Optimal Water Activity Research Articles

Rechargeable zinc-water battery for sustainable hydrogen generation

Metal-water primary batteries hold promise for distributed hydrogen production but suffer from limited renewability of metal electrodes in aqueous electrolytes. Here, we introduce a novel concept of a rechargeable zinc-water battery featuring a reversible zinc anode paired with a bifunctional water electrolysis electrode, realized in a specially designed aqueous electrolyte-a mild zinc triflate aqueous electrolyte with the addition of ethylenediaminetetraacetic acid disodium (EDTANa2). The system enables high-purity hydrogen production during discharge and high-purity oxygen production during charge in a membrane-free setup. In the zinc-water battery, EDTANa2 enhances the water-splitting electrode's performance by replacing hydrophobic OTF- anions, ensuring optimal water activity. Additionally, EDTANa2 enhances Zn electrode reversibility by chelating Zn2+, preventing solvated water decomposition during zinc deposition. This integrated battery continuously undergoes charge-discharge cycles for over 55 h at a current density of 6 mA cm-2. Moreover, it achieves a high hydrogen evolution rate of 12.5 mL cm-2 h-1, enabling cost-effective, high-purity hydrogen production without expensive membranes. These findings open new avenues for sustainable hydrogen generation and energy storage in nano energy systems.

Identifying the optimal temperature and water activity conditions of phytopathogenic fungi recovered from Al-Baha province

AbstractFungi are responsible for many plant infections. Indeed, fungi are responsible for most plant spoilage that occurs in the field or in storage, causing symptoms of dieback, leaf spot, rot, rust and wilt. A more serious issue is that fungi produce mycotoxins, which can contaminate crops. Samples of leaf, fruit and root tissues were collected from sick crops, pre- and post-harvest within Al-Baha region. Using molecular markers, twenty fungal isolates were identified that represent eight genera and thirteen species. The most common species were Penicillium spp. (45%), followed by Aspergillus spp. (25%). The remaining 30% were comprised of multiple species (Alternaria alternata, Fusarium oxysporum, Geotrichum candidum, Lasiodiplodia theobromae, Megasporoporia minor and Rhizopus arrhizu). The majority of these isolates are recognised as spoilers of crops and producers of mycotoxins. The study evaluated which temperatures optimised fungal growth. Half of the isolates thrived best at 25 °C; six isolates favoured 30 °C, whilst four isolates grew best at 20 °C. The study also evaluated the optimal water activity (aw) for fungal growth, at four points (0.995, 0.99, 0.90 and 0.85 aw). The isolates were categorised as being either xerophilic, mesophilic or hydrophilic. The majority of isolates (70%) were xerophilic (Aspergillus and Penicillium spp.), 10% were mesophilic (Alternaria alternata and Rhizopus oryzae spp.) and 20% were hydrophilic (Lasiodiplodia theobromae, Geotrichum candidum, Megasporoporia minor and Fusarium oxysporum spp). The information derived from this study will assist in building effective strategies to control these pathogens, minimising crops losses and mycotoxin contamination.

Water desorption isotherms and thermodynamic properties of Ora-pro-nóbis (Pereskia aculeata Miller)

Desorption isotherms of ora-pro-nóbis leaves were determined at storage (5 °C, 10 °C, 20 °C, 30 °C, and 40 °C) and drying (40 °C, 50 °C, 60 °C, 70 °C, and 80 °C) temperatures by the gravimetric static method using saturated saline solutions to obtain relative humidities ranging from 5.20% to 98.48%. The net isosteric heat of desorption and thermodynamic properties such as differential enthalpy, differential entropy, and Gibbs free energy were also estimated. The GAB model presented the best parameters of fitting and the lowest Akaike and Bayesian information criteria values. The desorption isotherm patterns presented a sigmoid shape and were categorized as BET Type II sigmoid shape. The monolayer moisture content was estimated in 0.06 kg of water/kg of dry matter using the GAB model, and it remained constant at all temperatures. The leaves presented an optimal water activity equal to 0.35 at storage temperatures. The net isosteric heat of desorption decreased with increasing Xeq, and differential entropy increased with rising equilibrium moisture content (Xeq > 0.07). The enthalpy-entropy compensation was evaluated, and the desorption process is revealed to be entropy-driven and non-spontaneous.

Preclinical Potential of Probiotic-Loaded Novel Gelatin-Oil Vaginal Suppositories: Efficacy, Stability, and Safety Studies.

The current study describes a suppository base composed of aqueous gelatin solution emulsifying oil globules with probiotic cells dispersed within. The favorable mechanical properties of gelatin to provide a solid gelled structure, and the tendency of its proteins to unravel into long strings that interlace when cooled, lead to a three-dimensional structure that can trap a lot of liquid, which was exploited herein to result in a promising suppository form. The latter maintained incorporated probiotic spores of Bacillus coagulans Unique IS-2 in a viable but non-germinating form, preventing spoilage during storage and imparting protection against the growth of any other contaminating organism (self-preserved formulation). The gelatin-oil-probiotic suppository showed uniformity in weight and probiotic content (23 ± 2.481 × 108 cfu) with favorable swelling (double) followed by erosion and complete dissolution within 6 h of administration, leading to the release of probiotic (within 45 min) from the matrix into simulated vaginal fluid. Microscopic images indicated presence of probiotics and oil globules enmeshed in the gelatin network. High viability (24.3 ± 0.46 × 108), germination upon application and a self-preserving nature were attributed to the optimum water activity (0.593 aw) of the developed composition. The retention of suppositories, germination of probiotics and their in vivo efficacy and safety in vulvovaginal candidiasis murine model are also reported.

Effect of 60Co γ-rays on dried figs adsorption isotherms and thermodynamic properties.

Irradiation is one of the promising food preservation techniques, but few are known about its impact on foods' water vapor change. In this research, the impact of gamma irradiation on moisture adsorption isotherms of dried figs, one of the most emblematic foods of the Mediterranean diet, at increasing doses (0, 1, 1.5, and 2 kGy) was investigated. The isotherms data of equilibrium points displayed a sigmoid-shaped curve of the type II pattern for both controlled and irradiated dried figs, with a notable effect of irradiation on equilibrium moisture content, which revealed a decreasing pattern as irradiation dose and temperature increase. This effect was also seen in data fitting, where GAB model showed the best prediction statistics for control samples, while Peleg model displayed the most suitable samples irradiated at 1 and 1.5 kGy, then the Enderby model for those treated with 2 kGy. Results of Net isosteric heat of adsorption suggested that high irradiation dose increases the spontaneity of moisture adsorption. Hence, gamma irradiation exhibited a significant effect on the water-specific surface area of which the magnitude was proportional to the increasingly applied doses. This effect was also visibly significant on the optimum water activity [aw (op)] for proper dried fig storage. Indeed, aw was about 0.4243 for control samples, which is much higher compared to irradiated ones (aw = 0.2). Information from this research suggests that gamma irradiation at a dose up to 2 kGy extended the dried figs' shelf life. Since many aspects related to the impact of gamma irradiation on the moisture adsorption isotherms and thermodynamic properties of dried figs as well as in other foods have yet to be further investigated, this study provides interesting results that may be a useful reference for future research direction.

Investigación de la cinética de secado y las condiciones de secado sobre parámetros bioquímicos, sensoriales y microestructurales de arilos de granada “Sefri” (Punica granatum L. una variedad marroquí)

The study evaluated the application of four drying temperatures inside a newly developed hybrid indirect solar dryer in forced convection (at 40, 50, 60, and 70°C) compared to a direct solar dryer (Greenhouse) for the processing of the Moroccan Sefri pomegranate arils. The thermodynamical analysis allows characterizing the physical properties of the arils using some parameters such as optimal water activity, net isosteric heat of sorption, and effective moisture diffusivity. The biochemical analysis studied included total proteins, sugars, vitamin C, and total anthocyanins, hygrometric properties, microstructure modification, and sensory evaluation. Generally, drying led to a reduction in all parameters. However, lower drying temperature processes (indirect convective solar drying at 40°C and 50°C) give the best results for pomegranate arils. Greenhouse dried samples had almost the lower quality in all parameters. The color is more preserved at indirect convective solar drying at 40°C. However, indirect convective solar drying at 50°C was most appreciated by consumers with higher scores on the sensory evaluation test. As the first study of the thermodynamic and biochemical investigation of dried pomegranate arils in Morocco, this work intended to be the first step in developing controlled new high-quality products for the Moroccan market.

Effect of Drying Techniques on the Moroccan Pelargonium graveolens L’Hér. Leaves Essential Oil: Yield, Composition, Total Polyphenol Content, Antioxidant Activity, and Hygroscopic Parameters

The hygroscopic behavior and the effect of different drying methods (shade, oven and forced convective drying at 40°C, 50°C, and 60°C, natural convective, and greenhouse drying) on Pelargonium graveolens leave essential oils' quantity and quality parameters were studied. The optimal water activity for storage was estimated at awap = 0.363±0.005 and the net isosteric heat of sorption was 61.20±1.01 kJ.mol−1. The GAB model was the best fitting model for the experimental data. The essential oil yields were between 0.3±0.08% (w/w) and 1.27±0.21% (w/w) calculated on a dry weight basis. The highest yield was obtained by natural convective drying while greenhouse caused the most important loss of essential oils. β-Citronellol was the main compound, the ratios were from 25.8% to 12.1%. Natural convective drying had the highest content for total polyphenol content (6.71±0.38 mg GAE/g DM). The same for the antioxidant activity, the highest antioxidant activity was found for shade (384.78±15.59 µg/ml), followed by natural convective drying (424.19±17.86 µg/ml). While the lowest antioxidant activity was revealed by forced convective drying at 60°C (724.54±15.82 µg/ml). Greenhouse gives the lowest values. The color evaluation revealed that forced convective drying at 40°C preserves the appearance of Pelargonium leaves. The biochemical parameters were significantly affected by the drying technique, temperature, and air velocity. Convective drying was more suitable for drying the Moroccan rose geranium leaves. It will contribute to the development of a working methodology for food industries to solve problems related to the deterioration of the quality of the dried Moroccan rose geranium leaves.

Effect of Argan oil, thyme, and rosemary on the drying process of Sardina Pilchardus fillets

This work aims to study the drying kinetics of sardine fillets marinated with Argan oil, thyme, and rosemary at 70°C via the hybrid solar dryer. The static gravimetric method has been used to determine the sorption isotherms at 50, 60, and 70°C. Histamine content, TVBN, fatty acids, carbohydrates, and pH levels were analyzed as well. Finally, a statistical analysis of the results was accomplished using PCA. The sardine drying kinetics was accelerated with increasing air temperature in a synchronous manner. The optimal water activity for the conservation of sardines is aw = 0.32. The results obtained have led to an increase in the shelf life of sardine fillets marinated and dried on the basis of argan oil and thyme, unlike the product with argan oil, rosemary, and without marinade that will be destroyed in a few weeks. The findings results be explained by the antioxidant activity of thyme. Novelty impact statement The drying kinetics of sardine fillets was determined experimentally, as well as the characteristic drying curve. Determination of the optimum water activity for the conservation of sardines is aw = 0.32. The combination of marine products with argan oil and thyme provides the longest preservation period while also adding a new quality and taste dimension to sardine conservation.

Characteristic properties of spray-drying Bifidobacterium adolescentis microcapsules with biosurfactant

The surfactants used for emulsion is one of the best techniques for microencapsulation of lactic acid bacteria (LAB) since it is economical. The biosurfactants have many advantages such as lower toxicity, higher biodegradability. In this study, microcapsules were prepared via spray drying using Bifidobacterium adolescentis species cultured in soy milk extract with biosurfactant prepared using Alcaligenes piechaudii CC-ESB2 to improve their powder properties. The soy milk was used to increase the health benefits instead of the milk. The optimum bacterial strain viability, water activity, and moisture content of the microcapsules were achieved at a spray dryer inlet/outlet temperature of 120/60°C. The composition of the carrier affects the particle size of the microcapsules. Using 90% maltodextrin (MD), 5% isomalto-oligosaccharide syrup (IMOS) and 5% biosurfactant as a carrier increased the viability of the LAB. Scanning electron microscope observations showed that the LAB microcapsules were able to effectively retain their completeness. Furthermore, microcapsules added with a biosurfactant prepared using A.piechaudii CC-ESB2 displayed significantly better flow properties than those without the surfactant and biosurfactant, which indicates that the biosurfactant assists in enhancing the powder properties of the microcapsules. It also has sufficient biological activity as a LAB product because the probiotics exceed 106CFU/mL The spray-dried abandoned supernatant with biosurfactant exhibited superior bacteriostasis, which suggests that the supernatant of B.adolescentis during microencapsulation not only retains its bacteriostatic effect under high spray drying temperatures, but also provides additional antibacterial effects for the microcapsules.

PHYSICAL QUALITY OF GAMMA RAYS-IRRADIATED MEATBALL STORED AT ROOM TEMPERATURE

This study was aimed to investigate the meatballs physical qualities that are irradiated with high-doses of gamma rays. This study used the irradiation method with the dosage of 20, 25 and 35 kGy and storage at room temperature. For the control (0 kGy), storage was done in the freezer. The results showed that at 0 month, the samples water contents at 20; 25; 35 kGy were 67,03%; 67,50%; 66,67%, with significant difference (p<0.05) to control 68,73%. Water content (%) at 2 months were 65,03%; 66.00%; 67.50% and control 63,23% 2 months has significant difference (p<0.05) but still meet the SNI standard (<70%). Optimum water activity was obtained at irradiation dose of 35 kGy. The pH results doses of 20; 25; 35 kGy for 0 month were 6,35; 6,34; 6,39 and 2 months were 6,59; 6,47; 6,46, respectively. pH of control was 5,87 at 0 month and 6,49 at 2 months. The pH of samples stored for 0 month were relatively higher than the control pH. At 2-month storage, the pH of the samples was lower than the control, but still meets the standard. Meatball irradiation up to 35 kGy can be used as an alternative for preservation at room temperature.

Preparation of spray-dried soybean oil body microcapsules using maltodextrin: Effects of dextrose equivalence

Spray-drying can stabilize high-moisture-content oil bodies (OBs) against adverse environmental conditions and improve the nutritional value of foods containing OBs. This study investigates the effect of the dextrose equivalent (DE) of maltodextrin (MD) on the physicochemical properties and oxidative stability of soybean OB microcapsules during spray-drying. Adding MD to OB microcapsules reduced the surface-oil content and improved the drying yield and encapsulation efficiency. Microcapsules produced by MD having a DE of 10 (MD 10) returned the highest microencapsulation yield (88.84 g/100 g) and efficiency (93.41 g/100 g). OBs stabilized by MD 10 (OB-MD 10) also exhibited optimal water content, water activity, reconstitutability, hygroscopicity, density, and flowability. The addition of MD 10 reduced the size and narrowed the size distribution of microcapsules, thereby reducing agglomeration. Furthermore, MD 10 produced a more effective interfacial barrier, thereby improving the thermal and oxidative stability of the microencapsulated OBs, which can be explained by the molecular structure of the carrier. MD 10 was found to be the most effective wall material for stabilizing OBs. This work establishes spray-drying as a promising method for the industrial production and application of OBs as functional oil products that can carry biologically active ingredients.

Exploring the sorption and thermodynamic proprieties of white truffle (Terfezia boudieri)

AbstractIn this work the sorption behavior of Terfezia boudieri truffle was studied and evaluated using the static gravimetric method. This approach permits the measurement of the sorption isotherms at three given temperatures 30, 40, and 50°C. Where in the first step experimental sorption data was collected, and then was used in order to identify the thermodynamic properties of truffle. Several results were found by conducting this study. First, the optimal water activity (aw) for conserving T. boudieri truffles was determined and found to be in range of the values 0.24 and 0.31 as a function of temperature. Additionally, net isosteric heat and entropy of sorption, which are two parameters studied during this study, were found to be decreasing when the water content increased; where the existence of the compensation theory of enthalpy–entropy for Terfezia boudieri was confirmed. Second, net isosteric heat and entropy of sorption, which are two parameters studied during this study, were found to be decreasing when the water content increased; where the existence of the compensation theory of enthalpy–entropy for Terfezia boudieri was confirmed. Finally, the isokinetic temperatures were 338.69 and 324.35 K for desorption and adsorption, respectively. As well as the free Gibbs energy was found to be positive for sorption which indicates that the sorption process as a non‐spontaneous one. Moreover, the spreading pressure varied in a range of 0.03–0.25 J/m2, while the aw increased. This study is a contribution to the drying, packaging, and conservation of white truffle.Practical applicationsWhite truffle has been widely used in many food products related applications, and pharmaceutic industry. White truffle is only available in certain seasons; consequently its storage process for long periods is a necessity in order to ensure the supply chain over the year. Furthermore, this particular food product needs a very specific storage conditions which may affect its quality and shelf‐life. This work aimed to determine and evaluate the water sorption properties in an adequate range of temperature and relative humidity. The mathematical models and the thermodynamic analysis conducted throughout this study, in addition to the reported data are useful to find the optimal and adequate storage conditions to preserve the quality and prolong the white truffle shelf‐life.

Palm Oil Decanter Cake Wastes as Alternative Nutrient Sources and Biomass Support Particles for Production of Fungal Whole-Cell Lipase and Application as Low-Cost Biocatalyst for Biodiesel Production

This is the first report on the possible use of decanter cake waste (DCW) from palm oil industry as alternative nutrient sources and biomass support particles for whole-cell lipase production under solid-state fermentation (SSF) by newly isolated fungal Aspergillus sp. MS15 and their application as a low-cost and environment-friendly biocatalyst for biodiesel production. The results found that DCW supplemented with 0.1% K2HPO4, 0.05% MgSO4·7H2O, 1% peptone and 2% urea and pH adjusted to 6.0 was optimal for whole-cell lipase production. The optimal moisture content and fermentation temperature was 60% and 37.5 °C, respectively. Environmentally friendly biodiesel production, through either esterification or transesterification using whole-cell lipase immobilized on DCW as a biocatalyst, was optimized. The optimal reaction temperature for both reactions was 37 °C. The whole-cell lipase effectively esterified oleic acid into >95% biodiesel yield through esterification under optimal water activity at 0.71 and an optimal methanol to oleic acid molar ratio of 2:1, and also effectively transesterified palm oil under optimal water activity at 0.81 and an optimal methanol to oil molar ratio of 3:1. The fuel properties of produced biodiesel are close to the international biodiesel standards. These results have shown the circular utilization of palm oil mill waste for the low-cost production of an effective biocatalyst, and may contribute greatly to the sustainability of renewable bioenergy production.

The Role of Water Activity in Terms of Enzyme Activity and Enantioselectivity during Enzymatic Esterification in Non-conventional Media

During enzymatic esterification in non-conventional media, the activity and enantioselectivity of the enzyme is significantly influenced by the water content of the reaction medium, which continuously changes as water is produced during the esterification. To provide constant reaction parameters, water activity should be kept constant. The commonly used salt hydrate pairs may be difficult to apply and often hinder enzyme activity. During the enantioselective esterification of racemic 2-bromopropionic acid in various solvents (organic solvents, ionic liquids), it was proven that the conditions related to the optimal water content required for kinetic examinations can be provided without using any salt or salt hydrate pairs. This conclusion is based on the realization that the optimal water activity can be set by first determining the initial water content that is necessary to achieve the maximum reaction rate in the given solvent.

Water sorption isotherms and drying characteristics of rupturewort (Herniaria hirsuta) during a convective solar drying for a better conservation

Free water contained in porous structure of food plays a fundamental role in proliferation of microorganisms and bacteria that can damage the product materials. This work presents a thermo-kinetic study carried out in a natural and forced convection solar dryer; the objective was to establish the optimal conditions for drying and storing Herniaria hirsuta by testing the impact of different aerothermal conditions (air temperature, air velocity) on water loss of fresh Herniaria hirsuta. The kinetics of drying is studied for three temperatures (50, 60 and 70 °C) in two-air velocities (0.09 and 0.18 m/s). The optimal water activity which is related to conservation is 0.28. The LESPAM model was found to be the most appropriate for describing the sorption curves. The air drying temperature is a principal factor influencing the drying kinetics; the drying rate decreases in low air drying temperature, the air velocity had a small impact on the drying kinetics of Herniaria hirsuta. The Midilli-Kuck model was found to be the best fitted drying curves in thin layers for Herniaria hirsuta. The effective diffusivity of moisture water values changed from 2.5312 10−9 to 18.0511 10−9 m2·s−1, and increased simultaneously with the increase of temperature. The average activation energy of the diffusion process is obtained to be 2938.46 kJ/kg; it expresses the temperature effect on the diffusion coefficient. Dried Herniaria hirsuta under the maximum drying parameters showed highest retention of antioxidant activity, while the total phenolics and flavonoids were decreased by 10 and 46%, respectively.

Moisture sorption measurements and Thermophysical characterization of the Taraxacum officinale leaves and root

This paper aims at investigating the hygroscopic behavior and the thermodynamic characterization of the dandelion (Taraxacum officinale) leaves and root during moisture sorption phenomena. This study has been conducted by using the saturated salt solutions at different temperatures 30 °C, 40 °C and 50 °C. The obtained isotherms curves of all samples were of sigmoidal Type II. The optimal water activity was determined. Moreover, thirteen models are fitted and compared in order to choose the most suitable model that perfectly represents the relationship between moisture sorption content and water activity. The comparison of these models has been based on the coefficient of correlation as well as the standard error of estimate. Furthermore, several equations are used to determine the net isosteric heat of sorption, the sorption differential entropy, the spreading pressure, the specific surface area of sorption, and the enthalpy-entropy compensation theory. All these thermodynamic properties allow us to analyze the thermodynamic behavior of the leaves and the dandelion root during the sorption processes.

Physicochemical study of the conservation of Moroccan anchovies by convective solar drying

Local fish markets are often saturated during periods of full production. Solar drying offers a suitable alternative to reduce losses of surpluses, and to preserve products for a longer period. In this respect, this work was carried out to study the effect of the air indirect solar convective drying process on the dehydration kinetics of anchovy. Experimental drying kinetics was measured at four air temperatures (50, 60, 70 and 80 °C) and for a constant air flow of 300 m3/h. The moisture desorption isotherms of the anchovy were determined at three temperatures (30, 40 and 50 °C), using the static gravimetric method to determine the optimum water activity for conservation of the nets anchovy. Experimental results showed that the drying kinetics of the anchovy was accelerated synchronously with the increase of the air temperature. The value of optimal water activity for conservation of anchovy is aw = 0.30 and the desorption isotherms suggest a non spontaneous process. Nine drying models were adapted to the drying data; the Logarithmic model allowed better adaptation than the other models. The effective diffusion coefficient value Deff determined by Fick’s second law varied from 3.84 10−9 to 5.60 10−9 m2/s and the activation energy value was Ea = 12.90 kJ/mol.

Selection of dietary fibres for sucrose replacement in functional Chhana‐murki (Indian Cottage cheese‐based dessert) and their effect on sensory, physical and instrumental texture parameters

With a wide range of beneficial effects on human health, various dietary fibres such as microcrystalline cellulose (MCC), inulin, oat fibre and wheat fibre were screened based on their bulking ability in the functional Chhana‐murki (FCM) with respect to sensory and physical properties. Sensory scores were maximum for MCC at 7.5% having optimum moisture content and water activity and minimum hardness, whereas oat and wheat fibres increased the hardness of the product while decreasing the moisture content and water activity thus lowering the sensory scores. Further, replacement of MCC with inulin in 1:1 ratio improved the product characteristics.

Valorization of co-products of sardine waste by physical treatment under natural and forced convection solar drying

This work aims to valorise a co-product resulting from the sardine processing chain (Sardina pilchardus) in order to obtain the compounds of interest by the implementation of soft techniques seeking a wider investment, low energy cost and low environmental pollution impacts caused by conventional systems, which are valid also for other co-products of fresh sardine waste. For this purpose, a thermo-kinetic study was carried out in a natural and forced convection solar drying in order to establish the optimal conditions for drying and storing sardine heads, which are an important source of high quality proteins for human and animal nutrition. Static gravimetric method was used to determine the optimal water activity for conservation of sardine heads. Kinetics of drying is studied for three temperatures 60, 70 and 90 °C, in a two air–flow drying 150 m3 h−1and 300 m3 h−1. The air drying temperature is the most important factor influencing the drying kinetics of sardine heads. Total energy consumption showed a downward trend with increasing temperature and an upward trend with increasing air flow. The exergy loss, exergy transfer rate from evaporation and exergy efficiency of the drying chamber were investigated in this study.

Optimising water activity for storage of high lipid and high protein infant formula milk powder using multivariate analysis

High lipid and high protein infant formula milk powders were stored at water activity of 0.11, 0.33 and 0.53 for up to fourteen weeks at 40 °C to investigate the effect of storage water activity on physicochemical properties and formation of volatiles to thereby recommend optimal storage water activity conditions. Water activity of the powders was determined during storage together with surface colour, glass transition temperature combined with dynamic headspace sampling followed by gas chromatography/mass spectrometry. The principal component analysis (PCA) showed that the optimal water activity for storage of high lipid infant formula milk powder, for which lipid oxidation was found to be the critical quality parameter, is aw = 0.33 with lowest lipid oxidation, while for high protein infant formula milk powder, for which protein degradation was found to be the critical quality parameter, aw = 0.11 is optimal to limit formation of Maillard reaction products.