The transport of water in four EVOH copolymers commonly used in high barrier food packages was characterized through permeation (continuous flow) and gravimetric experiments at different rela tive humidities and 23 ± 2°C. Water sorption isotherms were fitted with the D'Arcy and Watts' equa tion. From these data, the value of the solubility coefficient (S, as defined by Henry's law) was deter mined and was found constant within a 0.2-0.75 water activity (a w) range. Water uptake at the same a w increased as the EVOH ethylene content decreased. The permeability coefficient (P) for water through EVOH was determined as a function of water activity. The permeability was constant within the range of 0.3-0.75 a w and decreased with EVOH ethylene content. At high relative humidities (a w > 0.75) the value of permeability increased by up to two orders of magnitude. In this range, the higher the ethylene content the lesser the value of P.

In the present paper, a mathematical model able to predict the water barrier properties of cellophane film as a function of the water activity at the upstream and downstream side of the film is presented. To validate the model water sorption, and permeation tests were performed at 30°C and at several water vapor activities. Despite the approximations involved in deriving the model, its ability to predict the water permeability of the investigated film is quite satisfactory. The proposed model was then applied to hypothetical measuring conditions in which the water activity at one side of the film was set equal to zero (like in a permeation test) or equal to 0.6 (like in the real working conditions), while the water activity of the other side changes between 0 and 0.6. A substantial difference has been observed between the two examined cases, showing the need for a more accurate analysis of the transport phenomena in the case of water sensitive packaging films like cellophane.

Zein, corn prolamine, was dissolved in several organic solvents to make films and their properties were examined. Ethanol with 20% water and acetone with 30% water were found to dissolve zein well and transform it into a transparent flexible film after moderate drying. Both films showed similar breaking strength to that of commercial thin film of polyvinylidene chloride for food use and were digested with proteases. Only the film prepared from acetone solution showed a relatively low water permeability. This water permeation was found to depend strongly on the rate of diffusion. 1,2-Epoxy-3-chloropropane (ECP) was added into the acetone solution to cross-link the zein molecules for the purpose of improving the breaking strength and water-resistant properties of the film. Alpha-chymotrypsin was found to digest the film even after the modification with ECP. However, this cross-linking resulted in little improvement in the water-resistant properties of the film and also reduced its flexibility.

This paper presents a mathematical model able to predict the water barrier properties of nylon film as a function of the water activity at the upstream and downstream side of the film. To validate the model, water sorption and permeation tests were conducted at 25 °C. The fitting and predictive ability of the proposed model was successfully tested by fitting the model to the sorption data and by predicting the nylon water permeability coefficient, respectively. The implications of the adopted approach on practical aspects of packaging were pointed out by comparing the nylon water barrier properties as evaluated by means of a permeation test and that in the real working conditions.

In this paper, multilayer pectin-beeswax/colophony-pectin (P-BC-P) films including different proportions of beeswax/colophony mixtures were prepared in order to reduce the water vapor permeability. FTIR, XRD, DSC, polarized light microscopy (PLM), and water vapor permeation assays were performed. Characterization techniques showed (i) polar interactions between beeswax and colophony at the amorphous phase, (ii) changes in beeswax crystalline phase from sponge-like to needle-like structure, and (iii) formation of a eutectic mixture at BC3 70/30 ratio which guides the epitaxial crystallization of beeswax. Pure pectin films showed low resistance to the water vapor permeation (361 × 10⁻¹³ g m m⁻² s⁻¹ Pa⁻¹), while multilayer films showed major control over the transport process. P-BC3-P showed one of the lowest water vapor permeability (WVP) values (56 × 10⁻¹³ g m m⁻² s⁻¹ Pa⁻¹) and the closest WVP value to that of polyethylene films (LDPE 5.8 × 10⁻¹³ g m m⁻² s⁻¹ Pa⁻¹). This result was attributed to the ordered crystalline structure reached by the epitaxial crystallization of beeswax within the hydrophobic phase.

In food packaging systems, moisture content influences chemical and physical film properties, also determining processes such as food spoilage, and properties of food texture and crispiness level. The study of water permeation and sorption processes of new materials intended to be used as packaging is very important to determine the best application conditions and to predict the film behavior under different moisture conditions inside and/or outside the packaging. In order to determine the suitable temperature and water activity (aw) application conditions for whey protein isolate (WPI)/polyvinyl alcohol (PVOH) blends as food flexible packaging, water permeation and water sorption thermodynamic behavior of these materials were evaluated. WPI/PVOH films and blends had solubility preponderant over the diffusion on the water permeation process. Water sorption experimental data were well described by the GAB model, and curves showed a more expressive increase of water sorption at aw > 0.75, with lower equilibrium moistures (Ye) at room than at chilled temperatures. Differential enthalpy decreased and differential entropy increased by the Ye gain, and the occurrence of enthalpy-entropy compensation was confirmed with enthalpy driving the sorption process. The addition of PVOH to the WPI matrix made the water sorption process more spontaneous. Water sorption thermodynamic analysis indicates that the application of WPI/PVOH blends as packaging is best suitable for foods and external environments with aw below 0.75 and at room temperature.

One of the most common materials used for packaging is low density polyethylene film. To improve the water vapour transfer of the film, zeolite¡polymer composite films and perforated films are produced. The solid-low density polyethylene composite films were prepared by extrusion of polyethylene beads coated with hot zeolite particles of a definite size range in an industrial extruder (-420/+212, -212/+106, -106/+53 microparticles/g of polyethylene beads). A needle (0.2, 0.5 and 1.75 mm in diameter) attached to the tip of a soldering gun was used for the production of the perforated polyethylene films (1, 3, 6, 12, 18 and 24 holes per 38.5 cm2). The overall evaluation indicates that the water vapour transfer rates can be modified by the composite and the perforated films, which provides packaging material variety for foods of different moisture content. The solid- polyethylene composite films showed less permeability to water vapour than the polyethylene film. This may be attributed to two reasons: the available polyethylene area is reduced by the presence of solid particles and these solid particles have an important sorption property. The water vapour transfer rates increased by the perforated films.

The consequences of humidity exchanges between food and environment are always very important for the preservation of microbiological and sensorial quality of the product. For a realistic shelf-life evaluation of sensitive food-products is therefore essential to know exactly the water vapour transmission rate (WVTR) through the packaging material. The measurement of this important diffusional property is commonly performed without regard of the exchange direction and in conditions very far from those of reality: extremes temperature and humidity combinations as 38 deg C and 90% of RU. Thus, it was considered useful and interesting to verify if the permeability phenomenon could be affected by the direction of flow and by the contact of dry or moist product. To such purpose, measures of water vapour permeability were realized using PET and OPP pouches, filled with water or calcium chloride. The results achieved excluded the influence of the contact of dry or wet substances with the pouches walls and of the flow direction on the determination of the WVTR for the materials and the conditions examined | Le conseguenze di uno scambio di umidita' tra alimento ed ambiente risultano sempre molto importanti per la conservazione della qualita' biologica ed organolettica del prodotto. Per una reale valutazione della conservabilita' dei prodotti alimentari sensibili all'umidita' e' quindi essenziale conoscere la velocita' di trasmissione al vapore acqueo (WVTR) attraverso il materiale di confezionamento. I metodi convenzionali di misura di questa importante proprieta' diffusionale sono solitamente riferiti a condizioni lontane da quelle reali sia per le combinazioni temperatura-umidita' relativa in cui si effettuano le determinazioni (38 gradi C e 90% di UR), sia per quanto riguarda le modalita' in cui il fenomeno di permeazione avviene. Non si tiene infatti in considerazione ne' la direzione di flusso del vapore d'acqua, ne' che nel caso reale il prodotto (umido o secco) si puo' trovare a diretto contatto con il materiale. Si e' cosi' ritenuto importante poter verificare se il fenomeno di permeabilita' fosse influenzato da queste condizioni e dalla direzione del flusso. A tal fine si sono effettuate misure di permeabilita' impiegando buste realizzate con PET ed OPP, riempite con acqua o cloruro di calcio. I risultati ottenuti hanno escluso l'influenza del contatto e della direzione di flusso sulla determinazione della WVTR per i materiali e le condizioni considerate

Natural biopolymers have become key players in the preparation of biodegradable food packaging. However, biopolymers are typically highly hydrophilic, which imposes limitations in terms of barrier properties that are associated with water interactions. Here, we enhance the barrier properties of biobased packaging using multilayer designs, in which each layer displays a complementary barrier function. Oxygen, water vapor, and UV barriers were achieved using a stepwise assembly of cellulose nanofibers, biobased wax, and lignin particles supported by chitin nanofibers. We first engineered several designs containing CNFs and carnauba wax. Among them, we obtained low water vapor permeabilities in an assembly containing three layers, i.e., CNF/wax/CNF, in which wax was present as a continuous layer. We then incorporated a layer of lignin nanoparticles nucleated on chitin nanofibrils (LPChNF) to introduce a complete barrier against UV light, while maintaining film translucency. Our multilayer design which comprised CNF/wax/LPChNF enabled high oxygen (OTR of 3 ± 1 cm³/m²·day) and water vapor (WVTR of 6 ± 1 g/m²·day) barriers at 50% relative humidity. It was also effective against oil penetration. Oxygen permeability was controlled by the presence of tight networks of cellulose and chitin nanofibers, while water vapor diffusion through the assembly was regulated by the continuous wax layer. Lastly, we showcased our fully renewable packaging material for preservation of the texture of a commercial cracker (dry food). Our material showed functionality similar to that of the original packaging, which was composed of synthetic polymers.

Engineering the interface of oil-in-water emulsion droplets with biopolymers that modify its permeability could provide a novel technique to improve flavour retention in dry powders. The objective of this study was to determine if volatile compounds were more retained in dry emulsions stabilized by pea protein isolate (PPI)/pectin complex than that stabilized by PPI alone. The retention of ethyl esters during spray-drying increased with decreasing volatility of the encapsulated compound and ranged from 28% to 40%. The addition of pectin to feed emulsions was quite effective in markedly improving the retention of the three studied flavour compounds. In our previous work (Gharsallaoui et al., 2010), we showed that pectin was able to improve physical integrity of emulsion oil droplets during spray-drying. However, the pectin positive effect on both the droplet stability and the flavour retention at the time of spray-drying can also be explained by a protein molecular structure protective effect. Indeed, the obtained FTIR results showed that pectin was able to preserve the β-sheet secondary structure of pea protein when pea globulins/pectin complexes are heated. The study of the release characteristics of a flavour compound from dried powders showed that pectin addition did not affect the release profile mainly accomplished by the diffusion mechanism.