Equilibrium Relative Humidity Research Articles

Moving beyond species: fungal function in house dust provides novel targets for potential indicators of mold growth in homes

BackgroundIncreased risk of asthma and other respiratory diseases is associated with exposures to microbial communities growing in damp and moldy indoor environments. The exact causal mechanisms remain unknown, and occupant health effects have not been consistently associated with any species-based mold measurement methods. We need new quantitative methods to identify homes with potentially harmful fungal growth that are not dependent upon species. The goal of this study was to identify genes consistently associated with fungal growth and associated function under damp conditions for use as potential indicators of mold in homes regardless of fungal species present. A de novo metatranscriptomic analysis was performed using house dust from across the US, incubated at 50%, 85%, or 100% equilibrium relative humidity (ERH) for 1 week.ResultsGene expression was a function of moisture (adonis2 p < 0.001), with fungal metabolic activity increasing with an increase in moisture condition (Kruskal–Wallis p = 0.003). Genes associated with fungal growth such as sporulation (n = 264), hyphal growth (n = 62), and secondary metabolism (n = 124) were significantly upregulated at elevated ERH conditions when compared to the low 50% ERH (FDR-adjusted p ≤ 0.001, log2FC ≥ 2), indicating that fungal function is influenced by damp conditions. A total of 67 genes were identified as consistently associated with the elevated 85% or 100% ERH conditions and included fungal developmental regulators and secondary metabolite genes such as brlA (log2FC = 7.39, upregulated at 100% compared to 85%) and stcC (log2FC = 8.78, upregulated at 85% compared to 50%).ConclusionsOur results demonstrate that moisture conditions more strongly influence gene expression of indoor fungal communities compared to species presence. Identifying genes indicative of microbial growth under damp conditions will help develop robust monitoring techniques for indoor microbial exposures and improve understanding of how dampness and mold are linked to disease.-X5AkW-U2mftBzktcaxDSrVideo

Physicochemical properties in relation to the flow behavior of soybean meal

Abstract Caking of soybean meal during storage and the resultant difficulty in discharging from storage bin is a practical problem in animal feed‐related industries. This study investigated the physicochemical factors related to soybean meal flowability and the effect of anticaking agents. Results showed the soybean meal had a D50 of 389.1 µm and a D90 of 1.098 µm. The equilibrium relative humidity of soybean meal at various ambient temperatures ranged from 57 % to 69 %. Moisture had a major influence on soybean meal flowability and the critical moisture content for loss of free flow capacity was around 17.81 % (wet basis, wb). Soybean meal was characterized as amorphous by X‐ray diffraction analysis, and its glass transition temperature is greatly affected by the moisture content. The addition of silicon dioxide helps keep soybean meal free flowing when stored at a relative humidity of 90 % and a temperature of 45 °C possibly due to its low affinity for moisture. Overall, moisture absorption is perceived as the main factor causing the occurrence of caking of soybean meal.

Thermodynamic water adsorption analysis of biodegradable films based on corn starch-chitosan added with triblock copolymers

Adding triblock copolymers to hydrophilic films is an option to improve the functional properties and water resistance under high equilibrium relative humidity (RHeq) environments. Sorption isotherms of corn starch-chitosan based films added with triblock copolymers (L64 and P123) measured at 4, 20, and 36 °C were fitted using the Guggenheim-Anderson-De Boer equation. Thermodynamic analysis allowed allocating the minimum integral entropy value between 0.09 and 0.50 of water activity. The compensation enthalpy-entropy showed that the entropy driven the process at low water activities (0.10–∼0.33) and the enthalpy driven the water sorption at high water activities (∼0.33–∼0.90).

The Hygroscopic Properties and Sorption Isosteric Heat of Coix Seeds

Coix seeds are one of the most difficult-to-store cereal foods, and in order to maintain their quality during storage, the present study was conducted to determine the moisture adsorption and desorption isotherms of five varieties of coix seeds in the ranges of 10-35 °C and 11.3%-96.0% equilibrium relative humidity (ERH) using a static gravimetric method. The isotherms showed sigmoidal curves, and there was a hysteresis between adsorption and desorption isotherms. Six equilibrium moisture equations were used to fit the isotherms, and the Modified Chung-Pfost (MCPE), Modified Guggenheim-Anderson-deBoer (MGAB), Modified Henderson (MHE), Modified Oswin (MOE) and our developed modified Caurie (MCaurie) equations were suitable for fitting the data, among which MCPE was the best fitting equation. The monolayer water content decreased with increasing temperature, and the content of monolayer water, the density and layer number of adsorbed water, and the content of bound water for desorption were significantly higher than those of adsorption. The absolutely (ERH 65%) and relatively (ERH 70%) safe moisture contents (MC, wet basis, w.b.) of coix seeds were respectively 12.45%-12.82% and 13.15%-13.69% at 25 ℃. At equilibrium moisture content (EMC) less than 14.9% w.b., the desorption isosteric heats of coix seed were greater than the adsorption isosteric heats, and both decreased sharply in a hyperbolic form, approaching the latent heat of pure water at 14.9% w.b. The sorption isosteric heat of large-grain coix seed was slightly less than that of small-grain seed due to more cracks in the kernel back surface and more micropores in starch granular surface and resultantly more moisture sorption capacity. These results suggest that the desorptive and adsorptive behaviors of coix seeds should be differentiated for cooldown aeration, demoisturizing and remoisturizing operation, and the average isotherm can be used for common storage management.

Fungal diversity differences in the indoor dust microbiome from built environments on earth and in space

Human occupied built environments are no longer confined to Earth. In fact, there have been humans living and working in low-Earth orbit on the International Space Station (ISS) since November 2000. With NASA’s Artemis missions and the age of commercial space stations set to begin, more human-occupied spacecraft than ever will be in Earth’s orbit and beyond. On Earth and in the ISS, microbes, especially fungi, can be found in dust and grow when unexpected, elevated moisture conditions occur. However, we do not yet know how indoor microbiomes in Earth-based homes and in the ISS differ due to their unique set of environmental conditions. Here we show that bacterial and fungal communities are different in dust collected from vacuum bags on Earth and the ISS, with Earth-based homes being more diverse (465 fungal OTUs and 237 bacterial ASVs) compared to the ISS (102 fungal OTUs and 102 bacterial ASVs). When dust from these locations were exposed to varying equilibrium relative humidity conditions (ERH), there were also significant fungal community composition changes as ERH and time elevated increased (Bray Curtis: R2 = 0.35, P = 0.001). These findings can inform future spacecraft design to promote healthy indoor microbiomes that support crew health, spacecraft integrity, and planetary protection.

Study on the variation regularities of minimum explosion concentration of moist magnesium dust/derived hydrogen hybrids under multiple working conditions

Magnesium is widely used but often accompanied by frequent magnesium powder explosion accidents. If the variation regularity and mechanism of the minimum explosion concentration (cm) of magnesium powder under the multi-factor coupling effect can be understood, the occurrence of magnesium powder explosion accidents can be fundamentally avoided, and intrinsic safety can be achieved. In this paper, experiments were conducted using a self-made 20 L explosion device to explore the effects of particle size, initial temperature, and equilibrium relative humidity (ERH) coupling on the cm of magnesium powder. The study found that an increase in ERH of moist magnesium powder would lead to easier agglomeration of the dust, making it less prone to activation. Additionally, excessive moisture also absorbed more heat, reducing the ignition sensitivity of the dust cloud and resulting in a continuous increase in cm. However, increasing the initial temperature and decreasing the dust particle size both decreased the cm of moist magnesium powder, weakening the effect of ERH on cm. Furthermore, using the analysis methods of orthogonal experimental range and AHP model, it was determined that the influence weights of the factors coupling effects on the cm of magnesium powder, from highest to lowest weight, were: particle size > ERH > initial temperature.Furthermore, in order to deeper understand the mechanism of the action process that affect the cm of moist magnesium powder, additional experiments were conducted to further confirm that the addition of hydrogen derived from the erosion reaction of moist magnesium powder to the explosion system can reduce the cm of magnesium dust clouds. Moreover, a quantitative mathematical model for predicting the cm of magnesium powder/hydrogen two-phase system was also established.

Seed Longevity and Ageing: A Review on Physiological and Genetic Factors with an Emphasis on Hormonal Regulation.

Upon storage, seeds inevitably age and lose their viability over time, which determines their longevity. Longevity correlates with successful seed germination and enhancing this trait is of fundamental importance for long-term seed storage (germplasm conservation) and crop improvement. Seed longevity is governed by a complex interplay between genetic factors and environmental conditions experienced during seed development and after-ripening that will shape seed physiology. Several factors have been associated with seed ageing such as oxidative stress responses, DNA repair enzymes, and composition of seed layers. Phytohormones, mainly abscisic acid, auxins, and gibberellins, have also emerged as prominent endogenous regulators of seed longevity, and their study has provided new regulators of longevity. Gaining a thorough understanding of how hormonal signalling genes and pathways are integrated with downstream mechanisms related to seed longevity is essential for formulating strategies aimed at preserving seed quality and viability. A relevant aspect related to research in seed longevity is the existence of significant differences between results depending on the seed equilibrium relative humidity conditions used to study seed ageing. Hence, this review delves into the genetic, environmental and experimental factors affecting seed ageing and longevity, with a particular focus on their hormonal regulation. We also provide gene network models underlying hormone signalling aimed to help visualize their integration into seed longevity and ageing. We believe that the format used to present the information bolsters its value as a resource to support seed longevity research for seed conservation and crop improvement.

Hydrophilic or hydrophobic coating of whey protein aerogels obtained by supercritical-CO2-drying: Effect on physical properties, moisture adsorption and interaction with water and oil in food systems

Aerogel monoliths, prepared by water-to-ethanol substitution and supercritical-CO2-drying of whey protein hydrogels, were dip-coated with hydrophilic (alginate, AL; agar, AG) or hydrophobic (ethylcellulose, EC) polymers. AL coating induced aerogel collapse, due to solvent absorption. AG and EC rapidly set onto aerogel surface, forming layers of 65 and 100 μm thickness, respectively. While AG-coating induced 20% volume shrinkage, 25% apparent density increase and 75% firmness increase, EC-coating maintained the original aerogel structure. Upon exposure to 100% equilibrium relative humidity, aerogels showed moisture uptake in the order AG-coated>uncoated>EC-coated. When immersed in water or oil, the AG-coated aerogel showed an uptake respectively 40 and 60% lower than the uncoated control. The oil barrier capacity of AG-coated aerogel was also demonstrated in a lipid food system (stearin-oil mixture). Although not reducing oil uptake, EC-coating reduced water uptake by 30% and its water barrier properties were demonstrated upon immersion in an aqueous food system (water-flour batter). Industrial relevanceThe obtained results indicate tailored coating as a feasible strategy to enhance aerogel functionality in food. This would open further possibilities, including the use of aerogels as smart food ingredients able to modulate aroma and bioactive delivery both in the food product and during digestion. These findings are thus important in supporting the industrial development of aerogel-based ingredients with customized functionalities.

Bulk Grain Cargo Hold Condensation Based on Computational Fluid Dynamics

In order to assess whether condensation will occur on the shipside of a bulk grain cargo hold during transportation at sea, this paper has established a ventilation model for the bulk cargo hold of the ship, and optimized the model according to the characteristics of the solid bulk grain stowed on a moving ship at sea. The temperature field, micro-airflow field and relative humidity field of the bulk grain in a cargo hold are simulated by using fluent software (v.2020). Incorporating the impact of grain moisture exchange, the Equilibrium Relative Humidity (ERH) method is introduced alongside the Dew Point (DP) method to determine the condensation on the shipside of the cargo hold. The results of simulation are in agreement with the practical observation results obtained from an actual ship with a heavy cargo damage claim. Conclusively, this paper finds that the risk of the condensation on the shipside of a bulk grain cargo hold always exists if the inner part of the shipside is directly in contact with the grain. Meanwhile, when the grain temperature near the shipside decreases, the moisture in the cargo hold will migrate to the shipside due to the temperature gradient. Furthermore, the longer the voyage, the more obvious the migration of moisture from the central part of the bulk grain to the shipside, and the greater the risk of condensation.

Viability of ‘ōhai Sesbania tomentosa seeds after 3 decades of ambient conditions

Abstract The plant species Sesbania tomentosa (‘ōhai; Fabaceae) is endemic to the Hawaiian Islands, federally listed as endangered in the USA and has been proposed for categorization as Vulnerable on the IUCN Red List. In 2021, c. 12,000 seeds from 12 seed lots collected during 1990–1992 from across the Hawaiian Islands were discovered in ambient herbarium conditions (55% relative humidity (RH) at 20 °C). International gene bank standards suggest drying seeds in equilibrium with 15% RH and stored at −18 °C. To investigate seed viability, we mechanically scarified then sowed 15 seeds from each accession at daily alternating regimes of 12 h light and 12 h dark at temperatures of 25/15 °C, respectively. Germination was observed after 7 days and ended after 34 days. Mean final germination was 88.9 ± SD 0.1% (range 73–100%). Each seed lot was accessioned into the National Tropical Botanical Garden's Seed Bank and Laboratory. In seeds with a water-impermeable seed coat (i.e. physical dormancy), such as S. tomentosa, seeds can desorb but not absorb water. Therefore, if the seeds were initially dried, although exposed to high RH for up to 32 years, seed equilibrium RH may have remained low, which may in part explain the observed high germinability. This study holds significance for managers who are working to conserve this endangered Hawaiian species and suggests that even suboptimal conditions may still yield highly viable seeds several decades into the future.

Effect of equilibrium relative humidity on explosion characteristics parameters of humid magnesium dust

In a humid environment, active metal magnesium is susceptible to the hydrogen evolution reaction with water, which significantly increases the risk of explosions in areas where magnesium is produced and used. In this paper, the effects of equilibrium relative humidity (ERH) on the explosion characteristics parameters of magnesium dust under various initial conditions (concentration, particle size and temperature) were studied using a 20 L explosion device. Additionally, the explosion mechanism was thoroughly analyzed by incorporating the oxygen content results of the explosion products. The research revealed that explosion characteristics parameters (Pmax, (dp/dt)max) of magnesium dust cloud initially increased and then decreased with rising ERH when the explosion system was in an “oxygen-rich” state. The maximum increments in Pmax and (dp/dt)max are 130 kPa and 10.73 kPa/ms, respectively. Moreover, a decrease in particle size and an increase in temperature facilitated the generation of more hydrogen from the humid magnesium dust. This phenomenon effectively improved the explosion characteristics parameters of the humid magnesium dust, thereby increasing the sensitivity and risk of the explosion system. However, in the case of a high degree of “oxygen-poor” state, the derived hydrogen instead became burdensome, resulting in an excessive amount of magnesium dust that was unavailable for reaction. This led to a decrease in the explosion characteristics parameters of humid magnesium dust, with the maximum decreases in Pmax and (dp/dt)max being 45.8 kPa and 2.1 kPa/ms respectively.

Efficacy of acidified water-in-oil emulsions against desiccated Salmonella as a function of acid carbon chain-length and membrane viscosity.

Sanitizing low-moisture food (LMF) processing equipment is challenging due to the increased heat resistance of Salmonella spp. in low-water activity (aw) environments. Food-grade oils mixed with acetic acid have been shown effective against desiccated Salmonella. In this study, different hydrocarbon chain-length (Cn) organic acids were tested against desiccated Salmonella by using 1% v/v water-in-oil (W/O) emulsion as the delivery system for 200 mM acid. Fluorescence lifetime imaging microscopy (FLIM) was utilized with a BODIPY-based molecular rotor to evaluate membrane viscosity under environmental conditions such as desiccation and temperature elevation. Drying hydrated Salmonella cells to 75% equilibrium relative humidity (ERH) increased the membrane viscosity from 1,199 to 1,309 mPa·s (cP) at 22°C. Heating to 45°C decreased the membrane viscosity of hydrated cells from 1,199 to 1,082 mPa·s, and decreased that of the desiccated cells from 1,309 to 1,245 mPa·s. At both 22°C and 45°C, desiccated Salmonella was highly susceptible (>6.5 microbial log reduction (MLR) per stainless-steel coupon) to a 30-min treatment with the W/O emulsions formulated with short carbon chain acids (C1-3). By comparison, the emulsion formulations with longer carbon chain acids (C4-12) showed little to no MLR at 22°C, but achieved >6.5 MLR at 45°C. Based upon the decreased Salmonella membrane viscosity and the increased antimicrobial efficacy of C4-12 W/O emulsions with increasing temperature, we propose that heating can make the membrane more fluid which may allow the longer carbon chain acids (C4-12) to permeate or disrupt membrane structures.

Contrasting seed moisture sorption behaviour between two species and the implication for seed longevity

AbstractUnderstanding seed moisture desorption and adsorption isotherms is important for seed quality maintenance and better predicting seed storage lifespan. Freshly harvested oilseed rape and barley seeds were dried and then rehydrated twice. Seed equilibrium relative humidity (eRH) and moisture content (MC) were determined at different humidity levels so that two cycles of desorption and adsorption could be constructed. In addition, seeds were dried to 30% RH and then rehydrated to 50% RH for five cycles to determine whether they shift to the adsorption isotherm. Monolayer MC was determined using the Gugenheim-Anderson-de Boer model. Storage experiments were conducted for seeds equilibrated at 30, 40, 50, 60 and 70% RH for two cycles of desorption and adsorption at 45°C. Isotherm curves’ shapes were similar for oilseed rape and barley, although spanning a greater MC range in barley. The hysteresis effect was observed for oilseed rape and barley seeds when dried over silica gel at &lt;10% RH. However, this effect was only observed for barley seeds when dried to 30% RH, but not for oilseed rape seeds. Longevity was greater for adsorbing seeds than desorbing seeds at a given eRH, however, there was no significant difference in σ (the standard deviation of the normal distribution of seed deaths over time)–MC log–log relationship. The relationship shifted for seeds on the second cycle. In conclusion, if seed lots are stored at a specific RH, reaching equilibrium by desorption or adsorption can strongly influence their longevity. Also, when seeds of different species are dried to low RH, they will respond differently to a subsequent increase in RH, which could profoundly affect their longevity.

Oil-Based Sanitization in Low-Moisture Environments: Delivery of Acetic Acid with Water-in-Oil Emulsions.

Contamination with Salmonella spp. and Listeria monocytogenes is concerning across low-moisture food (LMF)-processing environments due to the pronounced survival of these organisms under dry conditions. This study treated desiccated bacteria with acetic acid delivered by oil with and without water-in-oil (W/O) emulsion. The influences of cellular desiccation, emulsion water concentration, water activity (aw), and treatment temperature were investigated. Acetic acid dissolved in oil (i.e., acidified oil) showed low levels of antimicrobial efficacy. After treatment with acidified oil (200 mM acetic acid at 22°C for 30 min), Salmonella enterica serovar Enteritidis phage type 30 cells desiccated to 75% equilibrium relative humidity (ERH) and 33% ERH were reduced by 0.69 and 0.05 log CFU/coupon, respectively. The dispersion of a low level of water (≥0.3%, vol/vol) within the acidified oil with the surfactant (i.e., acidified W/O emulsion) significantly enhanced the antimicrobial efficacy. After treatment with the acidified W/O emulsion (200 mM acetic acid at 22°C for 20 min), desiccated Salmonella (4-strain cocktail) and L. monocytogenes (3-strain cocktail) cells were reduced by >6.52 log most probable number (MPN)/coupon, regardless of the desiccation levels. Increased efficacy was observed with temperature elevation. Reduced efficacy was observed when glycerol was added to the aqueous phase of the emulsion to decrease the solution aw, indicating that the enhanced efficacy of the acidified W/O emulsion was associated with differential osmotic pressure. The antimicrobial mechanism may be due to the membrane disruption induced by acetic acid, in combination with the hypoosmotic stress provided by W/O emulsion, creating cellular lysis, as illustrated by electron micrographs. IMPORTANCE Aqueous-based cleaning and sanitation are undesirable in processing facilities that manufacture low-moisture foods such as peanut butter and chocolate. Alcohol-based sanitization is advantageous because it leaves no residue on the contact surface but requires the processing facility to close temporarily due to flammability. At >6.52 log kill of desiccated Salmonella and Listeria monocytogenes cells, the developed oil-based formulation has the potential to be an effective dry sanitation method.

Effect of Wood Extractives on the Equilibrium Moisture Content of Six Sudanese Hardwood Species

The objective of this investigation was to study the effect ofextractive content on the wood sorption isotherms of six Sudanese hardwoodspecies i.e. Acacia nilotica, A.senegal, Anogeissus leiocarpus, Boswelliapapyrifera, Ailanthus excelsa and Calotropis procera growing in North andSouth Kordofan States. For each species, wood samples were collected fromsix trees, from which specimens were prepared. The effect of extractives onequilibrium moisture content was studied by comparing the equilibriummoisture content of hot water extracted and unextracted wood. Experimentalequilibrium moisture content values for extracted and unextracted specimenswere obtained at different levels of relative humidity. These specimens wereplaced in a closed desiccator, which contained saturated salt solution ordifferent concentrations of sulphuric acid to maintain relative humidity andthen kept in an oven at the specified temperature (60 ○C) until equilibriummoisture content was obtained. Desorption and adsorption isotherms of thesix wood species exhibited sigmoid curves. The results showed directrelationship between equilibrium moisture content and relative humidity thatcould be well explained by third-order polynomial functions. The effect ofextraction was significant at few relative humidity values in some species;unextracted wood had higher equilibrium moisture content than extractedwood.

A Physicochemical Study of Cost-Effective Liquid Desiccants for Use in an air conditioning systems

Liquid desiccant systems (LDS) have attracted attention as promising low-energy alternative cooling solutions relative to conventional systems. An integral part of the LDS dehumidification capability depends on the composition of the hygroscopic desiccants utilized. The vapour pressure of different hygroscopic salt solutions and mixtures thereof have been measured at a temperature of 298.15K using a Yamamoto configuration. The initial validation of the measurement configuration using a single salt solution has exhibited a satisfactory correlation with vapour pressures reported by previous authors at various concentrations. The performance of MgCl2 solution was found to be comparable to that of LiCl. The results have shown that MgCl2 solution with 30% w/v concentration is sufficient to maintain the equilibrium relative humidity (ERH) at 50%, the recommended value for the human comfort zone, a value close to that obtained from LiCl solution (ERH = 55%) with the same concentration. Moreover, the best performing salt solution mixtures were found to be magnesium and lithium chlorides. Considering that the cost of LiCl is 23 times higher than that of MgCl2, the potential replacement of LiCl with MgCl2 in LDS is very promising from both a performance and cost point of view. The concentrated seawater brines have also shown a very promising performance comparable with that of 50% CaCl2– 50% MgCl2 artificial mixture.

An adaptive grain-bulk aeration system for squat silos in winter: Effects on intergranular air properties and grain quality

Grain can be stored for long periods under suitable storage conditions. The present study investigated the effects of cooling aeration on the intergranular air properties and grain quality of wheat stored in two squat silos during winter. In the first silo, 4759 tonnes of bulk wheat were downward-aerated in a suction-type way by four 11 kW centrifugal ventilation fans at an airflow rate of 10.1 m3/(h·t). The fans were firstly controlled by software based on a smart de-moisturization aeration model, and the grain bulk lost 0.8% moisture content (MC) and its average temperature was decreased by 5.8 °C. When the fans were then controlled using smart cooldown aeration model, the average bulk temperature decreased from 17.0 to 5.2 °C, and the average bulk MC was reduced by 0.6%. The cooling fronts moved predictably through the bulk layers during cooldown aeration, which consumed energy at a rate of 0.067 . In a second silo, 4,675 tonnes of wheat were also downward-aerated at 9.8 m3/(h·t) using smart cooldown aeration model and four 5.5 kW mixed-flow fans. There was a 0.7% MC loss and the average bulk temperature decreased by 6.7 °C. Except for the middle part (fourth and seventh) bulk layers, the other bulk layers in this silo had cooling fronts that moved at similar speeds. The energy consumed by cooldown aeration was 0.040kWh(t·∘C)−1 and 58% unit energy consumption was lowered when compared to a local grain squat silo with geosynclinal ventilation ducts under artificially controlled cooling-ventilation operations. The running conditions for the ventilation fans during cooldown aeration in the squat silos were verified. (i) The temperature difference between the grain bulk and ambient air was ≥ 4 °C. (ii) The humidity ratio of the grain bulk was higher than that of the ambient air. The equilibrium relative humidity of the intergranular air tended to decrease in both silos. After cooldown aeration, the wheat kernels had a higher water absorption rate and fatty acid value, retentive peak temperature of gelatinization, and a higher dough development time, protein network strength, and starch gelatinization rate. The proposed aeration control system has good application potential in squat silos used for grain storage.

On the rate of cooling of aerated food grains

Aeration is one of the most powerful tools available to the managers and handlers of stored grains. Irrespective of the initial temperature and moisture content of the grains, the biological and chemical phenomena that occur in the stored grains are significantly influenced by the wet bulb temperature of the air entering the grain. Several authors have developed mathematical expressions to estimate the rate at which aerated stored grains and other hygroscopic materials cool. They refer to ‘difficulties in comprehension’, remark that ‘results are difficult to interpret’ and ‘necessarily complicated’. The principal objective of this work is to clarify and quantify the factors that determine the rate of cooling aerated food grains. This is achieved by deriving an equation that arises as a direct consequence of the conservation of energy and moisture in aerated grains. It is found that the rate of cooling of aerated grains depends strongly on the sorption isotherm, a mathematical function that relates grain moisture content to the equilibrium relative humidity and temperature of their surrounding atmosphere. The integral heat of wetting, a function of the sorption isotherm, contributes to the effective specific heat of grains. However, its effects are typically neglected in analyses of the rate at which aerated grain cools because published sorption isotherms are insufficiently accurate for them to be included. It is proposed that a multidisciplinary approach be taken to measuring the psychrometric properties of food grains. • A new and simple equation is derived for the rate of cooling of aerated grains. • The equation highlights the factors that govern the rate of grain cooling. • Published sorption data lead to inconsistent values of the heat of sorption.

Storage Conditions and Adsorption Thermodynamic Properties for Purple Corn.

Adsorption isotherms provide insight into the thermodynamic properties governed by food storage conditions. Adsorption isotherms of purple corn of the Canteño variety were evaluated at 18, 25, and 30 °C, for the equilibrium relative humidity (ERH) range between 0.065 and 0.95. The equilibrium moisture (Xe) was determined by the continuous weight-change method. Seven mathematical models of isotherms were modeled, using the coefficient of determination R2, mean absolute error (MAE), and estimated standard error (ESE) as the convergence criterion. Thermodynamic parameters such as isosteric heat (qst), Gibbs Free Energy (ΔG), differential entropy (ΔS), activation energy (Ea), and compliance with the isokinetic law were evaluated. It was observed that the adsorption isotherms presented cross-linking around 75% ERH and 17% Xe, suggesting adequate storage conditions at these values. The GAB and Halsey models reported better fit (R2 > 97%, MAE < 10%, ESE < 0.014 and random residual dispersion). The reduction of Xe from 17 to 7%, increases qst, from 7.7022 to 0.0165 kJ/g, while ΔG decreases considerably with the increase in Xe, presenting non-spontaneous endergonic behavior, and linear relationship with ΔS, evidencing compliance with the isokinetic theory, governed by qst. Ea showed that more energy is required to remove water molecules from the upper layers bound to the monolayer, evaluated using CGAB. The models predicted the storage conditions, and the thermodynamic parameters show the structural stability of the purple corn grains of the Canteño variety during storage.

Evaluating isotherms and isosteric heat utilization during sorption characteristics of feed barley

A well-formulated sorption model defines the grain moisture and also the energy expenses associated with drying and/or rehydration. Though literature contains adsorption and desorption models that are used to identify the hysteresis, they are not efficient to implement in sensors simultaneously when monitoring stored grain transient conditions. This study modifies the existing sorption model to fit transient monitoring criteria based on harvest moisture conditions between 11.3 and 85.9% RH at three temperatures (15, 25 and 35 °C). Feed barley was taken for the sorption study and fitted with equilibrium moisture content (EMC) and equilibrium relative humidity (ERH) equations of five widely used isotherm models, respectively. Model was fitted with EMC's attained at individual temperatures and the transfer phases between them.Sorption isotherms showed a non-smooth Type II sigmoidal trend with positive correlation between RH and EMC. The time taken to reach EMC irrespective of RH was inversely proportional to the temperature difference noted from the transfer phase. The Modified-Oswin equation (EMC) was found to be appropriate to represent the sorption isotherm of feed barley. For the transfer phases, EMC at higher temperature showed negligible difference with initial EMC phase except at 15 °C with higher RH (adsorption). Heat of sorption showed a decreasing trend with moisture and was 27% (average) higher than the latent heat of vaporization. Sorption heats for transfer phases were higher than initial EMC phases but not significantly different. Energy difference went up to 250 kJ kg−1 between 9 and 14% db moisture showing a normal distribution below and above the moisture range, respectively. Thus, future storage models should consider sorption heats for proper estimation of energy expenses during drying and rehydration.