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Models for Sorption Isotherms for Foods: A Review
Drying Technology
Abstract
This article presents basic concepts related to the thermodynamics of sorption of water and measurement of sorption isotherm for food materials. A comprehensive review of the widely used sorption models is presented. Various statistical techniques used to ascertain the effectiveness of a model to describe the sorption data are discussed. It is anticipated that this article will provide useful information to researchers pursuing work on sorption behavior of food materials as well as modeling of drying processes.
... (6)): (6) and the value of the root mean square error (RMSE) (Eq. (7)) expressed in %: (7) where: N -number of data, v e -experimental equilibrium water content (g H 2 O 100 g -1 d.m.), v o -equilibrium water content predicted with the model (g H 2 O 100 g -1 d.m.) as the criteria most frequently used in statistical analysis (Basu et al., 2006;Ocieczek et al., 2022;Pałacha and Sas, 2016). ...
... This relationship, however, is definitely more complex than the mutual ratio of these two components and will therefore be subject to in-depth analysis later in the work. Sorption isotherms are one of the best tools for both examining the mechanism of surface adsorption and providing the basis for determining such parameters as monolayer capacity, the extent of change in energy accompanying the sorption process or estimating the radii of capillaries filled after initiating capillary condensation, and estimating the total volume of capillaries in the capillary condensation area (Basu et al., 2006). The obtained data (Fig. 1) indicate that the sorption mechanism followed the same pattern in all the tested powders and that the sorption isotherms had a sigmoidal shape (Figura and Teixeira, 2007;Ocieczek and Makała, 2019;Ocieczek et al., 2022). ...
... However, taking into account that the BET model is a special case of the GAB model (Kludský et al., 2018) and that it has certain limitations in describing sorption isotherms, the sorption parameters were estimated also based on the GAB model (Table 5), which is used for a much wider range of a w data, i.e., a w <0.93 (Basu et al., 2006;Aviara, 2020). ...
... Compared to other chemical compositions, water has a prime impact on reaction and quality of foods (Al-Muhtaseb et al., 2002). In this case, water activity, which is expressed as aw, can be used to control food stability since it may reduce microbial growth rate and chemical reactions (Basu et al., 2006). At a constant temperature, the relationship between moisture content and aw is depicted in a moisture sorption isotherm (MSI), which reveals a non-linear line or a sigmoidal pattern in most food products, and these foods are classified as isotherm type II (Al-Muhtaseb et al., 2002). ...
... At a constant temperature, the relationship between moisture content and aw is depicted in a moisture sorption isotherm (MSI), which reveals a non-linear line or a sigmoidal pattern in most food products, and these foods are classified as isotherm type II (Al-Muhtaseb et al., 2002). Moreover, MSI curve can be applied to estimate changes of food stability and shelf life and suggest suitable packaging (Basu et al., 2006). However, intensive studies discussing drying rate, MSI models, and the role of aw on physical and chemical properties of walang leaves under different drying procedures have not been carried out. ...
... Most models of MSI curves were proposed in literatures (Basu et al., 2006). In this work, GAB, Oswin, Chen-Cleyton, Smith, Halsey, Henderson, and Caurie models were presented (Table 1) and applied to determine the most suitable models. ...
Water activity (aw) plays a crucial role in controlling microbial growth and chemical reactions in food products. This study explores the impact of aw on the physical and chemical properties of walang leaves dried using five different methods: sun drying (SD), sun drying with fan (SDF), fluidized bed drying (FBD), air drying (AD), and freeze drying (FD). The drying methods produced varying drying rate equations. The Wang and Singh model was identified as the most suitable for describing the drying rate. Moisture sorption isotherm (MSI) models varied, with SDF and AD aligning with the Hasley model, SD (Oswin model), and FBD (GAB model). Significant changes in moisture content, color, total phenolic content (TP), and antioxidant activity (AA) were observed across different aw zones, particularly in zone III. The Dunnett test revealed significant differences in TP, L*, and ΔE between dried leaves and FD controls (p 0.05), but no significant differences in MC, aw, color attributes, or AA (p>0.05). SD was recommended for drying walang leaves due to its comparable AA and the fastest drying rate.
... Numerous equilibrium sorption models have been applied to water vapor sorption in cellulosic materials in the literature [19][20][21][22][23][24][25][26][27]. These models range from simple empirical equations to theoretical models based on an idealized physical system. ...
... The original GAB model, named after Guggenheim [68], Anderson [69], and de Boer [70] is a three-parameter isotherm equation. This model has been widely used for cellulosic materials including agricultural products, paper, textiles, and wood [19,20,24,54,71,72]. The GAB model was derived from an idealized view of multilayer adsorption of molecules on the surface of an adsorbent. ...
... The original model of Oswin [73] is a two-parameter isotherm equation. It was modified to include temperature explicitly [74] and has been applied to a variety of materials including foods [20,33,75,76], wood [77], and a cellulosic membrane [78]. The abbreviation "OC3" is used for this model based on the names Oswin & Chen and the number of fitting parameters. ...
Water vapor sorption is a fundamental property of cellulosic materials. Numerous theoretical and empirical models have been developed to describe the relationship between water activity, temperature, and equilibrium moisture content (EMC). However, a meaningful connection between model parameters and thermodynamic properties related to the sorption process is often lacking. In cases where models yield thermodynamic properties, such as through use of the Clausius-Clapeyron equation, these are limited to temperatures where the ideal gas equation is applicable. In this paper we advance a thermodynamic framework and formulate a new semi-empirical sorption model based on the differential Gibbs energy of sorption as a function of EMC and temperature, intended for high temperature applications such as steam drying or fire modeling. We refer to this as the Comprehensive Analytical Sorption Thermodynamic (CAST) model. It has six parameters, includes temperature explicitly, and is invertible. The CAST model includes analytical equations for the differential enthalpy of sorption, the differential entropy of sorption, and the integral heat of wetting. The model is evaluated using sorption data and calorimetric data over a range of temperatures from the wood science literature and compared with several existing models. Overall, the CAST model fits the experimental sorption and calorimetric data with higher accuracy than existing models.
... Type III, the Flory-Higgins isotherm, indicates adsorption on macroporous adsorbents with weak adsorbate-adsorbent interactions. Although both types IV and V represent adsorption isotherms with hysteresis and great adsorption energy in mesoporous materials, type IV describes adsorption by a swellable hydrophilic solid until a maximum of hydration sites is reached (Basu, Shivhare, and Mujumdar 2006). Finally, type VI corresponds to either material with multiple pore sizes or a phase change of multilayer adsorption in which the adsorption process is realized in several steps. ...
... However, the BET isotherm equation demonstrates a strong correlation within the range of relative humidities from 5% to 45% (Chirife and Iglesias 1978), while the GAB model offers a more accurate fit across a wider range of relative humidities. Nevertheless, the GAB model underestimates water content values when the relative humidity exceeds 90% (Basu, Shivhare, and Mujumdar 2006;Yanniotis and Blahovec 2009). ...
... It is common practice to analyze the sorption isotherms of a substance individually for each temperature in relation to the corresponding relative humidity levels. The simultaneous prediction of sorption isotherms at various temperatures has been accomplished using multitemperature fitting techniques (Myhara et al. 1998;Karoglou et al. 2005;Basu, Shivhare, and Mujumdar 2006;Pakowski et al. 2011;Furmaniak 2014). To streamline the process, reducing the number of best-fit parameters is advantageous. ...
The temperature dependency of the adsorption isotherm renders its significance as one of the primary input parameters in models dealing with moisture transport. The present study involved the determination of the adsorption isotherm of sixteen building materials from various categories, including cladding, building paper, wood, sheathing boards, and insulations. The measurements were conducted under nine climatic conditions, a combination of three temperatures (3°C (37.4°F), 21°C (69.8°F), 45°C (113°F)) and three relative humidity levels (50%, 70%, 90%). The study indicated that relative humidity increased the building materials' equilibrium moisture content (EMC). In opposition, an increase in temperature decreased the EMC of the tested materials. It was discovered that cellulose fibre and wood-based materials had a greater capacity to store moisture than others. Conversely, the minimum moisture content was observed in brick, Densglass gold gypsum, and EPS products. Furthermore, we used the ABC model as an adaptable mathematical equation for a novel nonlinear surface fitting of adsorption isotherms of tested materials to make optimal use of the experimental data and effectively analyze the simultaneous impact of all temperatures and relative humidities. Tested against the measured experimental data, we obtained the best R-squared values from the second-order polynomial Equation.
... he basis of several statistical parameters, but all favore indices of model selection by the goodness of fit, including the correlation coefficient or coefficient of determination, root mean squared error and the mean relative deviation. The selection of a sorption isotherm model with graphical evaluation of the residual randomness is also popular (Basu et. al., 2006;Ruiz-Lopez et. al., 2009). ...
... e two data sets. The closer (R 2 ) the values are to 1, the better is the fit. The (RMSE) and the (MRD) are both measures of deviation between experimental and predicted value. Low values of (RMSE) and (MRD) indicate higher ability of the model to describe the experimental data. These statistical parameters were combined into the performance index (Basu et. al., 2006). ...
... Plotting of the residuals against independent variable is a measure of distribution errors. If the sorption model is correct, then the residual should be only random independent errors with a zero mean, constant variance and arranged in a normal distribution. If the residual plots indicate a clear pattern, the model should not be accepted (Basu et. al.,2006;Ruiz-Lopez et. al., 2009). ...
In this paper, the results of comparative analysis between transcendental and cyclometric sorption isotherm models are presented. In order to find which model gives the best results, some numerical experiments were made. The experimental data set for equilibrium moisture content and the water activity for apple, pear, kiwi and banana at two different temperatures were used from the scientific literature. For each model and data set, several statistical parameters were calculated and models were ranked after-wards. The performed comparative analysis shows that the cyclometric models in many cases have higher values of the coefficient of determination, and lower values of the root mean squared error and the mean relative deviation than transcendental the isotherm models. All these results show that the cyclometric sorption isotherm models give the best overall fit to experimental data. After choosing the best transcendental and cyclometric model with the high value of statistical performance index, the residual plot was checked graphically. REZIME U ovom radu su prikazani rezultati uporedne analize između transcedentalnih i ciklometriskih modela izoterme sorpcije. Da bi pronašli koji model najbolje aproksimira ekeperimentalne rezultate izoterme sorpcije urađeni su numerički eksperimenti. Iz literature su korišćeni eksperimentalni podaci za sadržaj ravnotežne vlage i aktivnost vode za jabuke, kruške, kivi i banane za dve različite temperature. Za svaki model i set podataka proračunato je nekoliko statističkih parametara i onda su modeli rangirani. Iz uporedne analize očigledno je da ciklometriski modeli u većem broju slučajeva imaju visoke vrednosti za koeficijente detreminacije, kao i niske vrednosti za srednje kvadratne greške i srednje relativne devijacije nego transcedentalne modele. Svi ovi rezultati pokazuju da cik-lometriske modele bolje aproksimiraju eksperimentalne rezultate izotreme sorpcije. Nakon odabira najboljeg transcendentalnog i ciklometriskog sorpcionog modela sa visokim vrednostima statističkog indeksa, grafički su provereni njihove ostatci regresije.
... The sorption isotherms of biological and food materials are mostly of sigmoid shape (Brunauer, 1943;Blahovec & Yanniotis, 2009), and they had been classified according to their shape and processes (Bell & Labuza, 2000). The isotherms most frequently found in food products are the sigmoidal types 2, 3 and 4 (Blahovec & Yanniotis, 2009;Basu et al., 2006;Mathlouthi & Roge, 2003). The water sorption isotherms usually describe the relationship between the equilibrium moisture content and water activity at a certain temperature. ...
... The GAB isotherms of Dambun Nama at 33.8 o C and 50 o C are generally shaped like the type 4 isotherms for food products. Type 4 isotherms indicate the behaviour of a swell-able hydrophilic solid (Basu et al., 2006). The two curves on each graph indicate the adsorption and desorption behaviour of the product at a particular temperature condition and a specific storage period. ...
Water adsorption isotherms of Dambun Nama, a ground beef product, were determined over a storage period of six months, at an average ambient temperature of 33.8 o C and an accelerated temperature of 50 o C, using the static gravimetric method. The study was aimed at establishing the moisture sorption profile of a traditional meat product Dambun Nama common in Northern Nigeria, produced from beef and stored over a period of six months. The sample was produced using a standardized method; it was sterilized, packaged in six airtight glass containers and stored at ambient temperature as the sample stock for the analyses over a period of six months. Data was generated from the sorption studies based on the isopiestic transfer method using concentrated sulphuric acid solutions. The isotherms are generally shaped like the type 4 isotherms for food products. Between 33.8 o C and 50 o C adsorption, the monolayer moisture content ranged from 0.036 to 0.048 gH2O/g solids, and between 0.037 to 0.049 gH2O/g solids for desorption. There was a general increase in the GAB constants K and C. The correlation coefficient (R) values obtained for adsorption ranged from 0.941 to 0.959, and for desorption, the values ranged from 0.940 to 0.957, indicating that the GAB model was suitable in describing the moisture sorption profile of Dambun Nama within the prescribed water activity ranges and storage period.
... The sorption isotherms of biological and food materials are mostly of sigmoid shape (Brunauer, 1943;Blahovec & Yanniotis, 2009), and they had been classified according to their shape and processes (Bell & Labuza, 2000). The isotherms most frequently found in food products are the sigmoidal types 2, 3 and 4 (Blahovec & Yanniotis, 2009;Basu et al., 2006;Mathlouthi & Roge, 2003). The water sorption isotherms usually describe the relationship between the equilibrium moisture content and water activity at a certain temperature. ...
... The GAB isotherms of Dambun Nama at 33.8 o C and 50 o C are generally shaped like the type 4 isotherms for food products. Type 4 isotherms indicate the behaviour of a swell-able hydrophilic solid (Basu et al., 2006). The two curves on each graph indicate the adsorption and desorption behaviour of the product at a particular temperature condition and a specific storage period. ...
Water adsorption isotherms of Dambun Nama, a ground beef product, were determined over a storage period of six months, at an average ambient temperature of 33.8oC and an accelerated temperature of 50oC, using the static gravimetric method. The study was aimed at establishing the moisture sorption profile of a traditional meat product Dambun Nama common in Northern Nigeria, produced from beef and stored over a period of six months. The sample was produced using a standardized method; it was sterilized, packaged in six airtight glass containers and stored at ambient temperature as the sample stock for the analyses over a period of six months. Data was generated from the sorption studies based on the isopiestic transfer method using concentrated sulphuric acid solutions. The isotherms are generally shaped like the type 4 isotherms for food products. Between 33.8oC and 50oC adsorption, the monolayer moisture content ranged from 0.036 to 0.048 gH2O/g solids, and between 0.037 to 0.049 gH2O/g solids for desorption. There was a general increase in the GAB constants K and C. The correlation coefficient (R) values obtained for adsorption ranged from 0.941 to 0.959, and for desorption, the values ranged from 0.940 to 0.957, indicating that the GAB model was suitable in describing the moisture sorption profile of Dambun Nama within the prescribed water activity ranges and storage period.
... Cellulose starts decomposing at 275°C and hemicellulose above 150°C, while lignin shows degradation at 250 to 500°C. 36,37 So change in weight represented by arrow 1 may be due to cellulose and hemicellulose, while arrow 2 shows weight loss due to lignin decomposition. In A. hypogaea biochar a major weight change was observed at 350°C due to lignin loss. ...
... By increasing Ni ion concentration more ions are available to attach on the surface of the adsorbent, so a positive trend in adsorption was observed but further raise in concentration have no prominent effect on the rate of adsorption as the surface of the adsorbent is completely saturated by metal ions and no more spaces are available to attach metal ions. 36,39 The removal of the Cd ion concentration increased because of the positive effect of both biochar and native A. hypogaea; however, adsorption on biochar was found higher for both metal ions. Biochar provides an increase in surface area and hence more active sites for the attachment of these metal ions ( Figure S3). ...
Biochar derived from plant biomass has great potential for the decontamination of aqueous media. It is the need of the hour to test biochar derived from economical, easily available, and novel materials. In this regard, the present study provides insight into the sorption of two heavy metals, i.e., cadmium (Cd) and nickel (Ni), using native Arachis hypogaea and its biochar prepared through pyrolysis. The effect of different factors, including interaction time, initial concentration of adsorbate, and temperature, as well as sorbent dosage, was studied on the sorption of Cd and Ni through a batch experiment. Characterization of the native biowaste and prepared biochar for its surface morphology and functional group identification was executed using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Results revealed the presence of different functional groups such as −OH on the surface of the adsorbent, which plays an important role in metal attachment. SEM reveals the irregular surface morphology of the adsorbent, which makes it easy for metal attachment. Thermogravimetric analysis shows the stability of A. hypogaea biochar up to 380°C as compared with native adsorbent. The adsorption efficacy of A. hypogaea was found to be higher than that of native A. hypogaea for both metals. The best adsorption of Cd (94.5%) on biochar was observed at a concentration of 40 ppm, an adsorbent dosage of 2 g, a contact time of 100 min, and a temperature of 50°C. While the optimum conditions for adsorption of Ni on biochar (97.2% adsorption) were reported at a contact time of 100 min, adsorbent dosage of 2.5 g, initial concentration of 60 ppm, and temperature of 50°C. Results revealed that biochar offers better adsorption of metal ions as compared with raw samples at low concentrations. Isothermal studies show the adsorption mechanism as physical adsorption, and the negative value of Gibb's free energy confirms the spontaneous nature of the adsorption reaction. An increase in entropy value favors the adsorption process. Results revealed that the sorbent was a decent alternative to eliminate metal ions from the solution instead of costly adsorbents.
... The isotherm gives valuable information on the thermodynamics of food material that is convenient for process design computation and final moisture content prediction during the drying process (Langrish, 2009). The MSI can be obtained by three methods gravimetric, manometric, and hygrometric (Basu et al., 2006). Mathematical models based on the thermodynamic concept can also determine the MSI. ...
... It is also known as wetting enthalpy (Basu et al., 2006). The thermodynamic properties such as differential isosteric enthalpy and entropy (ΔH is andΔS is ) and integral enthalpy and entropy (ΔH in andΔS in ) and ...
In the present investigation, the black jamun extract was used to prepare microcapsules by freeze‐drying method with three different wall materials: maltodextrin, guar gum, and xanthan gum. The formed microcapsules were analyzed for different physicochemical properties. Moisture content and water activity were less than 6.50 g water/ 100 g and 0.38, respectively, indicating that the microbial activity can be restricted. The formed microcapsules were purple in color suggested by the positive values of color parameter “a”. The hygroscopicity, solubility, and degree of caking for the microcapsules were found to be in the range of 11.14–15.77 g/100 g, 70.12%–76.36%, and 22.31%–30.22%, respectively. The glass transition temperature was in the range of 88–135°C for the formed microcapsules. The encapsulation efficiency, total anthocyanin content, and antioxidant activity were higher for the maltodextrin‐based microcapsule that was found to be 71.88%, 6.01 C‐3‐G mg/g and 94.16% DPPH radical scavenging activity, respectively.
Practical application
Black jamun (Syzygium cumini) is a rich source of anthocyanin which is unstable due to light, oxygen and temperature. Moreover the fruit also contain health beneficial substances that are unstable at normal conditions. Therefore, the encapsulation method can improve the stability of the compounds and improve the release of active component in the microcapsule in food. Microencapsulation provide barrier to temperature, light and pH. In food industry microcapsules containing agricultural produce extract can be used for the fortification of food products in enhancing the nutritive value of the product while processing.
... While Hay et al. (2023) suggest that a w should be used directly without converting to moisture content, seed moisture isotherms are commonly used to relate a w to moisture content. These isotherms show the relationship between water content and a w at a constant temperature and can be either absorbing or desorbing (Bell and Labuza, 2000;Basu et al., 2006;Rezaei et al., 2023Rezaei et al., , 2024. Here, we determined 'partial isotherms' over the a w range 0.3-0.65 to help us understand whether the a w measurements could be related to seed moisture content for treated seeds. ...
Seed moisture is a crucial aspect of seed quality which reflects the physiological status of the seed tissues. The International Seed Testing Association (ISTA) currently requires seed moisture to be reported as the percentage – by weight – of the sample that is water, most often determined using the constant temperature oven method. The introduction of water activity ( a w ) as an alternative method is being evaluated, hence in this study, we determined the moisture relations of film-coated or pelleted vegetable seeds to see whether a w measurement is a reliable method to assess seed moisture status. The film coating used on these seeds did not significantly change the relationship between seed moisture content (MC; % fresh weight) and a w for carrot and endive seeds. There were some differences in the relationship between control (non-coated) and film-coated lettuce seeds. The sowing unit of pelleted seeds of lettuce (primed seeds) and chicory showed very much lower moisture contents, suggesting that the pellet material had very different moisture relations compared with the seeds themselves. Moisture history, including priming, is an important consideration when reporting a w results.
... In addition, MSI help to determine appropriate packaging and storage conditions. [18,19] Therefore, the present study aimed to obtain and characterize the DFC of Mexican hawthorn fruit fractions (pulp, peel, and seed) and evaluate its properties as a potential food ingredient. The assessment encompassed dietary fiber composition, functional properties, and the hygroscopicity through sorption isotherms. ...
Mexican hawthorn fruit (Crataegus mexicana), also known as Tejocote, is an underexploited native Mexican fruit. This study aimed to determine the composition, antioxidant activity, and moisture isotherms of dietary fiber concentrates (DFC) obtained from Mexican hawthorn fruit fractions (pulp, peel, and seed) to assess their suitability as food ingredients. High molecular weight and low molecular weight soluble, insoluble, and total dietary fiber (SDFP and SDFS, IDF, and TDF, respectively) were also determined. Some techno-functional properties were measured including water and oil retention capacity, solubility, and swelling capacity. The TDF content followed the order seed >peel> pulp (92.84 ± 0.81, 59.44 ± 1.43, and 48.38 ± 0.42 g·100 g⁻¹ db). The highest SDF:IDF ratio was found in pulp DFC (0.08:1), highly correlated with its techno-functionality. Conversely, phenolic content and antioxidant activity were higher in the peel DFC. GAB and Peleg models were more suitable for fitting the experimental data for moisture isotherms, which displayed a BET type III behavior for both adsorption and desorption. This study provides novel and supportive information for revalorizing Mexican hawthorn fruit as a potential ingredient in food and functional products.
... In particular, the Aw of the FD products of G9, W8, and JX increased more rapidly than the WN and GN. Dried products with higher carbohydrate content are more prone to absorbing moisture from humid circumstances due to the larger vapor pressure deficit between the products and the circumstance (Basu, et al., 2006). Thus, a higher soluble sugar level (Table 1) might be the main reason for the rapid Aw increase in the G9, W8, and JX during storage. ...
Freeze-drying of restructured peaches provides more consistent quality at both macro and micro levels compared to freeze-drying of natural peach flesh, thereby enhancing precision, customization, and standardization in production. However, the impact of restructuring on the quality characteristics of freeze-dried products remains unclear. To investigate the applicability of restructuring in peach fruits and to assess the disparities in physicochemical characteristics between freeze-dried natural and restructured peaches, Green 9, White Honey 8, White Nectarine, Golden Nectarine, and Jinxiu Yellow Peach were subjected to restructuring followed by freeze-drying. The samples were then stored in a drying basin (with RH of 58% ± 2%, and temperature of 25°C). Throughout the study, the physicochemical properties of both intact and restructured peaches were measured before and after restructuring and freeze-drying. The results demonstrated that the eutectic temperature, glass transition temperature, and crispness of the restructured peaches increased significantly (p < 0.05) by 1.60–13.07%, 10.60–117.37%, and 17.89–512.57%, respectively. After freeze-drying, the density, hardness, and shrinkage of the restructured peaches decreased (p < 0.05) by 15.00–42.86%, 7.22–53.80%, and 43.085–66.65%, respectively, in comparison to intact peaches. Additionally, the increase in moisture sorption, water activity, and shrinkage of the restructured peaches during storage was effectively inhibited (p < 0.05). However, the antioxidant capacity of the restructured peaches decreased. In conclusion, restructuring is a more effective processing method for freeze-dried peaches compared to intact peaches, particularly in terms of texture and storage stability.
Graphical Abstract
... Also, the physical basis of the sorption isotherm, with a detailed description of the experimental methods and various empirical or mechanistic models to obtain the sorption isotherm have been summarized (Limousin et al. 2007). Theoretical models describing the kinetics of pollutant adsorption was reviewed (Plazinski et al. 2009), as have sorption models (Basu et al. 2006). In addition, the influence of temperature on sorption equilibrium and sorption kinetics for organic micropollutants was previously compiled (Hulscher and Cornelissen 1996). ...
Information about how different conditions affect the course of sorption is variously scattered and needs to be consolidated. The paper primarily focuses on identifying the optimal sorption conditions for acid and neutral mine drainages. In this review, key parameters were assessed, including temperature, pH level, sorbent dose, initial metal concentrations, and sorption duration. This overview also includes a comparison of the advantages and disadvantages of selected types of sorbents. The sorption of many metals tends to be optimal at circumneutral pH values. The adsorptive capacity decreases with an increase in temperature for exothermic processes, whereas it increases in the case of an endothermic one. Increasing the initial concentration has a positive effect on adsorption until the sorbent is fully saturated, leading to a plateau in adsorption capacity. The knowledge gained from this research extends the spectrum of the potential sorption applications, especially in the processes of recovering the metals and sorbents by desorption.
... There will be an initial rapid loss of moisture as the seeds first dry to equilibrium with ambient RH, according to the relationship described by the moisture desorption isotherm. The moisture desorption isotherm shows the relationship between seed MC and corresponding water activity (a w ) at a specific temperature for seeds that are losing moisture (Basu et al., 2006;Hay et al., 2022). Thereafter, it is expected that the a w of most seeds will then fluctuate with the diurnal variation in RH until such time as they are dispersed or taken from the parent plant. ...
The study of seed moisture sorption isotherms helps us to understand the response of seeds to changes in moisture in their environment and how this might impact their longevity. A seed moisture isotherm shows the relationship between moisture content (MC) and water activity (a w) at a constant temperature. Seed MC is higher when it dries from a hydrated state (desorption) than when it rehydrates from a very dry state (adsorption) to the same RH, an effect known as hysteresis. Seeds on the desorption isotherm will age faster than seeds on the adsorption isotherm at the same RH due to higher MC, resulting in a more rapid decline in seed viability and vigour. In this study, moisture isotherms of seeds from diverse species were determined and modeled using the Guggenheim-Anderson-de Boer (GAB) model; the hysteresis effect was then quantified. The maximum hysteresis magnitude varied between 0.3 and 2.7% MC (occurring between 49 and 57% RH) when seeds were dried over silica gel (below 11% RH) and rehydrated. Cycling seeds between 30 and 50%, 20 and 50%, and 15 and 50% RH, it was found that seeds of barley, lupin, buckwheat, wheat and pea switch to the adsorption isotherm upon rehydration after drying at intermediate moisture levels. Thus, adsorbing seeds of these species have greater longevity than desorbing seeds at the same RH. In contrast, seeds of oilseed rape and yellow mustard do not show a hysteresis effect unless they are dried to very low MC (over silica gel), so the adsorbing seed longevity remains the same as desorbing seeds at a constant RH. It is important to consider the moisture history of seeds depending on species for better seed storage management.
... The root mean square error (RMSE) assesses the model's fitting ability relative to the number of data points; a smaller RMSE value, closer to zero, indicates better model performance. Additionally, the mean relative deviation modulus (P) reflects the fit quality, with values less than 5.0 indicating an excellent fit and values greater than 10.0 suggesting a poor fit (Alam and Singh, 2011;Basu et al., 2006). ...
... Food scientists and technologists envisaged MSI as an extremely valuable tool for predicting the potential changes in food quality and process development such as a selection of packaging material and determination of storage conditions [13,14]. MSI of an ideal food highly influences by the surface area and number of specific moisture-binding sites which is also associated with product physical characteristics including porosity and microstructure. ...
India is the largest milk producer in the world. For safe processing, distribution , and storage dairy industries require a mechanized system with modern technologies. Therefore, a major part of the fluid milk production is converted into traditional Indian dairy products. Approximately, 50% of total milk production is converted into dairy products where traditional dairy products share around 90% of the total milk products consumed in India. However, the shelf-life of traditional dairy products is the major concern due to their short shelf-life under ambient conditions. Several studies reported that by maintaining the optimum water activity, the shelf-life of traditional dairy products can be extended significantly. Most of the indigenous dairy products comes under the intermediate moisture range (a w > 6). The moisture sorption isotherm (MSI) of most indigenous dairy products showed a sigmoid type II pattern. The negative temperature coefficient of equilibrium moisture content (EMC) shows that water activity above 0.5 exerts an increasing interactive effect in most dairy products during storage at a temperature above 20 °C. The aim of current review was to study the effect of storage temperature on water activity and MSI as well as shelf-life of indigenous dairy products.
... To estimate the stability of food powders, a proper relationship between equilibrium moisture content and water activity at a particular temperature is established, commonly referred to as moisture isotherm (Basu et al., 2006;Sablani et al., 2007). The moisture isotherm plays a significant role in estimating food shelf life and reducing the time and cost of product development (Charoen et al., 2015;Muzaffar and Kumar, 2016). ...
Protein hydrolysates have become key ingredients in food sector that govern both nutritional and functional behavior of food systems. However, the hydrolysate powders in general are hygroscopic in nature making them unstable. The powder properties may vary under different processing and drying conditions which can further influence the powder stability. Thus, the study explores the effect of hydrodynamic cavitation (HC) pretreatment and drying conditions on stability and microstructure of egg white protein hydrolysate (EWPH) powder for wider food application. The HC-pretreated EWPH powder obtained from two different drying methods, namely, freeze and vacuum drying, was assessed for their stability at elevated temperatures of 25, 35, 40, 45, and 55 °C for moisture sorption isotherm analysis. The sorption isotherms of EWPH were found to have a typical type III sigmoid curve, representing a hygroscopic material that fitted the GAB model well. The HC-treated EWPHs did not have much variation with temperature showing better stability. The density of vacuum-dried samples was higher by ~ 50% compared to freeze-dried samples. From DSC, it was confirmed that HC aided in improving the stability of freeze-dried EWPH powder where the highest denaturation temperature was found as 106.2 °C. Overall, a lower temperature of 25 °C and a relative humidity of 40% were found suitable for maintaining the stability of EWPH powder. Moreover, the study demonstrated that a pretreatment like HC had profound effect in enhancing the stability of protein hydrolysate powder, especially after freeze drying.
Graphical Abstract
... The sorption properties of different foods have been thoroughly reviewed in the literature recently [10,11]. Of the many empirical, theoretical, and semi-theoretical equations for moisture sorption isotherms [12], commonly applied models include the Guggenheim-Andersone-de Boer (GAB), Cauries, modified equations of Oswin, Lespam, Halsey, Henderson, and Chunge-Pfost [12,13]. ...
Apricots offer diverse health benefits, making them a valuable component of an attractive diet. In addition to ensuring the physicochemical and microbiological stability during storage and the year-round availability of this nutrient-dense fruit, apricot preservation, especially through sorption isotherm processes, also considers economic, nutritional, and environmental factors. In the same context, this study explores the analysis of two common apricot cultivars in Morocco. The primary objective is to determine the optimal conditions for storing and conserving the investigated products using the standard gravimetric static method at 30 °C, 40 °C, and 50 °C—six one-liter glass jars with insulated lids made up the experimental set-up. A fourth of the glass jar was filled with a saturated salt solution. Weighing 0.100 g (±0.001) g for adsorption and 0.200 g (±0.001) g for desorption, duplicate samples were precisely weighed and put into the glass jars. The outcomes revealed that the adsorption-desorption isotherms for all samples conformed to the characteristic Type II sigmoid pattern. The ideal water activity values to preserve “Aurora” and “Carmen” are 0.36 and 0.38, respectively. It was determined that the best model to describe the sorption curves of “Aurora” and “Carmen” was LESPAM. Analysis of the adsorption-desorption data aimed to determine the moisture content of the monolayer (ranging from 3.4 to 9.7%) and examine the properties of sorbed water within their porous structures and surfaces.
... The sorption isotherms obtained by DVS measurement were fitted with two sorption models commonly used for wood analysis, i.e., Guggenheim, Anderson, and De Boer (GAB) model (Majka et al. 2017;Basu et al. 2006;Guo et al. 2019) and Hailwood-Horrobin (H-H) model (Yang et al. 2021;Yuan et al. 2022a, b). ...
During the dehydration of waterlogged archaeological wood (WAW), shrinkage inevitably occurs due to capillary force and hydrogen bond recombination as WAW loses free and adsorbed water. Existing drying techniques, including solvent displacement, freeze-drying, and supercritical fluid drying, only take effect by reducing or eliminating the surface tension of liquid. Nonetheless, the contribution of hydrogen bond recombination in shrinkage has long been neglected and a countermeasure concerning this problem is needed. In this study, we propose a simple aqueous phenylboronic acid (PBA) treatment that can help improve dimensional stability and reduce hygroscopicity of WAW. Analysis by Fourier transform infrared spectroscopy, density functional theory calculation and dynamic vapour sorption reveal that PBA can incorporate with hydroxyl groups (–OH) on cellulose through coordination and hydrogen bonds, occupy the water-cellulose binding sites, and possibly inhibit the formation of hydrogen bonds between adjacent cellulose chains.
... Preserving food quality depends on the moisture content, moisture migration, or moisture adsorption of the material during storage (Basu et al. 2006). Moisture sorption isotherms can be used to estimate the moisture content or water activity to reach the maximum storage stability of films (Aguirre-Loredo et al. 2022). ...
The importance of adding cellulose fibers to starch films is that they are used as reinforcement, reduce the interaction of films with water, and enhance stability at low water activity levels compared to films based on starch only, offering new options as materials intended for food packaging. The aim of this work was to analyze the thermodynamic properties of films composed of a) Commelina starch and b) Commelina starch added with cellulose fibers. The sorption isotherms were fitted to the Guggenheim-Anderson-De Boer equation (GAB). The thermodynamic analysis allowed allocating the minimum integral entropy value in the 0.23–0.55 range of water activity in both types of film. The lowest range of water activity was observed in films of Commelina starch added with cellulose fibers. According to the compensation enthalpy–entropy theory, at low water activity values (0.1 to ~ 0.39), the water vapor sorption process was mainly driven by enthalpy, while at high values of water activity (~ 0.39 to ~ 0.90) it was mainly controlled by entropy. The behavior of films with or without the addition of cellulose fibers could be akin to that of other non-ionic, hydrophilic biopolymers. This characterization is important for the handling and application of films intended for food packaging and storage.
... Water activity values below 0.20 indicate that water molecules are tightly bound to the biomolecule structure as a monolayer, preventing interference with powder flow [37]. At water activity values above 0.60, water molecules tend to bind to other water molecules [38]. At higher water contents, free water may form liquid bridges, reducing powder flowability [39]. ...
The flowability of food powders is a critical determinant of their processing efficiency, product quality, and overall operational success. This review delves into the intricacies of powder flowability, elucidating the factors that govern it and exploring various methods for its evaluation and enhancement. Particle size and distribution, particle shape, surface properties, moisture content, and storage conditions stand as the key determinants of powder flowability. Finer powders, with their increased interparticle cohesive forces, tend to exhibit poorer flowability. Particle shape also plays a role, with irregular or elongated particles flowing less readily than spherical ones. Surface properties influence interparticle friction, thereby impacting flow behavior. Moisture content significantly affects flowability, as increased moisture can lead to liquid bridge formation, hindering powder movement. Storage temperature, on the other hand, generally enhances powder flow due to reduced interparticle cohesive forces at higher temperatures. This highlights the need to understand the factors influencing food powder flowability and to employ appropriate evaluation strategies for optimizing food powder processing efficiency, product quality, and overall production success.
... DVS data was converted to water sorption isotherms of outer and heart leaf powders as shown in Figures 2 and 3, respectively, relating moisture content in terms of change in mass to the A w in terms of target relative pressure. The observed isotherm shapes indicate classification as Type III (Basu et al., 2006), typical of crystalline and coated materials (Decagon, 2009). Type III isotherms reflect low water adsorption of small amounts of water at low A w values, with sharp increases at higher values. ...
Romaine lettuce outer leaves, as opposed to the more commonly marketed heart, are typically discarded and present an opportunity for upcycling as dried powders. Duquesne Romaine lettuce was evaluated to quantify and compare quality attributes of fresh outer and heart leaves, dried powders following hot air drying, and dried powders following an infrared (IR) blanching pretreatment before drying. Attributes measured for fresh leaves included moisture, water activity (Aw), color, total soluble phenolics (TSP), and antioxidant capacity (AC). Drying kinetics and time/energy saving through IR blanching were evaluated. Attributes measured for dried powders included moisture, Aw, color, true density, water vapor isotherms, TSP, AC, cadmium (Cd) content, and pesticide residues. TSP, AC, Cd, and pesticide residues were higher, whereas moisture content and Aw were lower in fresh outer versus heart leaves. Hot air drying reduced TSP and AC to 63.6% and 35.2% of fresh values, respectively, whereas IR blanching further reduced TSP and AC to 37.3% and 25.4% in outer leave powders. On the other hand, TSP and AC increased 237% and 151%, respectively, for unblanched heart powders. Higher increase of TSP than AC in heart leaf powder may indicate synthesis of phenolic compounds activated by abiotic stresses such as cutting and high temperatures at the initial drying stage. IR blanching resulted in significant time/energy savings for drying of outer leaves. Microbial loads were substantially reduced during drying, although microbial population on outer leaves were more resistant. Safe to eat outer leaf Romaine lettuce powders can be produced, assuming appropriate agricultural practices.
... The remaining term to be determined is the equilibrium water content Me, which can be determined from the water sorption model. Food sorption isotherms describe the thermodynamic relationship between water activity and the equilibrium water content of food at constant temperature and pressure [35]. Seven selected sorption models were tested and the one with the good-of-fit was used in the modelling (Table 3). ...
In this study, CFD simulations that incorporate the inherent coupling between the moisture content of the mushroom and hot air flow in the tray dryer were performed. Conservation principles were applied to the fundamental quantities of mass, momentum, and heat. The source terms due to the moisture evaporation, the viscous and inertial resistance, and continuous evaporative cooling were determined through experimental results. Experiments were conducted to study and select the drying kinetics model at the optimum drying conditions and moisture sorption isotherm model at 30, 40, and 50°C temperatures. The best model describing the drying kinetics of mushrooms and moisture sorption isotherm model was chosen based on the lowest RMSE values and the highest R 2 value. Midilli et al.’s drying kinetics model and the modified Henderson sorption isotherm model were adopted in CFD modelling. The CFD software ANSYS Fluent was used for the 3D modelling of mushroom drying in a tray dryer. The mass and energy source term equations were added to the ANSYS Fluent software using a user-defined function (UDF). The parameter permeability of medium ( α ) and pressure-jump coefficient ( C 2 ) appearing in the momentum source term were directly introduced in the Fluent setup as cell zone conditions. The simulation results of the moisture removal and drying temperatures were validated against experimental data. Both results are in good agreement with the experimental data, with R 2 values of 0.9906 for moisture contents and 0.926 for drying temperature. Thus, simulation can be an option to study the drying mechanisms and alleviate some drawbacks of doing experiments.
... Water sorption models are suitable for describing the water sorption behaviour of products under different conditions [14]. A number of theoretical, semi-theoretical and empirical models have been suggested to determine the relationship between equilibrium moisture content (EMC) and Rh [15,16]. ...
Fennel (Foeniculum officinale Mill. var. dulce Mill) is an annual aromatic plant of the Lamiaceae family. Its fruits are processed to obtain essential oil for use in the food industry and cosmetics. The physical parameters of the fruits, i.e. length (5.50-8.00 mm), width (1.50-2.00 mm), volume of 100 fruits (1.36 × 10-6 m3), density of 100 fruits (935.82 kg/m3), average volume of one fruit (1.36 × 10-8 m3), average equivalent diameter of one fruit (2.96 mm), angle of repose, stainless steel (from 16 to 22°), angle of repose, black steel (from 19 to 28°), angle of repose, plywood (from 18 to 24°), and their chemical parameters, i.e. moisture (13.49%), ash (6.49%), protein (18.25%), essential oil (8.38%), vegetable oil (10.52%), and total carbohydrates (51.04%) were determined for the fruits. The adsorption and desorption isotherms of the fennel fruits were obtained using the static gravimetric method at two temperatures, 20 and 40 °C. The Halsey model provided a good description of the sorption isotherms, which were of type II according to Brunauer's classification. The increase in the temperature led to a significant decrease in the monolayer moisture. The contamination on the fruit surface at three relative humidities (0.43, 0.59, and 0.76) at 20 °C was determined.
... Seed moisture is a dynamic property of the seeds which fluctuates in direct relation to the surrounding air, i.e. relative humidity (RH) and temperature (Elias et al., 2018). A 'moisture sorption isotherm' is defined as the relationship between moisture content (MC) and corresponding equilibrium relative humidity (eRH) or water activity (a w ; where eRH ≅ a w × 100), at a constant temperature (Basu et al., 2006;Hay et al., 2022a). An adsorption isotherm is obtained by allowing dry material to take up moisture (hydration/humidification). ...
Understanding 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 <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.
... This equation treats the polymer as a rigid porous solid and keeping M s constant ensures that the degree of polymer porosity stays relatively constant. The Clausius-Clapeyron equation does assume that the system is at equilibrium, which makes application to epoxies difficult since the slow relaxation of the polymer can delay equilibrium to beyond the experimental timescale [65]. In many cases for large M s , H is approximately the heat of vaporization of pure water, and Eqn. ...
... In scientific literature, generally, for evaluation of thin-layer models that use approximation of experimental drying data, the values of the coefficient of determination or R 2 , correlation coefficient r, reduced chisquare χ 2 , root mean square error RMSE and mean bias error MBE are the most common criteria used to select the best model. The selection of a thin-layer model with graphical evaluation of the residual randomness is also popular [8], [9]. In this paper, one approach for the selection of best thin-layer drying model based on serial statistical criteria was proposed. ...
Drying of food materials is a complex process of simultaneous heat and mass transfer within dried material and from its surface to the surroundings, caused by a number of transport mechanisms. There are several different methods of describing the complex simultaneous heat and moisture transport processes within drying material. Thin-layer drying models are important tools in mathematical modeling of drying processes. In scientific literature generally for evaluation of thin-layer models, that use approximation of experimental drying data, the values of the coefficient of determination (R 2), correlation coefficient (r), reduced chi-square, root mean square error (RMSE), and mean bias error (MBE) are the most common criteria to select the best model. In this paper one approach for selection of a thin-layer drying model based on serial statistical criteria was proposed. Fresh banana were used in this study. The experimental data set of thin-layer drying kinetics of banana slices at four drying air temperatures (40, 50, 60 and 70 0 C) and three drying air velocities (1, 2 and 3 ms-1) were obtained on the experimental setup, designed to imitate an industrial convective dryer. The experimental data of drying kinetic of banana slices were fitted to twenty four thin-layer mathematical models by means of indirect non-linear regression analysis. For each model and data set, the statistical performance index was calculated and models were ranked afterwards. After that, several statistical rejection criteria were checked. The performed statistical analysis shows that the Modified Henderson-Pabis model gives the best results for approximation of experimental drying data. The single statistical criterion cannot be used to select the thin-layer drying model. The model must always be chosen based on multiple statistical criteria.
... The obtained C constants results with the BET and GAB models were in line with the stated report. The k constant is relevant to the free enthalpy between adsorbed water molecules in the pure liquid state and in the multilayer [39] and its value is 0 < k ≤ 1 [40]. The k value of the bee pollen sample ranged between 1.01-1.06 ...
The aim of this study was to reveal the moisture adsorption properties of multifloral bee pollen and determine some properties of adsorbed water at 15, 25, and 35 °C temperatures. The adsorption characteristics of bee pollen were evaluated by the BET, Caurie, GAB, Halsey, and Smith models. According to the results, while the equilibrium moisture content was 0.90-43.58 g/100 g, the monolayer moisture content calculated with the BET and GAB models was 4.91–6.05 g/100 g. The water adsorption of bee pollen showed Type II characteristic. The fitness of models can be ordered as BET > Caurie > GAB > Halsey > Smith at 15 and 25 °C according to P% values and the Caurie model was the best for representing moisture adsorption by bee pollen at all temperature and water activity levels. Additionally, the surface area of adsorption, the number of adsorbed monolayers, and the amount of total adsorbed water substantially decreased with the temperature increased from 15 to 35 °C. The net isosteric heat of adsorption was between 5.47- (-1.21) kJ/mol and the moisture absorption of bee pollen occurred as spontaneous because of ∆G < 0.
... The desorption model is a specific drying model that describes the process of moisture removal from the food surface. It is based on the principles of thermodynamics and kinetics, and it can be used to predict the drying rate and final moisture content of the food product (Basu, Shivhare, & Mujumdar, 2006). ...
... To date, a great deal of research by scientists has focused on modeling sorption isotherms for removing pollutants, including: foods (moisture reduction level) [13,14]; heavy metals [15,16], dyes [17,18] from aqueous media or volatile organic chemical mixtures [19,20]. In the case of mathematical modeling studies of adsorption equilibrium data concerning the removal of greenhouse gases from the mixture of fossil fuels, in particular CO 2 , there are noticeable shortcomings in the well-description of this comprehensive procedure in the literature. ...
This work is concerned with the calculations using eight different isotherm models (Langmuir, Freundlich, Halsey, Temkin, Toth, Sips, Radke-Prausnitz, and Redlich-Peterson) to fit the experimental isotherm data of CO2 on activated carbon (AC). Moreover, systematic and comprehensive modeling of non-linearized isotherms was performed by developing an algorithm for determining their parameters and analyzing seven error functions. To determine the best-fitted isotherm model and error function, we used the sum of normalized errors (SNE) procedure. The modeling results obtained showed that the Redlich-Peterson, Radke-Prausnitz, and Toth isotherm models are best suited to the empirical data, with relatively high R2 determination coefficients. Finally, the SNE method allowed the selection of the chi-square test (χ2) and the HYBRID error as universal indicators in nonlinear regression to select the set of optimized isotherm parameters. The interpretation of the assumptions of the isotherm models, which featured a strong correlation with the experimental data, allowed a conclusion to be drawn about the sub-monolayer adsorption mechanism on the heterogeneous surface of the AC. The acquired modeling findings are expected to establish a certain theoretical foundation for the characterization of CO2 adsorption equilibrium studies at the interface between porous solid materials and gases.
... Sorption kinetics have been studied and evaluated (Siepmann and Peppas 2011;Negrini et al. 2014; Amini-Fazl and Mobedi 2020) following different models, e.g., Ritger and Peppas (1987), Weibull (Weibull 1951) and Peleg (Peleg 1988), but so far no full explanation of the experimental data has been achieved for wood samples. Moreover, moisture sorption isotherms have been modeled using several physical and empirical approaches (Kollmann 1963;Nelson 1983;Basu et al. 2006), and the most widely used models for explaining the wood behavior are the original (GAB) (Anderson 1946) and the modified Guggenheim, Anderson, de Boer models (GAB*) (Viollaz and Rovedo 1999). One of the models that better explain the wood-water interactions during sorption processes is the Sorption Site Occupancy (SSO) model (Willems 2014(Willems , 2015. ...
Gravimetric vapor sorption experiments were performed on beech wood samples to determine the directional permeability, diffusion and sorption coefficients in the three orthotropic wood directions. Dynamic Vapor Sorption (DVS) experiments allowed for the direct evaluation of the diffusion coefficient from the analysis of the kinetic sorption profile using a double stretched exponential model with values ranging from 0.10 × 10⁻¹⁰ to 1.52 × 10⁻¹⁰ m²/s and depending on the wood direction of the sample and the RH-values. Moisture sorption isotherms (MSIs) were constructed and fitted to a modified Guggenheim-Anderson-de Boer and a Sorption Site Occupancy model, which allowed for the calculation of the sorption coefficient which was found to be between 2.4 and 3.0 mol/(m³ Pa). Dynamic Vapor Transport (DVT) experiments were performed to calculate the permeability coefficient from the vapor flow rate and it ranges between 0.56 × 10⁻¹⁰ and 4.38 × 10⁻¹⁰ mol/(m s Pa) as a function of the flow direction and RH conditions. These results indicate that such an experimental approach is suitable for determining wood–moisture interactions.
... Also, the white foam and white pulp powders had higher MMC than the yellow foam and yellow pulp powders at the different temperatures, respectively. Cassava powders that show lower MMC are regarded as more shelf-stable [42], therefore the CFP may be less stable in storage than the CPP. Chaux-Gutiérrez [43] reported in a similar study on mango foam powder an MMC ranging between 0.053 and 0.11 g/g. ...
This study evaluated the physical properties of cassava foam powder (CFP) produced from white and yellow cassava by foam mat drying, and compared them with cassava pulp powder (CPP). Cassava foams were prepared, dried and milled to foam powder. The white CFP and yellow CFP had a true density of 1.466 g/cm3 and 1.534 g/cm3, respectively. The flow properties determined include Carr’s index (CI), angle of repose (θ) and coefficient of static friction (μs). Micrographs of the CFP revealed that the foam powders were irregular, coalesced, and larger in size than CPP. The rehydration kinetics showed an estimated equilibrium water gain (WGeq) of 0.725 - 1.680 g/g at temperatures between 30 oC and 70 oC. Adsorption isotherm of the powders was best fit by the Halsey model. There were significant correlations between packed density and angle of repose (r = 0.972), CI (r =0.970) and mean
particle size (r =-0.957).
Using soft matter physics to understand food materials at different length scales creates new opportunities for scientists in academia and industry to enhance the properties, production, and nutritional quality of processed foods. Recognising the growing transfer of knowledge between the food science and soft matter communities, the editors have brought together a wealth of expertise with rich insights for both.
Beginning with the fundamentals, this book describes the behaviour of colloids, proteins, lipids, and carbohydrates in the context of soft matter science. Chapters on techniques and the behaviour of soft matter systems open the soft matter toolbox, providing food scientists with new approaches to characterise food. Taking a soft matter approach to a range of real food systems, chapters on applications provide a practical demonstration of the synergy between food science and soft matter.
The interest in insects as food has increased in the latest years. Their use as low-moisture food ingredients has led to study their behavior during storage. The moisture sorption isotherms of Mexican edible insect᾽s flours (cricket-Acheta domesticus, mealworm-Tenebrio molitor, superworm-Zophoba morio, grasshopper-Sphenarium purpurascens, escamol-Liometopum apiculatum) were determined through the dynamic method. Mathematical models were used for fitting the adsorption and desorption curves and Akaike Information Criteria (AICi) was used to evaluate their performance. Hysteresis was determined quantitatively. The samples presented a BET Type II behavior; for adsorption and desorption, GAB and Peleg᾽s were the models with the best fitting according to the AICi, respectively. GAB (R2 ≥ 0.991) was used to determine M0, with values ranging between 4.14 (superworm-adsorption) and 6.40 gH2O/100 g d.s. (mealworm-desorption). Also, escamol desorption GAB C value was up to 12.6 times higher than the one observed in adsorption, being this one the less stable sample. The lowest areas of hysteresis were observed for cricket (1.32) and grasshopper (1.63), resulting in stable materials; this agreed with the C values of GAB. More studies are needed for the establishment of processing conditions of insects, information required for local producers to increase the insect market in Mexico and in the world.
The purpose of this review is to report on the state-of-the-art on the interaction of moisture with natural materials and fabricated biomimetic functional materials, with an emphasis upon the hygro-responsive behaviour of wood. The primary objective is to examine how water sorption affects dimensional behaviour and how knowledge of this property in natural plant-based (mainly, but not exclusively wood) materials can be used to inform biomimetic design of moisture-responsive materials and devices. The study examines the literature on natural and bio-inspired materials, concentrating upon sorption kinetics, water migration and location of the sorbed water in the materials and their microstructure and mechanical response of the microstructure and how this affects molecular mobility of the sorbate translating to macrostructural changes. Also included within this review, it is an overview of the main experimental techniques which have been used to investigate the interaction of water with these materials at molecular length scales and how modern techniques can resolve the response of these materials at the cell wall level.
In the production of cast aluminum automotive parts, cores made of sand and binders are often used to create the complex features that cannot be formed by the mold, such as internal passages. Core binders can be grouped into two different categories: organic and inorganic, depending on the binder system used. Conventional organic binders use petroleum-based materials that are sources of harmful gases. In contrast, inorganic binders such as sodium silicates (water glass) are environmentally friendly. The fabrication of inorganic cores requires a drying step that involves thermal dehydration (using hot box and hot air injection) and chemical reactions (polymerization) to give the sand core the necessary strength to withstand the constraints developed during core storage and the casting process. This drying step increases the duration of the process and affects the production line. This study evaluated different thin layer drying models to understand the drying behavior of sand cores in the inorganic process that uses both hot air and warm box. The Page model was found to best describe the drying kinetics based on experimental measurements on a rectangular core. The sorption properties of the core were determined by characterizing the desorption isotherms at three different temperatures. The energy required to remove water from the core was estimated and it is found that the highest energy reached a theoretical maximum at a box temperature of around 135 °C.
The equilibrium moisture content of sago flour is essential information, especially for predicting the product’s shelf-life, which can be affected by various factors, such as temperature, relative humidity, and packaging condition. This research was conducted to study the characteristic of moisture sorption isotherm and determine the best mathematical equation model for studying sago flour’s isotherm sorption characteristics. Sago flour was stored in an incubator at a 10-80% humidity range with temperature variations of 30°C and 40°C. Humidity setting was done using various types of salt solutions. This study showed that all the sorption curves were found to be Type II. The higher the RH in the incubator, the higher the equilibrium moisture content of the material. Meanwhile, the water sorption capacity decreased with increasing temperature. Different models were fitted to the data, including Oswin, Chung-Pfost, and Halsey models. The Chung-Pfost model was found as the best model to represent the experimental data in the water activity range of 0.1-0.8.
Bio-drying is a practical approach for treating food waste (FW). However, microbial ecological processes during treatment are essential for improving the dry efficiency, and have not been stressed enough. This study analyzed the microbial community succession and two critical periods of interdomain ecological networks (IDEN) during FW bio-drying inoculated with thermophiles (TB), to determine how TB affects FW bio-drying efficiency. The results showed that TB could rapidly colonize in the FW bio-drying, with the highest relative abundance of 5.13%. Inoculating TB increased the maximum temperature, temperature integrated index and moisture removal rate of FW bio-drying (55.7 °C, 219.5 °C, and 86.11% vs. 52.1 °C, 159.1 °C, and 56.02%), thereby accelerating the FW bio-drying efficiency by altering the succession of microbial communities. The structural equation model and IDEN analysis demonstrated that TB inoculation complicated the IDENs between bacterial and fungal communities by significantly and positively affecting bacterial communities (b = 0.39, p < 0.001) and fungal communities (b = 0.32, p < 0.01), thereby enhancing interdomain interactions between bacteria and fungi. Additionally, inoculation TB significantly increased the relative abundance of keystone taxa, including Clostridium sensu stricto, Ochrobactrum, Phenylobacterium, Microvirga and Candida. In conclusion, the inoculation of TB could effectively improve FW bio-drying, which is a promising technology for rapidly reducing FW with high moisture content and recovering resources from it.
Biomass residues from large‐scale agro‐industrial processing plants are currently one of most attractive alternatives as source for bioenergy. Due to their high moisture content, it is interesting that these raw materials undergo drying to increase efficiency and reduce gas emissions of the thermochemical conversion processes. The goal of this chapter is to provide few guidelines for mathematical modeling of drying process towards its energy and cost analysis, as well as industrial‐scale process optimization. A brief survey of specific studies at laboratory scale necessary to obtain parameters for the mathematical model is given, such as material characterization, water activity and drying kinetics. Aspects referring to the most promising drying technologies for biomass drying are reported and discussed.
Moisture equilibrium data (adsorption and desorption) of semi-defatted (fat 10.6 % wet basis) pumpkin seed flour were determined using the static gravimetric method of saturated salt solutions at three temperatures 10 degrees C, 25 degrees C, and 40 degrees C. The range of water activities for each temperature was between 0.11 and 0.85. Equilibrium moisture content decreased with the increase in storage temperature at any given water activity. The experimental data were fitted to five mathematical models (modified Oswin, modified Halsey, modified Chung-Pfost, modified Henderson and Guggenheim-Anderson-de Boer). The GAB model was found to be the most suitable for describing the sorption data. The monolayer moisture content was estimated using the Brunauer-Emmett-Teller equation.
The effect of the fractal surface on physical adsorption has been analysed and a new three-parametric isotherm equation was derived. The model describes the multilayer adsorption on fractal surfaces within the framework of BET theory. It predicts lower buildup of the multilayer coverage on a fractal surface than on a, flat surface. The results of the simulation show that increasing the fractal dimension of the surface affects the adsorption isotherms; namely, the upward curvature of the isotherms at high relative pressures is decreased as D increases. For the submonolayer region, the curves become independent of the fractal nature of the absorbent. The isothermal data for water vapor sorption on grains and other starchy materials were used to evaluate the new isotherm equation. The parameters of the isotherms were calculated using computational regression techniques. Fractal dimension ranged from 2.6 to 2.9, approximately, indicating the contribution of the pore structure to the sorption capacity of the products investigated. Results show that the model allows an accurate and simple description of the sorption data for the whole range of water activity.
Adsorption isotherms of raw and roasted (at 100°C, 120°C, 140°C and 160°C) hazelnuts of Tombul variety were determined at 25°C, and over relative humidities ranging from 11 to 90% using the gravimetric static method. Eleven sorption models (GAB, BET, Modified BET, Halsey, Iglesias-Chirife, Oswin, Chung-Pfost, Smith, Kuhn, Harkins-Jura and Caurie) were evaluated by using the linear regression method. GAB (Guggenheim-Anderson-de Boer) model satisfactorily described adsorption characteristics of the samples over the experimental range of study. Monolayer values at 25°C were estimated from the GAB model as 0.0155 kg water/kg dry solid for raw and 0.0100–0.0163 kg water/kg dry solid for roasted hazelnuts. Caurie security moisture content for raw hazelnuts was also determined from Caurie model as 0.048 kg water/kg dry solid.
Water sorption isotherms of freeze dried fish sardines were determined at 25, 40 and 50°C using an isopiestic method. Water sorption modeling was carried out using the five parameter Guggenheim-Anderson-deBoer (GAB) equation. The GAB equation was able to predict equilibrium moisture content (EMC) with a mean relative error of 7.4%. The correlation coefficient (R2) of the relationship between the actual and predicted values of EMC was 0.986. Modeling with GAB equation predicted monolayer moisture content (Xm) of 4.94% (d.b.). Net isosteric heat of sorption, determined using Clausius-Clapeyron equation, varied from 12.07 to 0.86 kJ/mol asmois ture content changed from 2.76 to 37.5% dry basis (d.b). Chemical composition analysis showed that fish sardine contained 71% (d.b.) crude protein, 10% (d.b.) fat and 15% (d.b.) ash.
A model was developed on the basis of the literature for binding of water on solid starch by means of a combined sorption mechanism. Equations based on the theory of localized sorption on homogeneous surfaces (Langmuir and Brunauer, Emmett & Teller) were derived. An equation with three parameters from the theories of Guggenheim, Anderson and de Boer described experimental isotherms adequately up to a water activity of 0.9 and one based on polymersolvent interaction (Flory and Huggins) above that value. The experimental isotherms of water vapour on native starch were affected by temperature, gelatinization, partial hydrolysis and separation in components (amylose and amylopectin).
Sorption isotherms at 4, 13, and 27°C were obtained for two types of berries (strawberries and blueberries) and three types of commercial and wild mushrooms (Shiitake Lentinus edodes, Enoki Flammulina velutipes and Morel Morchella esculenta). The products had been freeze-dried for 72 h and equilibrated over saturated salt solutions in a range of relative humidity from 11 to 87%. The equilibrium moisture content was obtained when there was no appreciable change in sample weight. The sorption of powdered and whole pieces of mushrooms was studied in order to evaluate possible effects of particle size on sorption characteristics. Two equilibrium models, GAB and one previously developed by one of the authors, were tested against the experimental data in order to determine the most appropriate mathematical representation. The constants required for each model were determined by non-linear regression analysis.
The objective of this study was to experimentally determine sorption and desorption equilibrium moisture content isotherms for Virginia-type peanut kernels and hulls at various temperatures, to use the experimentally determined curves to evaluate the parameters of several published equations for equilibrium moisture content, and to investigate the implications of parameter values on such physical and thermal properties as surface area per unit mass of dry matter and heat of sorption or desorption of water by peanut components.
Four equilibrium moisture content/equilibrium relative humidity (EMC/ERH) equations (Modified-S.M. Henderson, D.S. Chung H.B. Pfost, Modified-G. Halsey and Modified-C.R. Oswin) are evaluated for their ability to fit data for grains and seeds. Thirty-six data sets comprising 18 crops are included. Comparisons are based on mean relative percentage deviation, standard error of the estimated value and residual plots. The Modified-Henderson and Chung-Pfost equations are good models for starchy grains and fibrous materials. The Modified-Halsey equation is a good model for high oil and protein products. The Modified-Oswin equation is a good model for popcorn, corncobs, whole pods of peanut and some varieties of corn.
The three-parameter GAB equation was evaluated for its ability to describe the sorption data for several agricultural products. The GAB equation describes the relationship between equilibrium moisture content and equilibrium relative humidity (ERH) or water activity (Aw) at a fixed temperature. With Aw as the dependent variable, the equation becomes very complex. The residual plots of this model showed that it does not fit well for starchy products. For most products, the parameters of the GAB equation did not exhibit the Arrhenius-type relationship with temperature. To incorporate the temperature term into the parameters, the number of parameters in the model increases, making it less useful. The GAB equation is not an adequate sorption model for all agricultural products.
A new model of water sorption isotherm is developed on the basis of Raoult’s law. It is assumed that water present in food occurs in two states, as free water with properties of the bulk water and as water of hydration. Hydrated molecules are considered as new entities with molecular weights larger than those of non-hydrated molecules. Hydration reduces the free concentration of water and thus affects water activity in solution.Application of the developed equation to food sorption data showed that it gives approximation of sorption isotherms much better than that offered by the GAB model. Moreover, it predicts infinite adsorption at aw=1, the property which is not offered by the GAB equation. The new equation makes it possible to interpolate isotherms at high water activities close to one. The probability that the new equation will fit the food isotherm with small RMS is higher than 90% and substantially exceeds that found for the GAB model. As a two-parameter model it makes substantial improvement over the three-parameter GAB equation.
The parameters of the `G.A.B.' equation are discussed from mathematical and physical point of view. Clear limits of those parameters are determined. The point of inflexion of the `G.A.B.' isotherm was also analysed with the conclusion that the `G.A.B.' isotherm behaves too rigidly to be able to describe complicated sorption cases. The different possibilities of some other isotherms for such a purpose were displayed.
A refinement of the Guggenheim-Anderson-de Boer (GAB) sorption model which allows for the existence of a third sorption stage, was used to analyze the behavior of adsorption isotherms of starches at very high water activity (aw). The results of experimental isotherm analysis with the new model revealed that above about aw=0·90 a change in the physical state of adsorbed water in starch occurred; i.e. the water molecules would be more ‘liquid-like’ than in the preceding layers. This transition corresponds with the unfreezable water content in starch, as determined by others.
Analysis of adsorption on a uniform surface using the quasi-chemical theory of interaction shows that the hypotheses of the BET theory lead to substantially no adsorption beyond the first layer if E2 = EL, and stepwise isotherms if E1>E2>E3>···>EL. For the monolayer adsorption of gases on silver, platinum, and steel, the heterogeneous nature of the adsorbing surface is clearly indicated. Cooperative adsorption on the non-uniform surface is treated, and the cooperative analog of the Freundlich equation derived. The typical multi-layer isotherm is shown to be composed of three regions: non-cooperative adsorption on a strongly heterogeneous surface; cooperative adsorption on a still heterogeneous surface; and cooperative multi-layer adsorption induced by small van der Waals perturbations some distance from the surface.
The isotherm p/p0=exp{—a/θr} is derived and shown to be a good representation of adsorption data that conform to the BET Type I, II, or III shapes.
The statistical B.E.T.-treatment of multimolecular sorption is extended to include three distinct sorption stages, viz.(I) the strongly sorbed monolayer, (II) the following h–1 layers, much less strongly sorbed, and (III) the remaining layers, up to infinity, of ‘pure liquid’ characteristics. The new three sorption stages (t.s.s.) isotherm embodies the classical two-parameter B.E.T. equation [stages 1(h= 1)–III] as well as the three-parameter Guggenheim–Anderson–De Boer (G.A.B.) equation [stages I–II (h=∞)].
Adsorption and desorption isotherms for potato, highly amylopectin and highly amylose starch powders were determined at 30, 45 and 60 °C using a gravimetric technique. Samples were equilibrated in desiccators containing sulphuric acid solutions of known water activity (0.05–0.95), and placed in temperature-controlled cabinets for approximately three weeks. The starch powders exhibited Type II behaviour. The sorption capacity decreased with increasing temperature. The data obtained were fitted to several models including two parameter relationships (Halsey, Oswin, Henderson, Modified-BET and Smith), three parameter equations (GAB, Ferro-Fontan) and four parameter equation (Peleg). A non-linear least square regression program was used to evaluate the models constants. The empirical Peleg model followed by the kinetic GAB and the semi empirical Ferro-Fontan models were found to best represent the experimental data in the water activity range 0.05–0.95. In the range of water activity 0.35–0.95 the Smith model was shown to give the closest fit to the experimental data.
A modification of the GAB isotherm (Guggenheim–Anderson–De Boer) is proposed in order to correlate the sorption data for water activities higher than 0.9. The proposed isotherm retains the desirable properties of the GAB isotherm, i.e. good fitting in the range of aw between 0.05 and 0.80, and also provides a noticeable improvement in the fitting quality for high values of aw, by introducing a new term with an additional constant. Sorption data for native potato starch and gluten at different temperatures (2°C, 20°C, 40°C and 67°C) were well correlated for the whole aw range. For starch at 67°C, the values of the constants of the proposed equation do not follow the same tendency obtained for lower temperatures, suggesting that the structure of the material could be changed due to the high temperature. The proposed isotherm can be of interest in the area of drying given that there are few isotherms that accurately represent sorption data at different temperatures in the zone of high aw. Also, it can be useful to predict other thermodynamic functions. In addition, a new procedure is proposed to determine the isosteric heat by using a second order polynomial for representing the variation of moisture as a function of temperature at a fixed water activity.
The fitting abilities of an isotherm equation originally developed by Ferro Fontán et al. (J. Food Sci., 47, 1590–4, 1982) (FF) was compared with the well-known GAB model. For this purpose literature data of 156 food isotherms (comprising 92 different food products) were examined with both models. The results of the evaluation indicated that the FF equation is an accurate tool for the mathematical description of food isotherms. The FF equation represents accurately the sorption isotherm of 92 different food products (proteins, starchy, cereals and oilseeds, meats, vegetables, miscellaneous) in the range of water activity 0.10–0.90 with only 2–4% average error in the predicted moisture content. In fact, the average error for the 156 isotherms examined was only 3.3%. The FF equation only has three parameters that need determining (as has the GAB model); thus it is proposed as an alternative equation to the widely used GAB model.
Equilibrium Moisture Content (EMC) data for medium rough rice grain, Lido variety were obtained by equilibrating rice samples at different Equilibrium Relative Humidities (ERH) and Temperatures. The employed models to fit the data were GAB, modified Chung-Pfost, modified Halsey, Modified Henderson, and modified Oswin. The data were evaluated using the standard error of moisture content, mean relative standard error (%P) of the model and the correlation coefficient r. The GAB model by indirect regression described the EMC the best, however its parameters lacked of physical meaning. The modified Chung-Pfost and modified Henderson equations presented a similar fit of the EMCERH relationships. The modified Chung-Pfost equation had lower residual values than the modified Henderson equation and was considered the best model to explain the EMC-ERH relationships.
Estimation of food sorption isotherms was developed using Ross, Raoult, Norrish and Henderson equations. Food average composition of main solutes (sucrose, glucose, fructose, xylose, maltose, lactose, and salts), nonsolutes (starch, protein, and fiber), and the solute solubility at different temperatures were taken into account. The individual water activity of a single solute was kept constant at moisture contents below saturation at given temperature. Water activities for non-solutes were evaluated with Henderson equation based on literature data for starch, protein and fiber. Sorption isotherms for apricot, raisins, potato, rice, bean and nonfat milk were predicted and compared with those reported in literature. Predicted isotherms represented an expected behavior of the experimental isotherms obtained by different authors.
A mathematical prediction of pineapple sorption isotherms was developed using Ross, Norrish and Henderson equations. The prediction considered to have the pineapple average composition oflhe main solutes: sucrose, glucose, fructose, citric acid, malic acid, NaCI, KC1 and cellulose as non-solute. Water activity of individual sugars and organic acids was obtained by Norrish's equation and for the two salts by Raoult's Law. Solute solubility at different temperatures was taken into account. Predicted isotherms were compared with the experimental isotherms obtained in laboratory at 30, 35, 40 and 45° C and with the isotherms reported in literature at 30 and 45° C. The generalized correlation coefficients ( r ) between predicted and experimental isotherms were in the range of 0.8 - 0.98.
The differences between the sets of values for the monolayer capacity and the energy constant obtained by sorption data regressions using two related multilayer sorption isotherms, the two-parameter BET (Brunauer–Emmett–Teller) and the three-parameter GAB (Guggenheim–Andersen–de Boer) isotherms, are analysed. Experimentally, it is found that the GAB monolayer value is always higher than the BET value and the GAB energy constant results always lower than the BET constant. Mathematical and physical reasons are given which explain these differences. The third GAB parameter determines the greater versatility of the GAB equation, which has a quite larger range of applicability than the BET isotherm. It is shown that in terms of the three GAB constants, the two BET parameters are qualitatively and quantitatively reproduced as well as their dependence on the regression interval used in the BET regression, justifying in this way the above-mentioned inequalities. The typical upswing in the BET plots after a (pseudo) linear range at lower activities of the sorbate is also explained. All these findings are exemplified using experimental sorption data of several systems of very distinct chemical nature. A complete regression procedure for sorption data in terms of the GAB isotherm is advanced.
The chemical composition, water activity, temperature and equilibrium moisture content (EMC) for 10 selected fruits were determined. Two methods of water sorption modeling, the GAB equation and the artificial neural network (ANN) method, were compared for their ability to predict water sorption behavior. Unlike the GAB equation, which uses only physical data for modeling, the ANN method uses both physical and chemical compositional data to make predictions. The ANN was superior, in most cases, to that of the GAB equation, in predicting EMC. This superiority was due to the availability of the additional chemical compositional information. The ANN method could predict EMC with a mean relative error of 9.85% and a standard error (S x ) of 1.59% EMC. The correlation coefficient (r 2) of the relationship between the actual and predicted values of equilibrium moisture content obtained by the ANN was 0.9938. The ANN model was able to show a temperature dependent crossing of water sorption isotherms, due to the dissolution of sugar crystals in the fruit. The ANN was also able to predict the extent of crossing, depending upon differences in the individual fruit chemical composition.
Stepless isotherms on a uniform surface have been calculated, using modifications of Hill's treatment of lateral interaction. However the assumptions necessary for success are so specific and unreal that the necessity of assuming surface heterogeneity for real isotherms is demonstrated.
ABSTRACTA multilayer adsorption equation, originally developed for physical adsorption on nonuniform surfaces, is used to describe the water sorption behavior of a great variety of foods and food components. Characteristic parameters of the sorption equation, for each of the products tested, were computed. A comparison was made between Halsey's equation and Henderson's classical one. Literature data for 220 food isotherms, comprising 69 different materials, were utilized to compare both equations. It was found that in most cases Halsey's equation has a better fit than Henderson's.
This work investigates the use of the Ross (1975) equation for the prediction of water activity (a), in aqueous electrolyte or non-electrolyte solutions to which a non-solute (casein) was added. Water activity of the ternary mixtures (casein-water-solute) was in the range of a, = 0.85-0.90 which is of interest for the development of intermediate moisture foods for human consumption. It was found that the use of the Ross equation coupled with a correction for the water strongly bound to casein gives good predictions of a.
The validity of the physical model on which the Hailwood and Horrobin (Trans. Far. Soc. 42B: 84; 1946) isotherm equation was developed was investigated. The results indicate that although the equation may fit sorption data for almost any type of food, it satisfies thermodynamic requirements (i.e. prediction of the temperature dependence) only for proteins and starchy foods. The results also show that plotting enthalpic changes against entropic changes for water sorption satisfies the enthalpy/entropy compensation phenomenon.
ABSTRACTA calibration procedure for the Sina-scope hygrometer is described. Four saturated salt solutions, covering a range from 0.755–0.967aw, and two foods, with a, levels in the intermediate moisture food range, were tested to determine the accuracy and precision of the Sina instrument. Accuracy, relative to averaged published a, levels for the four standard salts, was evaluated. Most measured values were slightly less than the averaged standards. The greatest difference noted was -1.06% of the standard. Estimates of instrument precision showed that the coefficient of variation decreased with measurement of successively higher a, standard solutions and did not exceed 1%. Instrument readings to two decimal places possessed standard deviations slightly lower than corresponding readings estimated to three decimal places. Standard deviations (20 replicates at each aw) ranged from o—0.004. Estimates of pooled, between-sensor standard deviation showed that there were no significant differences between the two sensors used in those studies. Equilibration periods of 45 or 60 min were almost equally precise. The number of replicates required to produce a given level of data confidence are calculated and presented. Similar results relative to estimates of precision were obtained with the two foods tested.