Magnetic resonance imaging (MRI) and pulsed nuclear magnetic resonance techniques were used to study the water mobility in sweet rolls during storage. Different fractions of water with distinguishable molecular mobility were identified. MRI provided information on the spatial distribution of water content and of water mobility. During storage, moisture migrated from the crumb to the crust, which was associated with the firming of the crumb. A spatial redistribution of water mobility within the sample was also observed. As storage time increased, the mobility of the less mobile water fraction decreased; whereas the mobility of the more mobile water fraction increased upon staling, suggesting a redistribution of water mobility within the water molecules in the samples. A relationship between water mobility and staling was discussed.

Gels are viscoelastic systems built up with a liquid phase entrapped in a three-dimensional network, which can behave as carriers for bioactive food ingredients. Many attempts have been made to design gel structures in the water phase (hydrogels, emulsion gels, bigels) or oil phase (organogels, bigels) in order to improve their delivery performances. Hydrogels are originated from proteins or polysaccharides, which are suitable for the delivery of hydrophilic ingredients. Organogels are mainly built up with the self-assembling of gelator molecules in the oil phase, and they offer good carriers for lipophilic ingredients. Emulsion gels and bigels, containing both aqueous and oil domains, can provide accommodations for lipophilic and hydrophilic ingredients simultaneously. Gel structures (e.g. rheology, texture, water holding capacity, swelling ratio) can be modulated by choosing different gelators, modifying gelation techniques, and the involvement of other ingredients (e.g. oils, emulsifiers, minerals, acids), which then alter the diffusion and release of the bioactive ingredients incorporated. Various studies have proved that gel-based delivery systems are able to improve the stability and bioavailability of many bioactive food ingredients. This review provides a state-to-art overview of different gel-based delivery systems, highlighting the significance of structure–functionality relationship, to provide advanced knowledge for the design of novel functional foods.