Sorption Isotherms and Drying Rates of Jerusalem Artichoke (Helianthus tuberosus L.)

Moisture sorption properties and drying behavior of Jerusalem artichoke roots were investigated. Sorption isotherms of dehydrated and freeze-dried material, its water insoluble components, fructose, glucose and sucrose were determined at 10, 25 and/or 40°C. Adsorption-desorption isotherms indicated a combination of sorption by soluble sugars, in the crystalline, amorphous and aqueous solution state, and sorption by polymeric material such as cellulose, inulin and protein. In drying experiments conducted at 50, 65, 80, and 95°C, and also at 65°C and four air velocities and four bed depths, it was found that temperature and drier load conditions are of critical importance to drying behavior, drying time and finished product color. Increasing the air velocity from 2.0 to 4.2 m/set, at a temperature of 65°C and a bed depth of 10.5 cm, did not change the rate for drying 1 cm cubes.     

Processing, Packaging, and Storage Effects on Quality of Freeze-Dried Strawberries

Water sorption isotherms of freeze-dried strawberries were determined using the interval sorption technique. The surface temperature during freeze-drying (from 20°C to 60°C) affected the hygroscopicity of the strawberries, particularly below 0.40 a_w. Over 1 yr, quality changes in dried strawberries were evaluated by sensory analysis at 3-month intervals. Crushing before drying and low processing temperatures improved sensory quality of dried strawberries and vacuum packaging improved storage stability.     

Drying characteristics and sorption isotherms of silverside fish (Atherina)

The aim of this work was to report drying characteristics and sorption isotherms of silverside fish. The sorption isotherm was determined at four temperature levels 40, 50, 60 and 70 °C and at water activities, ranging from 0.058 to 0.89, using the static gravimetric method. Five sorption models were fitted with the desorption data generated from the gravimetric method. It was found that the Peleg model suitably represents the sorption experimental data in the mentioned investigated ranges of temperature and water activities. Sorption isosteric heat was determined from sorption data using the Clausius–Clapeyron equation. The relationship between the net isosteric heat of sorption and the moisture content was best expressed by the Tsami’s equation. The drying characteristic curve and the drying rate expression of silverside fish have been established from experimental convective drying kinetics.     

Effect of Pre-treatment and Drying Method on Colour Degradation Kinetics of Dried Salak Fruit During Storage

Effect of heat treatment on colour stability of dried salak fruit during storage was investigated by using hot air (40–90 °C), heat pump (isothermal and intermittent modes, 26–37 °C) and freeze-drying. Influence of pre-treatment on the colour property was studied as well by blanching the sample at three levels of temperature (50–70 °C). Total colour change (∆E*) was used to assess the colour degradation kinetics and quantify the degree of browning during processing and storage. It was found that the dried pre-treated sample under heat pump isothermal drying recorded the highest ∆E* value during storage followed by non-pre-treated samples under heat pump intermittent drying, freeze-drying, hot air-drying and heat pump isothermal drying. Weibull model is found to better fit the experimental data as compared with zero-order and first-order kinetics models. Analysis on the kinetics constants reveals that the heat treatment could affect the microstructure, water sorption properties and concentration of reacting species of the dried product. This in turn contributes to the colour changes of the dried product during storage.     

Water Vapor Adsorption Isotherms of Guava, Mango and Pineapple

Isotherms were determined at 25° and 50°C, using an electronic water activity meter. For the 3 fruits temperature had practically no effect on the isotherms. Sorption capacity of freeze-dried pineapple was higher than that for vacuum dried. The higher sorption capacity of mango and pineapple in comparison to guava corresponded to the respective sugar contents of the fruits.     

Characterization of Spaghetti Prepared Under Different Drying Conditions

Spaghetti dried at low (max. 50 °C), high (max. 70 °C), and very high (max. 85 °C) temperatures were characterized by their color, surface structure, rupture strength, texture analysis, and sauce retention capacity. The texture and sauce retention capacity were estimated for cooked spaghetti. The color of the spaghetti's methanol extracts, as evaluated through absorbance at 440 and 466 nm, did not depend on the drying temperature. A trend was observed in the surface texture of spaghetti, as estimated by atomic force microscopy and mercury intrusion porosimetry, where the surface was rougher when dried at higher temperatures than at low temperatures. Furthermore, the rupture strength was also higher for the spaghetti dried at higher temperatures. This result can be ascribed to the formation of stronger gluten networks, promoted by denaturation of gluten at the higher temperatures. However, the hardness of cooked spaghetti was not affected by the drying temperature, a result attributable to the action of water sorption to offset any differences in hardness among the spaghettis dried at the 3 different temperatures. The sauce retention capacity of cooked spaghetti was evaluated using a dextran solution as a simulated sauce, and by this method, the capacity of the spaghetti dried at a low temperature was shown to be significantly lower than that of the spaghetti dried at higher temperatures. This can be ascribed to the smoother surface of cooked spaghetti dried at the lower temperature and also to the leakage of amylose onto the surface during cooking.     

Effect of postharvest handling on valerenic acids content of fresh valerian (Valeriana officinalis) root

Valerian (Valeriana officinalis) is a medicinal herb native to Europe and North Asia, the roots and rhizomes of which are used as a sedative for nervous tension, sleeplessness, anxiety and stress. The impact of washing and drying on the valerenic acids concentration in valerian roots was investigated. The valerenic acids content of roots that were washed, soaked or cut prior to drying was not significantly different from that of whole valerian roots that were dried without washing, but cutting markedly decreased the drying time. Increasing the drying temperature from 15 to 70 °C reduced drying time by 176 h, with a 23% loss of valerenic acids from 15 to 40 °C. A further 36% loss occurred from 40 to 50 °C but no further significant change was evident at higher temperatures. The use of a heat pump dryer reduced the drying time at 40 °C by 25% compared with a hot air drier operated at the same temperature with no significant difference in the level of valerenic acids. There was no significant change in the level of valerenic acids in fresh whole roots held at ambient conditions for 10 days but a considerable decrease in water content. Hence valerian growers can separate or soak roots prior to washing and can store fresh roots before drying without concern over loss of valerenic acids. However, drying at the lowest feasible temperature is recommended. Copyright © 2005 Society of Chemical Industry     

Water Sorption Isotherms of Raisins, Currants, Figs, Prunes and Apricots

Moisture sorption isotherms of dried fruits [Sultana raisins, Corinthian (black) currants, figs, prunes, and apricots] were determined at 15, 30, 45, and 60°C, using the standard static gravimetric method developed by the European Cooperation Project COST 90. Experimental curves showed an inverse effect of temperature at high moisture content due to high sugar content of dried fruits. The hysteresis between adsorption and desorption was verified experimentally. The GAB equation was used to predict experimental data for water activity range 0–0.95.     

Equilibrium Water Content and the State of Water in Dehydrated White Cabbage

The water sorption isotherms for freeze-dried cabbage were determined at 15°C and 23°C, and the state of the water was studied using differential scanning calorimetry (DSC). The water sorption capacity of the freeze-dried cabbage depended on the temperature. The effects of free sugars were clear in both adsorption and desorption. The thermal behavior of freeze-dried cabbage was highly moisture dependent. In the capillary condensation range (>0.9 a_w) solution of low molecular components of the freeze-dried cabbage affected its freezing behavior.     

Moisture sorption isotherms of potato slices

Water vapour sorption isotherms of Norchip, Russet Burbank and Norland potatoes were determined by the salt solution technique at 10, 25 and 40°C. The adsorption isotherms of potatoes were of sigmoid shape and were affected by drying method, temperature and sugars addition. The freeze dried products adsorbed more water vapour than the vacuum dried materials. Addition of glucose, sucrose or lactose to the potatoes caused the equilibrium moisture content to decrease in the low and intermediate water activity ranges. The sorption was temperature independent in the a _w range 0.11–0.35 and showed a hysteresis loop at intermediate moisture levels.     

Physicochemical properties and storage stability of spray‐dried soya bean sprout extract

Amylase is a very important enzyme due to its wide food applications. To preserve amylase activity in soya bean sprout extract (SSE), SSEs were spray‐dried with 10% maltodextrin and 0–3% alginic acids, and their physicochemical properties and storage stability were compared with freeze‐dried one. SSE exhibited maximum amylase activity at pH 7.0 and 60 °C, with the most active substrate specificity towards soluble starch. Spray‐dried SSEs exhibited higher water solubility index (WSI) and in vitro relative amylase activity but lower water vapour sorption (WVS) and smaller particle size than freeze‐dried SSE. For spray‐dried SSEs, particle size, WSI and in vitro relative amylase activity increased while WVS decreased with increasing % alginic acid. This study demonstrated that spray drying of SSE, especially with 10% maltodextrin and 2% alginic acid, was effective in keeping amylase active and stable during 7‐week storage at room temperature (25 °C).     

Equilibrium moisture characteristics of dried eggplant and okra

Equilibrium moisture characteristics of dried eggplant and dried okra were studied at 20 °C and 27 °C Moisture sorption isotherms of these dried vegetables were derived using the static method. Sorption data were treated according to some well-known isotherm equations. The parameters of these equations were obtained and goodness of fit of data to these equations were tested. The trends in monolayer moisture contents at different temperatures were examined. Finally, the heat of sorption data were derived with the use of Clausius Clapeyron type equation and presented in graphical form.     

Moisture Sorption Characteristics of Freeze Dried Blueberries

Moisture sorption isotherms of freeze dried lowbush blueberries at 4, 16, 25, 35, and 45°C were determined using indirect gravimetric method. Moisture sorption kinetics at these temperatures and 75% RH were also investigated. The isotherms followed a type III shape with a temperature inversion effect at 0.9 water activity. They were best described by the GAB equation. Net isosteric heat of moisture sorption in freeze dried blueberries, determined using the Clausius Clapeyron equation, varied from 5.5 to 0.25 kJ/mol as moisture content changed from 8 to 36% (dry basis). Moisture adsorption kinetics in freeze dried blueberries were well described by the first order kinetics equation. The rate constant followed the Arrhenius relationship with an activation energy of 38.6 kJ/mol.     

Water sorption and cooking time of red kidney beans (Phaseolus vulgaris L.): part I – Effect of freezing and drying conditions on water sorption and cooking time

Water sorption and cooking time of kidney beans were determined. The beans were manually harvested at 19.2 ± 0.1% moisture content and stored at ?20 and ?10 °C for about half a year. The beans were further dried at 30, 40 and 50 °C inside a thin‐layer drier for 7.5 h or under room conditions for 4 week. The freezing storage temperature before the beans were dried did not influence their cooking time and water sorption. The saturated kernel volumes decreased approximately 7% after drying. The beans decreased their sphericity during water sorption and had a larger swelling ratio in the thickness direction than in other directions. Lower initial moisture content, especially with a higher drying temperature, decreased water sorptivity and resulted in higher percentage of uncooked kernels if the beans were not soaked before cooking. However, there was no relationship between initial moisture content and uncooked percentage if the beans were soaked before cooking. High drying temperature resulted in hard‐to‐cook (HTC) phenomenon.     

Moisture sorption characteristics and glass transition temperature of apple puree powder

The aim of this study was to characterise the influence of different foam‐mat‐drying methods on the moisture sorption characteristics and glass transition temperatures of apple puree powder. Apple puree was foamed with the addition of 2.5% egg albumin and 0.5% methylcellulose. Convective air‐drying and microwave‐drying techniques were used. Also foamed puree with and without maltodextrin (6% or 15% w/w) was freeze‐dried. Moisture equilibrium data of powders were determined by using a static desiccator method in a water activity range of 0.0–0.903. Modulated differential scanning calorimetry (MDSC) was used to obtain the glass transition temperature. No effect of drying method on sorption properties and glass transition temperatures of apple puree powders was observed. The addition of maltodextrin to the apple puree caused an increase in T_g by 10–30 °C depending on the amount of incorporated additive. Addition of maltodextrin significantly reduced the hygroscopicity of apple puree powders.     

Sorption equilibrium moisture and isosteric heat of adsorption of Chinese dried wheat noodles

Equilibrium moisture content (EMC) data for dried wheat noodles of ten Chinese varieties were collected by a gravimetric method at 11–96% equilibrium relative humidity (ERH) and 15 °C, 20 °C, 25 °C, 30 °C, and 35 °C. Five models were fitted to the sorption data, namely the modified Chung Pfost equation (MCPE), modified Henderson equation (MHE), modified Guggenheim Anderson deBoer equation (MGAB), modified Oswin equation (MOE), and a polynomial equation. The best fitting equations were MGAB and the polynomial equation. At a constant ERH, the EMC decreased with increasing temperature, despite the minor effect of temperature on the sorption isotherms of dried noodles. Initially, the isosteric heats of adsorption for dried wheat noodles decrease rapidly with increasing sample moisture content (m.c.); however, after the moisture content is more than 15% of the dry basis (d.b.), they decrease slowly with increasing m.c. The heat of vaporization of Chinese dried wheat noodles approaches the latent heat of pure water at a moisture content of ∼20% d.b., which is ∼2500 kJ/kg. The isosteric heats of sorption of Chinese dried noodles predicted by MCPE and MHE models at lower temperatures were higher than those at higher temperatures. When the equilibrium relative humidity (ERH) is 60%, the safe-storage moisture content of Chinese dried wheat noodles are 11.74% and 11.57% d.b. at 25 °C and 35 °C, respectively. Among ten varieties of dried wheat noodles, the egg-flavoured noodle had the highest onset temperature (T_o), peak temperature (T_p), and conclusion temperature (T_c) of gelatinization, but the golden-silk egg noodles had the highest peak enthalpy of gelatinization. The gelatinization T_o, T_p, and T_c of golden-silk egg noodles were the lowest. Most of the ten varieties of dried wheat noodles demonstrated similar thermal properties and hygroscopic behaviour.     

Effect of Microwave Power Coupled with Hot Air Drying on Sorption Isotherms and Microstructure of Orange Peel

Drying is one of the most cost-effective methods of worthwhile by-product valorisation. This study had two main objectives. The first was to determine the effect of hot air drying (HAD) combined with microwave (MW) irradiation on the treatment kinetics and the macrostructural and microstructural properties of the dried product. The second aim was to develop engineering tools to predict the extent of dehydration. Drying was performed using hot air at 55 °C and the combined (HAD?+?MW) treatment at different power intensities (2, 4, and 6 W/g). After 5, 15, 40, 60, and 120 min, the mass, surface, volume, water activity and moisture were measured in fresh and dried samples. Sorption isotherms were obtained and fitted to the GAB model, with high correlation coefficients. The macroscopic and microscopic analyses showed shrinkage and swelling in the peel tissue caused by the MW treatment. The HAD?+?MW methods not only resulted in increased moisture reduction but also induced microstructural changes that generated higher sorption capacity.     

Effect of vacuum‐drying,hot air‐drying and freeze‐drying on polyphenols and antioxidant capacity of lemon (Citrus limon) pomace aqueous extracts

The aim of this study was to investigate the effect of freeze‐drying, hot air‐drying and vacuum‐drying at 70, 90 and 110 °C, on dried lemon pomace polyphenols and antioxidant capacity. The total phenolic content and antioxidant capacity were higher in lemon pomace dried by hot air or under vacuum than those dried by freeze‐drying and increased as the temperature increased. The highest total flavonoid content was recorded in the pomace dried under vacuum at 70 and 90 °C. Lemon pomace dried by freeze‐drying had the highest neohesperidin content, whereas pomace dried under vacuum at 70 °C had the highest rutin and p‐coumaric acid content. The highest gallic acid content was recorded in the pomace dried by hot air at 110 °C. The results of this study indicate that drying technique should be carefully selected according to the bioactive compounds aimed to be extracted.     

Effect of drying method on the moisture sorption isotherms for Inonotus obliquus mushroom

Moisture sorption isotherms of Inonotus obliquus mushroom were studied over a selected temperature range (20-50 °C). Sigmoid sorption isotherms were observed for these samples. The sorption data were analyzed using various conventional models. The Oswin model was found to be the best model for predicting the equilibrium moisture content of mushroom in the range of water activity 0.08-0.96. The monolayer moisture content decreased as temperature increased and was affected by the drying method used. The net isosteric heat of sorption was determined using the Clausius-Clapeyron equation and the value decreased with increase in moisture content of mushroom.     

Moisture sorption properties of smoked chicken sausages from spent hen meat

Moisture sorption characteristics of smoked chicken sausages from spent hen meat were investigated at 5, 25 and 50°C over a water activity (a_w) range of 0.11–0.87. Sigmoidal (type-II) desorption isotherms were observed for these samples. The sorption data were analysed using mathematical equations of Caurie, Halsey, GAB and Oswin. The Halsey equation gave the best fit over the entire temperature range. GAB model also described the isotherms fairly well. The GAB and BET monolayer moisture values were not significantly different (P>0.01) and decreased with increasing temperature. The number of adsorbed monolayers, density and amount of bound water and surface area of adsorption also decreased as the sorption temperature increased. The pores, in general, enlarged with rising temperature.