Effects of Cellulose Diameter on the Formation and Rheological Properties of Edible Walnut Oleogels Structured by Cellulose Nanofiber

Oleogel of edible vegetable oils structured by cellulose nanofiber (CNF) via emulsion-templated method has attracted many interests due to its potential substitute of saturated or trans-fats in food industry. The gelation mechanism of liquid oil is dominated by different intermolecular non-covalent interactions, while the type and strength of these interactions are greatly influenced by the structure and properties of the gelator factors. Here, the effect of different CNF diameter ranges (5-10 nm, 10-20 nm and 20-60 nm) was investigated for CNF-based walnut oil oleogels, under the same fiber length and surface carboxyl content of CNFs. The results showed that CNFs with diameters of <20 nm exhibited better emulsification properties, and effectively restrained droplet size increasing and aggregation, compared to CNF with diameter of 20-60 nm. The resultant oleogels with smaller CNF diameter exhibited higher oil-binding capacity (OBC, similar to 85%) and better thermal stability of the resultant oleogels. More compact structure and stronger mechanical strength of oleogels were achieved with CNF diameters of <20 nm, which was verified by stronger textural hardness of the oleogels (0.46 N), as well as higher storage modulus (up to 1.1 x 10(5) Pa) and apparent viscosity in rheological measurement. The enhanced OBC and structure strength of oleogels with smaller CNF diameter could be attributed to the enhanced hydrogen bonding interactions between CNF molecules and CNFs with oil molecules during oleogelation, as the rigorously fibrillation exposed more surface hydroxyl groups as accessible hydrogen bonding sites during CNF preparation. This study improved the understanding about gelling properties of CNFs with different fiber diameters and provided an empirical basis for the construction of CNF-based oleogels with tunable hydrogen bonding interactions.