Cellulose nanofibrils as rheology modifiers and stabilizers in food systems
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Food additives are components used in many food products to improve qualities such as flavor, appearance or texture. In low-fat and non-fat food products, food additives called fat-replacers are added to the food products to compensate for the removal of fat. In food emulsions, such as mayonnaise or salad dressings, additives can be used to enhance the stability of the emulsions, preventing it from separating into its distinct oil and water-phases. Nanocelluloses, such as cellulose nanofibrils (CNFs), have been proposed as a new class of food additives, as they have some properties that may make them effective as stabilizers and viscosifiers. CNFs, thin fibrils consisting of cellulose molecules, originate from plant materials, where they provide strength to the plant cell walls. As the fibrils are produced by plants, these materials are highly renewable. Their ability to form gel networks with high viscosity at low concentration have made them strong candidates for use as viscosifiers. In addition, CNFs have been shown to stabilize emulsions, another attractive property for use in food applications. However, the differences between CNFs based on preparation methods and sources, as well as the interactions between CNFs and common food ingredients, must be thoroughly understood in order to choose the right quality of CNFs for any given food application. The goal of this thesis has been to obtain a better understanding of the variables affecting the performance of CNFs as a viscosifying agent and emulsion stabilizer in food applications. This has been achieved through 1) studies of the rheology and transmittance of suspensions of highly charged CNFs, upon variations in CNF concentration, ionic strength and amount of the food additive xanthan gum. And 2) by following differences and changes in droplet size distributions, visual stability, and emulsion morphology of various types of CNF stabilized emulsions. While the first studies focused on the viscosifying or emulsion stabilizing effects of the CNFs, these properties were later combined in a model mayonnaise system. In the end, CNFs were used as a fat replacer for low-fat and full-fat mayonnaise, in a pilot scale experiment, where the CNF containing mayonnaise samples were compared to reference samples based on visual appearance, emulsion morphology, droplet size distributions, viscosity and moduli.