Molecular thermodynamics modeling of equilibrium moisture in foods

Moisture content in foods affects many aspects of processing and storage, as well as quality and pathological activity. Understanding its behavior is very important in the food industry for designing effective long-term food management strategies, in particular transportation and storage. Most approaches found in the literature dealing with moisture in foods consist of measuring it as a function of relative humidity and temperature and then fitting the data to empirical or semi-empirical models for interpolation or correlation purposes. Most semi-empirical models are modifications of early gas adsorption models on hard surfaces, which fundamentally are not well suited to describe water in softer materials such as foods. In this work, we propose and use a more general framework based on equilibrium molecular thermodynamics to model and correlate equilibrium moisture content (EMC) in foods that takes into account other non-adsorption phenomena such as mixing and swelling of the biopolymers in foods. The framework is general, and the current model shows very good results correlating and modeling EMC. The model parameters provide insight into the nature of the water activity in food products, providing potentially useful information for food processing and modeling.     

Water agar-agar equilibrium: determination and correlation of sorption isotherms

Summary Water activity in hygroscopic solids determines the behaviour of many materials in storage as well as in drying and freezing operations. Available data concerning phycocolloid gels, such as those of agar-agar and derivatives, are scarce in spite of their interest for pharmacology and the food industry. Thus, we have determined the isotherms of adsorption and desorption of agar-water gels by means of a gravimetric procedure, at 25, 40, 60 and 80 °C, determining the effect of temperature on the heat of desorption by the isosteric heat method, using the Henderson model.     

等压灌装阀中弹簧设计的探讨

弹簧设计对于等压灌装阀的性能起着决定性的作用。本文探讨密封力等因素对弹簧设计的影响。     

CO2膨胀回收塔中沉积物挥发及半挥发性成分分析

为寻找膨胀后烟丝香气损失较大,刺激性增加,口感不理想等缺陷的原因,对气态、液态CO2回收塔中的沉积物进行了吸附热脱附-气相色谱/质谱分析,发现其中有许多烟草中的致香物质,特别是新植二烯、十六酸和十八酸等在沉积物中的含量很高.认为膨胀过程中某些致香物质的大量流失可能是膨胀烟丝品质变差的主要原因.     

Estimating the theoretical energy required to dry rice

The total heat of desorption of rice (Q_t) was determined for several rice types as a function of moisture content (MC), and kernel temperature, using a semi-theoretical approach in which desorption isotherms were used in conjunction with the Clausius-Clapeyron equation. Q_t decreased exponentially as MC increased, decreasing sharply for MCs above 15% and approaching the latent heat of vaporization of free water at MCs around 20%. Q_t of parboiled rice at 12.5% MC was significantly less than that of non-parboiled lots. Q_t of medium-grain “Jupiter” was significantly greater than that of long-grains at 12.5% MC. Equations that predict the energy required to dry a unit mass of rice from an initial MC to a final MC were derived.     

冷等离子体处理的小麦次粉单分子层水和结合水特性研究 （网络首发、推荐阅读）

为了解释冷等离子体（CP）处理提高小麦次粉吸水率,采用动态水分吸附仪测定120W低压强射频氦或氧CP处理不同时间样品的水分吸着等温线。结果表明,Caurie方程能够拟合出等温线,其系数C0给出样品吸附水的密度,对吸附或解吸样品,随着同一功率氦或氧CP处理时间增加,吸附水的密度没有差异,而系数M0给出样品单分子层吸附水含量,对吸附或解吸样品,随着同一功率氦CP处理时间增加,单分子层水含量显著增加;对氧等离子体处理的样品,其吸附单分子层水含量随着处理时间增加则先减少后增加,而解吸单分子水含量随着处理时间增加呈现减少趋势。为了提高Caurie方程的拟合度,将M0修正为A+Bt(t是温度,A和B是常数)。分析修正Caurie方程的系数显示,随着120 W氦CP处理次粉时间（0～180 s）的增加,单分子层水、吸附水分子层数、结合水含量及水吸附表面积均呈现持续增加的趋势;对氧CP,这些指标在前60s处理呈现增加趋势,之后再延长处理时间则显示减少趋势。结果表明,与氧冷等离子体比较,高能量的氦冷等离子体改善了次粉蛋白质和多糖的亲水性,随着处理时间延长,这些大分子吸附水的表面积和层数、单分子层和结合水...     

Desorption isotherms of shelled maize: whole, dehulled and hulls

Water vapour desorption isotherms of whole kernel maize were determined at 40, 50 and 60°C, and those of dehulled kernels and hulls at 50 and 60°C. It was found that while whole and dehulled kernels show similar equilibrium moisture contents, the hull gives lower values. Equilibrium data were modelled with two-parameter equations. It was found that the Henderson equation is best for describing the equilibrium data for whole kernels, while the Halsey equation was more appropriate for hulls. A simple semi-theoretical equation was used to model the effect of temperature on the equilibrium values of whole maize kernels for the three temperatures investigated. BET heats of desorption and the isosteric heat curves were calculated for whole kernels and hull. It was found that the BET heat values correlate quite well with the isosteric heat values at the monolayer moisture content.     

Water activity of multicomponent mixture of solutes and non-solutes

An equation has been derived to calculate the water activity (A_w) of multicomponent mixtures of solutes and non‐solutes. The equation is based on a previous Caurie adsorption equation and it depends on the number of component ingredients and the initial moisture contents of the ingredients in the mixture. Solute and non‐solute/water interaction effects in solution were identified as playing important roles in determining accurate equilibrium A_ws of the aqueous mixtures. The new equation allows for interaction effects in mixed solution/suspensions and has been tested on model foods (the data was taken from the literature) containing up to five solutes and non‐solute components. The equation displays a high degree of accuracy. Unlike the Ross equation, which applies only approximately to mixtures of dilute solutions, the new equation applies to mixtures at all solution concentrations and to wet solids.     

Microbial modeling in foods

Predictive food microbiology is a field of study that combines elements of microbiology, mathematics, and statistics to develop models that describe and predict the growth or decline of microbes under specified environmental conditions. Models can be thought of as having three levels: primary level models describe changes in microbial numbers with time, secondary level models show how the parameters of the primary model vary with environmental conditions, and the tertiary level combines the first two types of models with user‐friendly application software or expert systems that calculate microbial behavior under the specified conditions. Primary models include time‐to‐growth, Gompertz function, exponential growth rate, and inactivation/survival models. Commonly used secondary models are response surface equations and the square root and Arrhenius relationships. Microbial models are valuable tools in planning Hazard Analysis, Critical Control Point (HACCP) programs and making decisions, as they provide the first estimates of expected changes in microbial populations when exposed to a specific set of conditions. This review describes the models currently being developed for food‐borne microorganisms, particularly pathogens, and discusses their uses.     

食品中氟离子的分析方法

介绍了近几年来离子选择电极法、比色法、离子色谱法、液相色谱法以及气相色谱法对食品中氟离子的分析进展,并对今后的发展作了展望。     

Increased supercooling in irradiated foods

The supercooling temperatures of γ-irradiated and control cod, mushroom, and two chicken samples were measured using a Differential Scanning Calorimeter (DSC). The mean supercooling temperatures were significantly lower in three out of the four samples of the irradiated foods, suggesting that the effect might be the result of irradiation. There was high variability between samples and a possible dependence on spoilage which require further investigation to assess the potential of the test for detecting irradiated foods.     

叶黄素在食品中的应用

探讨了叶黄素在饮料和果冻中的应用,并对其物理稳定性和化学稳定性进行评价。     

Occurrence of fumonisins in foods

Fumonisins (FB) are synthesized mainly by different species of the genus Fusarium and FB1 is the predominating fumonisin isolated in foods. FB1 shows different toxicological effects in humans and animals and has been associated with esophageal cancer in different countries. This review presents an overview of the worldwide occurrence of fumonisins in crops and human foods being corn and corn meal the most contaminated foods, and reviews variations of the presence of these mycotoxins in foods and in agricultural crops. In foods, these variations are due to the alkaline solutions, water and temperature. For agricultural crops, the role of climatic conditions and latitude, genotypes, spoilage and other fungal diseases is reviewed.     

Studying the effects of adsorption,recoalescence and fragmentation in a high pressure homogenizer using a dynamic simulation model

The emulsification in a high pressure homogenizer was studied using a dynamic simulation model based on the population balance equation. The model includes fragmentation, recoalescence and adsorption of macromolecular emulsifier and uses a simple flow model in order to link the hydrodynamics in the homogenizer to the three physical processes mentioned above.     

Determination of phthalate diesters in foods

Methodology for the determination of 15 phthalate diesters (dimethyl phthalate, diethyl phthalate, diisopropyl phthalate, diallyl phthalate, diisobutyl phthalate, di-n-butyl phthalate, di-n-pentyl phthalate, di-n-hexyl phthalate, benzyl butyl phthalate, dicyclohexyl phthalate, di-(2-ethylhexyl) phthalate, di-n-octyl phthalate, diisononyl phthalate, diisodecyl phthalate, and di-n-decyl phthalate) is described. The method was validated in-house and its broad applicability demonstrated by the analysis of high-fat, high-carbohydrate and high-protein foodstuffs as well as combinations of all three major food constituents. Following on from the analysis of the 20 UK Total Diet Study samples, 261 foodstuffs were purchased and tested for their phthalate levels. Phthalate diesters were confirmed to be present in 77 samples. Di-(2-ethylhexyl) phthalate was the most frequently detected (66 samples), although the highest levels found were for the isomeric mixture diisononyl phthalate. Additional studies confirmed that, for some foodstuffs, packaging materials did contribute to the phthalate diester concentration in the foodstuff and one example is presented.     

食品中镉研究进展

镉是一种重金属毒物,除可造成急、慢性中毒,还有一定致畸、致癌和致突变作用。机体摄入镉的最主要途径是食品,而食品中镉主要来自环境污染,因此,监测环境、食品原料、食品包装材料及食品中镉含量,是控制人体镉摄入量,预防和减少镉对人体危害重要措施。该文主要综述近期对食品中镉的研究进展。     

Estimation of biogenic amines in foods

Biogenic amines in foods have been proposed as initiators of dietary-induced migraine. Studies of levels of 2-phenylethylamine, p-tyramine and the diamines histamine, putrescine and cadaverine in a number of Australian and other foods were made by ion exchange and high pressure liquid chromatographic methods. In the latter method the amines were chromatographed as their fluorescamine derivatives. The use of such derivatives also enabled confirmation of the identity of the amine by field desorption-mass spectrometry. Extraction procedures were devised to give satisfactory recoveries of amines in foods and to overcome problems associated with the binding of amines to other food constituents.     

食品中叔丁基对苯二酚的检测方法

随着食品工业的快速发展,食品添加剂违规添加现象屡禁不止。叔丁基对苯二酚是一种被广泛应用于油脂食品的抗氧化剂,其在食品中的检测日益受到重视。通过介绍食品中叔丁基对苯二酚检测的研究现状,综述样品前处理方法和仪器分析方法的研究进展,探讨各种方法的原理和应用,比较不同方法的优缺点,为开发快速、准确、灵敏地检测食品中叔丁基对苯二酚的新技术提供参考。     

纳米技术在功能性食品中应用

近年来,纳米技术在功能性食品中应用正处快速发展阶段,其作为高新技术在功能性食品领域应用研究得到越来越多关注;纳米技术不仅可用于功能性食品生产和加工,也可提高生物活性、吸收率、稳定性、降低毒性。该文重点介绍纳米技术在功能性食品中应用。