Effect of Encapsulating Materials on Water Sorption,Glass Transition and Stability of Juice From Immature Acerola

Immature acerola juice was dehydrated by spray drying, using as encapsulating material maltodextrin DE25, arabic gum, or a mixture of both in different proportions. A constant ratio of 1:1 was kept between juice solids and encapsulating material. The effect of encapsulation materials on water sorption, glass transition, and physical properties of encapsulated immature acerola juice was investigated. The monolayer moisture of the encapsulated juices, calculated according to the GAB theory, varied from 5.11 to 5.73g H₂O/100g of solids (25°C). The glass transition temperature (T_g) of maltodextrin and gum arabic varied from 60 (a_w 0.33) to 38°C (a_w 0.54), and from 62 (a_w 0.33) to 42.6°C (a_w 0.54), respectively. The addition of juice to the encapsulating materials decreased the T_g of the juice powder to 39.5–41.3°C (a_w 0.33) and 1.84–8.05°C (a_w 0.54), but no marked differences were found among the juice powders. The critical a_w, i.e., the point of onset of physical alterations in the encapsulated materials, was higher than the corresponding monolayer values. Stickiness was observed at temperatures close to T_g, and collapse occurred at temperatures of 20°C or more above the T_g. Maltodextrin DE25 and gum arabic offered equivalent contributions to the stability of the system.     

Phytochemical stability in dried apple and green tea functional products as related to moisture properties

In this study, apple products made with and without added green tea extract were freeze-dried and stored for up to 45 days at 30 °C in low and intermediate moisture environments (water activity, a_w, 0.11, 0.22, 0.32, 0.57, and 0.75). Kinetic models were developed for the changes in color and decreases in contents of selected green tea and apple monomeric and polymeric flavanols and ascorbic acid. Moisture isotherms were developed for each product. At various moisture levels, the glass transition temperature (T_g) was measured by DSC and water mobility by ¹H NMR. Chemical changes were related to T_g, a_w, and water mobility in the products.Phytochemical degradation occurred more rapidly at higher moisture contents, except for caffeine which was stable. In the product containing apple with green tea, the content of monomeric flavan-3-ols decreased by 34% and 39% after 45 days of storage at a_w of 0.56 and 0.75, respectively. Phytochemical degradation correlated with increasing a_w, T_g, and water mobility. This study showed that, in general, storage at a_w 0.75 most affected phytochemical stability and color.     

A convective multi-flash drying process for producing dehydrated crispy fruits

The aim of this work was to evaluate the application of a convective multi-flash drying process (CMFD) to producing dehydrated and crisp fruits. To accomplish this process, samples of banana (Musa sapientum L.) or mango (Mangifera indica L.) were heated to 60 °C by hot air, and a vacuum pulse was applied, which resulted in dehydration by a combination of convective drying and flash evaporation. Banana processed by CMFD had a moisture content of 0.293 g/g (dry basis) and a_w = 0.272 after 3 h of processing. Mango had a moisture content of 0.09 g/g and a_w = 0.359 after 4 h of processing. Puncture tests on fruits dehydrated by CMFD and on commercial freeze-dried fruits showed strain-force curves with many peaks (jagged curves). For CMFD much smaller global shrinkage was observed. These results indicate that the CMFD process can be applied for producing crispy fruits and is an alternative to the freeze-drying process.     

Phloridzin and other phytochemicals in apple pomace: Stability evaluation upon dehydration and storage of dried product

Apple pomace (mixed Red Delicious and Golden Delicious varieties) obtained from the industrial production of puree was both vacuum-dried at 40 °C and air-dried at 60 °C, ground and stored at water activity (a_w) in the range 0.11–0.75, for 9 months, at 30 °C. The aims were to investigate the effect of drying and long-term storage on phytochemical contents. Air-drying at 60 °C was better than vacuum-drying at 40 °C in terms of anthocyanin and flavanol retention; no adverse effect of drying was observed for flavonols, dihydrochalcones and hydroxycinnamic acids. The maximum stability occurred for all apple phytochemicals at the lowest a_w. At a_w 0.75 degradation of all phytochemicals occurred with the following stability ranking: phloridzin > chlorogenic acid > quercetin 3-O-galactoside > epicatechin > procyanidin B2 and cyanidin 3-O-galactoside. A promising feature of pomace is its exclusive high content of phloridzin, which showed relatively high stability during long-term storage.     

Physico-Chemical and Mechanical Properties of Apple Disks Subjected to Osmotic Dehydration and Different Drying Methods

The effect of sucrose infusion (SI) pretreatment and dehydration methods (freeze and air drying) on physical and textural properties of apple disks were analyzed. Dried samples were humidified between 11% and 43% relative humidity (RH) at 20 °C. Control samples (air- and freeze-dried) behaved similarly regarding water sorption and glass transition temperature. SI process caused important changes in the water sorption behavior of air-dried samples. Nuclear magnetic resonance relaxation times values (T ₂) for freeze-dried apples were higher than those for air-dried samples. Samples subjected to previous SI always presented lower T ₂ values because they had lower water contents. The dehydration method also affected the mechanic behavior. Air-dried samples exhibited higher F _max values during puncture assay than those obtained for freeze-dried samples. SI samples showed higher F _max values for both drying methods. The crust formed during air drying generated crispier materials along the whole RH range, while freeze-dried matrices were more deformable with the increase in RH. SI pretreatment also allowed diminishing browning development. The results obtained are useful in the choice of processing technologies of organoleptically acceptable dehydrated fruits for direct consumption or for their incorporation into compound foods.     

Sorption Behavior of Mechanically Mixed and Freeze-Dried Sucrose/Casein Mixtures

Interactions between sucrose and casein were investigated by adsorption isotherms. Mechanically mixed and freeze-dried sucrose/casein mixtures at sucrose percentages of 1, 5, 10, 15 and 20% (wet basis) were compared to calculated isotherms using the mass balance equation, over the a_w range 0.23–0.93 at 20°C. The mechanical mixtures did not exhibit solute/polymer interactions. The freeze-dried systems showed positive interaction (i.e., sorbed more water than calculated) for 1 and 5% sucrose at all a_w values. For the 10, 15 and 20% sucrose mixtures, positive interaction continued below 0.86 a_w; however, above 0.86 a_w, no interaction was apparent. That is, experimental sorption values equaled calculated values.     

EFFECT OF CaCl2 AND CONVECTIVE-OSMOTIC DRYING ON TEXTURE AND PREFERENCE OF APPLE

Conventional air‐drying combined with osmotic dehydration was researched as a potential method for drying apple cubes of superior quality. Samples were pretreated with CaCl₂ at different temperatures and times. Pretreated apple cubes were dehydrated in a tray dryer. Then, osmotic dehydration with sucrose solutions was carried out. The curves for osmotic dehydration showed that the gain of solids was higher when 40% of water was removed by convective drying while the loss of weight was lower at the same level of dehydration at 65°Brix. Texture measurements indicated that the temperature of pretreatment affected the hardness and cohesiveness. Hardness values were higher at 40C, while cohesiveness values were lower at the same temperature. The CaCl₂ at a given temperature did not have a significant effect on texture. Sensory evaluation showed that samples pretreated at 25C and osmotically dried at 50°Brix had the higher preference by the judges.     

Sorption Behavior of Mechanically Mixed and Freeze-Dried NaCl/Casein Mixtures

Adsorption isotherms of mechanically mixed and freeze-dried mixtures of NaCl/casein at solute percentages of 1, 5, 10, 15, and 20 (wet basis) were obtained over the a_w range 0.23–0.927 at 20°C. Experimental isotherm values were compared to those calculated by a mass balance equation. The mechanically mixed samples sorbed additively as predicted by the mass balance equation below 0.755 a_w, whereas the freeze-dried mixtures sorbed more water than predicted (positive interaction) below 0.755 a_w, Both types of mixtures sorbed less water than predicted by the mass balance equation (negative interaction) above the saturation a_w of the NaCl, 0.755.     

Browning,Starch Gelatinization,Water Sorption,Glass Transition,and Caking Properties of Freeze-dried Maca ( Lepidium meyenii Walpers) Powders

The browning, gelatinization of starch, water sorption, glass transition, and caking properties of freeze-dried maca ( Lepidium meyenii Walpers) powders were investigated and compared with a commercial maca powder. The freeze-dried maca powders had lower optical density (browning) and higher enthalpy change for starch gelatinization than the commercial maca. This resulted from a difference in thermal history. The equilibrium water contents of the freeze-dried maca powders were higher than those of commercial maca at each water activity ( a _w ) because of differences in amorphous part. The glass transition temperature ( T _g ) was evaluated by differential scanning calorimetry. There was a negligible difference in the anhydrous T _g (79.5–80.2 ºC) among the samples. The T _g -depression of freeze-dried maca powders induced by water sorption was more gradual than that of the commercial maca due to a difference in water insoluble material content. From the results, critical water activity ( a _wc ) was determined as the a _w at which T _g becomes 25 ºC. There was negligible caking below a _w = 0.328. At higher a _w , the degree of caking remarkably increased with a large variation depending on the samples. The degree of caking could be described uniformly as a function of a _w / a _wc . From these results, we propose an empirical approach to predict the caking of maca powders.     

Kinetic modelling of non-enzymatic browning of apple juice concentrates differing in water activity under isothermal and dynamic heating conditions

The kinetics of non-enzymatic browning in apple juice concentrates were investigated. The effect of a_w (in the range of 0.74–0.99) and/or reactant concentration on brown pigment formation was monitored under isothermal heat treatment at four temperatures (60, 70, 80 and 90 °C) in apple juice solutions having either the same or different concentrations of reactant solutes. The extent of the Maillard reaction was evaluated by spectrophotometric measurements at 420 nm (A₄₂₀). The absorbance–time curves were fitted to five different kinetic models (zero and first order, weibull, logistic and the parabolic model) and estimates of browning rate constants and other model parameters were obtained. Regression analysis revealed that the logistic model was the most appropriate for describing browning in apple juice. The initial reactant concentration, but not water activity, had a significant effect on the colour change of apple juice. The processing temperature also had a strong impact on browning kinetics. Secondary models, expressing the dependence of the best fitted primary model parameters on temperature and a_w, were further developed and validated by comparing the predicted model parameters with the values observed in independent isothermal experiments. Finally, the derived model was further evaluated against the observed browning responses of apple juice under dynamic heating conditions, underlining the applicability of the developed model as a practical prediction tool for the study of non-enzymatic browning.     

Air Drying Bacon Slices to Reduce aw: An Anti-Clostridial Alternative to Sodium Nitrite

Low temperature air drying studies were conducted on bacon slices to determine the practicality and effectiveness of this method for reducing water activity (a_w) as an anti-clostridial alternative to sodium nitrite. Isotherms were developed to determine the extent of moisture removal required to achieve a_w= 0.92 or lower; these levels have been found to inhibit C. botulinum. Drying to these levels of inhibition can be accomplished in approximately 1.75 hr. Drying rates are significantly affected by air temperature, air flow rate, and slice overlap. Experimental data indicate drying can be accomplished with no substantial change in product quality.     

Dehydration of salmon (Atlantic salmon), beef,and apple (Granny Smith) using Refractance window™: Effect on diffusion behavior,texture, and color changes

The aim of this research was to study the use of Refractance window™ (RW™) in the dehydration of salmon (Atlantic salmon), beef (lean), and apples (Granny Smith) through the analysis of the effective diffusivity determined through the Fick's model and the anomalous model.Salmon, beef, and apple slices were dried at 55 and 95 °C, using either a conventional drying process or RW™. Water activity (a_w) was measured periodically by drying, and the effective diffusion (D_eff) was measured using Fick's second law and an anomalous model. Color changes (∆E) and firmness were also measured.The results showed that mass transfer in salmon and beef was not improved by RW™. In contrast, in apple slices dehydrated using RW™, the D_eff and processing times were significantly (p < 0.05) affected, reflecting a reduced drying time required to attain an a_w of 0.6.RW™ is a powerful tool that allows for the dehydration of fruit using temperatures of 95 °C and provides a 50% reduction in drying time.     

Formulation of a Dry Green Tea-Apple Product: Study on Antioxidant and Color Stability

ABSTRACT: A dry apple product enriched with green tea (GT) extract was designed as a novel food to deliver relevant amounts of catechins. The target water activity (a_w) range between 0.11 and 0.32 was chosen for the GT-fortified apple, since it corresponds to low water mobility and, consequently, maximum stability of dehydrated apples. The GT-fortified product and a control dehydrated apple product were stored in air, at 30 °C, and evaluated for color, antioxidant contents (monomeric flavan 3-ols, total procyanidins, ascorbic acid, chlorogenic acid and dihydrochalcones), ferric reducing/antioxidant power (FRAP), and 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl radical (DPPH) scavenging capacity. After 1 mo of storage at the lowest a_w level (0.11), the GT-fortified product retained 80 and 100% of the initial contents of the monomeric flavan 3-ols and total procyanidins, respectively. With increasing a_w level to 0.32, the stability of antioxidants slowly decreased. The addition of GT to the apple product increased the FRAP value and the DPPH scavenging capacity by 3.6-fold and 4.6-fold respectively, which remained almost unchanged during storage. The GT-fortified product was similar in color to commercially available dehydrated apples. Results highlighted some advantages of using dehydrated apples as a target for green tea fortification, which deserve further trials to investigate potential applications for fortification of other dehydrated fruits.     

Correlation of Proton T1 with Polymer and Solute Waters in Starch-Sucrose Mixtures

Proton pulsed NMR methodology was applied to correlate the observed spin-lattice (T₁) and spin-spin (T₂) relaxation times with the amount of water associated to sucrose (SOL) and that to starch (POL) in a sucrose-starch model system containing both. Sucrose, starch and four mixtures were equilibrated to four water activities (a_w, 0.86-0.97). Calculations for T₂ were invalid due to an undeterminable amount of molecular diffusion caused by field inhomogeneity in the magnet. Model equations were developed for calculating SOL and POL from T₁ and a_w; These values showed high correlations (R²>0.97) with SOL and POL as determined from sorption data for sucrose and starch. This validated the use of this instrument with the mathematical models developed.     

Moisture sorption and the applicability of the Brunauer-Emmet-Teller (BET) equation for blanched and unblanched mushrooms

Moisture sorption isotherms of blanched and unblanched mushrooms over 0.11–0.75 a_w were determined at 27°C and 37°C by using the static gravimetric method. Adsorption and desorption behaviors of blanched and unblanched mushrooms were compared. The unblanched material adsorbed more water than that of the blanched. In desorption isotherms, the equilibrium moisture contents of the unblanched material were found to be higher than those of the blanched throughout the entire a_w range. The BET equation was tested to fit the experimental moisture sorption data over the 0.11–0.43 a_w, 0.11–0.55 a_w, 0.11–0.64 a_w, and 0.11–0.75 a_w. Nonlinear regression analysis was used for the determination of the parameters in the equation. The quality of the fit of the BET model over each a_w range was judged from the value of the relative percent root mean square (% RMS). The moisture sorption behavior over 0.11–0.43 a_w of mushrooms has indicated that the BET equation is applicable generally up to 0.43 a_w. Monolayer moisture contents and C constants in the BET equation obtained for each a_w interval were reported. The water activities corresponding to the monolayer values have been determined and discussed related to mushroom storage. The net isosteric heats of adsorption and desorption were estimated from equilibrium sorption data, using the integrated form of the Clausius-Clapeyron equation. The heats of adsorption/desorption decreased with increase in moisture content and approached to a constant value. It was concluded that moisture adsorption/desorption occurred by physical mechanisms at high moisture contents, but at low moisture contents, besides physical adsorption, chemisorption was also observed.     

Effect of maltodextrin weight fraction on the amorphous state and critical storage conditions of freeze-dried juices

Diagrams relating to water activity (a_w), equilibrium moisture content (X_w) and glass transition temperature (Tg) are valuable tools for predicting amorphous fruit powders' storage procedure and stability. Thus, T_g–a_w–X_w diagrams were constructed to characterise the amorphous state and define the critical values of water content (X_wc) and water activity (a_wc) of freeze-dried juices of strawberry, pineapple, kiwi and prickly pear prepared with maltodextrin at the dry mass fraction (W_MD) of 0, 0.4 and 0.8. The T_g and sorption data were fitted with a polynomial equation and the Guggenheim–Anderson–de Boer (GAB) model respectively. A Tukey test was performed to evaluate the difference between critical values of the powders (P < 0.05). The a_wc and X_wc increase with W_MD and depend on the chemical composition of the powders. The highest critical values were found in pineapple powders, ranging from 0.174 to 0.632 and 0.029 to 0.142 dry basis (d.b.), and the lowest ones in kiwi juice powders ranging from 0.029 to 0.550 and 0.013 to 0.129 (d.b.). For W_MD of 0.8, however, regardless of juice composition, stable powders in an amorphous state were obtained up to an a_w of 0.52 at 25°C.     

Moisture Transfer Properties of Dry and Semimoist Foods

Equilibrium moisture content, mass diffusion coefficients, and densities were collected for wheat flour, shredded wheat, raisins, nonfat dry milk, and freeze-dried apple, turnip, and ground beef at 25 ± 1°C. Flour adsorbing to 0.75 a_w had the largest mass diffusion co-efficient, 1.15 × 10^?7 m²/hr and raisins had the smallest value of 0.015 × 10-⁷ m²/hr. Two of the food uroducts. flour desorbing to 0.11 a_w, and the freeze-dried turnip, exhibited diffusion coeffcients which were dependent on the moisture content. Most of the foods reached equilibrium within 1 wk based on an objective criterion of no more than a 0.5% dry basis moisture difference over three successive readings at 1 wk interval.     

Modelling the Dynamic Inactivation of the Probiotic Bacterium <Emphasis Type="Italic">L. Paracasei</Emphasis> ssp. <Emphasis Type="Italic">Paracasei</Emphasis> During a Low-Temperature Drying Process Based on Stationary Data in Concentrated Systems

In order to better understand inactivation of cells during a drying process, the inactivation kinetics of concentrated Lactobacillus paracasei ssp. paracasei (F19) was measured under stationary conditions for different combinations of water activities and temperatures in a water activity range of a _w = 0.23–a _w = 0.75 and temperatures between 4°C and 50°C. It was shown that the inactivation kinetics of the probiotic bacterium L. paracasei at moderate temperatures could, for all conditions, be formally described by a first-order reaction with activation energies that are much lower than for thermal inactivation (E _a = 61 kJ/mol). With regard to the water activity, the reaction rate constants exhibit a maximum inactivation rate at intermediate water activity a _w = 0.52. As this behavior has direct implications for the stability of cells in a drying process, the stationary data were used to model the inactivation during test vacuum drying processes, where both temperature and water activity dynamically change. It is shown that—depending on the drying rate—dynamic effects have to be taken into account when modeling the survival during drying. Nevertheless, the model based on stationary inactivation data is capable to predict the characteristics of inactivation during a drying process. Therefore, it can serve as basis to optimize the drying process with regard to maximum survival of cells. However, a further refinement of the model with regard to the drying rate is necessary.     

Effect of Pomace Drying on Apple Pectin

The effect of temperature used for drying apple pomace on apple pectin characteristics, including chemical composition, color and gelpoint temperature (T_g) was determined. Pomace was obtained from commercial Granny Smith apples and dried in a rotary drier at different air temperatures (T_dr = 60, 70, 80 and 105 °C). Pectin was extracted from dried pomace in nitric acid solution (pH = 2.5) at 80 °C. Major minerals in apple pectin were Ca>Na>Mg. Galacturonic acid content (% AGA=60.6±1.8) was practically unaffected by drying temperature. Conversely, T_dr affected both the degree of methoxylation (DM) and the molecular weight (M_w) of extracted pectin. M_w was estimated by applying the Mark Houwink - Sakurada equation, through determination of intrinsic viscosity of pectin solutions. M_w reduced withT_dr from approximately 122,000 (60°C) to 57,000 (105°C). Pectin color, as Hunter ΔE, was also affected by T_dr. A lighter color was obtained at 80°C. The higher gelpoint value (T_g= 80°C) was obtained with pectin from pomace dried at 80°C. Gelpoint was shown to be more sensitive to T_dr than other quality parameters: while DM had the same value both at 80 and 105°C, minimumT_g occurred at the higher temperature. T_g was also very sensitive to pH.     

Changes in the catechin and epicatechin content of grape seeds on storage under different water activity (aw) conditions

Storage effect on antioxidant content and capacity of grape seeds under different a_w conditions (a_w 0.33; 0.53; 0.75/50 days, 25 °C) was examined. Total phenol content (determined by the Folin–Ciocalteu method) decreased during storage though changes were trivial for samples stored at 33% or 53% RH. High level of humidity (75%) accelerated degradation and resulted in a ∼50% reduction of total phenol content. Minor loss of the DPPH radical scavenging activity (%RSA) of the extracts was observed. Catechin and epicatechin content monitored by RP-HPLC was reduced during storage, particularly at 75% RH. Epicatechin content proved to be less sensitive to water activity conditions than catechin content. Results of various in vitro assays (Folin–Ciocalteu, FRAP, DPPH, ABTS, CBA, ORAC and copper induced liposome oxidation) did not support difference in terms of resistance to oxidation. Based on the continuous release of gallic acid, our finding was related to hydrolytic reactions. Control of a_w of grape seeds can be of practical importance for the wine industry.