Thermodynamics of Moist Grain

From thermodynamic theory, equations are developed for relating the heat of wetting of wheat flour to the relative humidity of air. For limited data on several grains and flours and for cotton fiber, the three pertinent parameters: ø, the thermodynamic potential; K, the equilibrium constant; and Ws, the saturation moisture content were determined. While K is remarkably uniform over all substances, ø varies with temperature and Ws with time and substance. The relative humidity relationship has the virtue of simplicity so that either relative humidity or moisture content can be calculated one from the other without difficulty once the parameters are known.     

Textural attributes of commercial biscuits. Effect of relative humidity on their quality

Two commercial biscuits of semi‐sweet type, ‘Marie’ and ‘Petit Beurre’ were used for investigating: (i) their texture variability as a function of the location and the side of puncturing and (ii) the influence of storage under different relative humidity on their texture, porosity and colour. Significant texture differences were found as a function of the location of puncturing (centre or periphery of biscuit area), as well as between the upper and the opposite side of a biscuit. At small relative humidity changes (11–32%) a distinct relationship between texture and moisture content was not noticed. In ‘Petit Beurre’ at a_w 0.32 a peak was observed in the puncture force values. In both biscuits porosity increased with their moisture content, accompanied by an area expansion. Significant differences in colour were mainly noticed between the upper and opposite side of the biscuits. Colour was less influenced by relative humidity changes.     

EFFECT OF STORAGE ON THE SAFETY AND QUALITY OF FUFU FLOUR

Studies were carried out on the physicochemical characteristics and the fungi involved in the spoilage of fufu flour under storage at different relative humidities in ambient temperature.The physicochemical characteristics showed an increase in moisture content, decrease in swelling power, water‐binding capacity and pH throughout the storage period. Fungi growths were noticed on the samples at different times. Relative humidity of 33% and 76% for 56 days and 48 days, respectively, had the minimum number of growth when compared to others. The fungi that were isolated from the fufu were Aspergillus niger, Rhizopus spp., Geotrichum candida and Candida spp. This study therefore showed that fufu flour will keep best when it is stored under the condition of 33% relative humidity at room temperature.     

SORPTION ISOTHERM BEHAVIOR OF OSMOCONVECTIVELY DEHYDRATED CARROT CUBES

Carrot cubes, osmotically pretreated with aqueous sodium chloride (10%, w/v), sucrose syrup (55°Brix), and mixture of sucrose and sodium chloride (50°Brix + 10%, w/v), were convectively dehydrated at 65C temperature up to final moisture content of 4–5% (wet basis). To study their equilibrium moisture content (EMC) behavior, the dehydrated carrot cubes were stored at temperature ranging from 10 to 50C and relative humidity ranging from 15–95% using static desiccator technique. Five isotherm equations, viz, Chung–Pfost, modified Henderson, modified Halsey, modified Oswin and modified exponential were applied to examine the data. Among the applied models, modified Oswin model was best fit for control (untreated) and salt‐treated samples, modified Hesley model for sucrose‐treated samples and two‐term exponential model for mixture of sucrose–salt treatment over the entire range of relative humidity and temperature. The EMC values of cubes osmotically pretreated with sodium chloride solution were highest among all pretreatments, and were lowest for control (unosmosed) samples.     

Desorption isotherms and thermodynamic properties of sweet corn cultivars (Zea mays L.)

The desorption isotherms and thermodynamic properties of two cultivars of sweet corn were obtained during the drying process of these products. The isotherms were determined by a dynamic method for various temperature and humidity conditions. Equilibrium moisture content (X_eq) data were correlated by the Guggenheim–Anderson–de Boer model and an artificial neural network (ANN) model. These models were fitted to the experimental data. The X_eq for corn grain increased with an increase in the relative humidity at fixed temperature and decreased with an increase in temperature at a constant relative humidity. The experimental data were analysed by a thermodynamic approach to obtain the isosteric heat of desorption (ΔH), differential entropy (ΔS), activation energy (E_a) and Gibbs free energy (ΔG). The ΔH and ΔS increased with a decrease in moisture content, while ΔG decreased exponentially with an increase in X_eq. The Arrhenius equation was used to obtain E_a values, with Supersweet corn having higher E_a.     

ACCELERATED STORAGE, SHELF LIFE AND COLOR OF MANGO POWDER

Vacuum‐dried mango powder was produced from mango pulp through the addition of glycerol monostearate and tricalcium phosphate at 0.015 kg each per kg mango solids and maltodextrin at 0.62 kg per kg dry mango solids. The mango powder was packed in aluminum foil‐laminated pouches and stored in an accelerated storage environment maintained at 90% relative humidity (RH) and 38 ± 2C. The sticky‐point moisture content at 38 ± 2C was considered as the maximum moisture content to which the mango powder would remain stable. The shelf life of the powder predicted from this consideration and the Guggenheim‐Anderson‐de Boer (GAB) model for the water activity moisture content relationship was 114.68 days, whereas the actual shelf life was 105 days. The color change of the powder during storage followed first‐order reaction kinetics with a rate constant of 0.038 per day.     

Equilibrium moisture content of groundnut and chillies

Hygroscopic material, when it comes into contact with atmospheric air, desorps or absorps the moisture from the surroundings until it reaches equilibrium. In the present study, groundnut and chillies were dried in a controlled air supply (at a particular temperature and relative humidity). The equilibrium moisture content (e.m.c.) and relative humidity (r.h.) relationships were studied at different temperatures. Values of constants c and n of Henderson's equation were computed and desorption isotherms were drawn for groundnut components and chillies. It was observed that e.m.c. depends upon type of material, the temperature and r.h. of the air.     

Drying kinetics of whole durum wheat pasta according to temperature and relative humidity

Drying kinetics of bran-free and bran-rich pasta (whole durum) was determined according to temperature (40, 60 or 80 °C) and relative humidity (65%, 75% or 85%). Compared to temperature, relative humidity in drying chamber had a greater effect on pasta effective moisture diffusivity (α<0.01), and both parameters responded to a modified Arrhenius-type equation. Activation energy of pasta (11.4 kJ mol⁻¹) was lower than reported in the literature. Bran changed the course of pasta drying, depending on temperature and relative humidity. When relative humidity was higher than 75%, effective moisture diffusivity of bran-rich pasta decreased but the reverse was observed below 75%. Above 76 °C, equilibrium moisture content of bran-rich pasta was higher than bran-free pasta. In conclusion, optimal drying conditions for bran-rich pasta were different than standard (bran-free) pasta. Close control of relative humidity in pasta drying unit would be critical, especially under high relative humidity and high temperature conditions.     

WATER DIFFUSION COEFFICIENT AND MODELING OF WATER UPTAKE IN PACKAGED YERBA MATE

Effective water diffusion coefficient (D_eff) was determined from the kinetics of moisture gain in a yerba mate bed. A value of 1.5 × 10^?9 ± 0.4 × 10^?9 m²/s was obtained at 40C and 90% relative humidity, by fitting experimental data to the series solution of Fick's second law. A model was developed to predict moisture profile and water uptake in packaged yerba mate. In order to simulate moisture gain in the packaged food, the model considers that the global process of humidity gain is controlled by combined mechanisms of package permeability, product sorption balances and water diffusion within the food bed. The explicit finite difference method was used to numerically solve the resulting equations. The validity of the model was tested by comparing predicted and experimental moisture profiles for high (WVTR ≤ 20 g/m²/day) and low (WVTR ≥ 400 g/m²/day) barrier packages. The model was found to adequately predict the profile of moisture content.     

Equilibrium moisture content and heat of desorption of saffron

The equilibrium moisture contents of saffron (Crocus sativus L.) stigmas were determined experimentally using the standard gravimetric method at temperatures 30, 45 and 60 °C and water activity ranging from 11% to 83%. The sorption isotherm curves of saffron were sigmoidal in shape and decreased with increased temperature at constant relative humidity. Five selected isotherm models GAB, modified Henderson, modified Chung‐Pfost, modified Halsaey and modified Oswin were tested to fit the experimental isotherm data. Modified Oswin and modified Henderson models were found acceptable for predicting desorption moisture isotherms and fitting to the experimental data, respectively. The isosteric heats of desorption, determined from equilibrium data using the Clausius‐Clapeyron equation, were found to be a function of moisture content. The net isosteric heat of desorption of saffron varied between 1.38 and 5.38 kJ mol^?1 at moisture content varying between 2% and 20% (d.b).     

Measurement and Modeling of Moisture Sorption Isotherm of Litchi (Litchi Chinensis Sonn.)

The equilibrium moisture contents of litchi (Litchi Chinensis Sonn.) were experimentally determined using the dynamic method at temperatures of 30, 40, and 50°C over a range of relative humidity values of 12 to 95%. Five models were tested to fit the experimental isotherm data of litchi. The GAB model fitted the best to experimental isotherm data. The agreement between experimental and predicted values of this model is excellent (RMSE 1.8 to 3.4%). The isosteric heats of sorption water were also determined from the equilibrium data using the Clausius-Clapeyron equation and it was found to be a function of equilibrium moisture content.     

Synergism of phosphatidylcholine on the antioxidant properties of α‐tocopherol in corn oils under different relative humidity

The effects of phosphatidylcholine on the antioxidant properties of α‐tocopherol (84 ppm) were determined in stripped corn oil with various moisture contents at 60 °C. The degree of oxidation in the oils was determined by analysing headspace oxygen content and conjugated dienoic acids (CDA). Generally, phosphatidylcholine acted as an antioxidant in stripped corn oils, whereas it accelerated the rate of lipid oxidation in nonstripped corn oils. As the relative humidity and moisture content increased, the antioxidant properties of phosphatidylcholine increased significantly (P < 0.05). Strong synergistic antioxidant effects were observed in samples containing both phosphatidylcholine and α‐tocopherol compared to samples with only phosphatidylcholine or α‐tocopherol. Oils containing phosphatidylcholine or α‐tocopherol under different moisture contents had different oxidative stabilities.     

Untersuchungen zu Diffusionsvorgängen in mehrschichtigen Massivholzplatten

Multilayer solid wood spruce panels with different glueing and structure type were tested for water vapor diffusion for a wet climate (relative humidity ranging from 100% to 65% at 20°C) and for a dry climate (relative humidity ranging from 0% and 65% at 20°C). Results showed that the water vapor diffusion resistance for the dry climate is distinctly higher in comparison to the wet climate. The water vapor diffusion resistance is stronger related to the number of glue layers per panel thickness than to the type of adhesive. The average moisture content of the panels in a wet climate was 20%. If one considers a water saturation point of 28% (spruce wood) on the wet side, and 12% moisture content on the dry side (normal climate) of the panel a linear moisture gradient can be expected. Since the average moisture content of the solid wood panels was about 11.3% in a dry climate, and thus corresponding approximately to the equilibrium moisture content of spruce wood exposed to normal climate, the partial pressure gradient on equilibrium caused water uptake corresponding to the normal moisture content for spruce wood.     

Abhängigkeit der Druckfestigkeit kunststoffvergüteten Holzes von der Holzfeuchtigkeit

Zusammenfassung Kiefern- und Buchenholz, das mit Diisocyanat, Polyester/Styrol und Formaldehyd behandelt worden war, wurde nach Aush?rtung, teils mit, teils ohne Gamma-Strahlung, in verschieden feuchtem Klima gelagert. Die Druckfestigkeit wurde nach Ausgleich der Feuchtigkeit im Darrzustand, bei ϕ=40%, 65%, 85% und 100% und im wassergetr?nkten Zustand geprüft. Es ergaben sich dabei charakteristische Unterschiede in der Wirkung dieser drei Stoffe auf die Festigkeit der beiden Holzarten in Abh?ngigkeit von der Feuchtigkeit. Bei Diisocyanat verst?rkte sich der relative Einflu? auf die Festigkeit mit zunehmendem Feuchtigkeitsgehalt. Ebenso verhielt sich die Kombination von Holz mit Polyester/Styrol mit Ausnahme des Darrzustandes bei Fasers?ttigung sowie im wassersatten Zustand. Formaldehyd wirkte im Bereich zwischen ungef?hr 20 und 90% relativer Luftfeuchtigkeit festigkeitssteigernd.

---

Dependence of the crushing strength of plastic-improved wood on its moisture content

Summary Pine and beech wood, which was treated with diisocyanate, polyester/styrene, and formaldehyde was stored after setting partly with, partly without gamma radiation in a climate of different humidity. After reaching the equilibrium moisture content, the compression strength was tested in the oven-dry state at 40, 65, 85, and 100% of relative humidity of the air and in a water-saturated state. Depending on the moisture content, the results showed characteristic differences in the effect of these three materials on the strength. With diisocyanate, the relative effect on the strength of the material increased with growing moisture content. The combination of wood with polyester/styrene behaved likewise, except in the case of the oven-dry as well as the fibre- and water-saturated state. Within the range of 20% to 90% of relative humidity of the air, formaldehyde was effective in a strength-improving way.

---

---

Mitteilung aus der Bundesanstalt für Materialprüfung Berlin-Dahlem, fachgruppe “Biologische Materialprüfung, Holzschutz und Holztechnologie”     

Effect of gamma irradiation on aflatoxin production in barley

Barley was inoculated with conidia of Aspergillus parasiticus NRRL 2999, and at 0°C was left to equilibrate at three moisture levels: 17, 20 and 25%. Gamma irradiation at five doses, 0, 50, 100, 200 and 400 krad, was applied to the grain either soon after moisture equilibration (3 days after inoculation) or 10 days later (13 days after inoculation). Increasing the radiation dose resulted in decreasing aflatoxin formation, with one exception: 200 krad applied 13 days after inoculation on barley stored at a moisture level of 25% (100% relative humidity) and 25°C led to higher aflatoxin production than at 100 or 50 krad. For the control of aflatoxin contamination in barley, storage at low moisture content appears to be more practical and effective than irradiation.     

The moisture content-equilibrium relative humidity relationship of cocoa beans

The moisture content-equilibrium relative humidity relationships for cocoa beans grown in nine different countries were similar to each other, and the maximum safe storage moisture content in equilibrium with 70% relative humidity was between 6.0 and 7.9% at 25°C. There was a large variation between the moisture content of individual beans within each sample, the maximum standard deviation observed in a sample of thirty beans being 0.97, after the moisture content had been increased by adding water.     

Moisture absorption characteristics of food thickeners used for the management of swallowing dysfunctions

Six commercial food thickeners, based on starch, and guar and xanthan gums, were investigated for their moisture absorption properties. The thickeners were exposed to 100% relative humidity as well as soaked in water for selected time periods. The gum-based thickeners dissolved in water to yield 100% water solubility index. The water absorption index of the starch-based thickeners ranged from 14.7 to 18.0 g/g dry solids of thickener. The starch-based thickeners sorbed less moisture than the gum-based ones, with the xanthan gum-based thickeners having the highest sorptive ability on mass basis. The Peleg model was the most suitable (r ²=0.966–0.997) of the sorption models investigated to describe the sorption data. The diffusion rate constant of the thickeners ranged from 8.7 to 13.5 day%⁻¹, while the equilibrium moisture content was between 35.7 and 46.8%. The sorptive ability explained viscosity development in some of the thickeners, but was unsuitable in fully describing comparisons of the solutions viscosities of starch-based and xanthan gum-based thickeners.     

A study of some factors promoting kiln brown stain formation in radiata pine

Kiln drying of radiata pine (Pinus radiata D. Don) sapwood induces a brown discolouration, commonly called kiln brown stain. Kiln brown stain generally occurs 0.5–1.5 mm under the surface of the dry sawn lumber. However, subsequent planing of the wood can expose the stain causing substantial revenue loss in the New Zealand highvalue export markets. In the present study, the effects of kiln schedule temperature, wood moisture content and kiln relative humidity on kiln brown stain formation were investigated. The results showed that kiln brown stain was greatly reduced by using kiln schedules of less than 50°C as opposed to 90°C and was also more pronounced in the kilning at 30% kiln relative humidity, than at 80% humidity. Furthermore, the occurrence of kiln brown stain tended to intensify with decreasing wood moisture content, irrespective of kiln temperature and kiln humidity used. The practical implication of this work and the mechanisms of kiln brown stain formation are discussed.     

环境相对湿度对干法再造烟叶加热卷烟关键指标的影响

以"宽窄"原味加热卷烟产品作为研究对象,分析在不同环境相对湿度下存放7 d,烟支发烟段含水率、吸阻、烟气成分(烟碱、总粒相物、水分)及感官指标的变化情况.结果表明:①烟支发烟段含水率、吸阻、总粒相物和烟气水分与相对湿度呈正相关.②环境相对湿度对实验期间烟支圆周和圆度无明显影响,但与烟气烟碱释放量呈负相关.③较低相对湿度...