Effect of Sodium Sulfite, Sodium Dodecyl Sulfate, and Urea on the Molecular Interactions and Properties of Whey Protein Isolate-Based Films

Whey protein coatings and cast films are promising for use as food packaging materials. Ongoing research is endeavoring to reduce their permeability. The intention of this study was to evaluate the effect of the reactive additives sodium sulfite, sodium dodecyl sulfate (SDS), and urea on the oxygen barrier, water vapor barrier, and protein solubility of whey protein cast films. The concentration of the reactive additives was 1 to 20 wt.-%. Dried whey protein cast films were used as substrate materials. The water vapor transmission rate, the oxygen permeability, and the protein solubility were measured. Effective diffusion coefficients and effective sorption coefficients were calculated from the results of the water vapor sorption experiments. The presence of sodium sulfite resulted in an increased number of hydrophobic interactions and hydrogen bonds and a slightly decreased number of disulfide bonds. The oxygen permeability decreased from 68 to 46 cm3 (STP/standard temperature and pressure) 100 μm (m2 d bar)−1 for 1 wt.-% SDS in the whey protein cast film. The water vapor transmission rate decreased from 165 to 44 g 100 μm (m2 d)−1 measured at 50 to 0% r. h. for 20 wt.-% SDS in the whey protein cast film. The reduction in the water vapor transmission rate correlated with the lower effective diffusion coefficient

Wasserdampfsorption in Polymerfolien mit dispergierten Sorbentien

Gegenstand dieser Arbeit war die Entwicklung von Folien zur Nutzung im Verpackungsbereich, die Wasserdampf absorbieren und desorbieren und dadurch die relative Luftfeuchte in ihrer Umgebung regulieren. Es wurden vier verschiedene Typen von feuchteabsorbierenden und "feuchteregulierenden" Einschichtfolien als disperse Systeme aus Sorbentien in Trägerpolymeren entwickelt und deren Sorptionseigenschaften charakterisiert. Die Sorbentien Silicagel, Calciumoxid, Calciumchlorid bzw. Natriumchlorid wurden in die Trägerpolymere Polyethen, Polypropen oder Polymilchsäure durch Extrusion dispergiert. Folien mit den Sorbentien Calciumchlorid bzw. Natriumchlorid wurden zusätzlich geschäumt und bzw. oder gereckt. Die Sorptionseigenschaften wurden durch einfache, analytische Gleichungen beschrieben

Humidity regulation

Salt Containing Films. Novel humidity regulating polymer composite films contain salts such as calcium chloride and sodium chloride as active substances. These reversibly absorb water vapor. Due to that property they can stabilize the relative humidity in their environment. In packaging related applications undesired effects of humidity can be avoided thereby

Retail Price Differences between Packaged and Unpackaged Fruits (Apples) and Vegetables (Tomatoes, Peppers)

Since, according to many scientific studies, price is a very important factor when buying fruits and vegetables, it is interesting to study whether price differences between them occur in retail markets. Because of the discussion regarding sustainability, we performed an observational, orienting study on the retail prices of frequently bought packaged and unpackaged fruits and vegetables (apples, tomatoes, and bell peppers) in the Munich area in February and March 2022. We also differentiated between organic and non-organic produce. The relationship between the type of packaging (packaged versus unpackaged) and the retail price (EUR/kg) was determined by means of correlation coefficients, and we examined whether unpackaged products were more expensive than the packaged variants. The results differed for the organic and non-organic variants of the products, as well as among the individual fruit and vegetable varieties. We found a tendency towards unpackaged products being more expensive than packaged fruits and vegetables, in three out of four cases for the non-organic and two out of three cases for the organic products. For all cases, single products and single cost values were observed where the opposite was found