Edible Films and Coatings Functionalization by Probiotic Incorporation: A Review.

Edible coatings and films represent an alternative packaging system characterized by being more environment- and customer-friendly than conventional systems of food protection. Research on edible coatings requires multidisciplinary efforts by food engineers, biopolymer specialists and biotechnologists. Entrapment of probiotic cells in edible films or coatings is a favorable approach that may overcome the limitations linked with the use of bioactive compounds in or on food products. The recognition of several health advantages associated with probiotics ingestion is worldwide accepted and well documented. Nevertheless, due to the low stability of probiotics in the food processing steps, in the food matrices and in the gastrointestinal tract, this kind of encapsulation is of high relevance. The development of new and functional edible packaging may lead to new functional foods. This review will focus on edible coatings and films containing probiotic cells (obtaining techniques, materials, characteristics, and applications) and the innovative entrapment techniques use to obtained such packaging.

Protein/polysaccharide interactions and their impact on haze formation in white wines.

Proteins in white wines may aggregate and form hazes at room temperature. This was previously shown to be related to pH-induced conformational changes and to occur for pH <3.5. The aim of the present work was to study the impact of wine polysaccharides on pH-induced haze formation by proteins but also the consequences of their interactions with these proteins on the colloidal stability of white wines. To this end, model systems and purified global pools of wine proteins and polysaccharides were used first. Kinetics of aggregation, proteins involved, and turbidities related to final hazes were monitored. To further identify the impact of each polysaccharide, fractions purified to homogeneity were used in a second phase. These included two neutral (mannoprotein and arabinogalactan) and two negatively charged (rhamnogalacturonan II dimer (RG-II) and arabinogalactan) polysaccharides. The impact of major wine polysaccharides on wine protein aggregation at room temperature was clearly less marked than those of the pH and the ionic strength. Polysaccharides modulated the aggregation kinetics and final haziness, indicating that they interfere with the aggregation process, but could not prevent it.

White wine proteins: how does the pH affect their conformation at room temperature?

Our studies focused on the determination of aggregation mechanisms of proteins occurring in wine at room temperature. Even if the wine pH range is narrow (2.8 to 3.7), some proteins are affected by this parameter. At low pH, the formation of aggregates and the development of a haze due to proteins sometimes occur. The objective of this work was to determine if the pH impacted the conformational stability of wine proteins. Different techniques were used: circular dichroism and fluorescence spectroscopy to investigate the modification of their secondary and tertiary structure and also SAXS to determine their global shape. Four pure proteins were used, two considered to be stable (invertase and thaumatin-like proteins) and two considered to be unstable (two chitinase isoforms). Two pH values were tested to emphasize their behavior (pH 2.5 and 4.0). The present work highlighted the fact that the conformational stability of some wine proteins (chitinases) was impacted by partial modifications, related to the exposure of some hydrophobic sites. These modifications were enough to destabilize the native state of the protein. These modifications were not observed on wine proteins determined to be stable (invertase and thaumatin-like proteins).

Stability of white wine proteins: combined effect of pH, ionic strength, and temperature on their aggregation.

Protein haze development in white wines is an unacceptable visual defect attributed to slow protein unfolding and aggregation. It is favored by wine exposure to excessive temperatures but can also develop in properly stored wines. In this study, the combined impact of pH (2.5-4.0), ionic strength (0.02-0.15 M), and temperature (25, 40, and 70 °C) on wine protein stability was investigated. The results showed three classes of proteins with low conformational stability involved in aggregation at room temperature: ß-glucanases, chitinases, and some thaumatin-like protein isoforms (22-24 kDa). Unexpectedly, at 25 °C, maximum instability was observed at the lower pH, far from the protein isoelectric point. Increasing temperatures led to a shift of the maximum haze at higher pH. These different behaviors could be explained by the opposite impact of pH on intramolecular (conformational stability) and intermolecular (colloidal stability) electrostatic interactions. The present results highlight that wine pH and ionic strength play a determinant part in aggregation mechanisms, aggregate characteristics, and final haze.

Protein aggregation in white wines: influence of the temperature on aggregation kinetics and mechanisms.

High temperatures (typically 80 °C) are widely used to assess wine stability with regard to protein haze or to study mechanisms involved in their formation. Dynamic light scattering experiments were performed to follow aggregation kinetics and aggregate characteristics in white wines at different temperatures (30-70 °C). Aggregation was followed during heating and cooling to 25 °C. Results were coupled with the study of the time-temperature dependence of heat-induced protein aggregation. At low temperature (40 °C), aggregation developed during heating. Colloidal equilibria were such that attractive interactions between species led to the rapid formation of micrometer-sized aggregates. At higher temperatures (60 and 70 °C), enhanced protein precipitation was expected and observed. However, high temperatures prevented aggregation, which mainly developed during cooling. Depending on the wine, cooling induced the formation of sub-micronic metastable aggregates stabilized by electrostatic repulsions, or the rapid formation of micrometer-sized aggregates, prone to sedimentation.