Designing Food Composites for improved human health

The word “foods” includes a very broad category of safe edible biomaterials which must be consumed to sustain life. From a structural perspective, foods are multiphase colloidal systems, heterogeneous at the mesoscale structural level where ingredients characterised by different physico-chemical properties co-exists in a meta-stable state. Among all food ingredients, oils and fats represent a key component in our diets which have been shown to play a key role on human health. In particular the consumption of trans- and saturated fats is known to have negative implications on our health. This awareness, together with an increasing consumer demand for natural and sustainable ingredients, is pushing the food industry to find new alternative ingredients for food manufacture. In this scenario, this presentation will cover two topics: oleogels and oil bodies as new food biomaterials for the design of food composites to improve human health. 

Oleogels are lipophilic colloidal systems where the gelling component (“oleogelator”) forms a 3-dimensional thermo-reversible network physically trapping the oil phase. Rice bran wax (RBW) is a promising oleogelator known to form crystalline networks with great ability to entrap oil. The presentation will share work done to elucidate the effect of processing (cooling rate, setting temperature) and formulation (wax concentration and addition of lipophilic surfactants) on microstructural, textural and rheological properties of RBW oleogels in edible oils. The minimum RBW gelling concentration was 5% (wt%) for a cooling rate of 0.5°C/min which decreased to 0.5% when cooling at 2°C/min. Firmness, yield stress and oil binding capacity of the oleogels increased with increasing RBW concentration and increasing cooling rate. Microstructure visualisation using temperature controlled polarised light microscopy revealed that the network was always formed by crystals appearing as long needle-like particles, with cooling rate only affecting size of crystals: when cooling at 0.5, 5 and 50°C/min the average crystal length was 130, 100 and 50 μm, respectively.

These findings suggest that a system made up of many small crystals with a high degree of inter-connectivity is developed when applying fast cooling which results in a higher shear elastic modulus (G’) and ability to bind oil. G’ remained constant up to temperatures close to the onset of melting, suggesting material properties remain constant over a large temperature range. PGPR and Span 60 addition to RBW oleogels significantly increased and reduced the onset of crystallisation, respectively, and all systems containing surfactants displayed a lower G’ than bulk RBW oleogels. At the microstructural level only Span 60 modified the crystalline particle shape, which became spherulitic. Examples of application of olegeols in food will also be shown. This work is the first to demonstrate that lipophilic surfactants can be used to tailor the microstructural properties of RBW oleogels, which offer a new route for the design of functional systems to replace fats.

Oil bodies (OBs) are sub-micron size droplets functioning as oil storage organelles in oil rich seeds. These organelles are characterised by a liquid oil core stabilised by an half unit membrane of phospholipids and proteins. OBs organelles can be recovered using a wet-milling (i.e. milling in presence of water) process to preserve their natural structure as opposite to conventional oil recovery approaches using organic solvents which destroy the OB integrity. Therefore, OB emulsions are an attractive natural ingredient for the food and pharma industry. The process used to prepare these emulsions consists of three main steps: (I) seeds soaking in an aqueous medium; (II) wet milling to release the OBs from the seed matrix; (III) repeated washing cycles to remove exogenous material from the OB preparation. Although common in literature, this approach requires long incubation times and extensive water usage, which may limit the large scale upgrade of OB emulsions. The aim of this work here described was to evaluate for the first time the functionality of cryo-milling to recover intact OBs. This approach requires to cool seeds to sub-zero temperatures prior to their dry milling into a particulate material from which OBs are recovered using an aqueous medium. Various processing parameters (cooling regime, milling time and extraction conditions) were systematically investigated for OB recovery from rapeseeds. Three cooling regimes (-20˚C, -80˚C, and liquid nitrogen cooling) were assessed and compared to room temperature milling (control). Intact OBs were recovered only from seeds cooled with liquid nitrogen, which was attributed to the ability to maintain a deep cooling (below -70˚C) on milling. Increasing the cryo-milling time from 20 to 60 seconds resulted in a more finely comminuted material with 40% and 95% (wt%) of seed particles below 425 µm for 20 and 60s, respectively, and a higher recovery yield but induced OBs mechanical damage. Recovery conditions were optimised to 20s of milling followed by 1h of stirring in a 0.1M NaHCO3 buffer for the seed particulate material. The produced OB emulsion displayed the same microstructure, isoelectric point, and particle size as the one obtained using a conventional wet-milling approach. This study demonstrate that cryo-milling could be used as novel approach to reduce processing time and the water usage to recover OBs.

The presentation will also provide an overview of the main research themes ongoing at the University of Nottingham and of funding opportunities to stimulate collaboration.