Critical Water Activity Research Articles

Effects of trehalose and corn starch on the mechanical glass transition temperature and texture properties of deep-fried food with varying water and oil contents

The effects of trehalose and corn starch on the mechanical glass transition temperature (Tg) and texture properties of a deep-fried sample (particles of deep-fried batter) with varying water and oil contents were investigated. Tg decreased linearly with increases in both water and oil contents, attributable to their plasticizing effects. Tg was elevated by the addition of trehalose, likely due to its anti-plasticizing effect. Corn starch had a negligible effect on Tg. The critical water content and water activity (water content and water activity at Tg = 25 °C) were determined by extrapolation, and obtained values were validated by isothermal mechanical relaxation. The texture of the samples changed from brittle to ductile near the critical water content and water activity. The trehalose-added sample maintained a brittle texture at a higher water content than the non-additive and corn starch-added samples, as trehalose elevated the critical water content of the deep-fried samples.

Fast Determination of Phase Stability of Hydrates Using Intrinsic Dissolution Rate Measurements

The critical water activity (aw,c) at a fixed temperature and transition temperature (Tt) in water between an anhydrate and its corresponding hydrate determine their physical stability. Hence, thei...

The Shelf Life and Recommended Dietary Allowances (RDA) Analysis of Cassava (Manihot esculenta Crantz) Flakes Enriched with Bean Flour (Phaseolus vulgaris L.)

Food processing in commercial industry generally aims to extend shelf life, change or increase products’ characteristics (color, flavor, texture), ease treatment and distribution, increase economic value, and maintain or improve quality, particularly nutritional quality, digestibility, and nutritional value. The objective of this research is to determine the shelf life of products made from cassava flour which is fortified by red bean flour, and to understand whether there is a decrease in nutritional value during the storage period, as well as to calculate the Recommended Dietary Allowances (RDA). The Recommended Dietary Allowances of Cassava Flakes with Red Bean Flour for breakfast has a very important function. For instance, children who are in school need plenty of energy to start their activities and stay focused at school. Breakfast food needs to fulfill the 20-25% of the RDA for children, who need a total of 2,000 kilo calories per day. An alternative option for breakfast is nutritious flakes that can be consumed with a quick preparation time. The method to determine the shelf life is carried out using the Accelerated Self Life Testing (ASLT) and critical water activity methods, whereas to determine the proximate nutritional value we used the gravimetric method to determine the ash content and water content. In addition, we used the Kjehdahl method to determine the protein content, the sokhlet method for the fat content, and by difference method for the carbohydrate content. The result obtained for the nutritional value throughout the storage period is that the nutritional value of the flakes decreased after being stored for 10 weeks. The result of determining the shelf life using a critical water activity method is 307.5 days of storage. RDA or the Recommended Dietary Allowance is the percentage of the amount of a nutrient contained in the food consumed based on the daily needs of the healthy person. Generally this daily requirement is based on daily caloric requirement of 2000 kcal, but some also use base 2500 kcal. RDA's guidance in Indonesia can follow the guidance given by POM RI based on Decree of the Head of POM RI No. HK.00.05.52.6291 on Food Label Nutritional Reference.

Continuously Distributed Glass Transition of Maca (Lepidium meyenii Walpers) Powder and Impact on Caking Properties

Water sorption isotherm, glass transition temperature (Tg), and caking properties of maca (Lepidium meyenii Walpers) powder were investigated. A broad endothermic shift reflecting continuously distributed glass transition was detected by differential scanning calorimetry, which prompted the evaluation of onset Tg and offset Tg. From the onset and offset Tg curves and water sorption isotherm, critical water activity (water activity at glass transition temperature of 25 °C) was determined to be 0.258 for the onset Tg and 0.480 for the offset Tg. The critical water activity values were validated by isothermal mechanical relaxation measurement. Caking properties of maca powder were compared with maltodextrin. The degree of caking and cake hardness for maltodextrin increased at a water activity just above critical water activity for onset Tg. Maca powder, on the other hand, showed a small degree of caking in the water activity range of 0.225 to 0.576, and the degree of caking drastically increased at a higher water activity. The hardness of maca cakes increased gradually at water activity values greater than 0.432. Since maca powder showed a continuously distributed glass transition, the molecular mobility required for caking was considered to have been provided incrementally by the increase in water activity above critical water activity for the onset Tg.

Determination of the structural stability of a premix powder through the critical water activity

This paper analyses the structural stability of a premix powder that consists of a mixture of whey protein isolate, soy protein isolate, sodium caseinate, carrot juice, and honey bee, which are mixed together by spray-drying. The structural stability of the powder is determined by means of its critical water activity (RHc) at 25 °C, which is determined by three different procedures, namely, by the conventional graphical method, by calculating the inflection points in the adsorption isotherms, and by digital image analysis on the powders stored at different water activities ( $$0.11\le a_{w}\le 0.53$$ ). These three methodological approaches can predict the value of RHc reliably.

Least squares fitting-polynomials for determining inflection points in adsorption isotherms of spray-dried açaí juice (Euterpe oleracea Mart.) and soy sauce powders

The modelling of adsorption isotherms is an important method for analysing the stability of spray-dried powders. These properties are intimately related with the inflection points of the isotherm curve. The accurate calculation of the inflection points provides a method to determine the critical water activity (RHc) of powders. Though the inflection points can be estimated from standard models such as BET or GAB, in the present work we employ Least Squares Fitting-Polynomials for representing the adsorption isotherms, which in turn leads to a minimum error in the calculation of the inflection points. Then we investigate the physicochemical sense of the inflection points thus calculated for spray-dried açaí juice (Euterpe oleracea Mart.) and soy sauce powders and compare with the results reported in literature. Here we observe that from the LSF-polynomials, the inflection points may give an approximation of the value of the monolayer moisture content, and the critical water activity.

Water sorption, glass transition, and freeze-concentrated glass-like transition properties of calcium maltobionate–maltose mixtures

The water sorption, glass transition, and freeze-concentrated thermal transition properties of calcium maltobionate (MBCa)–maltose mixtures were investigated. At lower maltose molar fractions, the water content of the mixtures increased sigmoidally with water activity (aw). At higher maltose molar fractions, maltose preferentially crystallized in an aw condition, and water sorption isotherms deviated from sigmoidal behavior. The glass transition temperature (Tg) decreased with increasing water content because of a water-plasticizing effect, described as a Tg curve. The critical water content (Wc) and critical water activity (awc) (i.e., water content and aw at Tg = 298 K) were determined from the water sorption isotherms and Tg curves. The values of Wc and awc decreased linearly with increasing maltose molar fraction. The DSC curve of the MBCa–maltose aqueous solutions showed a large endothermic shift before the endothermic peak due to melting ice, and freeze-concentrated glass-like transition temperature (Tg′) was evaluated from the endothermic shift. The Tg′ of the MBCa–maltose aqueous solutions decreased with increasing maltose molar fraction. These results are useful for predicting the physical stability (collapse, crystallization of maltose, and powder caking) of MBCa–maltose mixtures during freeze-drying and subsequent storage.

Inhibition of lactose crystallisation in the presence of galacto-oligosaccharide

The stabilization of lactose in the form of amorphous (i.e. non-crystalline form) is the basic requirement to maintain the quality of relevant food and pharmaceutical products. The physiochemical properties of amorphous lactose mixed with galacto-oligosaccharide (GOS) were investigated. Water sorption, glass transition temperature, and crystallisation behaviour of lactose in the present of GOS (1:1 w/w) were measured at various water activity (0.11–0.75 aw, 25 °C) and lactose mutarotation was also evaluated. All of them were compared with the physiochemical properties of trehalose-lactose (1:1 w/w). The addition of GOS to lactose increased the hygroscopicity of the mixture, as well as slightly increased the glass transition temperature compared to lactose alone. The critical water activity (at 0.68 aw) of lactose crystallisation was increased by the addition of GOS as compared to that of trehalose-lactose (1:1 w/w) (at 0.58 aw) or lactose alone (at 0.44 aw). The dramatical inhibition of lactose crystallisation with a lower crystallisation kinetic constant and the alternation of lactose crystal forms in the presence of GOS was observed as compared to the crystallisation behaviour of trehalose-lactose (1:1 w/w) and pure lactose at 0.68 and 0.75 aw, 25 °C. Without affecting its Tg, the significantly delayed crystallisation of lactose in GOS-lactose mixture (1:1 w/w) was more likely due to the change of lactose mutarotation. As comparing to trehalose that is an effective inhibitor, GOS has a stronger ability to prevent lactose from crystallisation in hydrous matrices.

COMPORTAMIENTO DE SORCIÓN DE PELÍCULAS DE PECTINA CÍTRICA CON GLICEROL Y ACEITE DE OLIVA

The effect of glycerol and olive oil on water sorption isotherms of orange (FOP) and grapefruit (FGP) peel pectin films was studied. Additives decreased the equilibrium moisture content (X) and the extent of the observed hysteresis. Abrupt changes in the adsorption isotherms of the films were noted, and were very well correlated to one of the maxima of the second derivative of X as function of aw. Converted adsorption data for GAB regression (aw/X) generated curves with a sharp peak, linked to the isotherms inflection points. aw/X vs aw diagrams were valuable to identify order–to-disorder transitions in pectin films. Glycerol concentration reduced the critical water activity in FGP. GAB model described adsorption isotherms above the transition (R2 > 0.932), and Halsey model exhibited a better fit (R2 > 0.984). Desorption phenomena was better described by Peleg model (R2 > 0.959).

Thermodynamic analysis for assessing the physical stability of core materials microencapsulated in taro starch spherical aggregates

Taro starch has the ability of producing spherical aggregates under spray-drying without the addition of binding agents. This property makes taro starch suitable for microencapsulation of dietary compounds. This study addressed the physical stability of hydrophilic and hydrophobic core materials microencapsulated by spray-drying into taro starch spherical aggregates determined from a thermodynamic standpoint via vapor adsorption isotherms. Ascorbic acid and almond oil were used as compound models. Encapsulation efficiency, GAB sorption parameters, differential and integral thermodynamic properties, Gibb’s free energy, entropy-enthalpy compensation, spreading pressure, effective diffusion rate, activation energy and critical water activity were determined. The encapsulation efficiency of ascorbic acid and almond oil was 99% and 56%, respectively. Monolayer moisture content was relatively low for ascorbic acid microcapsules. The adsorption process was driven by entropic mechanisms. The physical stability of taro starch spherical aggregates microcapsules with different core material was guaranteed for a range of water activities and temperatures.

Effect of water sorption on the glass transition temperature and texture of deep-fried models

The purpose of this study was to understand effect of water sorption on the glass transition temperature (Tg) and texture of deep-fried models, namely, bits of deep-fried tempura batter. Two types of deep-fried models (normal and glucose-added samples) were employed. Tg was investigated by thermal rheological analysis (TRA); although TRA measurements for pellet samples showed an unclear glass transition, the measurements for bulk samples showed a large force-drop induced by this effect. Isothermal mechanical relaxation measurement confirmed that the Tg value of the deep-fried samples could be evaluated from the departure point of the force-drop. The Tg decreased with increase in water content because of the water plasticizing effect; the glucose-added sample had a higher Tg than the normal sample at each water content. The fracture property of the samples changed from brittle to ductile at the critical water content and/or water activity (i.e., those at Tg = 25 °C).

Water state diagram and thermal properties of fructans powders

The thermal analyses and the water state diagrams of agavin and inulin were investigated. The thermogravimetric analysis and differential scanning calorimetry (DSC) were used to know the difference between fructans. Linear inulin (220.0 °C) showed a higher thermal stability than the branched agavins (206.7 °C). The samples displayed different physical states and lightness depending on the water activity of storage (a w). The agavin showed different physical states: powder (a w < 0.33), soft lump (a w ≈ 0.43), sticky (0.55 < a w < 0.77), and liquid (a w > 0.85), while inulin showed two physical states: an amorphous powder at a w < 0.55 and a semicrystalline solid at a w > 0.69. These physical states decreased the lightness of fructans. The GAB equation and the Gordon–Taylor equation showed a good fit to the experimental data (R 2 > 0.95). The K constant of GAB equation predicted a lower water affinity of inulin powder, while the agavin powder presented a higher water affinity. The DSC showed a glass transition temperature of 118.1 and 135.3 °C for agavin and inulin anhydrous powders, respectively. An increase in water content in agavin showed a higher depression in the glass transition temperature than in inulin. Also, the inulin exhibited a melting point while agavin not. The water state diagrams showed the critical water activity at which the agavin (0.50) and inulin (0.59) powders were stable to physical changes. This knowledge is used to understand the physical and structural behaviors of agavin and inulin at the different water activities.

Development and characterization of a new encapsulating agent from orange juice by-products

The replacement of maltodextrins as carriers for the spray drying of sticky and sugar based bioactives is an important development for the food industry. In this work, orange juice industry by-product was used to obtain a high dietary fiber powder to be used as carrier material. This powder was characterized with respect to its physical and chemical properties related to the process of encapsulation by spray drying. Adsorption isotherms of orange waste powder were determined at 30, 45, and 60°C. The data were fitted to several models including two-parameter (BET, Halsey, Smith, and Oswin), three-parameter (GAB), and four-parameter (Peleg) relationships. The GAB model best fitted the experimental data. The isosteric heat of sorption was determined from the equilibrium sorption data using the Clausius-Clapeyron equation. Isosteric heats of sorption were found to decrease exponentially with increasing moisture content. The enthalpy-entropy compensation theory was applied to the sorption isotherms and indicated an enthalpy controlled sorption process. Glass transition temperatures (Tg) of orange waste powder conditioned at various water activities were determined and a strong plasticizing effect of water on Tg was found. These data were satisfactory correlated by the Gordon and Taylor model. The critical water activity and moisture content for the orange waste powder were 0.82 and 0.18g water/g solids, respectively, at a storage temperature of 25°C.

Microstructure investigation and its effects on moisture sorption in fried potato chips

It is important to understand the influence of processing conditions to design a desirable food product. The microstructure and water sorption capacity of three types of fried potato chips were evaluated in order to gain an understanding of how the different processing conditions impacted their structures and further, their textures and shelf life. Pore structures were quantified and analyzed using both the capillary penetration technique of a mercury porosimeter and the imaging technique of X-ray computed tomography (μCT). Additionally, the water vapor sorption isotherm was quantified using a Pro Umid SPSx-1μ system. The results indicated that ridged potato chips (RPC) showed the highest porosity (50.78 ± 3.02%), followed by flat potato chips (FPC) (41.15 ± 3.56%), and batch cooked potato chips (BCPC) (32.58 ± 4.21%). A similar trend was exhibited in the data obtained from X-ray μCT. The solids distribution in RPC, FPC, and BCPC was 21.56 ± 7.97%, 24.87 ± 5.83%, and 34.28 ± 9.49%, respectively, determined by μCT. μCT cross-section images displayed a highly porous microstructure in FPC, while RPC appeared to have thicker walls and larger cells than the others. The data suggested that the critical water activity (aw) of the three types of potato chips ranged from 0.70 to 0.85. At higher aw (above 0.85), RPC displayed the highest moisture absorption capacity, followed by FPC, and BCPC. The results also showed that a higher percentage of porosity is followed by higher moisture content in the potato chips. The findings propose that water vapor sorption of the three types of potato chip was governed by the Flory-Huggins model. In addition, the oil significantly blocked water sorption in the samples (p < 0.05).

Experimental and Computational Hydrate Screening: Cytosine, 5-Flucytosine and Their Solid Solution.

The structural, temperature- and moisture dependent stability features of cytosine and 5-flucytosine monohydrates, two pharmaceutically important compounds, were rationalized using complementary experimental and computational approaches. Moisture sorption/desorption, water activity, thermal analysis and calorimetry were applied to determine the stability ranges of hydrate ↔ anhydrate systems, while X-ray diffraction, IR spectroscopy and crystal structure prediction provided the molecular level understanding. At 25 °C, the critical water activity for the cytosine hydrate ↔ anhydrate system is ~0.43 and for 5-flucytosine ~0.41. In 5-flucytosine the water molecules are arranged in open channels, therefore the kinetic desorption data, dehydration < 40% relative humidity (RH), conform with the thermodynamic data, whereas for the cytosine isolated site hydrate dehydration was observed at RH < 15%. Peritectic dissociation temperatures of the hydrates were measured to be 97 °C and 84.2 °C for cytosine and 5-flucytosine, respectively, and the monohydrate to anhydrate transition enthalpies to be around 10 kJ mol-1. Computed crystal energy landscapes not only revealed that the substitution of C5 (H or F) controls the packing and properties of cytosine/5-flucytosine solid forms, but also have enabled the finding of a monohydrate solid solution of the two substances which shows increased thermal- and moisture-dependent stability compared to 5-flucytosine monohydrate.

Thermodynamic and molecular investigation into the solubility, stability and self-assembly of gabapentin anhydrate and hydrate

Solubility of gabapentin anhydrate/monohydrate in alcohol-water mixtures was experimentally determined. An interesting trend of the solubility was found, which showed both maximum and minimum solubility with different solvent compositions at one temperature. Molecular dynamics simulations were carried out to explore the effect of solvent composition on the solubility, indicating that the water association played an important role. Critical water activity and the transition temperature of gabapentin anhydrate/hydrate were also determined, and a relationship between them was established to investigate the factors influencing the hydration. Furthermore, the ternary phase diagram of (gabapentin-ethanol-water) at 293.15K was built by slurry experiments for further understanding of the crystal form transformation, which confirmed the stability regions of anhydrate/monohydrate and verified the above established relations. Then the dehydration/hydration process in the solution can be predicted and controlled, thus obtaining the desired product.

Degradation Kinetics and Storage Stability of Vacuum Spray-Dried Micro Wet-Milled Orange Juice (Citrus unshiu) Powder

The aim of this work was to evaluate the degradation kinetics and stability of micro wet milled orange juice powders obtained by vacuum spray drying, using maltodextrin as a carrier agent. Powders were produced with four combinations of orange juice solids/maltodextrin solids 60:40, 50:50, 40:60, and 30:70 by weight. Ascorbic acid degradation, color, and antioxidant activity of powders were evaluated throughout 90 days. Powders were stored at 10, 25, and 35 °C and relative humidity of 33%. Temperature and storage time negatively influenced the stability of ascorbic acid and color, whereas antioxidant activity increased at the beginning of storage at a higher temperature then decreased slightly after 60 days. For stability study, powders were stored at different water activities (0.11 to 0.84) in order to determine the plasticizing effects of water on glass transition temperature. Both water activity and glass transition temperature were used to predict the critical conditions for storage. Vacuum spray dried powder produced with a ratio of 30:70 (orange juice solids/maltodextrin solids) was considered as the most stable, since it showed highest critical water activity (aw = 0.61) and lowest moisture content (0.11 g water/g of dry solid) among the four powders. Vacuum spray drying using superheated steam as the heating medium was proven to be an effective way of producing orange juice powders with minimum loss of nutrients.

Inactivation of Lipase and Lipoxygenase of Wheat Germ with Temperature-Controlled Short Wave Infrared Radiation and Its Effect on Storage Stability and Quality of Wheat Germ Oil.

Wheat germ (WG) is quite susceptible to deterioration due to the presence of lipase (LA) and lipoxygenase (LOX). Therefore it is indispensable to adopt a stabilization step to decrease the activity of LA and LOX while retaining a maximum level of nutrients. But over-drying can make foodstuffs more susceptible to autoxidation. So a stabilization protocol for inactivating LA and LOX of WG with a temperature- controlled short wave infrared (SIR) radiation system was adopted to retard its rancidity and retain a maximum level of fat-soluble nutrients. Meanwhile, the critical storage water activity (Aw) of WG for inhibiting both hydrolytic and oxidative rancidity was appraised. Results indicate that WG irradiated at 90°C for 20 min acquired the optimal stabilization effect, and its residual LA and LOX activity were 18.02% and 19.21%, respectively. At this condition, the free fatty acids (FFA) content and peroxide value (PV) increment of WG oil at 40°C remained below 5% and 2.24 meq O2/kg for 60 days, respectively. The residual Aw of this WG sample was 0.13, and it is near the Aw corresponding to its monolayer. No significant decrease of fatty acids was observed during SIR processing, while about 96.42% of its original tocopherols still retained in WG treated at 90°C for 20 min.

Scanning Kelvin Probe Blister test measurements of adhesive delamination – Bridging the gap between experiment and theory

The delamination of an epoxy-adhesive film from a zinc coated steel substrate was studied by means of the electrochemical Height Regulated Scanning Kelvin Probe Blister Test (HR-SKP-BT11HR-SKP-BT: Height Regulated Scanning Kelvin Probe Blister Test.) under controlled atmospheric conditions, applied pressure and interfacial electrode potential. The experimental studies focused on the analysis of the critical environmental water activity that leads to a corrosive delamination process under applied mechanical load and the analysis of the corrosion and delamination mechanisms at the front of delamination. The influence of applied pressure and relative humidity on the increase in the maximum blister height and the delamination rate was measured under constant polarization of the defect. 90° peel-tests were performed in order to correlate the water activity with the resulting peel force. The corrosion products that formed across the delamination front were analyzed by Raman microscopy. Through these HR-SKP-BT studies, a critical value was found for relative humidity for the delamination process. A transition zone was detected in which electrochemical degradation precedes mechanical delamination. In addition to the experimental studies, the critical energy release rates of the blister were calculated in finite element (FE22FE: Finite Element.) simulations so as to enable a better understanding of the delamination of adhesives on metal surfaces. The combined experimental and theoretical studies show that the delamination process is controlled by the interfacial electrochemical reactions at the delamination front and that a transition area of few hundred micrometers exists in which the adhesion strength is lowered by the cathodic oxygen reduction process to a value which can be overcome by the mechanical stress in this area.

Effect of different DE values of malto-dextrin on properties for Schisandrae Chinensis Fructus spray-dried powder

The purpose of this study was to compare the effect of different DE values of malto-dextrin on Schisandrae Chinensis Fructus spray-dried powder. The glass transition temperature (Tg) of the spray-dried powder, powder properties and microscopic morphology were determined, and then the moisture absorption isotherms and the glass transition temperature were used to predict its storage stability. The study showed that after adding malto-dextrin, the powder rate was increased; moisture content was decreased; Tg was increased; mobility got better; produced spherical microstructure; and Tg was increased with the decrease of DE value. The water activity-equilibrium moisture content (aw-EMC) relationship in GAB models showed, the moisture absorption of powder was increased with the rising of DE value; and the equilibrium moisture content-glass transition temperature (EMC-Tg) relationship in Gordon-Taylor models showed that, Tg was decreased with the increase of moisture content. As a result, the storage critical condition of the spray-dried powder was improved, and along with the decrease of DE value, the critical water activity and the critical water content were increased. Therefore, the smaller the DE value, the greater the stability of the spray-dried powder.