Role of active nanoliposomes in the surface and bulk mechanical properties of hybrid hydrogels

Nanoliposomes are widely used as delivery vehicles for active compounds. Nanoliposomes from rapeseed phospholipids were incorporated into interpenetrating polymer network hydrogels of gelatin methacryloyl and alginate. The multiscale physicochemical properties of the hydrogels are studied both on the surface and through the thickness of the 3D network. The obtained composite hydrogels exhibited strong mechanical properties and a highly porous surface. The blend ratio, as well as the concentration of nanoliposomes, affects the properties of the hydrogels. Nanofunctionalized hydrogels induced keratinocyte ​growth. These advantageous characteristics may open up many applications of the developed hydrogels in drug delivery and tissue engineering.

Development of decision tools to assess migration from plastic materials in contact with food

Testing the specific migration limits of all substances intentionally added to polymer material according to European Union (EU) regulation is a time-consuming and expensive task. Although mathematical modeling offers an interesting alternative, it can significantly overestimate the migration in situations which are strongly conservative due to significant uncertainty in transport properties. In addition, its application is of little use for end-users or enforcement laboratories, which do not have access to the formulation. This paper revises the paradigm of migration modeling by combining modeling with deformulation experiments and iterative modeling in the framework of decision theory. The complete approach is illustrated for polyolefins in contact with 50% ethanol for eight typical migrants, including hindered phenolic antioxidants and low molecular weight surrogates. Results from a French ACTIA project on the identification of formulation fingerprints and on the prediction of partition coefficients with alcoholic and aqueous stimulants is described. When the true migration was close but still lower than the limit of concern, the proposed compact decision tree, including up to four sources of uncertainty, showed that the chance of demonstrating compliance was about 3 : 4 in the presence of one source of uncertainty, whereas it fell below 2 : 4 and 1 : 4 with two and three sources of uncertainty, respectively. The recommendations for further food packaging safety surveys and future developments are discussed.

Lactose Crystallization Delay in Model Infant Foods Made With Lactose, β-Lactoglobulin, and Starch

Handling and storage alter infant food powders due to lactose crystallization and interactions among components. Model infant foods were prepared by colyophilization of lactose, beta-lactoglobulin (beta-LG), and gelatinized starch. A mixture design was used to define the percentage of each mixture component to simulate a wide range of infant food powders. The kinetics of crystallization was studied by a gravimetric method (dynamic vapor sorption) at 70% relative humidity (RH). After freeze-drying, lactose was amorphous and crystallized at 70% RH. The delay before crystallization depends on the contents of beta-LG and starch in the formulations. A mathematical model was proposed to predict crystallization time (delay) at 70% RH. For the formulation containing 50% lactose, 25% beta-LG, and 25% starch, lactose was still amorphous after 42 h at 70% RH, whereas pure amorphous lactose crystallized after approximately 70 min. Calculated and experimental results of adsorbed moisture from the formulations were compared. Adsorbed water of formulation containing lactose could not be calculated from moisture sorption properties of each component at a given RH because beta-LG and gelatinized starch prevented lactose crystal growth.

Influence of Calcium Salt Supplementation on Calcium Equilibrium in Skim Milk During pH Cycle

Calcium is a mineral essential for humans, especially for bone constitution. Yet most of the worldwide population does not satisfy their Ca needs. Hence, Ca supplementation is of major importance, even in western countries where some specific populations at risk do not satisfy the recommended daily intake of Ca. More than 70% of dietary Ca comes from dairy products. Calcium supplementation of naturally Ca-rich sources such as skim milk is then of special interest. To our knowledge, few data are available concerning milk Ca (MC) supplementation of milk, particularly when followed by pH cycle. In this paper, MC supplementation is studied and compared with Ca chloride (CC) supplementation as a well-known source of Ca. The effect of Ca salt supplementation followed by pH cycle was studied in reconstituted skim milk. Calcium supplementation was carried out with CC and MC at 25 mmol of Ca/kg of skim milk. Ionized Ca concentration and turbidity variations were followed in situ by Ca ion selective electrode and turbidimetry using light reflection. From normalized data on ionized Ca concentration and turbidity vs. pH, it appeared that hysteresis areas were smaller for CC-supplemented milk, whereas unsupplemented milk and MC-supplemented milk behaved similarly. For these 3 dairy systems, pH cycles to pH 5.0 led to a larger hysteresis area than pH cycles to pH 5.5. The shrinkage of the hysteresis area could be interpreted as a reinforcement of casein micelles with Ca ions over the pH cycle.

Dairy Powder Rehydration: Influence of Protein State, Incorporation Mode, and Agglomeration

A simplified method to study rehydration was used on different dairy powders. The method involved dispersing powder in a stirred vessel equipped with a turbidity sensor. The changes of turbidity occurring during powder rehydration highlighted the rehydration stage, and the influence of the proteins' state on rehydration was clarified. Casein powders had a quick wetting time but very slow dispersion, making the total rehydration process time-consuming. On the other hand, whey powders were found to have poor wettability but demonstrated immediate dispersion after wetting. Mixing casein (80%) and whey (20%) before spray drying greatly improved rehydration time compared with casein powder; whereas mixing whey powder with casein powder at the same ratio after spray drying caused a dramatic deterioration in the rehydration properties. Moreover, agglomeration was found to significantly improve the rehydration time of whey protein powder and to slow down the rehydration time of casein powder. These opposite effects were related to the rate-controlling stage (i.e., wetting stage for whey protein and dispersion stage for casein).

Modeling of Lactose Crystallization and Color Changes in Model Infant Foods

Lactose crystallization and color changes in formulas containing beta-lactoglobulin and gelatinized starch were investigated. Model infant formulas were prepared by colyophilization of 3 components (lactose, beta-lactoglobulin, and gelatinized starch). A mixture design was used to choose the percentage of each mixture component. These formulas were stored for 3 mo at different relative humidities (RH), ranging from approximately 0 to 94.6%, to study the lactose crystallization and color changes. Crystallization kinetics was studied by gravimetric methods, and lactose state (crystalline vs. amorphous) was verified before and after storage by differential scanning calorimetry. Before storage, lyophilized lactose was amorphous, but during storage it crystallized, depending on the RH. The lactose crystallization RH depended on the quantity of beta-lactoglobulin and gelatinized starch, and by increasing these quantities, the crystallization RH increased. For some formulas, the crystallization RH was noted at 3 different RH during storage. The first was noted after 1 d of storage and the second and third were observed later on, showing that crystallization is a time-dependent phenomenon. Nonenzymatic browning was studied in model infant formulas by yellow color changes of samples at 11.3, 43.2, 54.5, and 75.4% RH. In this study, 7 mathematical models were proposed to predict the moisture sorption properties and color changes at different RH, and the models were validated by experimental results.

Surface composition of dairy powders observed by X-ray photoelectron spectroscopy and effects on their rehydration properties

The surface composition of three dairy powders was investigated by X-ray photoelectron spectroscopy. These spray-dried casein powders were more or less enriched in hygroscopic material (lactose and/or minerals). The principal limitation of these high protein content powders is their poor rehydration ability. Consequently, information about surface composition is required in order to get a better understanding of rehydration behaviour (i.e. wetting time and time of rehydration). The obtained results indicate that the surface of the three powders was dominated by proteins. Lactose and minerals are marginal compounds at the surface whereas the surface coverage of fat was over represented. A correlation between the lactose surface content and the wetting time of the powders was found, but no relationship with the surface fat. Moreover, as the surface is partly depleted in minerals and lactose, it is concluded that these compounds are principally located in the bulk of the particle. Therefore this observation could be related with a wetting time of the powders only slightly affected by the addition of hygroscopic material whereas the time of rehydration was strongly improved; powder wetting being more affected by the surface composition whereas powder dispersion being more influenced by the powder bulk composition.

Partition coefficients in food/packaging systems: a review

Food contamination can result from various interactions between food and packaging materials. Migration of volatiles, additives, monomers and oligomers from packaging materials into food or adsorption of volatile compounds from the food by the polymer are important considerations from safety, hygienic and economic points of view. The term 'migration' includes two phenomena (partition and diffusion) that can be important in determining the concentration of contaminants in a food system at any time. An estimation of the partition coefficient, K, in food/packaging systems has been the major objective of numerous different studies. Various parameters can influence K such as temperature, pH, the chemical structure of the migrant, molecular size and structure, fat content, and degrees of crystallinity. Some theoretical approaches such as the quantitative structure-property relationship method could be of interest in the near future.

Properties of Sodium Caseinate Film-Forming Dispersions and Films

The flow properties of sodium caseinate (NaCAS) film-forming dispersions were studied as a function of protein and glycerol concentration. Apparent viscosity vs. concentration profiles showed a disruption at about 10% (wt/wt) NaCAS. This was interpreted in terms of protein-water and protein-protein interactions. The presence of glycerol in the NaCAS film-forming suspensions reduced the viscosity of aqueous NaCAS as a consequence of decreasing protein-protein and protein-solvent interactions through the hydrogen bonding formation between the glycerol, the polypeptide chain of NaCAS, and water molecules. For higher concentration of glycerol, viscosity of NaCAS dispersions increased as a result of increasing total solid content. The glass transition temperature for solid films of 10% (wt/wt) NaCAS decreased with the glycerol content. The glycerol-protein interactions reduced the protein-protein interaction and, thus, increased the intermolecular spacing, leading to higher protein chain mobility and water vapor permeability.

Lactose/β-Lactoglobulin Interaction During Storage of Model Whey Powders

The objective of this study was to evaluate the presence or absence of interaction between lactose and beta-lactoglobulin during storage of model whey powders at different water activities (a(w)). Model whey powders were prepared by colyophilization of lactose with increasing quantities of beta-lactoglobulin. These colyophilized beta-lactoglobulin:lactose powders, assigned as BL powders, were stored from 0.11 to 0.95 a(w). The water sorption behavior of BL powders was studied gravimetrically, and the state of lactose was investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Before storage, BL powders were amorphous. After storage, a loss of water was observed on moisture sorption isotherms of BL powders. It was related to the formation of lactose crystals, detected by DSC and SEM analysis, and to the structural collapse of the powders. Water loss due to lactose crystallization was shifted to higher a(w) with increasing beta-lactoglobulin content in BL powders. Moreover, kinetics of moisture sorption demonstrated that beta-lactoglobulin was also responsible for a slower crystallization process in BL powders. Then, the water sorption behavior of BL powders was very different from the behavior of the 2 compounds mixed after separate lyophilization. All these results pointed out interaction between lactose and beta-lactoglobulin, which appeared during lyophilization and still occurred during storage. This lactose/beta-lactoglobulin interaction stabilized model whey powders against lactose crystallization.

Food materials adhesion: a review

This article reviews the various theories of adhesion mechanism and, more specifically, studies concerning foodstuffs adhesion to industrial equipment and packaging surfaces. Adhesion is governed by mechanical interlocking, wetting, electrostatic and chemical forces, and diffusion. Direct conclusions about the validity of one of these theories were seldom made in the empirical studies reviewed. The different food adhesion determination methods were detailed: direct observations, evaluations (weighting, UV absorbance, and adhesive loss), adhesion strength measurements, and indirect measurements via the wetting theory (tilted plane method, contact angle, and surface tension). The importance of proteins, product rheological properties, solid surface rugosity, and wetting phenomena in many adhesion cases is highlighted. Conclusions were made that fundamental mechanisms of food-contact surfaces interactions still need to be investigated to improve understanding in the science of food materials.