Effect of temperature on the deliquescence properties of food ingredients and blends

Interactions in plasticizer mixtures used for sugar replacement

In our quest for novel ingredients to be used in sugar replacement strategies, we have investigated the thermodynamics of polycarboxylic acids, such as citric acid. We have demonstrated the applicability of the Flory-Huggins (FH) theory to describe the thermodynamics of polycarboxylic acids solutions. Moreover, for citric acid we can describe the complete phase diagram with the theory. It shows that polycarboxylic acids have similar plasticizing and hygroscopic properties as sugars and polyols. Regarding mixtures of polycarboxylic acids and carbohydrates, the FH theory is able to describe a) the water activity of the mixtures, b) the solubility of ternary mixtures of acids and sugars, c) the lowering of the deliquescence point for binary mixtures of crystals, and d) the melting point depression in eutectic mixtures. Unexpectingly, our investigations show there is a strong non-zero FH interaction parameter between carboxylic acids and carbohydrates. In our prior sugar replacement strategy we have assumed zero interactions between plasticizers. Here, we will readdress this assumption. Carefull investigations of solid-liquid equilibrium of eutectic mixtures involving polycarboxylic acids and/or carbohydrates, shows nearly zero interaction in eutectic mixtures consisting only of two carbohydrates or two polycarboxylic acids. We now hold the hypothesis that there is strong non-zero interaction if the mixture contains plasticizers strongly differing in the amount of hydrogen bonding groups. This strong interaction explains why these mixtures, like polycarboxylic acids and carbohydrates, are excellent candidates as deep eutectic solvents. Furthermore, we conclude that polycarboxylic acids are useful additions to the toolbox of sugar replacers, albeit that there are some limitations to their amounts used.

Predicting Deliquescence Relative Humidities of Crystals and Crystal Mixtures

The presence of water in the form of relative humidity (RH) may lead to deliquescence of crystalline components above a certain RH, the deliquescence RH (DRH). Knowing the DRH values is essential, e.g., for the agrochemical industry, food industry, and pharmaceutical industry to identify stability windows for their crystalline products. This work applies the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) to purely predict the DRH of single components (organic acids, sugars, artificial sweeteners, and amides) and multicomponent crystal mixtures thereof only based on aqueous solubility data of the pure components. The predicted DRH values very well agree with the experimental ones. In addition, the temperature influence on the DRH value could be successfully predicted with PC-SAFT. The DRH prediction also differentiates between formation of hydrates and anhydrates. PC-SAFT-predicted phase diagrams of hydrate-forming components illustrate the influence of additional components on the hydrate formation as a function of RH. The DRH prediction via PC-SAFT allows for the determining of the stability of crystals and crystal mixtures without the need for time-consuming experiments.

The effect of relative humidity and formulation variables on chewable xylitol-sorbitol tablets

Changing relative humidity levels challenge the manufacturing of chewable xylitol-sorbitol based tablets. The aim of the study is to investigate how the formulation of chewable xylitol-sorbitol tablets affects the properties of the powder blends and the tablets in an environment of different relative humidity levels. In all, 30 batches containing different ratios of sorbitol, xylitol and magnesium stearate were prepared at three different relative humidity levels. Powder blends were made into tablets using an instrumented eccentric tableting machine. To demonstrate the effect of variables on powder blend and tablet properties, multiple linear regression analysis was performed. It was found that xylitol-sorbitol powder blends and tablets benefitted from the large amount of magnesium stearate, and the high lubricant level negatively affected the quality of the tablets only at high relative humidity. In the presence of high environmental humidity, the amount of sorbitol in the powder mixture must be limited in order to prevent sticking whereas at low relative humidity, higher content of sorbitol is needed to decrease the friability of tablets. Results indicate that alternating relative humidity levels truly challenge the production of xylitol-sorbitol based tablets and if the humidity is not controllable, there is a need for additional filler-binders.

Moisture sorption behaviors, water activity-temperature relationships, and physical stability traits of spices, herbs, and seasoning blends containing crystalline and amorphous ingredients

Spices, herbs, and seasoning blends containing both crystalline and amorphous ingredients are common throughout the food industry but may exhibit unwanted clumping or caking during storage. Crystalline and amorphous ingredients are known to respond differently to increases in relative humidity (RH) and temperature. The aim of this study was to better characterize what happens to moisture sorption behaviors, water-solid interactions, and physical stability when crystalline and amorphous ingredients are co-formulated in seasoning blends. Spices, herbs, and seasoning blends, 25 in total, were studied individually and in blends of increasing complexity (binary, ternary, and quaternary) with sucrose, salt, and maltodextrin. The effects of increasing temperature and RH on moisture content, moisture sorption profiles, water activity (a_w), glass transition temperature (T_g), including Gordon-Taylor modeling, physical appearance, and degree of clumping were measured. Crossover points, the temperature at which the a_w of the amorphous ingredient(s) and the deliquescence RH of the crystalline ingredient(s) in a blend intersect, were also calculated. Caking was observed when storage conditions (RH and/or temperature) exceeded the T_g of a blend or the deliquescence RH of a crystalline ingredient in the blend. When amorphous and crystalline ingredients were blended, synergistic moisture sorption and increased caking was observed. When multiple crystalline ingredients were present, mutual deliquescence further increased the sensitivity of the blend to moisture. When environmental conditions exceeded the crossover temperature, degree of caking increased, and physical appearance was altered due to the induced deliquescence of the crystalline ingredient(s) by the a_w of the amorphous ingredient(s). In general, as complexity of blends increased, sensitivity to moisture also increased, and physical stability of the blends decreased. The results of this study provide valuable information for increasing the physical stability of complex seasoning blends based on moisture sorption behaviors.

Relative humidity-temperature transition boundaries for anhydrous β-caffeine and caffeine hydrate crystalline forms

Caffeine is a hydrate-forming polymorphic crystalline compound that can exist in α, β, and hydrate forms. Phase transitions between hydrate and anhydrous forms of a crystalline ingredient, and related water migration, can create product quality challenges. The objective of this study was to determine the relative humidity (RH)-temperature phase boundary between anhydrous β-caffeine and caffeine hydrate. The β-caffeine→caffeine hydrate and caffeine hydrate→β-caffeine RH-temperature transition boundaries were determined from 20 to 45 °C using a combination of water activity (a_w ) controlled solution and vapor-mediated equilibration, moisture sorption, powder X-ray diffraction, and Fourier-transform infrared spectroscopy techniques. Two transition boundaries were measured: the β-caffeine→caffeine hydrate transition boundary (0.835 ± 0.027 a_w at 25 °C) was higher than the caffeine hydrate→β-caffeine transition boundary (0.625 ± 0.003 a_w at 25 °C). Moisture sorption rates for β-caffeine, even at high RHs (>84% RH), were slow. However, caffeine hydrate rapidly dehydrated at low RHs (<30% RH) into a metastable transitional anhydrous state with a similar X-ray diffraction pattern to metastable α-caffeine. Exposing this dehydrated hydrate to higher RHs (>65% RH) at lower temperatures (20 to 30 °C) resulted in full restoration to a 4/5 caffeine hydrate. This transitional anhydrous state was unstable and converted to a less hygroscopic state after annealing at 50 °C and 0% RH for 1 day. It was postulated that the caffeine hydrate→β-caffeine was the true β-caffeine↔caffeine hydrate phase boundary and that β-caffeine could be metastable above the caffeine hydrate→β-caffeine transition boundary. These caffeine RH-temperature transition boundaries could be used for selecting formulation and storage conditions to maintain the desired caffeine crystalline form. PRACTICAL APPLICATION: Caffeine can exist as either an anhydrous (without water) or hydrate (internalized water) crystalline state. The stability of each caffeine crystalline form is dictated by humidity (or water activity) and temperature, and these environmental stability boundaries for the caffeine crystalline forms are reported in this manuscript. Conversions between the two crystalline states can lead to deleterious effects; for example, the presence of caffeine hydrate crystals in a low water activity food (e.g., powder) could lead to the relocation of the water in caffeine to other ingredients in the food system, leading to unwanted water-solid interactions that could cause clumping and/or degradation.

RH-Temperature Stability Diagram of the Dihydrate, β-Anhydrate, and α-Anhydrate Forms of Crystalline Trehalose

Trehalose crystals exhibit polymorphic, deliquescent, and hydrate-forming traits and can exist in dihydrate, β-anhydrate, or α-anhydrate (isomorphic desolvate) forms. The objective of this study was to identify the relative humidity (RH) and temperature boundaries for phase changes of these different trehalose crystal forms. The deliquescence points (RH₀ s) of the anhydrate and dihydrate trehalose crystals were determined from 20 to 50 °C using a combination of water activity and dynamic vapor sorption measurement techniques. Increasing temperatures from 20 to 50 °C resulted in decreases in RH₀ from 95.5% to 90.9% RH for the dihydrate and 69.9% to 62.0% RH for the β-anhydrate. The effects of temperature on the anhydrate-hydrate RH boundaries were also determined, using a combination of equilibration in controlled water activity solutions, powder X-ray diffraction, and Fourier-transform infrared spectroscopy techniques. Increasing temperatures resulted in increases in the anhydrate-hydrate RH boundaries. The irreversible β-anhydrate to dihydrate boundary increased from 44.9% to 57.8% RH, and the reversible α-anhydrate to dihydrate boundary increased from 10% to 25% RH, as temperature increased from 20 to 50 °C. This is the first report of an RH-temperautre stability map for crystalline trehalose. PRACTICAL APPLICATION: The manuscript addresses the issue of the physical stability and phase transformations of crystalline trehalose stored in different temperature and relative humidity environments. Unwanted hydrate formation or dehydration of crystal hydrates can lead to other undesirable water-solid interactions and/or physical modifications that have the potential to influence product quality and delivery traits. Therefore, this study identified relative humidity and temperature stability boundaries of the different trehalose crystal forms, using a variety of established and novel techniques to create a relative humidity-temperature stability map of crystalline trehalose from 20 to 50 °C.

Optimizing the Quality of Food Powder Products: The Challenges of Moisture-Mediated Phase Transformations

Water is ubiquitous in the environment and is present to varying degrees even within dry powder products and most ingredients. Water migration between the environment and a solid, or between different components of a product, may lead to detrimental physical and chemical changes. In efforts to optimize the quality of dry products, as well as the efficiency of production practices, it is crucial to understand the cause-effect relationships of water interactions with different solids. Therefore, this review addresses the basis of moisture migration in dry products, and the modes of water vapor interactions with crystalline and amorphous solids (e.g., adsorption, capillary condensation, deliquescence, crystal hydrate formation, absorption into amorphous solids) and related moisture-induced phase and state changes, and provides examples of how these moisture-induced changes affect the quality of the dry products.

Predicting the solubility of mixtures of sugars and their replacers using the Flory-Huggins theory

In this paper we investigate whether the Flory-Huggins theory can describe the thermodynamics of solutions of simple carbohydrates, like sugars and polyols. In particular, we focus on the description of the solubility of the carbohydrates in water. This is investigated for both binary and ternary mixtures, having two types of these carbohydrates. This research question arises especially in the case of bakery products, where one seeks to replace sucrose with other simple carbohydrates - which are often polyols. Based on the model parameters obtained from fitting the theory to the experimental data of binary solutions, we show that the theory can predict (a) solubility data for ternary mixtures, over a broad range of concentrations and temperatures, and (b) the deliquescence point of binary mixtures of carbohydrate crystals as a function of temperature. The theory can even be applied to carbohydrates, which form hydrate crystals. Together with our earlier theories on the thermodynamics of complex food mixtures, we have now a complete thermodynamic framework to describe the phase and state transitions of food materials as confectionery and bakery products, where the question of sucrose replacement is urgent.

Phenolic and physicochemical stability of a functional beverage powder mixture during storage: effect of the microencapsulant inulin and food ingredients

BACKGROUND

The need for a convenience herbal iced tea product with reduced kilojoules merited investigation of the shelf-life of powder mixtures containing a green Cyclopia subternata Vogel (honeybush) extract with proven blood glucose-lowering activity and alternative sweetener mixture.

RESULTS

Prior to long-term storage testing, the wettability of powder mixtures containing food ingredients and the compatibility of their components were confirmed using the static sessile drop method and isothermal microcalorimetry, respectively. The powders packed in semi-sealed containers remained stable during storage at 25 °C/60% relative humidity (RH) for 6 months, except for small losses of specific phenolic compounds, namely mangiferin, isomangiferin, 3-β-d-glucopyranosyliriflophenone, vicenin-2 and 3',5'-di-β-d-glucopyranosylphloretin, especially when both citric acid and ascorbic acid were present. These acids drastically increased the degradation of phenolic compounds under accelerated storage conditions (40 °C/75% RH). Accelerated storage also caused changes in the appearance of powders and the colour of the reconstituted beverage solutions. Increased moisture content and a_w of the powders, as well as moisture released due to dehydration of citric acid monohydrate, contributed to these changes.

CONCLUSION

A low-kilojoule honeybush iced tea powder mixture will retain its functional phenolic compounds and physicochemical properties during shelf-life storage at 25 °C for 6 months. © 2017 Society of Chemical Industry.

RH-temperature phase diagrams of hydrate forming deliquescent crystalline ingredients

Several common deliquescent crystalline food ingredients (including glucose and citric acid) are capable of forming crystal hydrate structures. The propensity of such crystals to hydrate/dehydrate or deliquesce is dependent on the environmental temperature and relative humidity (RH). As an anhydrous crystal converts to a crystal hydrate, water molecules internalize into the crystal structure resulting in different physical properties. Deliquescence is a solid-to-solution phase transformation. RH-temperature phase diagrams of the food ingredients alpha-d-glucose and citric acid, along with sodium sulfate, were produced using established and newly developed methods. Each phase diagram included hydrate and anhydrate deliquescence boundaries, the anhydrate-hydrate phase boundary, and the peritectic temperature (above which the hydrate was no longer stable). This is the first report of RH-temperature phase diagrams of glucose and citric acid, information which is beneficial for selecting storage and processing conditions to promote or avoid hydrate formation or loss and/or deliquescence.

Measurement of the Raman spectra and hygroscopicity of four pharmaceutical aerosols as they travel from pressurised metered dose inhalers (pMDI) to a model lung

Particle inhalation is an effective and rapid delivery method for a variety of pharmaceuticals, particularly bronchodilation drugs used for treating asthma and COPD. Conditions of relative humidity and temperature inside the lungs are generally very different from the outside ambient air, with the lung typically being warmer and more humid. Changes in humidity, from inhaler to lung, can cause hygroscopic phase transitions and particle growth. Increasing particle size and mass can negatively affect particle deposition within the lung leading to inefficient treatment, while deliquescence prior to impaction is liable to accelerate drug uptake. To better understand the hygroscopic properties of four pharmaceutical aerosol particles; pharmaceutical particles from four commercially available pressurised metered dose inhalers (pMDIs) were stably captured in an optical trap, and their composition was examined online via Raman spectroscopy. Micron-sized particles of salbutamol sulfate, salmeterol xinafoate, fluticasone propionate and ciclesonide were levitated and examined over a range of relative humidity values inside a chamber designed to mimic conditions within the respiratory tract. The effect of temperature upon hygroscopicity was also investigated for salbutamol sulfate particles. Salbutamol sulfate was found to have significant hygroscopicity, salmeterol xinafoate showed some hygroscopic interactions, whilst fluticasone propionate and ciclesonide revealed no observable hygroscopicity. Thermodynamic and structural modelling is used to explain the observed experimental results.

Comparison of methods for determining the deliquescence points of single crystalline ingredients and blends

Many crystalline food ingredients undergo dissolution at a critical relative humidity known as the deliquescence point (RH0). Blends of crystalline ingredients exhibit deliquescence lowering, resulting in a deliquescence point (RH0mix) lower than the individual ingredient RH0s. To determine the effects of method type and data collection parameters, these deliquescence measurement methods were compared: saturated solution water activity, dynamic vapor sorption profiles (DVS), and dynamic dewpoint sorption profiles (DDI). Water activity measurements were broadly applicable for measuring deliquescence points when 1-4 g sample, 50-125 μL/g water:solid ratio, and 24-48 h equilibration were used. DVS and DDI techniques should be limited to samples containing 1-2 ingredients due to crystal contact point effects on RH0mix measurement. Recommended DVS parameters are: 1% RH step, 0.01% equilibrium criteria, and 3h maximum time. DDI profiles were consistent with 50-150 mL/min vapor flow rates. Ingredient mutarotation, solute interactions in solution, and contact point limitations affect the determination of deliquescence points.