Monolayer Moisture Content Research Articles

Sorption isotherms of tobacco (Nicotiana tabacumL.) seeds

The moisture sorption capacity of tobacco seeds is decisive for their safe long-term storage; therefore, the analysis of the sorption isotherms, in a wide temperature and water activity range, is essential for seed quality maintenance in storage. In this study, the equilibrium sorption isotherms of tobacco (N. tabacumL.) seeds, “Kroumovgrad 90” variety of Oriental tobacco, were determined. The experimental data were obtained by the static gravimetric method at different temperatures and water activities. Sorption isotherms showed a typical Type II sigmoidal profile, with a significant hysteresis effect and a decrease of seed sorption capacity with the increase of temperature. The best fitting with tobacco seed sorption isotherms were the modified Chung-Pfost (desorption) and Oswin (adsorption) models. The monolayer moisture content, important for the safe storage of tobacco seeds, was also determined. The outcomes from the study might be of practical use in tobacco seed conditioning and storage design.

Сорбционни характеристики на брашнени смеси обогатени с брашно от гроздови семки от български и френски суровини

The aim of the present scientific research is to study the moisture sorption characteristics of flour mixtures of Bulgarian and French origin. The mixtures are enriched with grape seeds flour in its being an enological residue. Equilibrium moisture content are determined at three different temperatures at 10 °C, 25 °C and 40°C through the standard static gravimetric method in the compulsory presence of water activity within the range from 0.1 to 0.9. The obtained adsorption and desorption isotherms have an S-shape profile i.e. they are from the IInd class typical of the majority of food products. The results confirm a regularity that the sorption capacity decreases with increasing of the temperature in the presence of constant water activity which is valid for both products as well as for both processes (adsorption and desorption). The mathematical modified models of Chung–Pfost, Oswin, Halsey and Henderson are evaluated for the description of the sorption data. The monolayer moisture content (MMC) of flour mixtures is calculated through the linearization of Brunauer-Emmett-Teller equation. For the Bulgarian mixture the values varied from 2.54% to 4.29% and for the French mixture – from 2.67% to 4.13%.

Sorption Isotherm of Corn Chips Made from Blends of Corn Flour and Bambara Groundnut Nut Flour

The adsorption equilibrium moisture contents of corn chips (kokoro) made from blends of maize flour and Bambara nut flour was investigated by measuring water activities at 27°C, 37°C and 40°C using the static gravimetric method. Sorption isotherms followed a type II shape in water activities range from 0.10 - 0.80 showing characteristics of most biological tissues. Five isotherm model equations were used which are BET, GAB, Oswin, Halsey and Henderson. The experiments were performed using polythene packaging and exposed petri dishes. The samples were weighed at two days interval until equilibrium was attained when three identical measurements were obtained. The equilibrium moisture content (EMC) decreased with increase in temperature at constant water activity and polythene packaging had lower EMC compared to petri-dishes. Oswin and Henderson model were best fit at 27°C with RSS = 1.929×10^-5, SEE = 0.00011, R² = 0.99531 and RSS = 0.001192, SEE = 0.00011, R² = 0.9807 for polythene and petri-dish respectively. Oswin model was best fit for both storage conditions at 37°C and 40°C. The monolayer moisture content at the three temperatures ranged from 0.0193 - 0.0752 and the general model observed for this study that could predict the sorption behavior of Bambara-corn chips was Oswin model.

Physical and moisture sorption thermodynamic properties of Sukkari date (Phoenix dactylifera L.) powder

ABSTRACT Physical properties of Sukkari date powder (SDP) at different particle sizes, namely, moisture content, water activity, tapped and bulk densities, compressibility index, Hausner ratio, water absorption, and solubility indices, swelling capacity, and color parameters were experimentally determined. The SDP moisture sorption experiments were conducted using a dynamic vapor sorption instrument in the relative humidity range 10%–90% at 20, 40, and 60°C. Among the ten tested sorption models, the GAB and modified GAB models best fitted SDP sorption data. The monolayer moisture content decreased with increasing temperature. The differential enthalpy and entropy, and net integral enthalpy and entropy decreased consistently with increasing moisture content. The linear relationship between differential enthalpy and entropy confirmed the applicability of the compensation theory. The estimated values of the isokinetic and harmonic temperatures and the Gibbs free energy change revealed that the sorption process is non-spontaneous and enthalpy driven.

Sorption Characteristics of Bulgarian Penny Buns (Boletus Edulis)

The present study determined the sorption characteristics of Bulgarian penny buns (Boletus) for eight water activities in the 10 % 90 % range and at three temperatures, of 10 °С, 25 °С and 40 °С. The coefficients of the modified Oswin, Chung-Pfost, Halsey and Henderson models were obtained statistically. The modified Halsey model is recommended as a description of adsorption and desorption isotherms since it corresponds to the criteria for model assessment and suitability. Via BET model linearization, the values of the monolayer moisture content for water activity of aw > 0.5 and temperatures of 10 °С, 25 °С and 40 °С were established. The approximate physico-chemical composition of Bulgarian penny buns (Boletus) – moisture content – 10.80 %, protein – 32.23 %, carbohydrate 0.99 %, fat – 6.62 %, ashes – 6.20 % - was also determined.

GAB model and the thermodynamic properties of moisture sorption in soursop fruit powder

The aim of this study was to model and determine the thermodynamic properties of moisture sorption in soursop fruit powder. The isotherms were determined by the static method at temperatures of 10, 20, 30, 40 and 50 °C, and a water activity of between 0.113 and 0.868 (decimal). The GAB model effectively described the moisture sorption phenomenon of soursop powder. The monolayer moisture content ranged from 12.589 to 9.109% db. The enthalpy values related to the GAB model were negative, with -2581.035 kJ kg-1 for C0 and -107,758 kJ kg-1 for K0. The isosteric heat of sorption, entropy and Gibbs free energy had a high correlation with the equilibrium moisture content, and the correlation between enthalpy and entropy was confirmed for moisture sorption in soursop powder.

Moisture sorption isotherm, isosteric heat and adsorption surface area of whole chia seeds

This study aimed to evaluate moisture sorption isotherm of whole chia seed. The equilibrium moisture content (EMC) of seeds were detected by saturated salt solutions which have the water activity (aw) range of 0.2–0.9. The isosteric sorption heat was calculated by the Clausius-Clapeyron equation using three different sorption temperatures (15 °C, 25 °C and 35 °C). The adsorption surface area of seeds was also calculated by monolayer moisture content obtained from BET and GAB equation. The EMC content of seeds had an increasing trend and determined as 18–20 g H2O/100 g solid at the highest aw level. The whole chia seeds became less hygroscopic with the rising sorption temperatures at constant aw. The moisture sorption isotherm was determined as Type II. The monolayer moisture content was determined as 2.39–2.91 g H2O/100 g solid. BET and Peleg were the best-fitted models. The isosteric and net isosteric heat were 77.74 and 34.74 kJ/mol at lowest moisture content, respectively. Additionally, the adsorption surface area changed between 95.31 and 102.72 m2/g.

Effect of drying methods on the sorption isotherms of plantain flour

The demand for plantain flour has increased in recent years due to its health benefits and industrial applications, however, there is dearth of information on the effect of drying methods on the sorption isotherm of plantain flour. In the present study, moisture sorption properties for unripe plantain flour using four drying methods at temperatures 27 °C, 37 °C and 42 °C were determined for water activity 0.10 to 0.80. The data generated were modelled using Peleg, GAB, Oswin, BET and Langmuir. The results revealed that the Equilibrium Moisture Contents decreased with an increase in temperature at all the water activities considered. Also, moisture isotherms of the plantain flour were not significantly (p>0.05) affected by temperature. The coefficient of determination (R2) for the used models ranged from 0.640 and 0.986 and Peleg was the most appropriate for the adsorption isotherm of plantain flour out of all the models. The monolayer moisture content of the flour also showed that all the unripe plantain flours could be stored for longer periods at all the temperatures studied, as their Mo falls within acceptable range for storage

Studies on thermal stability of high-power short time microwave dried paprika (Capsicum annuum L.) considering the interaction of water molecules with sorption sites

The moisture adsorption isotherms of high-power short time microwave dried paprika (Capsicum annuum L., a pulverized product of dried red pepper) were determined for thermodynamic analysis and assessment of its stability at elevated temperatures. The thermal stability of paprika was evaluated based on alterations in quality characteristics due to the interaction of water molecules with sorption sites during the adsorption process. The GAB model constants revealed the physical significance and the exothermic interaction of the water molecules with the sorption sites on the surfaces of the paprika. The differential enthalpy was found to decrease with increasing water activity due to the existence of highly active polar sites on the surface of paprika at low water activity. The differential entropy decreases due to a rise in water activity as molecular water movement was highly restricted at an elevated water activity. The safe water activity levels corresponding to monolayer moisture content (M o) of paprika at 30°, 40°, 50°, and 60 °C were found to be 0.58, 0.49, 0.43, and 0.30, respectively. Moreover, the acceleration in quality degradation of paprika was found to increase beyond M o at the respective adsorption temperature.

Moisture Sorption Characteristics and Storage Study of Grape Seeds Flakes

The current scientific research is focused on the sorption isotherms, monolayer moisture content and storage study of full-fatted grape seeds flakes (FGSF) of different grape variety locally grow in Bulgaria (Mavrud, Cabernet Sauvignon, Syrah, Merlot, Dimyat and Sauvignon Blanc). To determine the sorption characteristics of FGSF, we are used a static gravimetric method of saturated salt solution and relative humidity from 0.11 to 0.90 at three different temperatures – 10, 25 and 40°C. In the condition of constant water activity and increasing temperatures, the sorption capacity of the product decrease. We are recommend the modified Henderson model for description of sorption isotherms of FGSF. The monolayer moisture content values are obtained by linearization of Braunauer-Emmett-Teller (BET), in the range of Mmads = 2.32 ÷ 3.41, Mmdes = 2.59 ÷ 3.68. The three months storage study of samples was monitored at moisture value reduced to a value corresponded to the calculated monolayer moisture content. FGSF was packed in a co-extruded barrier film with copolymer covering for heat sealing, in the conditions for storage - temperature 18 ÷ 25°C and relative humidity 75 ÷ 85%. No living cells of pathogenic organisms (Escherichia coli, Staphylococcus aureus and Salmonella spp.) or apparent molding were detected. The flour particle size has not changed either.

Moisture Sorption Isotherms of Edible Coated Solid Sugarcane Jaggery

The moisture sorption isotherms (MSIs) of solid sugarcane jaggery, coated with five edible coatings, namely whey protein concentrate, wheat gluten, zein, gelatine and gum arabic at three levels of concentrations, i.e. 0.5, 1.5 and 2.5%, were calculated by using the technique of static gravimetric based on isopiestic vapour transfer technique using saturated salt solutions at three levels of temperatures, i.e. 25, 35 and 45 °C. The experimental MSI data were fitted into the three models, namely Iglesias and Chirife and Modified Halsey and GAB. The isotherms for edible coated solid sugarcane jaggery samples were found Type-III isotherms. Among the three MSI models, GAB model was found to be best fit with the experimental data followed by other two models, i.e. Halsey and Iglesias and Chirife model. For the control sample (solid sugarcane jaggery samples without edible coating), the monolayer moisture content (M0) was maximum of 4.368 (%db.) at 25 °C and minimum 3.740 (%db.) at 45 °C. A decreasing trend of M0 values of the solid sugarcane jaggery samples with edible coatings was found with increase in coating concentration (0.5–2.5%) and temperature (25–45 °C). The highest value of M0, i.e. 4.886 (%db.), was found with 0.5% concentration of wheat gluten coating at 25 °C temperature.

Preparation of rooibos extract-chitosan microparticles: Physicochemical characterisation and stability of aspalathin during accelerated storage

Green rooibos extract containing high levels of aspalathin, a dihydrochalcone antioxidant, and the carrier chitosan, both an antioxidant and antimicrobial agent, was used to produce a dual-purpose food ingredient powder by spray-drying for incorporation into processed meat products. Green rooibos extract was shown to inhibit growth of Escherichia coli, Staphylococcus aureus and Listeria monocytogenes, adding to the functionality of such a powder. Three formulations (50, 100 and 150 g chitosan/kg powder) were compared to the pure spray-dried extract and maltodextrin-containing powders (250 and 500 g maltodextrin/kg powder) in terms of physicochemical properties (particle size and morphology, moisture sorption isotherms, compatibility, bulk density and compressibility) and aspalathin stability during accelerated storage. All the formulations produced amorphous, hygroscopic powders with deliquescence at relative humidity (RH) > 65%. The moisture content of the powders was lower than their monolayer moisture content calculated using the BET and GAB models. Isothermal microcalorimetry showed no interaction between extract and carbohydrate polymers. Aspalathin degradation in the powders, subjected to accelerated stability testing (40 °C/75% RH for 96 h), followed fractional conversion kinetics. The presence of chitosan in the powders decreased the stability of aspalathin during storage compared to the pure extract and maltodextrin-containing powders.

Effect of drying process of esterified plantain starch on sorption, thermodynamic and shelf-life characteristics

The plantain starch was modified with octenylsuccinic anhydride (OSA) and spray and convection dried. The degree of substitution (DS), the sorption and thermodynamic characteristics were evaluated. The drying process affected the DS (0.009 and 0.015 to spray and convection drying, respectively). The monolayer moisture content was 7.46–9.01 and 7.33–8.04 g H2O 100 g−1 (db) to convection and spray dried OSA-plantain starch, respectively. The isokinetic temperature was ∼255 K, less than harmonic temperature (308 K), indicating that the water adsorption was entropy driven. The free energy showed that adsorption process was spontaneous. The shelf life of convection and spray dried OSA-starch was 434–1566 days to PET/FOIL/PE and 64–616 days to polypropylene packing. Thermodynamic differences in the adsorption process of OSA-plantain starch influenced by the drying method were not found. Spray-drying process could be used for the OSA-plantain starch production without altered the thermodynamic and transport properties of the amphiphilic material.

Utilization of legume flours in wafer sheets

AbstractIn this study, it was aimed to analyze the impacts of replacement of 20% of wheat flour by lentil, chickpea, or bean flours on batter rheology as well as hardness, weight loss, sorption characteristics, and color of the wafer sheets. All formulations showed shear thinning behavior obeying power law. Lentil flour‐containing formula gave the highest flow behavior index and the lowest consistency coefficient value. Hardness of wafer sheets increased when legume flours were used. Increase in hardness value was less when chickpea flour was used as compared with the other legume flours. It was observed that upon baking, legume flour‐added samples had lower weight loss values. Usage of chickpea flour resulted in the lowest weight loss. Sorption results implied localized sorption indicating multilayer water molecules showing similar properties to liquid water. Wafers containing legume flours were not significantly different than the control wafer in terms of monolayer moisture content, K and C values of Gugenheim, Anderson and de Boer (GAB) model. The color of chickpea flour‐containing wafer was the closest to that of control sample. Overall, wafer sheets prepared by replacement of 20% wheat flour by chickpea flour was agreed to be the best in terms of the analyzed parameters.

Construction of a design space for goat milk powder production using moisture sorption isotherms

AbstractIndustrialization of goat milk is critical to meet increasing demand. For process optimization and proper preservation of the product, information given by sorption isotherms can be fundamental. Therefore, the objective of this work was to determine the sorption isotherms of the goat milk powder and use that information to build a design space for the spray drying process. By fitting different mathematical models (GAB, Cavalcanti Mata, Thompson, and Oswin) to the experimental data, thermodynamic data was also determined as a function of equilibrium water content. The results allowed the construction of a phase diagram based on glass transition temperatures, and moisture content of 2.40% at the monolayer which provided a reference for the range of stability of water activity and a target for the final moisture content. By determination of net isosteric heat, it is clear that the values of energy for drying goat milk beyond the monolayer moisture content is much higher than for pure water vaporization enthalpy. Finally, using the fitted GAB model it was possible to construct a design space for the spray drying process of goat milk, and optimal spray drying parameters were determined.Practical ApplicationsThe construction of a production design space is critical for process scale‐up. On our work, we developed a new method to build such design space using the information provided by the moisture sorption isotherm and a fundamental model for the spray drying process. Therefore, a theoretical design space can be built with minimal resources which can be very useful for new products.

The use of different temperatures and inulin:whey protein isolate ratios in the spray drying of beetroot juice

Beetroot juice powders produced by spray drying under different temperatures and inulin:whey protein isolate (IN:WPI) ratios as carrier agents were evaluated. When it was used higher temperature, higher WPI concentration resulted in particles with higher betalains content (412.2 mg/100 g d.b.). For the antioxidant activity, values were found in a range of 61.5–90.8%. The color parameter values of the beetroot juice powders indicated intermediate lightness and saturation of coloring, which was closer to red. The mathematical model that best adjusted to the adsorption isotherms was the GAB and the monolayer moisture contents were between 5.1 and 6.5 g/100 g (d.b.). The higher concentration of IN resulted in lower stability of the powders when stored in environments with different water activities. Temperature of 170°C and IN:WPI proportion of 1:2 provided the best properties to the beetroot juice powder, which has the potential for the use and aggregation of functional properties in food matrices. Practical applications The use of natural colorant in processed foods and beverages is important for increasing the consumer acceptability of these products and beetroots are an excellent source of betalains, quite used by the food industry as a natural colorant. The results of this study represent the possibility of the attainment of an extract powder rich in betalains, being formed of polymeric materials with innovation grade for the food industry by applying them in food matrices to create synergy between the functional properties of several products.

Moisture sorption isotherm and shelf‐life prediction of anticaking agent incorporated spray‐dried soursop (Annona muricata L.) powder

AbstractThe moisture sorption isotherm (MSI) and shelf lives of soursop powders that had been incorporated with two commercial anticaking agents, calcium silicate (CS) and tricalcium phosphate (TCP), and inserted into aluminum laminated polyethylene pouches under room (RT, 25 ± 1°C) and elevated (ET, 38 ± 1°C) temperature, maintained at 93 ± 1% RH, were investigated. The powder possessed a Type III Brunauer's classification isotherm curve. The monolayer moisture content (Mo) was 0.023 ± 0.001 g H2O/g ds. A combination of low mean relative percent deviation modulus, E (2.18–3.75%), small sum of square residual, SSR (1.03 × 10−5–8.51 × 10−6), and high coefficient of determination (R2 > .99) indicating the moisture sorption data was sufficiently good fit using GAB model. Powder without anticaking agent stored at ET has the shortest estimated shelf life (~86 days) while 1.0 g/100 g TCP stored at RT exhibited the longest shelf life (~316 days). This study demonstrated that the incorporation of anticaking agents is effective to maintain the quality of powder by extending the shelf life by lowering moisture adsorption. The acceptability of reconstituted soursop powder based on hedonic test showed the scores for all attributes were higher than six.Practical applicationsUp to date, limited information describes the preservative effect of anticaking agents throughout the storage period. Hence, this work provides an insight to look into detail of how the incorporation of anticaking agents improve or retain the quality of the dried powder especially the moisture sorption isotherm (MSI) behavior. To achieve this, enzymatic pre‐treated spray‐dried powder was incorporated with anticaking agent. MSI was carried out and the behavior was determined by fitting the data into Guggenheim–Anderson–de Boer (GAB) model. Prediction of shelf life was studied by considering the critical moisture content (X c), which is the moisture content of powder that undergoes transition changed. The outcome of this work was expected to be beneficial to food powder industry to comprehend the protective effect of anticaking agents as a functional additive. Production of anticaking agent treated spray‐dried soursop powder was expected to broaden its potential applications as functional ingredient.

Osmotic-ultrasound dehydration pretreatment improves moisture adsorption isotherms and water state of microwave-assisted vacuum fried purple-fleshed sweet potato slices

Effect of osmotic-ultrasound dehydration pretreatment on the moisture adsorption isotherms of microwave-assisted vacuum fried purple-fleshed sweet potato (PSP) was determined at 30, 45 and 60 °C and fitted with six models. Absorbed water state of microwave-assisted vacuum fried purple-fleshed sweet potato was measured by low-field nuclear magnetic resonance (LF-NMR). Results indicated that the optimized conditions of osmotic-ultrasound dehydration pretreatment were 11.21 min for ultrasound time, 56.99% sucrose concentration and 74.84 min for osmotic dehydration time. Moisture adsorption isotherms showed type II sigmoid shape. GAB model had the best fit evaluated by the higher values of R2 (>0.9868) and the lower values of RMSE (<0.0074) and χ2 (<9.4893 × 10−5) for untreated and pretreated fried purple-fleshed sweet potato slices. Monolayer moisture content from GAB model decreased from 0.0598 at 30 °C to 0.0452 at 60 °C. The net isosteric heat of adsorption for untreated and pretreated fried PSP was calculated by the Clausius-Clapeyron equation and decreased with increasing moisture contents. The correlation between the bound water population (T21) peak areas of absorbed water and equilibrium moisture content was respectively high for untreated PSP (R2 > 0.9595) and pretreated fried PSP (R2 > 0.9845) by using LF-NMR.

Effects of Maltodextrins on the Kinetics of Lycopene and Chlorogenic Acid Degradation in Dried Tomato.

Maltodextrins (MD) are frequently used as processing aids in tomato drying. The aim of this study was to investigate the effect of the addition of MD on the stability of lycopene and chlorogenic acid, which are the main lipophilic and hydrophilic antioxidants in processed tomato, respectively. Tomato powder added with 10% MD (dextrose equivalents, DE 12) and a control tomato powder were stored in the water activity (aw) range 0.17–0.56, for 180 d at 30 °C. At the aw level of 0.17, which was below the monolayer moisture content (Mo), chlorogenic acid was stable, while lycopene content decreased faster in tomato added with MD than in control tomato, probably due to a decrease in matrix hydrophilicity and greater oxygen diffusion in the oil phase. Maximum stability occurred in both tomato powders at aw of 0.3, that was in close proximity to Mo (first-order rate constant for lycopene, k = 7.0 × 10−3 d−1 in tomato added with MD). At high aw levels, MD increased the rate of lycopene degradation with respect to the control, possibly by hampering its regeneration by chlorogenic acid, which conversely was found to be more stable than in the control tomato.

Drying kinetics and sorption behavior of two varieties banana (sagor and sabri) of Bangladesh

The study was concerned with determining the drying kinetics and sorption behavior of two varieties ripe banana of Bangladesh namely, Sagor and Sabri. The fresh ripe banana collected from the local market were sliced into three different thicknesses (4 mm, 6 mm and 8 mm) and dried at 45°C, 55°C and 65°C in a cabinet dryer. The result showed that the drying rate increases with the increase in temperature and decreases with the increase in slice thickness. The sorption properties of dried banana were studied over a wide range of water activity (0.11-0.93). The BET and GAB models were fitted to the sorption data. It was found that both varieties gave sigmoid (type II) shape isotherm and GAB equation gave the much higher value of monolayer moisture content compared to BET equation. The chemical compositions of fresh and dried banana were determined. The dried products gave substantially higher solid content as well as protein, ash and carbohydrate.&#x0D; SAARC J. Agri., 16(2): 181-193 (2018)