Effects of filler-matrix morphology on mechanical properties of corn starch–zein thermo-moulded films

Improvement of mechanical, barrier properties, and water resistance of konjac glucomannan/curdlan film by zein addition and the coating for cherry tomato preservation

The mechanical, barrier properties, and water resistance of packaging materials are crucial for the preservation of fruits and vegetables. In this study, zein was incorporated as a hydrophobic substance into the konjac glucomannan (KGM)/curdlan (KC) system. The KC/zein (KCZ) showed good compatibility with the zein aggregates uniformly distributed in the network formed by an entanglement of KGM and curdlan micelles based on hydrogen bonds. The presence of zein inhibited the extension of the KC entangled structure and enhanced the solid-like behavior. The high content of zein (>6 %) increased zein aggregation and negatively affected the structure and properties of KCZ. The zein addition significantly improved the water vapor permeability, tensile strength, and elongation at break. The hydrophobicity of the KCZ films was significantly enhanced, accompanied by the water contact angle increasing from 81° to 112°, and the moisture content, swelling, and soluble solid loss ratio decreasing apparently. The K56C40Z4 coating exhibited an excellent preservation effect to inhibit the respiration of cherry tomatoes, significantly reducing the water loss and firmness decline and maintaining the appearance, total solid, total acid, and ascorbic acid content. This work provided a strategy to fabricate hydrophobic packaging for the preservation of fruits and vegetables.

Filler functionality in edible solid foams

We review the functionality of particulate ingredients in edible brittle foams, such as expanded starchy snacks. In food science and industry there is not a complete awareness of the full functionality of these filler ingredients, which can be fibers, proteins, starch granules and whole grains. But, we show that much can be learned about that from the field of synthetic polymeric foams with (nano)fillers. For edible brittle foams the enhancement of mechanical strength by filler ingredients is less relevant compared to the additional functionalities such as 1) the promotion of bubble nucleation and 2) cell opening-which are much more relevant for the snack texture. The survey of particulate ingredients added to snack formulations shows that they cannot be viewed as inert fillers, because of their strong hygroscopic properties. Hence, these fillers will compete with starch for water, and that will modify the glass transition and boiling point, which are important factors for snack expansion. Filler properties can be modified via extrusion, but it is better if that processing step is decoupled from the subsequent processing steps as mixing and expansion. Several filler ingredients are also added because of their nutritional value, but can have adverse effect on snack expansion. These adverse effects can be reduced if the increase of nutritional value is decoupled from other filler functionality via compartmentalization using micropellets.