Micronized Sugar Beet Pulp Particles As Pickering Emulsifiers: Mechanism and Applications
Creators: name: Lin, Jiawei
Publisher: name: RMIT University
Year: 2025
Subjects: classificationCode: 300607
subject: Food technology

description: There is a need for the food industry to adopt principles of green and sustainable food processing. As the main by-product of the beet sugar industry, sugar beet pulp (SBP) is available on a large scale globally, but the industrial utilization of SBP is still limited to animal feed and organic fertilizer. The industrial chain is short and the added value is low. Therefore, the exploration of a new strategy to broaden the high-value utilization of SBP is of great research interest.
Based on the concept of fully utilising agricultural by-products, this project focuses on fiber-rich SBP as the research subject, using micronized sugar beet pulp (MSBP) particles directly to stabilise emulsions without any separation or chemical modification. The properties and mechanism of this type of ‘whole particles’ Pickering emulsifier, which is utilized to stabilize Pickering emulsion, were investigated. It was confirmed that heating pretreatment combined with ultrasound efficiently break downs sugar beet pulp, and the mechanism of efficient particle dissociation was clarified. The emulsification mechanism of complex particles was systematically described from the perspective of soluble/insoluble fractions. Pickering emulsion techniques were applied in mayonnaise-like emulsions and fruit preservation. This work provided a feasible way to develop a Pickering emulsifier with cost-efficiency and high utilization rate, understand the contribution of various components in complex particles to emulsification, create high dietary fiber food ingredients and health foods, and improve the added value of the beet sugar-related industries. The main findings are as follows:
(1) The ‘top-down’ particle micronization technique was established using heating and ultrasonication, resulting in MSBP with good suspension stability and elucidating the dissociation mechanism. High-temperature (120 °C) softened the compact particle structure of SBP, thus forming a porous inner particle structure with a larger specific surface, which facilitated the micronizing process. During ultrasonication, the SBP particles were broken into smaller sizes with a fibrous morphology (diameter of 50-300 nm and dozens of micrometers), which was accompanied by progressive dissolution. The soluble substance was verified to be pectic polysaccharides, and the porous particle structure adsorbed most of the ultrasonic energy to prevent the degradation of the soluble polysaccharides. Micronization greatly improved the emulsifying capacity of the SBP particles. Both the tangled network of fibers and the surface-active soluble substance contributed to emulsification.
(2) The emulsification characteristics of MSBP were studied and the contribution of soluble substances and insoluble fibrous particles (IFPs) to emulsification was preliminarily investigated. Compared with high-speed shearing homogenization with low energy input, ultrasonic homogenization and microfludization homogenization with high energy input help to adsorb MSBP at the oil-water interface, thus forming a smaller particle size and a more stable emulsion. The fabricated emulsion shows a flocculated state, which can be disturbed by sodium dodecyl sulfate (SDS). The flocculation index was up to 500% with the increase of MSBP concentration (0.05–1.00 wt%) and the decrease of oil weight fraction (0.05–0.40). After storage, the flocculated oil droplet clusters and tangled fiber networks improved the gel-like properties and physical stability of the emulsions. The proportion of soluble substances and IFPs in MSBP was ~40% and ~60%, respectively. Both showed interfacial activity and played a synergistic effect in emulsification. Due to the steric hindrance between micron-scale IFPs, some empty emulsion surfaces are covered by soluble substances, forming a compact hybrid interface layer. This provides the emulsion with robust steric repulsion force, preventing oil droplets from coalescing. The presence of soluble components contributed to the formation of a smaller particle size emulsion and strengthened its gel properties.
(3) The interaction mechanism between soluble substances and IFPs and their contribution to emulsification were studied, thereby establishing a complex emulsification mechanism model for MSBP. The soluble substances mainly consisted of sugar beet pectic polysaccharides (SBPS). The quartz crystal microbalance test showed that SBPS and IFPs can interact through multi-layer adsorption, and the adsorption between them is irreversible and driven by hydrophobic interaction forces. In addition to the interaction between the neutral sugar side chain of SBPS and the hydrophobic cellulose crystal surface of IFPs, the non-sugar components of SBPS and IFPs (ferulic acid, protein, and lignin) also contributed to the irreversible adsorption. During the emulsification process, SBPS was first adsorbed onto IFPs to form SBPS-coated IFPs (IFPs(SBPS)), and then SBPS and IFPs(SBPS) are adsorbed together on the oil-water interface to form a hybrid interface layer. Emulsion droplets stabilized by soluble-insoluble binary system were covered by a hybrid interfacial layer with SBPS-coated IFPs and SBPS, and the interfacial adsorption proportion was significantly larger than the corresponding solo emulsifier. The tangled fiber network wrapped the oil droplets, acts as a physical barrier to restrict the movement of the oil droplets, and maintained the stability of the emulsion together with the compact interfacial layer.
(4) The potential of MSBP to stabilize the gel-like Pickering high internal phase emulsions under different preparation parameters was explored, and it was used as a replacement for egg yolk in the preparation of mayonnaise-like emulsions (oil content 75 wt%). Using a one-pot homogenization strategy, stable gel-like emulsions with controllable properties were fabricated by increasing the oil-volume fraction (≥ 0.4) and MSBP concentration (≥ 0.9 wt%). These emulsions showed good tolerance under a wide pH range (2–10), high ionic strength (1000 mM Na+), storage, and thermal treatment. MSBP can partially or completely replace egg yolks to create mayonnaise-like emulsions with appearance and rheological properties similar to commercial mayonnaise (CM). The presence of MSBP can delay the oxidation of oil and inhibit the hydrolysis of oil in mayonnaise-like emulsions. It has similar tribological properties to CM, but its lubricity still needs improvement.
Overall, this study adopted a thermomechanical strategy to transform SBP into a Pickering emulsifier. Although the micronization process did not reduce the size of MSBP to the nanoscale, MSBP in micron-scale still depicted excellent emulsification performance. SBP was substantially dissociated into soluble substance and fibrous particles, which showed an adsorption interaction and thus made contribution to the emulsification. Based on the results, the emulsification mechanism was established and MSBP was also used as a mayonnaise stabilizer. It provided a novel strategy to used ‘whole particles’ with complex composition as Pickering stabilizers.