Determination Of Water Activity Research Articles

Efficient Determination of Critical Water Activity and Classification of Hydrate-Anhydrate Stability Relationship

For a pair of hydrated and anhydrous crystals, the hydrate is more stable than the anhydrate when the water activity is above the critical water activity (awc). Conventional methods to determine awc are based on either hydrate-anhydrate competitive slurries at different aw or solubilities measured at different temperatures. However, these methods are typically resource-intensive and time-consuming. Here, we present simple and complementary solution- and solid-based methods and illustrate them using carbamazepine and theophylline. In the solution-based method, awc can be predicted using intrinsic dissolution rate (IDR) ratio or solubility ratio of the hydrate-anhydrate pair measured at a known water activity. In the solid-based method, awc is predicted as a function of temperature from the dehydration temperature and enthalpy obtained by differential scanning calorimetry (DSC) near a water activity of unity. For carbamazepine and theophylline, the methods yielded awc values in good agreement with those from the conventional methods. By incorporating awc as an additional variable, the hydrate-anhydrate relationship is categorized into four classes based on their dehydration temperature (Td) and enthalpy (ΔHd) in analogy with the monotropy/enantiotropy classification for crystal polymorphs. In Class 1 (ΔHd< 0 and Td ≥ 373 K), no awc exists. In Class 2 (ΔHd>0andTd≥373K), awc always exists under conventional crystallization conditions. In Class 3 (ΔHd<0andTd<373K), awc exists when T>Td. In Class 4 (ΔHd>0andTd<373K), awc exists only when T<Td. The hydrate-anhydrate pairs of carbamazepine and theophylline belong to Class 4.

Comparative analysis of meat products made from various chicken meat raw material

Animal food, especially meat, has played an important role in the history of mankind. Different meats can be used in the production of meat products. In addition to lean meats, mechanically deboned meat (MDM) and mechanically separated meat (MSM) can also be used in meat products. However, the latter does not qualify as meat due to damage to the muscular structure due to the high pressure applied during the separation, therefore cannot be included in the meat content of products. The aim of our research work was to compare the characteristics of Bologna sausages made from chicken fillet, chicken MDM and poultry MSM. After evaluating our measurements (cooking loss, colour measurement, instrumental chemical composition measuring, stock measurement, determination of water activity, pH measurement, and sensory evaluation), we concluded that in the case of production with MSM, we produced a lower quality product using the same amount of meat raw material, which can be improved by using more additives (e.g. carminic acid, tetrasodium-pyrophosphate).

Ready-to-Use Vegetable Salads: Physicochemical and Microbiological Evaluation

Ready-to-use vegetable salads are minimally processed products, rich in antioxidants, but are associated with a high microbiological risk and possibly, in some cases, with a high content of nitrites. The purpose of this study was to investigate the physicochemical and microbiological properties of different ready-to-use vegetable salad assortments on the Romanian market. Seventeen types of salad vegetables were evaluated for the determination of water activity, antioxidant activity and nitrite concentration and tested for the presence of microorganisms. The water activity of the samples varied from 0.873 to 0.933, and the IC50 values were between 1.31 ± 0.02 and 5.43 ± 0.04 µg/mL. Nitrites were present in all samples investigated (ranging from 290.6 to 3041.17 mg/kg). Staphylococci and Enterobacteriaceae were detected in 35.3% and 70.5% of the samples. Furthermore, 17.6% of the salads were contaminated with Escherichia coli, and Listeria was detected in 29.4% of the samples. Salmonella was detected in only one sample, and Faecal streptococci were not present in any of the samples. The results indicated high nitrite values and also revealed pathogens’ presence. Producers should make more efforts to lower microbial contamination, while maximum limits for nitrites in vegetables should be set based on the impact on human health.

Water activity and surface tension of aqueous ammonium sulfate and D-glucose aerosol nanoparticles

Abstract. Water activity (aw) and interfacial energy or surface tension (σ) are key thermodynamic parameters to describe the hygroscopic growth of atmospheric aerosol particles and their ability to serve as cloud condensation nuclei (CCN), thus influencing the hydrological cycle and climate. Due to size effects and complex mixing states, however, these parameters are not well constrained for nanoparticles composed of organic and inorganic compounds in aqueous solution. In this study, we determined aw and σ by differential Köhler analysis (DKA) of hygroscopic growth measurement data for aerosol particles smaller than 100 nm composed of aqueous ammonium sulfate (AS), D-glucose (Gl), and their mixtures. High-precision measurements of hygroscopic growth were performed at relative humidities (denoted RH) ranging from 2.0 % to 99.6 % with a high-humidity tandem differential mobility analyzer (HHTDMA) in three complementary modes of operation: hydration, dehydration, and restructuring. The restructuring mode (hydration followed by dehydration) enabled the transformation of initially irregular particles into compact globules and the determination of mass equivalent diameters. The HHTDMA-derived growth factors complemented by DKA allows for determination of water activity and surface tension from dilute to highly supersaturated aqueous solutions that are not accessible with other methods. Thus, for mixed AS / Gl nanoparticles with mass ratios of 4:1 and 1:1, the upper limit of solute mass fraction (Xs) was 0.92 and 0.98, respectively. For pure AS and Gl, the DKA-derived aw is in good agreement with electrodynamic balance and bulk measurement data. For AS particles, our aw data also agree well with the Extended Aerosol Inorganics Model (E-AIM III) over the entire concentration range. In contrast, the UNIFAC model as a part of AIOMFAC (Zuend et al., 2011) was found to overestimate aw in aqueous Gl particles, which can be attributed to unaccounted intermolecular interactions. For mixed AS and Gl nanoparticles, we observed a non-monotonic concentration dependence of the surface tension that does not follow the predictions by modeling approaches constructed for mixed inorganic/organic systems. Thus, AS / Gl particles with a 1:1 mass ratio exhibited a strong decrease of σ with increasing solute mass fraction, a minimum value of 56.5 mN m−1 at Xs≈0.5, and a reverse trend of increasing σ at higher concentrations. We suggest that D-glucose molecules surrounded by ammonium sulfate ions tend to associate, forming non-polar aggregates, which lowers the surface tension at the air–droplet interface. We analyzed the uncertainty in the DKA-derived water activity and surface tension, related to the instrumental errors as well as to the morphology of the nanoparticles and their phase state. Our studies have shown that under optimal modes of operation of HHTDMA for moderate aqueous concentrations, the uncertainty in aw and σ does not exceed 0.2 %–0.4 % and 3 %–4 %, respectively, but it increases by an order of magnitude in the case of highly concentrated nanodroplet solutions.

Lipid microspheres of different waxes containing urea enriched with a sulfur source for slow release in the rumen

The objective of this study was to obtain and characterize slow-release urea microspheres (SRU) from carnauba wax (CW) and beeswax (BW) with and without enrichment of sulfur source (S). In the 1st experimental stage, we obtained and characterized slow-release urea (SRU) microspheres with a fixed ratio of 2:1(wax:urea), enriched or not of sulfur (magnesium sulfate heptahydrate) from the emulsification/lyophilization technique using urea as core into carnauba wax matrix added (CWUS) or not (CWU) of S source, and urea into beeswax matrix added (BWUS) or not (BWU) of S source. All formulated microencapsulated systems showed high yield values, raging 92.9–107% for BWU and CWU, respectively, with the highest SRU yields (P < 0.001) from CW compared to BW, and higher yields on materials without the presence of sulfur (S). The highest (P < 0.001) microencapsulation efficiency was observed in the SRU using BW, while the lowest yield occurred in the SRU-CWUS, where there was sulfur in the particle (P < 0.001). As for the determination of water activity, with values ranging 0.47–0.72, for BWU and CWUS, respectively. Thermal analyses (TG and DSC) indicated that the presence of the S source reduced the effectiveness of urea protection, and beeswax as an encapsulant showed higher thermal stability. In the 2nd experimental stage, five rumen-fistulated sheep with average body weight 48.9 ± 5.23 kg and age of 24 ± 2 months were assigned in a 5 × 5 Latin square design, with five consecutive 18-day periods divided into 13-day adaptation and five treatments [Urea free (U) as control and four SRU (BWU, BWUS, CWU, and CWUS)]. The SRU showed smooth surfaces with little cavities mainly for BW particles. The use of free urea provided lower concentrations of total proteins and creatinine and higher (P < 0.05) concentrations of BUN and AST compared to animals receiving SRU regardless of the type of encapsulant or the presence of S. However, the serum concentrations of albumin, AST, cholesterol, creatinine, total protein, and triglycerides showed no significant effect comparing only SRU. The sheep show higher concentrations of serum urea 8 h after feeding in comparison to the collection before (0 h) of feeding. Although all microparticles showed potential for SRU in the rumen, the system without added S and with beeswax showed higher encapsulation efficiency and is the most suitable for the diet of adult sheep.

Isopiestic Determination and Simulation of Water Activity in the LiCl−KCl−H2O Ternary System at 323.15 K

Isopiestic Determination and Simulation of Water Activity in the LiCl−KCl−H2O Ternary System at 323.15 K

Sensorial and physicochemical characterisation of snack bar with gum arabic (Acacia seyal) addition

Non-communicable diseases such as diabetes, atherosclerosis, myocardial infarction, and hypertension have rapidly increased. The scenario is due to unhealthy eating habits and unhealthy foods with high fat and oil, and high sugar on the market. A snack bar is one of the most suitable products as ready-to-eat food. It would be an ideal healthy food due to consumer demand for fast-growing natural foods. The application of Gum Arabic to confectionaries (snack bars) in the food industry is still low. Gum Arabic produced by the stem and branches of Acacia seyal has an excellent functional value of dietary fibre and the potential as an effective source in the formulation of a high fibre GA snack bar. This study was conducted to evaluate the sensorial and physicochemical characteristics of GA snack bar formulation with different concentrations of Gum Arabic of 10%, 20%, and 30%. Sensory analysis was conducted by using an acceptance test which is a 5-point hedonic scale. The attribute consists of colour, appearance, hardness, crispness, taste, and overall acceptance. For physicochemical properties, the colour, texture (i.e., hardness and crispness), pH, total soluble solid, water activity, moisture, crude protein, crude fat, crude ash, crude fibre, carbohydrate, and calorie determination are included. However, the value of a*, b* and protein were significantly (p&lt;0.05) decreased with increasing the Gum Arabic concentrations. Besides, there was a significant difference in all attributes for sensory evaluation except for appearance. In conclusion, the addition of Gum Arabic up to 30% into the GA snack bar caused significantly (p&lt;0.05) increased the lightness (L*), texture, total soluble solid, water activity, moisture, crude fat, crude ash, crude fibre, carbohydrate as well as calories.

Serbian Traditional Goat Cheese: Physico-Chemical, Sensory, Hygienic and Safety Characteristics.

This research project aimed to investigate the physico-chemical, sensory, hygienic and safety characteristics of raw goat milk, whey, brine and traditional goat cheese during the ripening period of 28 days. Physico-chemical parameters included the determination of dry matter, fat, ash, protein, pH, water activity and NaCl content. The presence of Enterobacteriaceae and fungi was estimated on milk and cheese samples, and a sensory panel evaluated the products’ features and acceptability during ripening. The results show that the cheese under study belongs to the acid full-fat cheese group. A consumer panel attributed high scores to the goat cheese, until the 21st day of ripening. After this period, the overall features altered significantly, including augmented bitterness, odor intensification and the development of molds on the surface. The presence of fungi, associated with Enterobacteriaceae, suggests that the hygiene of the production processes needs to be improved. Regarding microbial safety, the detection of putative pathogens and antibiotic resistances recommend an active surveillance of traditional foods to avoid foodborne infections and/or the dissemination of resistant microorganisms along the food chain.

A thermodynamic framework for determination of gas hydrate stability conditions and water activity in ionic liquid aqueous solution

The formation of gas hydrates in pipelines and plugging of the gas flow path are a major cause of operating expenses, safety issues, pressure drop, and fatal accidents. Therefore, the inhibition of gas hydrate formation is of paramount importance. The utilization of a new class of inhibitors such as ionic liquids (ILs) is currently of great interest. In this regard, adjusting water activity in the inhibitor blend (water + IL) is a vital factor. Several models have been developed to calculate the activity of water in the presence of IL(s). The major disadvantage of these models is their correlative basis. This study aimed to propose a rigorous predictive model for the calculation of water activity in the presence of IL(s), which would then be applied in the prediction of the gas hydrate stability conditions. The model is made up of a molecular term (the short-range interactions from Free-Volume-Flory-Huggins (FVFH) activity model) as well as a contribution from ionic interactions as a result of IL(s) dissociation in water (the long-range electrostatic interactions from the extended Debye–Hückel (EDH) model). The overall absolute temperature deviation and the average absolute relative deviation percent in the calculated gas (methane and carbon dioxide) hydrate dissociation temperatures for the whole databank (500 data points including 37 ILs) were found to be 0.61 K and 0.22%, respectively. This proves the superiority of the model over the previous correlative-basis ones. Finally, it is concluded that the higher temperature, the higher the IL(s) concentration, and the lower IL(s) molecular weight(s) result in larger model deviations.

Physicochemical characterization of agro-industrial residues for second-generation ethanol production

Ethanol production from renewable sources, such as lignocellulosic materials, is already underway in several countries. The interest in the technology stems from concerns about global warming and the environmental impacts of solid waste disposal. Moreover, the conversion of agro-industrial wastes into ethanol is a value-adding strategy. This study aimed to evaluate the physicochemical characteristics of three lignocellulosic materials— rice straw bran, sugarcane bagasse, and corn peel bran—and determine, on the basis of these analyses, their suitability as feedstocks for second-generation ethanol production. Physicochemical characterization included the determination of particle size, moisture, ash, total solids, water activity, crude fat, protein, total extractives, soluble and insoluble lignin, holocellulose, cellulose, hemicellulose, and total carbohydrates. Rice straw bran is composed of 38.33% cellulose and 19.73% hemicellulose, sugarcane bagasse is composed of 27.09% cellulose and 5.61% hemicellulose, and corn peel bran is composed of 55.75% cellulose and 12.93% hemicellulose. The characterization showed the high concentration of cellulose in the residue of the corn peel bran. The results indicate that the three biomasses are suitable raw materials for biofuel production.

Microwave Nondestructive Sensing of Moisture Content and Water Activity of Almonds

HighlightsMoisture and water activity were determined nondestructively and in real time from measurement of dielectric properties.Moisture and water activity calibration equations were established in terms of the dielectric properties.Situations in which bulk density was known or unknown were considered.SEC ranged from 0.41% to 0.68% for moisture and from 0.02 to 0.04 for water activity.Abstract. A method for rapid and nondestructive determination of moisture content and water activity of granular and particulate materials was developed. The method relies on measurement of the dielectric constant and dielectric loss factor at a single microwave frequency. For the purpose of illustration, the method was applied to predicting the moisture content and water activity of almond kernels. A free-space transmission technique was used for accurate measurement of the dielectric properties. Samples of Bute Padre almond kernels with moisture content ranging from 4.8% to 16.5%, wet basis (w.b.), and water activity ranging from 0.50 to 0.93 were loaded into a Styrofoam sample holder and placed between two horn-lens antennas connected to a vector network analyzer. The dielectric properties were calculated from measurement of the attenuation and phase shift at 8 GHz and 25°C. The dielectric properties increased linearly with moisture content, while they showed an exponential increase with water activity. Situations in which the bulk density was known and unknown were considered. Linear and exponential growth regressions provided equations correlating the dielectric properties with moisture content and water activity with coefficients of determination (r2) higher than 0.96. Analytical expressions of moisture content and water activity in terms of the dielectric properties measured at 8 GHz and 25°C are provided. The standard error of calibration (SEC) was calculated for each calibration equation. Results show that moisture content can be predicted with SECs ranging from 0.41% to 0.68% (w.b.) and water activity with SECs ranging from 0.02 to 0.04 for almond kernel samples with water activity ranging from 0.5 to 0.9 and moisture contents ranging from 4.8% to 16.5% (w.b.). Keywords: Bulk density, Dielectric constant, Dielectric loss factor, Free-space measurements, Loss tangent, Microwave frequencies, Moisture content, Water activity.

Sorption isotherms of ingredients and diets for poultry

This study aimed to determine sorption isotherms of ingredient and poultry diet. The samples were encapsulated in capsules and dehydrated by oven-drying in a desiccator for more than 24 hours. The samples were transferred to desiccator containing water in the base and placed in the oven, with one sample of each material being removed at incremental intervals. The sample was weighed and for determination of water activity and for dry matter. The moisture and water activity data were evaluated by eight mathematical models. The GAB mathematical model fitted the experimental data to constitute the isotherm for each material. Type II sorption isotherms were found, except for BHT: demonstrated values that did not fit the isotherm determination. The hygroscopic behavior of the ingredients in ascending order were: L- threonine, limestone, BHT, DL- methionine, L-valine, L- tryptophan, phosphate, kaolin, vitamin supplement, salt, mycotoxin deactivator, pelleted rooster diet, mash rooster diet, mash layer diet, pelleted layer diet, corn, bacitracin zinc, vitamin mineral supplement, phytase, rice bran, wheat bran, mineral supplement, soybean meal, coccidiostat, L- Lysine HCl and choline chloride. Ingredients and diets have different hygroscopic behavior: can lead to deterioration and low accuracy in nutritional values of diet, since formulation is based on as-is fed basis.

An Innovative Olive Pâté with Nutraceutical Properties.

Food plays a central role in health, especially through consumption of plant-derived foods. Functional foods, supplements, and nutraceuticals are increasingly entering the market to respond to consumer demand for healthy products. They are foods, supplements, and ingredients which offer health benefits beyond the standard nutritional value. Some benefits are associated with phenolic compounds and phytochemicals with antioxidant properties. An olive pâté (OP) was added with antioxidants derived from olive mill wastewater (OMWW) to obtain a functional product rich in phenolic compounds. The olive pâté is produced from the ground olive pericarp, which shows an excellent natural antioxidant content. The OMWW is a waste product from oil processing, which is also rich in phenolic compounds. The result was a product rich in trans-resveratrol, OH tyrosol, and tyrosol in concentrations such as satisfying the European community’s claims regarding the possible antioxidant action on plasma lipids with excellent shelf-life stability. The total phenolic content was assayed by a colorimetric method, the antioxidant activity by the ABTS [(2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)] test, the phenolic profile by Q Exactive Orbitrap LC-MS/MS. The shelf-life stability was confirmed by yeast, molds, and total microbial count, pH, and water activity determinations, and the best pasteurization parameters were determined. The palatability was judged as excellent.

Use of the Hygrometric Method for Determination of Water Activity of an Aqueous Hydrochloric Acid System at 298.15 K

This paper aims to extend the application field of the hygrometric method to systems containing volatile electrolytes. In this way, the aqueous hydrochloric acid–water solution and the aqueous hydr...

Factors Affecting the Retention Efficiency and Physicochemical Properties of Spray Dried Lipid Nanoparticles Loaded with Lippia sidoides Essential Oil.

Essential oils (EOs) are widely used in various industrial sectors but can present several instability problems when exposed to environmental factors. Encapsulation technologies are effective solutions to improve EOs properties and stability. Currently, the encapsulation in lipid nanoparticles has received significant attention, due to the several recognized advantages over conventional systems. The study aimed to investigate the influence of the lipid matrix composition and spray-drying process on the physicochemical properties of the lipid-based nanoparticles loaded with Lippia sidoides EO and their retention efficiency for the oil. The obtained spray-dried products were characterized by determination of flow properties (Carr Index: from 25.0% to 47.93%, and Hausner ratio: from 1.25 to 1.38), moisture (from 3.78% to 5.20%), water activity (<0.5), and powder morphology. Zeta potential, mean particle size and polydispersity index, of the redispersed dried product, fell between −25.9 mV and −30.9 mV, 525.3 nm and 1143 nm, and 0.425 and 0.652, respectively; showing slight differences with the results obtained prior to spray-drying (from −16.4 mV to −31.6 mV; 147 nm to 1531 nm; and 0.459 to 0.729). Thymol retention in the dried products was significantly lower than the values determined for the liquid formulations and was affected by the drying of nanoparticles.

Postharvest durability of tomatoes with PVA covering

ABSTRACT Plastic packaging from petroleum derives used in the food industry represents serious environmental problems. Alternative solutions to these problems consist of the development of biodegradable packaging, such as films and edible coatings including the polyvinyl alcohol (PVA). In this research we evaluated the effect of the PVA application by two different techniques aiming to increase shelf life of ripe tomatoes, cultivar Carmen. The methodology of this study consisted in covering tomatoes with a PVA solution and also with PVA impregnated tracing paper. The different fruit lots were kept in polystyrene trays for 19 days on a laboratory bench at a controlled temperature of 25±3ºC. The fruit analyzes were compared to the control fruits without any treatment, being evaluated firmness, pH, titratable total acidity, mass loss, total soluble solids content, water activity and color determination of fruit surface. Among the different treatments, the PVA coating applied directly to the fruits contributed to control the firmness and the mass loss, as well as this treatment influenced the total soluble solids content, the luminosity and the red color of fruits with statistical difference compared to the control and covered with tracing paper (with or without PVA). The PVA coating solution applied directly on the fruits contributed to maintain the postharvest quality of the ripe tomatoes.

Non-thermal inactivation of Listeria spp. in a typical dry-fermented sausage: "Bergamasco" salami.

Aim of the present study was the evaluation of the growth potential of Listeria spp. inoculated in the typical North Italian dry fermented sausage “Bergamasco” salami during its production. As it was necessary to carry out the challenge test in the production line of the industry, according to the guidelines of the European Reference Laboratory for Listeria monocytogenes, a non-pathogenic “surrogate” microorganism was used: for the inoculum, two strains of Listeria innocua (1 ATCC, 1 strain isolated from a similar substrate) were used. The inoculation of the samples occurred during grinding and mixing of the sausage mass, before the filling. To avoid cross-contamination, the control samples were produced before the contaminated ones. After the dripping, salamis were subjected to the normal production process (drying and maturation in five steps at specific temperatures and humidity rates). The inoculated products were subjected to the enumeration of Listeria spp. at T0 (day of inoculation) and at T4 (post-drying), and every 10 days during curing (T10, T20, T30, T40, T50, T60, T70, T80 and T90), as this salami is generally sold as whole piece with varying levels of curing (from T20 to T90). Since the product may be cut in half and vacuumpacked, at each of the times starting from T20, half salami was vacuum-packed and stored for 30 days at 12°C, at the end of the which Listeria spp. enumeration was performed again. At all times and for each type of samples of each of the three batches, the enumeration of the natural microflora (Total Viable Count, lactic acid bacteria, Pseudomonas spp., Enterobacteriaceae) and the determination of water activity and pH were performed on control samples. The product was characterized by a high concentration of microflora (8-8.5 Log UFC/g), consisting mainly of lactic acid bacteria, added to the mixture at the beginning of the production process. The pH showed a decrease over time, expected for this type of products, due to the development of lactic acid bacteria (final pH: 5.42-5.55). The water activity reached values able to inhibit the development of Listeria spp. (final aw: 0.826-0.863). Listeria counts in the tested batches of “Bergamasco” salami showed the absence of significant growth in the product with a reduction of loads if compared to T0, between -0.59 and -1.04 Log CFU/g. Even in the samples subjected to vacuum packaging and storage at 12°C, the absence of significant increase of lactic acid bacteria in the product was highlighted with further decrease of bacterial loads (-0.70/-0.79 Log CFU/g if compared to T20). Considering the worst case scenario (thus the batch with the highest growth potential), in the products stored in the curing room at 14-16°C, at humidity of 80% and in the samples stored at 12°C and vacuum packaged, the threshold indicated by the EURL Lm guidelines (+0.5 Log CFU/g) for the growth of Listeria spp. was not reached, allowing to classify “Bergamasco” salami in the category 1.3 of the EC Reg. 2073/2005 as “Ready-to-eat food unable to support the growth of Listeria monocytogenes”.

Determination of water activity, osmotic coefficient, activity coefficient, solubility, excess Gibbs energy and transfer Gibbs energy of KCl-D–sucrose-water mixture at 298.15 K

In this paper, we present the results of investigations of the KCl-D–sucrose-H2O ternary system using hygrometric method based on measurement of the relative humidity at the wide range of concentration to about saturation for both KCl and D–sucrose in different molalities of D–sucrose of (0.20, 0.50, 1.00, 2.00, 3.00, 4.00, 5.00 and 6.00) mol.kg−1 with the molality of KCl ranged from (0.20 to 4.50) mol.kg−1 at 298.15 K. The measured data are used to determine the water activities and osmotic coefficients. These studies are complemented using Pitzer-Simonson-Clegg model to understand different interactions involved between carbohydrates and KCl. Therefore, the water was considered as reference state in this study. Thus four mixture parameters are determined and used to predict the mean activity coefficients of KCl and D–sucrose. The solubility, excess Gibbs energy and transfer Gibbs energy are also calculated for this system.

Determination of ideal water activity and powder temperature after spray drying to reduce Lactococcus lactis cell viability loss

Spray drying presents a promising technology for preserving bacteria despite a low survival rate of heat-sensitive cultures when subjected to the drying process. The aim of this study was to determine the ideal powder parameters [water activity (Aw) and temperature (T°Cpowder)] needed to produce dehydrated Lactococcus lactis ssp. lactis with a high viability after drying. Cell concentrates injected into a spray dryer using varying cell concentrate flow rates (Fconcentrate = 0.3 to 1.0 kg/h), inlet air temperatures (T°Cinlet air = 115 to 160°C), and outlet air temperatures (T°Coutlet air = 70 to 115°C) resulted in powders with different values of Aw and T°Cpowder, and levels of cell viability loss. Lower cell viability reduction (∼0.43 log cycles) was obtained in conditions of Aw = 0.198 and T°Cpowder = 52°C, which can be met by using T°Cinlet air ∼126°C and T°Coutlet air = 88.9°C regardless of Fconcentrate values. After 60 d of storage at room temperature, cell population varied from 7.0 × 105 to 1.1 × 108 cfu/g. The initial powder Aw had no influence on cell death rate, but T°Cpowder influence was observed. The approach adopted in this study can be applied to other bacteria or spray dryer equipment to determine optimal drying conditions.

Determination of water activity, osmotic coefficients, activity coefficients, solubility and excess Gibbs free energies of NaCl-sucrose-H2O mixture at 298.15 K

The relative humidities on ternary NaCl-sucrose-H2O solution of 0.5, 1.0, 2.0, 4.0 and 5.5 mol·kg−1 of sucrose have been determined by the hygrometric method at 298.15 K in the molality range from 0.5 to 6.0 mol·kg−1 of NaCl. The obtained data allow the deduction of the water activities and osmotic coefficients. The experimental results are compared with the predictions of the extended composed additivity (ECA) rule, the Lin et al. equation, and Lietzke and Stoughton (LS II) models. The obtained results were interpreted by using Pitzer-Simonson-Clegg model. The four mixture parameters are determined and used to predict the activity coefficients of NaCl and sucrose in the mixed solution. The solubility, excess Gibbs energy and The Gibbs energies of transfer of sodium chloride are also calculated for this system.