No abstract

Cellulose nanostructures have been widely studied as components of materials for a variety of applications including food packaging. They are usually incorporated as a reinforcement phase in nanocomposites (as cellulose nanocrystals or cellulose nanofibrils). In other cases, cellulose nanostructures have been used as matrices for films-bacterial cellulose (BC) deserving a special attention in this context, since it is produced as naturally nanostructured membranes, which may grow in a medium containing other biopolymers (producing bottom-up built bionanocomposites), be impregnated with other components, or be disintegrated into nanofibribils or even nanocrystals. This review summarizes findings and prospective applications of nanocellulose for bio-based materials to be used in food packaging (including active packaging).

The group of Gram-negative bacteria capable of oxidising ethanol to acetic acid is called acetic acid bacteria (AAB). They are widespread in nature and play an important role in the production of food and beverages, such as vinegar and kombucha. The ability to oxidise ethanol to acetic acid also allows the unwanted growth of AAB in other fermented beverages, such as wine, cider, beer and functional and soft beverages, causing an undesirable sour taste. These bacteria are also used in the production of other metabolic products, for example, gluconic acid, l-sorbose and bacterial cellulose, with potential applications in the food and biomedical industries. The classification of AAB into distinct genera has undergone several modifications over the last years, based on morphological, physiological and genetic characteristics. Therefore, this review focuses on the history of taxonomy, biochemical aspects and methods of isolation, identification and quantification of AAB, mainly related to those with important biotechnological applications.

Coir fibers received three treatments, namely washing with water, alkali treatment (mercerization) and bleaching. Treated fibers were incorporated in starch/ethylene vinyl alcohol copolymers (EVOH) blends. Mechanical and thermal properties of starch/EVOH/coir biocomposites were evaluated. Fiber morphology and the fiber/matrix interface were further characterized by scanning electron microscopy (SEM). All treatments produced surface modifications and improved the thermal stability of the fibers and consequently of the composites. The best results were obtained for mercerized fibers where the tensile strength was increased by about 53% as compared to the composites with untreated fibers, and about 33.3% as compared to the composites without fibers. The mercerization improved fiber-matrix adhesion, allowing an efficient stress transfer from the matrix to the fibers. The increased adhesion between fiber and matrix was also observed by SEM. Treatment with water also improved values of Young's modulus which were increased by about 75% as compared to the blends without the fibers. Thus, starch/EVOH blends reinforced with the treated fibers exhibited superior properties than neat starch/EVOH.

Nanocellulose-based nanocomposite hydrogels are promising materials in different fields of application such as medicine, food, and agriculture.