Predicting the Quality of Dehydrated Foods and Biopolymers — Research Needs and Opportunities

ABSTRACT

Drying processes affect the quality of the final food biopolymer product. The texture, density, wetability, caking, rehydration capacity and mechanical properties of the dried food biopolymer depend on: the product properties, the drying process conditions and the product residence time distribution in the dryer. The interrelationship between dried product quality and drying process conditions is not sufficiently explored in literature because of limited understanding of the physico-chemical mechanisms affecting product quality, and of the effect of these mechanisms on transport properties. Recent ad- vances in material and polymer science research, however, provide the tools and methodologies needed to understand in depth the quality changes dur-ing drying. The current work reviews the approaches of conventional drying theories and presents recent advances in polymer science on modelling solvent absorption by glassy polymers based on the glass-transition theory. Oppor- tunities presented by the glass transition theory towards explaining quality changes during drying are identified and the framework of a recent rnathe- matical model that can be used to integrate the drying and polymer-science approaches is then presented.     

Thermo-mechanical response of UHPFRC at early age — Experimental study and numerical simulation

The thermal effects on the Ultra High Performance Fiber Reinforced Concrete (UHPFRC) behavior are still not completely known. Under high temperatures, the processes that interact at early age are thermo-activated. All the experimental results obtained within this research confirmed it. Besides, certain authors observed a non-monotonous effect of temperature on the autogenous shrinkage and the creep of normal and high performance concretes. To clarify the thermal effect on the early age UHPFRC behavior an extensive experimental study was carried out. Tests results showed a non-monotonous effect of temperature on the autogenous shrinkage. In addition, finite element numerical simulations were performed to predict the experimental results and to validate existing models for different curing conditions. These models are necessary to predict accurately the deformations, the stresses and the damage (cracking) in the case of structural elements subjected to in-situ temperature variations.     

Changes in the size of pores during shrinkage (or expansion) of cement paste and concrete

The often-argued and seldom-resolved issue of relating the bulk shrinkage of concrete to changes in the size of pores is analyzed using a simple model. It is shown that the pores in a composite containing both shrinking and nonshrinking solid phases can themselves either shrink or expand when the matrix shrinks, depending on the amount of restraint in the system. The analysis also applies to expansive deformations, which occur with some types of chemical attack of cement paste. A mathematical relationship between the degree of restraint in a composite and the relationship between bulk volume changes and pore volume changes is given. These observations provide guidelines for interpreting the meaning of gaps that often form between aggregate and paste in concrete.     

Effect of Water on the Quality of Dehydrated Products: A Review of Novel Characterization Methods and Hybrid Drying Technologies

The effect of water on the quality of dried products is reviewed in light of recent applications of novel characterization methods (nuclear magnetic resonance (NMR), X-ray spectroscopy, and Raman spectroscopy) in quantifying the state and mobility of water in dried products. The mechanical configuration and ability of a number of hybrid drying technologies that use novel heating sources (microwave, infrared, radiofrequency) and/or sub-atmospheric pressure in producing better-quality products are reviewed in considerable detail. The drying kinetics models, especially those related to the quality loss, are also reviewed. It appears that more and more drying research is now focused on the development of novel hybrid technologies to produce better-quality products and for energy savings. The novel characterization technologies listed above are capable of quantifying the dynamic mobility and state of water in dried food products; this information can be used to design more efficient drying processes.     

Research Needs and Opportunities in the Dry Conservation of Fruits and Vegetables

The consumer demand for healthy convenience meals with 'near fresh' properties challenges researchers and industry to develop new or improved conservation procedures for food products. However, this recent food trend towards fresh image on one ride and convenience on the other side often conflict. In most cases the fresh quality is negatively affected by the processing procedure. Therefore nowadays efforts ars focussed on extending the shelf life of fresh products. However, sophisticated energy demanding facilities are required for storage and transporation, whereas thc use of ecologically unsound cooling agents is a major drawback.

The development of a dehydration process on the basic of electromagnetic energy (EME) may bring about a major breakthrough with respect to the retention of product quality and improved rehydration characteristics. Due to the tenfold weight reduction established in the dehydration process transport and storage costs are minimised thus reducing energy consumption. In comparison with fresh and frozen products minimal storage facilities are required.

The strategy of a consortium of five EC-research centres and two dutch drying companies is to combine and fine tune hot air drying (low processing costs) and EME-drying (quality retention) into a hybrid process, to compare the performance with conventional methods and to include packaging and storage effects.

Optimisation of the rewettability is one of the major concems since food materials with near fresh properties can only be obtained from dry material if rehydration characteristics ars excellent. To establish such dried fruit and vegetables will be considered as blends of polymeric materials. Many quality deterioration mechanisms can be attributed to the mobility of the polymeric matrix and the diffusion of water. Properties thus depend on the composition, the physical properties of the polymers (mobility) and the overall structure of the dried material.     

The role of specimen geometry and boundary conditions on stress development and cracking in the restrained ring test

Early-age cracking can be a significant problem in concrete pavements, floors, and bridge decks. Various test methods have been developed to assess the potential for early-age cracking, however due to the economy and simplicity of the ring test, it has become widely used. Although the ring test procedures employed by various authors are similar, they vary in terms of curing duration, specimen geometry, and boundary conditions. This paper describes an experimental study of restrained ring specimens tested using different geometries and boundary conditions. Specimen geometry was found to have a significant effect on the stress development and age of cracking in the restrained ring specimens. Specimens that shrink uniformly along the radius show the greatest variation in the age of cracking with thicker specimens cracking at a later age. Acoustic emission testing has been used to illustrate that specimen boundary condition substantially influence crack development and propagation in the restrained rings.     

Enhancement of Drying Rate in Paper Machines with Multi-Functional Radial Jet Reattachment Blow Boxes — Theoretical Analysis

Multi-functional radial jet reattachment blow boxes deliver a dry air into the pockets of the dryer section of a paper machine by impinging directly onto the unsuppned sheet in the open diaw. The air flow also maintains or improves the sheet swbility.

The iadial jet reattachment blow box technology pmvides a significant enhancement in drying rates. The theoretical drying results are presented in terms of average drying rates, moisture and temperature pmfiles along the drying section with and without the presence of the multi-functional radial jet reaaachment blow boxes. The thcorclical results indicate that enhancements of drying rates within the range of 8% to 25% are feasible depending on ihe operating conditions and machine configuration.     

High‐Pressure Treatment of Wood – Combination of Mechanical and Thermal Drying in the “I/D Process”

Thermal drying of materials with internal pores is always a time‐consuming and energy‐intensive step within a production process. For chemical and pharmaceutical mass products and, in particular, for wood as an important raw material it is desirable to reduce the water content before thermal treatment by mechanical operations. The wood‐processing industry, facing a rising stress of competition, is forced more than ever to offer high‐quality products at lowest prices. Today, drying of timber is mostly done by air drying or by technical drying in kiln dryers. In any case, drying is necessary to prevent deterioration in quality by shrinkage, formation of cracks, discoloration or infestation. A new process of dewatering wood by combining mechanical and thermal means has been developed at the University of Karlsruhe. Compared to conventional drying processes, short drying times and a low residual moisture content can be achieved and, thus, energy consumption and costs can be reduced. In industrial wood drying only thermal processes (e.g., convective kiln drying, vacuum drying, etc.) have been established because so far no method has been known for removing liquid by mechanical force without significant change in wood structure. With the new I/D process chances for alternatives to conventional thermal drying or for mechanothermal applications are offered.     

阻燃增强尼龙66表面质量改善的研究

采用溴化聚苯乙烯(BPS)作为阻燃剂,短玻纤和玻璃微珠作为增强体系,与尼龙66(PA66)共混,经双螺杆挤出机挤出,制备了高表面质量、力学性能优良的阻燃增强PA66复合材料.研究结果表明,添加19份BPS后,PA66可以达到V-0级别的阻燃效果.使用0.8份硅酮润滑剂对PA66的表面质量有一定改善,并且对力学性能影响很小.将玻璃微珠与短玻纤复配,一定程度上可以改善PA66的表面质量,但玻璃微珠对PA66力学性能有不利影响,因此用量不能太大,控制在5份以内.     

The β‐δ‐Phase Transition and Thermal Expansion of Octahydro‐1,3,5,7‐Tetranitro‐1,3,5,7‐Tetrazocine

Phase behavior of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) is investigated by X‐ray powder diffraction (XRD). The XRD patterns at elevated temperature show that there is a co‐existing temperature range of β‐ and δ‐phase during the phase transition process. Additionally, mechanical forces can catalyze the conversion from δ‐ back to β‐phase. Based on the diffraction patterns of β‐ and δ‐phase at different temperatures, we calculate the coefficients of thermal expansion by Rietveld refinement. For β‐HMX, the linear coefficients of thermal expansion of a‐axis and b‐axis are about 1.37×10⁻⁵ and 1.25×10⁻⁴ °C⁻¹. A slight decrease in c‐axis with temperature is also observed, and the value is about −0.63×10⁻⁵ °C⁻¹. The volume coefficient of thermal expansion is about 1.60×10⁻⁴ °C⁻¹, with a 2.2% change from 30 to 170 °C. For δ‐HMX, the linear coefficients of thermal expansion of a‐axis and c‐axis are found to be 5.39×10⁻⁵ and 2.38×10⁻⁵ °C⁻¹, respectively. The volume coefficient of thermal expansion is about 1.33×10⁻⁴ °C⁻¹, with a 2.6% change from 30 to 230 °C. The results indicate that β‐HMX has a similar volume coefficient of thermal expansion compared with δ‐HMX, and there is about 10.5% expansion from β‐HMX at 30 °C to δ‐HMX at 230 °C, of which about 7% may be attributed to the reconstructive transition.     

Relating the Stickiness Property of Foods Undergoing Drying and Dried Products to their Surface Energetics

Stickiness is a common problem encountered in food handling and processing, and also during consumption. Stickiness is observed as adhesion of the food to processing equipment surfaces or cohesion within the food particulate or mass. An important operation where this undesirable behavior of food is manifested is drying. This occurs particularly during drying of high-sugar and high-fat foods. To date, the stickiness of foods during drying or dried powder has been investigated in relation to their viscous and glass transition properties. The importance of contact surface energy of the equipment has been ignored in many analyses, despite the fact that some drying operations have reported using low-energy contact surfaces in drying equipment to avoid the problems caused by stickiness. This review discusses the fundamentals of adhesion and cohesion mechanisms and relates these phenomena to drying and dried products.     

Colour Measurement in the Hungarian Textile Industry — Research and Application

Presented at the 13th Congress of the International Federation of Associations of Textile Chemists and Colourists in London on 21 September 1984. The Colour Measurement and Recipe Formulation Centre was opened some years ago to help dyehouses in the Hungarian textile industry. The work of the Centre and research conducted at various other institutions are discussed in this article. The main topics of research include linear approximations in colour calculations, statistical treatment of colour measurement data, the repeatability of textile dyeing, comparison of different methods for expressing the dyeing strength of dyestuffs, application of instrumental measurement in fastness evaluation, comparison of colour-difference formulae in establishing tolerances and in colour sorting, and the effect of mercerisation on the colour of dyed cotton.     

Effect of aromatic substitution on the kinetics and properties of epoxy cured tri-phenylether amines

The reaction kinetics and structure property relationships of isomeric tri-aromatic ether-linked amines based on the structure bis (aminophenoxy) benzene, cured with diglycidyl ether of bisphenol F (BisF) are investigated in this study. Reaction kinetics are explored using rheological and calorimetric measurements, whereas structure property relationships are determined from their flexural properties, dynamic mechanical properties (DMTA), and thermogravimetric analysis (TGA). A BisF network cured with 4,4 diamino diphenyl sulphone (44 DDS) is used as a benchmark to represent a commercially available high-performance resin system. Varying the substitution of the ether linkages on the aromatic groups from ortho, meta to para was found to have a significant impact on reactivity and network properties after cure. The variations are explained in terms of inductive and resonance effects primarily acting on the outer aromatic rings. Interestingly, however, these same effects acting on the central aromatic ring also impact upon reactivity despite their proximity from the amines. Mechanical and thermal properties are explained by changes in the short-range molecular mobility within the network architecture such as phenylene rotations or π flips and are experimentally validated from the breadth and position of the subambient γ relaxations. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47383.     

Mathematical modeling and simulation of shrunk cylindrical material's drying kinetics—Approximation and application to banana

In the present work, a diffusion-based model was adopted to represent the convective drying behavior of cylindrical banana samples, taking into consideration the shrinkage along drying. The developed model simulated a significant number of situations resulting from the variations of some operating conditions. The temperatures tested were 50, 60, 67 and 70 °C, the air velocities were 3, 4 and 4.5 m/s and the relative humidity range of the drying air was from 3.5 to 11.5%. The calculated drying curves were compared to the experimental ones in order to determine apparent moisture diffusivity. An empirical equation was suggested, describing the apparent moisture diffusivity within the banana versus product temperature and local moisture content. A good agreement was found between experimental and calculated drying kinetics.     

Effects of Peeled and Unpeeled Garlic Cloves on the Changes of Drying Rate and Quality

Reducing moisture content as fast as possible, together with minimizing loss of quality, is important to food processing. To reach these objectives, experimental investigations were conducted to examine the effects of both peeled and unpeeled garlic cloves as well as operating parameters such as temperature and superficial velocity on the drying rate and quality of dried product. Peel resistance to moisture diffusion is considerably dominated and yields the longer drying time. Drying at high temperature shows the shrinkage of garlic clove to be lower than that at low temperature, whereas the product color is browner and the sizes of produced pores as revealed by scanning electron microscope are larger. The loss of volatile oil is insignificantly different among low- and high-temperature drying. The peel effect exhibits negative results on the product color, giving lower luminosity than the peeled sample, in particular at low temperature, because of longer drying time.     

Effects of Peeled and Unpeeled Garlic Cloves on the Changes of Drying Rate and Quality

Reducing moisture content as fast as possible, together with minimizing loss of quality, is important to food processing. To reach these objectives, experimental investigations were conducted to examine the effects of both peeled and unpeeled garlic cloves as well as operating parameters such as temperature and superficial velocity on the drying rate and quality of dried product. Peel resistance to moisture diffusion is considerably dominated and yields the longer drying time. Drying at high temperature shows the shrinkage of garlic clove to be lower than that at low temperature, whereas the product color is browner and the sizes of produced pores as revealed by scanning electron microscope are larger. The loss of volatile oil is insignificantly different among low- and high-temperature drying. The peel effect exhibits negative results on the product color, giving lower luminosity than the peeled sample, in particular at low temperature, because of longer drying time.     

Removal of 3—(3,4—dichlorophenyl)—1, 1 dimethylurea from aqueous solution by natural and activated bentonite

The adsorption of 3-(3,4-dichlorophenyl)-1,1 dimethylurea (diuron) on bentonite desiccated at 110°C untreated, and acid treated with H₂SO₄ solutions over a concentration range between 0.25 M and 5.00 M, from aqueous solution at 30°C has been studied. In addition, adsorption of diuron on combined acid/heat treated samples (0.50 M and 2.50 M H₂SO₄/200°C and 400°C) has also been studied. The experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (K) of the samples; K values range from 0.92 μg g^?1 for the untreated bentonite up to 974.42 μg g^?1 for the 0.50 M H₂SO₄/400°C acid/heat treated bentonite. The removal efficiency (R) has also been calculated; R values ranging from 2.02% for the untreated bentonite up to 97.17% for the 0.50 M H₂SO₄/400°C acid/heat treated bentonite. The adsorption experiments show that bentonite heat treatment is more effective than bentonite acid treatment in relation to adsorption of diuron.