfer kinetics during osmotic dehydration of pomegranate arils in osmotic solution of sucrose was studied to increase palatability and shelf life of arils. The freezing of the whole pomegranate at -18 °C was carried out prior to osmotic dehydration to increase the permeability of the outer cellular layer of the arils. The osmotic solution concentrations used were 40, 50, 60°Bx, osmotic solution temperatures were 35, 45, 55 °C. The fruit to solution ratio was kept 1:4 (w/w) during all the experiments and the process duration varied from 0 to 240 min. Azuara model and Peleg model were the best fitted as compared to other models for water loss and solute gain of pomegranate arils, respectively. Generalized Exponential Model had an excellent fit for water loss ratio and solute gain ratio of pomegranate arils. Effective moisture diffusivity of water as well as solute was estimated using the analytical solution of Fick's law of diffusion. For above conditions of osmotic dehydration, average effective diffusivity of water loss and solute gain varied from 2.718 × 10(-10) to 5.124 × 10(-10) m(2)/s and 1.471 × 10(-10) to 5.147 × 10(-10) m(2)/s, respectively. The final product was successfully utilized in some nutritional formulations such as ice cream and bakery products.     

辣椒果肉的渗透脱水效果研究

研究了不同渗透溶液对辣椒果肉的脱水效果,从失水率、固形物增加率、含盐量和色泽变化等方面综合分析了不同浓度的纯糖溶液(50%和65%)、纯盐溶液(10%和20%)和糖盐混合溶液(10%盐,50%糖)的作用效果。结果表明,蔗糖和盐混合溶液的脱水效果最好,8h的失水率可以达到54.20%,可溶性固形物增加率仅有7.53%,且含盐量更是低于纯盐溶液的含盐量变化,只增加了2.62g/100g干基。在渗透后的颜色方面,混合溶液渗透后的变化差异没有纯溶液渗透后的明显。     

Mass transfer modelling of the osmotic dehydration of some fruits

An empirical model was developed to predict the water loss and solid gain during osmotic dehydration of apple, banana and kiwi fruit. The model is based on a first-order kinetic equation, in which the rate constant is a function of the main process variables (speed of agitation, solute concentration, size of fruit and process temperature). This model was applied to a wide range of experimental data on the osmotic dehydration of apple, banana and kiwi fruit, and its parameters were estimated using non-linear regression analysis. The results showed that all of the above process variables have a significant effect on the mass transfer phenomena during osmotic dehydration.     

Review characterization of edible films formulated with sodium alginate and low-methoxyl pectin in osmotic dehydration applications

The aim of this work was to evaluate the behaviour of two edible films (sodium alginate and low-methoxyl pectin) under different osmotic conditions (solutions: sucrose, glucose syrup and maltodextrin; concentrations: 40 °Brix and 60 °Brix; temperature 40 °C and processing times: 0.5, 1 and 2 h). From the experimental water loss and solid uptake kinetics, effective diffusion coefficients and the dehydration performance ratio were obtained. The microstructural characteristics of the osmodehydrated films were also analysed using pear as a food matrix. The results showed that films osmodehydrated with maltodextrin and glucose syrup solutions presented higher dehydration performance ratio values than those osmodehydrated with sucrose. A reduction in the thicknesses of edible coatings was observed. The best formulation was sodium alginate 2% and calcium lactate 5% according to the microstructural analysis and structural integrity for at least up to 16 h of osmotic dehydration.     

Osmotic dehydration of pomegranate seeds: mass transfer kinetics and differential scanning calorimetry characterization

Osmotic dehydration of pomegranate seeds was carried out at different temperatures (30, 40, 50 °C) in a 55°Brix solution of sucrose, glucose, and mixture sucrose & glucose (50:50, w/w). The most significant changes of water loss and solids gain took place during the first 20 min of dewatering. During this period, seeds water loss was estimated to 46% in sucrose, 37% in glucose and 41% in mix glucose/sucrose solution. The increase of temperature favoured the increase of water loss, weight reduction, solids gain and effective diffusivity. Differential scanning calorimetry data provided complementary information on the mobility changes of water and solute in osmodehydrated pomegranate seeds. The ratio between % frozen water and % unfreezable water decreased from 5 to 0.5 during the process. That involving the presence of very tightly bound water to the sample, which is very difficult to eliminate with this process. It also appeared that glass transition temperature depends on the types of sugar.     

Osmotic dehydration kinetics of carrot cubes in sodium chloride solution

Osmotic dehydration kinetics of carrot cubes in sodium chloride solution having concentrations 5%, 10% and 15% (w/v), solution temperature 35, 45 and 55 °C, sample to solution ratio (STSR) 1:4, 1:5 and 1:6 were studied up to 240 min duration. During the experimentation, effect of solution temperature and process duration was significant and that of solution concentration and STSR were non-significant on water loss. Among the different models applied (Penetration model, Magee Model, and Azuara model), Azuara model best fitted to the experimental data for water loss and solute gain during osmotic dehydration. Effective diffusivities of water and solute were calculated by using the analytical solution of Fick's unsteady state law of diffusion by iterative technique with a computer program. For the above conditions, the effective diffusivity of water was found to be in the range between 2.6323 × 10⁻⁹ and 6.2397 × 10⁻⁹ m²/s and that of solute between 3.1522 × 10⁻⁹ and 4.6400 × 10⁻⁹ m²/s.     

Mass transfer evaluation of ultrasonic osmotic dehydration of cherry tomatoes in sucrose and salt solutions

In order to elaborate dehydration and osmotic equilibrium characteristics of cherry tomatoes and to analyse the applicability of Peleg model in prediction of equilibrium moisture content and the methodology of Crank’s solution to Fick’s diffusion law in calculation of effective diffusivity, cherry tomatoes were osmotically treated in ternary solution (water, sucrose and NaCl) with or without ultrasound at 30 °C. Results indicated that, a time cumulative effect of ultrasound occurred about 30 min for water loss (WL), while for sugar gain it happened after 45 min, which made the dehydration efficiency index best at the ultrasonic power of 150 W for 40 min. As a function of salt content, the equilibrium WL followed well the first order exponential decay model, and the equilibrium salt content followed well the second order polynomial. A great relative error (29.13%) between the practical determination and the predicted value indicated that Peleg model was not suitable for prediction of equilibrium moisture content. A great truncation error (865%) occurred when moisture effective diffusivity (6.66 × 10^?9 m² s^?1) was calculated with Crank’s solution to Fick’s diffusion law by letting n = 1 as compared to that (0.77 × 10^?9 m² s^?1) by letting n = 100.     

Recent Development in Osmotic Dehydration of Fruit and Vegetables: A Review

Osmotic dehydration of fruits and vegetables is achieved by placing the solid/semi solid, whole or in pieces, in a hypertonic solution (sugar and/or salt) with a simultaneous counter diffusion of solutes from the osmotic solution into the tissues. Osmotic dehydration is recommended as a processing method to obtain better quality of food products. Partial dehydration allows structural, nutritional, sensory, and other functional properties of the raw material to be modified. However, the food industry uptake of osmotic dehydration of foods has not been extensive as expected due to the poor understanding of the counter current flow phenomena associated with it. However, these flows are in a dynamic equilibrium with each other and significantly influence the final product in terms of preservation, nutrition, and organoleptic properties. The demand of healthy, natural, nutritious, and tasty processed food products continuously increases, not only for finished products, but also for ingredient to be included in complex foods such as ice cream, cereals, dairy, confectionaries, and bakery products.     

Original article: Characterisation of water species revealed in the drying operation of Todarodes pacificus Steenstrup using water proton NMR analysis

For the discrimination of water molecules during the squid‐drying process, the water distribution was characterised by water proton NMR and moisture diffusivity (De) analysis methods as a function of the water content (W₀). The proton NMR spectrum showed three peaks indicating three different species (species‐A, ‐B, and ‐C) distributed in the squid muscle, each of which had a characteristic behaviour of the relaxation time (T₂) as a function of the W₀. The 1/T₂ of species‐A was drastically varied at W₀ = 120%‐d.b., indicating two further categories, i.e., species‐A₁ and ‐A₂. Species‐A₁ is available at W₀ > 120%‐d.b. and was characterised as having De = 5.1 × 10^?10 m² s^?1, activation energy of moisture diffusivity (E_D) = 17 kJ mol^?1, and relaxation rate 1/T₂ = 74 s^?1, as evaluated by the proton NMR spectrum without depending on W₀. Species‐A₂ is available at W₀ < 120%‐d.b., indicating a distribution of De = 4.8 × 10^?10–1.7 × 10^?10 m² s^?1, E_D = 25–35 kJ mol^?1 and 1/T₂ = 1.8 × 10³–1.5 × 10² s^?1 with increasing W₀. Species‐A₁ and ‐A₂ were assigned as weakly restricted water and strongly restricted water, respectively.     

健康信念模式在减重行为中的运用

肥胖患病率在世界范围内呈上升趋势,已经成为发达国家和发展中国家面临的最严重的公共卫生问题之一。导致超重或肥胖的危险因素主要有膳食、运动、饮酒等行为因素,行为改变对于预防和治疗超重和肥胖至关重要,其防治措施主要是建立健康的饮食、生活方式。健康信念模式是一个有效且合适的管理体重的工具。利用健康信念模式建立支持性的环境,树立肥胖者的信心,提供健康教育保证肥胖者理解肥胖的危害以及和许多疾病的相关性,可以达到减轻体重的目的。     

荧光观察方法检测水中大肠埃希氏菌的应用

目的比对2种荧光观察方法检测生活饮用水中大肠埃希氏菌的适用性、灵敏度及稳定性。方法使用全自动菌落计数器与传统多管发酵法2种方法对大肠埃希氏菌EC-MUG肉汤管进行荧光观察测试、分析。结果仪器法较传统法灵敏,EC-MUG肉汤管培养4h后使用仪器即可观察到蓝色荧光,6h后呈现深蓝色荧光,而传统法在6 h时荧光现象微弱呈淡蓝色, 10 h后荧光现象逐渐明显呈现蓝色。分别使用传统法与仪器法观察10组水样结果无差异。结论观察水中大肠埃希氏菌荧光现象时可使用仪器法和传统法,但仪器法更有优势,灵敏度高,操作简单,值得推广。     

《分析方法目的的适宜性》在农药残留检测领域的应用

目的以液相色谱-串接质谱联用仪(liquid chromatography-tandem mass spectrometry,LC-MS/MS)检测茶叶中丙草胺为例,按照欧盟《分析方法目的的适宜性》(以下称指南)进行方法确认。方法茶叶中的丙草胺用乙腈提取,经过石墨化炭黑和N-丙基乙二胺净化后,用液相色谱-串接质谱联用仪检测。结果目标化合物在0.039～0.625μg/L范围内线性关系良好,相关系数(r2)大于0.999。茶叶中丙草胺的定量限(LOQm)和检出限(LODm)分别为0.045、0.015μg/kg。不同加标浓度样品(LOQ、2LOQ、10LOQ)的平均回收率为90.0%～102.0%。重复性相对标准偏差为2.71%;中间精密度相对标准偏差为3.67%。结论本研究简化了样品前处理的方法,按照《指南》定义的9项要素对更改后的方法进行确认,并介绍了具体步骤。相关的检测结果均符合《指南》的要求,为单个实验室的方法确认和标准操作程序的编制提供参考。     

液相色谱-串联质谱法测定减肥降脂通便类保健食品中38种非法添加药物

目的建立液相色谱-串联质谱(liquid chromatography-tandem mass spectrometry,LC-MS/MS)测定保健食品中非法添加38种药物的方法。方法样品经甲醇超声提取,采用C18(2.1 mm×100 mm, 1.9μm)色谱柱,以0.1%甲酸水溶液-乙腈为流动相,梯度洗脱,流速0.3mL/min;质谱检测器为ESI源(正离子)选择反应监测模式进行定性、定量检测。结果 38种被测组分在5～100 ng/mL浓度范围内线性关系良好,相关系数均大于0.995。高、中、低3种添加浓度的平均回收率在70.8%～107.2%之间,相对标准偏差为2.1%～5.9%。方法学检出限均低于0.2μg/g。结论该方法专属性强、灵敏度高、操作简便、测定快速,可用于保健食品中38种非法添加药物的质量检控。     

Genotype and environment effects on nitrate accumulation in a diversity set of lettuce accessions at commercial maturity: the influence of nitrate uptake and assimilation, osmotic interactions and shoot weight and development

BACKGROUND: The causes of the natural variation in nitrate accumulation and associated traits are studied using a diverse population of 48 mature lettuce accessions grown hydroponically in winter and summer seasons. Information on the effects of genotype, environment and their interactions will inform future selection strategies for the production of low‐nitrate varieties more suited to meeting EU requirements for harvested produce. RESULTS: The effects of genotype (G), environment (E) and G × E interactions were all significant, with nitrate concentrations lower but covering a wider range in summer. Concentrations of nitrate‐N were positively correlated with those of water and total‐N and negatively with assimilated‐C in the shoot in both seasons, with all relationships partitioned according to morphotype and/or seasonal type. Corresponding relationships between nitrate‐N and assimilated‐N or with shoot fresh or dry weight were generally weak or inconsistent. Nitrate concentrations at an early growth stage were strongly related to those at maturity in winter, but not in summer when light levels were less variable. CONCLUSION: The effects of genotype and environment on nitrate accumulation in lettuce are strongly influenced by morphotype, with most G × E interactions between accessions within the same morphotype predominantly of the non‐crossover type. All low‐nitrate‐accumulating genotypes have increased concentrations of organic solutes (concentration regulation) and reduced water (volume regulation) to help stabilise osmotic potential within the shoots. Variability in nitrate accumulation arises more from differences in uptake than in efficiency of its chemical reduction. Genotypic differences in nitrate accumulation can be masked by changes in head morphology during maturation, provided that they are not confounded by substantial changes in intercepted light. Recent selection strategies do not appear to have produced lower‐nitrate‐accumulating cultivars. Copyright © 2011 Society of Chemical Industry     

Influence of an increased NaCl concentration on yield and quality of cherry tomato grown in posidonia (Posidonia oceanica (L) Delile)

Tomato plants cv Naomi were grown in posidonia (Posidonia oceanica (L) Delile) with two NaCl salinity levels in nutrient solution (EC: 3 and 6 dS m^?1) or with the NaCl level 3 dS m^?1, in the most frequently used substrate in soilless systems, eg rockwool, to determine the effect of substrate or EC on yield, contents of minerals, antioxidants with nutritional and health values (vitamin C, lycopene, α‐tocopherol and glutathione) as well as parameters affecting the organoleptic quality in cherry tomato fruits. Total yield was not influenced by substrate, but it was higher with 3 dS m^?1 than 6 dS m^?1 salinity. The yield reduction was compensated by the improvement of dry matter, total soluble solids, vitamin C and α‐tocopherol, while lycopene and glutathione contents were not affected by NaCl. On average, when tomato plants were grown in the presence of the higher NaCl level, the fruit diameter was between 25 and 35 mm (considered optimal for cherry tomato) while, with 3 dS m^?1, it was greater than 35 mm. Copyright © 2004 Society of Chemical Industry     

多种样品前处理方法在高分辨质谱法检测农药残留中的应用

食品、药品中的农药残留安全问题引起社会越来越多的关注, 农药残留检测方法为食品、药品安全监管提供技术支撑。高分辨质谱法由于具有较高的分辨率和质量精确度, 近年来在农药残留检测中的应用越来越多, 尽管高分辨质谱法能在一定程度上降低基质干扰, 但样品前处理仍然是必要的。样品前处理可以减少基质干扰成分, 提取、富集目标检测物, 对农药残留检测方法的准确度、灵敏度和重现性具有重要影响。本文对近年来高分辨质谱法检测农药残留所应用的前处理方法进行概述, 主要包括QuEChERS法、固相萃取法、极性农药快速提取法、在线前处理法等, 介绍了各前处理方法的原理和应用现状, 对不同前处理方法的优缺点进行分析, 并对高分辨质谱法检测农药残留所应用的样品前处理的发展趋势进行展望。     

超高效液相色谱-串联四级杆/飞行时间质谱法在 饮用水检测中的应用

目的应用超高效液相色谱-串联四级杆/飞行时间质谱结合二元比较的方法,对2种水样品进行检测研究,建立辨别饮用水质量的检测方法。方法样品经Oasis HLB固相萃取柱和滤膜过滤处理后,用含有10mmol/L乙酸铵的水溶液和含有10 mmol/L乙酸铵的甲醇溶液进行洗脱,再经超高效液相色谱分离后进入四级杆飞行时间质谱,实验通过保留时间、精确质量数、质量偏差等参数进行定性研究。结果通过二元比较找出2种水之间的差异,并鉴定出百治磷、阿特拉津、脱乙基阿特拉津、环嗪酮、莠谷隆、另丁津、邻苯二甲酸丁苄酯、噻嗪酮等8种污染物。结论此方法不仅能够直观地辨别出2种水样品的差异,而且可以准确鉴定差异化合物,适用于饮用水的检测研究。