Establishing the Most Suitable Storage Conditions for Microencapsulated Allspice Essential Oil Entrapped in Blended Biopolymers Matrices

The adsorption isotherms of allspice essential oil microencapsulated in biopolymers blend (whey protein concentrate [WPC], mesquite gum [MG], and maltodextrin DE10 [MD]) in different proportions (WPC17%-MG17%-MD66% w/w and WPC66%-MG17%-MD17% w/w) with wall-to-core material ratios of 4:1 were determined at 25, 35, and 40°C. The isotherms were fitted using the Guggenheim-Anderson-de Boer (GAB) model and the enthalpies and entropies, both differential and integral, were estimated by the Clausius-Clapeyron method. The minimum integral entropy was considered as the point of maximum stability where strong bonds between the adsorbate and adsorbent occurred, and water would be less available and likely to participate in spoilage reactions. The point of maximum stability was found between 13.79 and 15.11 kg H₂O/100 kg d.s. (corresponding to water activity, a _W , of 0.444–0.551) for the microcapsules with WPC17%-MG17%-MD66% w/w as wall material and 18.71–19.63 kg H₂O/100 kg d.s. (a _W  = 0.591–0.713) for the microcapsules with WPC66%-MG17%-MD17% w/w as wall material in the temperature range studied.     

Optimization of the Drying Process of Carrot (Daucus carota v. Nantes) on the Basis of Quality Criteria

The drying curves and the degradation kinetics of three different quality attributes (total carotenoids (TC) and total polyphenols (TP) contents and antioxidant activity (AA)) of carrots during drying at different temperatures (from 40 to 90°C) have been experimentally evaluated and modeled. A diffusional model taking into account the solid shrinkage and both the external and internal water transfer resistances was used to accurately represent the water transfer in carrot during drying (average mean relative error (MRE) of 3.3 ± 0.6%). The effective moisture diffusivity was found to follow the Arrhenius relationship (E_a = 76.0 kJ/mol) and the mass transfer coefficient a linear dependence with air temperature. The Weibull model was used to satisfactorily simulate the degradation kinetics of the three quality attributes considered (average MRE of 2.8 ± 1.2% for TC content, 5.7 ± 1.0% for TP content, and 3.6 ± 1.8% for AA); these were the E_a of 52.7 kJ/mol for TC; 22.1 kJ/mol for TP; and 27.5 kJ/mol for AA kinetics. By using the proposed models, the estimated optimum drying temperature to best retain the total carotenoids content ranged between ca. 42–46°C; meanwhile, in order to maintain the TP content and the antioxidant activity at the highest levels, the drying needed to be carried out at temperatures of ca. 60–75°C. These results indicate that the TC retention is more influenced by the drying temperature, while the TP and AA retentions are more sensitive to drying time exposure. However, it was possible to establish a global optimum air temperature which ranged between 52.6 and 57.7°C, decreasing the TC, TP, and AA retentions by less than 2.2% from their respective optimal values.     

Microencapsulation of Kaffir Lime Oil and Its Functional Properties

This paper describes the effects of spray drying temperature and wall materials on functional properties of kaffir lime oil microcapsules. The effects of spray drying were studied at inlet air temperatures at 160, 180, and 200°C. Two coating materials (konjac glucomannan and gum arabic) were employed in this study. The results indicate that kaffir lime oil had antibacterial activity against all tested pathogens and was able to inhibit Vibrio cholerae comparable to a standard antibiotic. The combination of konjac glucomannan and gum arabic (KGM+GA) can enhance the yield and retention of total oil in the microcapsules more than using konjac glucomannan alone as a wall material. Increasing inlet air temperature resulted in a decrease of antibacterial activity and amount of bioactive volatile compounds. Physical and chemical properties of the microcapsules did not differ significantly (p > 0.05) in terms of process yield, a _w , moisture content, efficiency in retention of total, surface and inner oil, water solubility index, and color except at inlet air temperature of 200°C. However, it was found that the kaffir lime oil microcapsules from KGM+GA produced at inlet temperature of 180°C had the best functional properties in terms of antibacterial activity and efficiency of retention of total encapsulated oil.     

Enthalpic and Entropic Mechanisms Related to Water Sorption of Yogurt

Moisture sorption isotherms of plain, concentrated, freeze-dried, and freeze-dried concentrated yogurts at 20, 35, and 50°C were used to calculate integral properties. Enthalpy-entropy compensation for all yogurt preparations showed two isokinetic temperatures. The first isokinetic temperature was observed at low moisture contents and was controlled by changes in the entropy of water, whereas the second isokinetic temperature was considered to be enthalpy-driven and was of the same magnitude for all yogurt products (T_B2  = 327.4 ± 0.7 K). Application of the Dubinin-Radushkevich equation suggested that the moisture zone controlled by entropy was produced when adsorption ocurred in the micropore range.     

Influence of Oil Load and Maltodextrin Concentration on Properties of Tuna Oil Microcapsules Encapsulated in Two-Layer Membrane

The two layers of tuna oil-in-water emulsions containing different oil loads (5–10 wt%) and maltodextrin concentrations (10–20 wt%) were stabilized by a lecithin–chitosan membrane. The liquid emulsions were then spray dried at an inlet air temperature of 180 ± 2°C and an outlet air temperature of 85 ± 5°C. The characteristics of liquid emulsion (creaming and mean droplet size) and spray-dried microcapsules (moisture content, water activity, color, morphology, glass transition temperature, and encapsulation efficiency) were measured. The results suggest that two-layer oil-in-water emulsions are an effective system to produce high oil-loaded microcapsules, which may lead to its wide application for use in food products.     

KINETICS OF ASCORBIC ACID DEGRADATION IN DRIED KIWIFRUITS DURING STORAGE

Retention of ascorbic acid (AA) in dried kiwifruit in storage is studied. The effects of storage temperature (30°C–50°C) and water activity (a_w: 0.51–0.82) are investigated. The degradation of AA follows a first order reaction. A decrease of approximately one order of magnitude in AA is observed when a_w is increased from 0.51 to 0.82 with the activation energy in the range of (38.0–62.3) kJ/mole. The effect of temperature on the rate constant followed the Arrhenius relationship. An empirical equation combining temperature, water activity rate constant has been developed.     

Physical and Thermal Stability of Spray-Dried Swiss Cheese Bioaroma Powder

The effect of water content on the glass transition temperature of Swiss cheese bioaroma microencapsulated with a spray dryer was determined using differential scanning calorimetry (DSC) while mass loss was determined by thermogravimetric analysis (TGA). The sorption isotherm behavior was assessed at 15–45°C. Data were fitted with different sorption models. The bioaroma microparticles were produced via spray drying in a matrix with a 1:1 ratio (w/w) of maltodextrin 20DE and modified corn starch (Capsul). The isotherms displayed Type II behavior, and the best fit was obtained by the Guggenheim–Anderson–de Boer (GAB) model (coefficient of determination R² ≥ 0.98). The DSC analysis showed that the increased equilibrium moisture content caused a significant reduction in the T_g of the microparticles. The samples stored at intermediate humidity showed thermal stability and the samples with equilibrium moisture content of 17.92% showed a lower mass loss.     

Thermodynamic sorption properties of potato and sweet potato flakes

The moisture sorption isotherms of potato and sweet potato flakes were determined using a gravimetric method at 15, 20, 25 and 30 °C for water activity ranging from 0.1 to 0.9. The GAB was found to be the most suitable for describing the relationship between equilibrium moisture content and water activity for the whole range of temperatures and relative humidities. The differential and integral thermodynamic functions of enthalpy and entropy were estimated from the sorption data for potato and sweet potato flakes. The differential enthalpy was determined using the Clausius–Clapeyron equation and decreased with increase in moisture content, the same behavior as found for differential entropy. From the values obtained for differential enthalpy and entropy, it was verified that the compensation theory could be applied, the process being carried out by enthalpy (T_β > T_hm) and non-spontaneous (ΔG > 0). The spreading pressures increased with increasing water activity for all the temperatures studied. With respect to the integral properties, it was observed that the enthalpy increased with moisture content, but the entropy decreased. It was also shown that for the moisture range evaluated, the values for integral entropy were negative.     

壳聚糖分子量对酵母细胞固定化培养的影响

以海藻酸钠-壳聚糖微胶囊（AC微胶囊）为研究对象,以酵母细胞S.cerevisiae BY4741为细胞模型,分别考察了相同成膜反应时间和相同成膜厚度两种情况下,壳聚糖分子量对微囊膜膨胀行为、微囊内细胞增殖情况及微囊化细胞培养过程中细胞泄漏的影响规律。研究结果显示,在成膜反应时间相同的情况下,壳聚糖分子量越小,向海藻酸钙凝胶网络扩散越容易,交联成膜越厚,微胶囊膜越能耐受渗透压膨胀。但在控制相同膜厚的情况下,大分子量壳聚糖由于分子链长,与凝胶微球表面海藻酸钠分子的作用位点多,易纠结相邻海藻酸钠分子链形成更致密的络合交联,呈现更高的耐受渗透压膨胀的特性。AC微囊化细胞培养48 h后,小分子量壳聚糖充分成膜反应制备的AC微胶囊,虽然膨胀不显著,但由于膜结构占据了更多微胶囊体积,既缩小了酵母细胞的增殖空间,又极大增加了传质阻力,反而限制了细胞增殖。培养过程中,各组微胶囊均未发现明显的细胞泄漏现象。     

Preparation and characterization of paraffin microcapsules for energy-saving applications

A series of microencapsulated phase-change materials (PCMs) with styrene–divinyl benzene shells composed of an n-octadecane (OD or C₁₈)–n-hexadecane (HD or C₁₆) mixture as the core were synthesized by an emulsion polymerization method. The effects of the core/shell ratio (C/S) and surfactant concentration (C_surf) on the thermal properties and encapsulation ratios of the PCMs were investigated. The chemical structures and morphological properties of the microcapsules were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy analysis, respectively. The characteristic peaks of the paraffin mixtures and shell material located in the FTIR spectrum of the microencapsulated PCMs proved that the encapsulation of the PCM mixture was performed successfully. The thermal properties of the paraffin microcapsules were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis. DSC analysis demonstrated that the microcapsules containing the maximum amount of paraffin mixture (C/S = 2:1) and the minimum C_surf (45 mmol/L) had the highest latent heat value of 88 kJ/kg and a latent heat of temperature of 21.06°C. Moreover, the maximum encapsulation ratio of the paraffin mixture was found to be 56.77%. With respect to the analysis results, the encapsulated binary mixture, which consisted of OD–HD with a poly(styrene-co-divinyl benzene) shell, is a promising material for thermal energy storage applications operating at low temperatures, such as in the thermal control of indoor temperatures and air-conditioning applications in buildings for desirable thermal comfort and energy conservation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47874.     

Fractal surface analysis and thermodynamic properties of moisture sorption of calcium–sucrose powders

Fractal analysis, using water adsorption and an image analysis technique, was applied to investigate the effect of surface irregularities on the thermodynamic properties of matrix calcium–sucrose powder moisture sorption. The sorption isotherms were evaluated at 15, 25, and 35°C for calcium–sucrose powders obtained by a cryogenic process (CP) and spray drying (SD). Solubilization of the powders was observed after 20 days of storage at 25°C, and the powder CP had greater physical stability than SD. There was good agreement among the fractal dimension computed by scanning electron microscopy analysis and water adsorption isotherm. The surface fractal dimensions were between 2.19 and 2.44 for CP and were larger than those obtained for SD, which were between 2.11 to 2.26. The differential and integral enthalpies increased as the surface geometry became more irregular, also increased the interactions between the powder surface and water molecules. These results suggested that the increase in the matrix irregularities for a product can displace the minimum integral entropy toward high water activity, thereby improving the storage stability.     

Effect of Selected Additives on Microencapsulation of Anthocyanin by Spray Drying

Microencapsulation of anthocyanin pigment present in Garcinia indica Choisy was carried out with maltodextrin of various dextrose equivalents (DE 06, 19, 21, and 33) and other additives such as gum acacia and tricalcium phosphate to enhance the stability of the pigment. The microencapsulated pigment containing 5.0% maltodextrin DE 21, 0.25% gum acacia, and 0.25% tricalcium phosphate was found to have lowest hygroscopic moisture content (4.38%), highest antioxidant activity (69.90%), and highest anthocyanin content (485 mg/100 g). The glass transition temperature was 44.59°C. The sorption isotherms for microencapsulated powder showed that the samples were stable up to water activity less than 0.43. The scanning electron microscope structures depicted that the particle size ranged from 5 to 50 μm with smooth spheres. Storage at 4°C increased the half-life twofold compared to that of the spray-dried product kept at ambient temperature (25°C).     

Thermal Degradation Kinetics of Carotenoids in Palm Oil

In the present work, a detailed study is performed for carotene thermal degradation in palm oil at four temperatures ranging from 170 to 230 °C. The heating process was carried out with injection of nitrogen, and the samples were collected every 20 min during a total heating period of 140 min. HPLC analysis was conducted to monitor the carotenoids and tocols variations over the heating time at each temperature. The experimental data were then compared to literature data concerning carotenoids thermal degradation. The thermal degradation kinetics of carotenoids in palm oil followed an order superior to 1. The dependence of constant rates with temperature obeyed the Arrhenius relationship. The activation energy for the carotenoids thermal degradation in palm oil was found to be 109.4 kJ/mol.     

Thermal Activation of Mendable Epoxy through Inclusion of Microcapsules and Imidazole Complexes

Epoxy resin was encapsulated in poly(urea–formaldehyde) microcapsules using an in situ dispersion polymerization technique. The efficiency of Ni and Cu–imidazole complexes as latent hardeners was compared to that of 2-methylimidazole. Calorimetric studies revealed higher reactivity of the nickel complex toward oxirane functionalities. Both the complexes could effectively cure the epoxy released from within the microcapsules in the event of damage followed by thermal treatment. The curing could be effected at lower temperature (T_onset = 145°C) using [Ni(2-Me-ImidH)₄Cl]Cl as compared to [Cu(2-Me-ImidH)₄Cl]Cl (T_onset = 152°C). A healing efficiency of 100 ± 2% could be achieved at 30% microcapsule loading, irrespective of the type of metal complex used.     

Improving thermal stability of SiC whiskers via nanoscale Ti3SiC2 coatings

Effects of SiC whiskers (SiC_w) on the mechanical properties of composites largely depend on their thermal stability at high temperature. In this study, pure SiC_w and Ti₃SiC₂ coated SiC_w were thermal treated at 1600–1800°C for 1 h. Their phase assemblage, morphology, and structural evolution were investigated. Oxygen partial pressures in the graphite furnace resulted in the breakdown of SiC_w into particles at 1600°C, and the degradation became more pronounced with temperature increasing. The thermal stability of SiC whiskers at 1600–1700°C was significantly improved by a thin Ti₃SiC₂ coating on them, as both thermodynamic calculations and experimental observations suggest Ti₃SiC₂ coating could be preferentially oxidized/decomposed, prior to the active oxidation of SiC. At 1800°C, the protective role of the coating on the whiskers became weakened. SiC was converted into gaseous SiO and CO, with the remaining of interconnected TiC micro-rods and amorphous carbon.     

Moisture Sorption Isotherms,Thermodynamic Properties,and Glass Transition of Pears and Apples

Moisture sorption isotherms of apples and pears were determined at 30, 45, and 60°C and water activity (a _w ) range of 0.04–0.83 using a standard static gravimetric method. The sorption isotherms of both fruits decreased with increasing temperature and exhibited type III behavior according to Brunauer–Emmett–Teller (BET) classification. The moisture desorption data fitted well with the Peleg model (0.997 ≤ r ≤ 0.999, 0.009 ≤ SE ≤ 0.071, and 4.840 ≤ p ≤ 13.779).

The glass transition temperature (T _g ) of both fruits decreased linearly with the increase in water activity (a _w ). The variation in glass transition temperature versus water activity (T _g  ～ a _w ) and glass transition temperature versus solid fraction of pears and apples (T _g  ～ W _s ) were adequately predicted by Khalloufi et al.'s model (0.998 ≤ r ≤ 0.999 and 0.007 ≤ SE ≤ 4.088) and the Gordon and Taylor model (0.879 ≤ r ≤ 0.979 and 9.798 ≤ SE ≤ 18.507). The thermal transition and desorption isotherms data were used to establish state diagrams of pear and apple and evaluate suitable fruits storage conditions.     

Sodium Humate as a Promising Coating Material for Microencapsulation of Beauveria bassiana Conidia Through Spray Drying

Microencapsulation of Beauveria bassiana (Bb) conidia with sodium humate (SH) was undertaken successfully through spray drying at a high inlet air temperature of 175°C with corresponding outlet air temperature of 86.5 ± 1.3°C using 0.2% SH. The obtained product was a free-flowing, dark-brown powder containing microcapsules of Bb conidia coated with sodium humate (Bb-SH). These microcapsules measured 2.47–3.57 µm and possessed an uneven, fluffy surface. The colony-forming units (CFU) of Bb-SH microcapsules spray-dried at 175°C were 21.54 LCFUg^?1, on par with 21.59 LCFUg^?1 for Bb conidial powder not subjected to spray drying. Bb-SH microcapsules resulted in a high mortality of 93.0% against six-day-old Helicoverpa armigera larvae within five days after treatment. Bb-SH microcapsules readily dispersed in water, releasing sodium humate from the conidial surface. Germination of conidia was not affected by sodium humate as visualized by scanning electron microscopy of the cuticular surface of treated larvae. Bb-SH microcapsules showed good viability (21.11 LCFUg^?1) at the end of six months of storage at room temperature (～30°). Thus, sodium humate is a promising biopolymer for encapsulation of Bb conidia for extended shelf-life at room temperature.     

Poly(divinylbenzene) Microencapsulated Octadecane for Use as a Heat Storage Material: Influences of Microcapsule Size and Monomer/Octadecane Ratio

Poly(divinylbenzene) (PDVB) microencapsulated octadecane (OD) (PDVB/OD) used as heat storage material were prepared by suspension polymerization at 70°C using benzoyl peroxide and polyvinyl alcohol as initiator and stabilizer, respectively. The influence of microcapsule size and divinylbenzene (DVB)/OD weight ratio on the microcapsule shape and thermal properties of encapsulated OD were considered. Thermal properties and thermal stability of PDVB/OD microcapsules were determined using differential scanning calorimeter (DSC) and thermogravimetric analyzer. The optical micrographs and scanning electron micrographs showed that the microcapsules have spherical shape only in the case of 50/50 (%w/w) of DVB/OD whereas they were nonspherical with the decreasing of DVB content. However, the core materials were still well encapsulated even increasing the OD content to 70%wt. From DSC analysis, in all cases, the melting temperature of encapsulated OD (28°C) was almost the same as that of bulk OD (30°C), yet it was quite different in the case of crystallization temperature (≤ 19°C and 25°C for encapsulated and bulk OD, respectively). The latent heats of melting and crystallization of encapsulated OD, in all conditions, were reduced from those of bulk OD (242 and 247 J/g, respectively).     

Surface Characterization of Ti and Ti (6% AI-4%, V) Metal Powders and Interaction with Primer Solutions

The surfaces of Ti and Ti (6% Al-4% V) powders were characterized by several techniques. BET surface areas as a function of temperature were measured using nitrogen adsorption. Heats of immersion (δ_wH) of these metal powders in water were measured after evacuation over the temperature range 100°–400°C. The δ_wH in water increased with increasing evacuation temperature and an anomalous increase was observed between 300° and 400°C. This was attributed to exposure of water to elemental titanium by cracking of the oxide layer at 400°C. XPS analysis did not support the possibility of metal migration through the oxide layer. Higher heats of immersion in water were determined for chemically pretreated compared to untreated Ti 6–4 powders. Water vapor adsorption isotherms were measured after evacuation of the metal powders at 100°C. Partial irreversibility of the water adsorption was observed on both powders. Water adsorption on Ti was temperature dependent. Heats of immersion measurements were used to study the interaction of primer solutions with these metal powders. Polyimide (LARC-13) and polyphenylquinoxaline (PPQ) interacted preferentially compared to the solvents with both powders. This polymer-metal interaction improved significantly after pretreatment of the Ti 6–4 powder by the Turco® 5578 and phosphate-fluoride processes. Again, an anomalous increase in the heat of immersion of Ti 6–4 evacuated at 400°C in the primer solution/solvents was observed. Anatase and rutile TiO₂ powders are not satisfactory models for the surface oxide layer on either Ti or Ti 6–4 powders.     

Microencapsulation of Rosemary Essential Oil: Characterization of Particles

This study evaluated the influence of wall material concentration (10–30%), inlet temperature (135–195°C), and feed rate (0.5–1.0 L · h^?1) on the properties of rosemary oil microencapsulated by spray-drying, with gum arabic as carrier. Powder recovery, surface oil, oil retention, and hygroscopicity varied from 17.25%–33.96%, 0.03%–0.15%, 7.15%–47.57%, and 15.87%–18.90%, respectively. The optimized conditions were determined to be a wall material concentration of 19.3%, an inlet air temperature of 171°C, and a feed flow rate of 0.92 L · h^?1. At this condition, particles presented no fissures and the compositions of pure and microencapsulated oil were similar. The sorption isotherms could be described by the GAB model.