The comparison of divalent (Ca2+, Zn2+, or Mg2+) and trivalent (Cr3+, Al3+, or Fe3+) cationic species at the same ionic strength, four pectins (sugar beet, high and low methyl esterified and okra), three dispersed phases (medium chain triglycerides (MCT), orange oil and hexadecane), time (30 days ageing) and pH (2.0 and 6.0) has been investigated in terms of formation and stability of oil-in-water emulsions. The aim of this research is to understand the different pectins that are used to create stable emulsions and to examine the influence of solution composition (pH, ionic strength and cation) on emulsion stability. Emulsions were examined with respect to the formation of their formation and stabilisation capacity by means of droplet size distribution analysis and electrokinetic potential measurements over a period of thirty days. Also, the Lifshitz-Slyozoy-Wagner (LSW) theory was employed to determine the early-stage coarsening kinetics of emulsions. Besides, the release of orange oil flavour compounds from different oil-in-water (o/w) pectin emulsions with different ions was evaluated by headspace (HS) analysis and in all conditions, limonene was the only primary terpene detected. Interfacial cross-linking was limited at low pH due to the repression of charges with negligible influence on emulsion stability compared to control emulsions (dilution with deionised water adjusted to either pH 2.0 or pH 6.0). However, the influence of cations was evident at high pH where it was possible to kinetically arrest emulsion coarsening depending on pectin type and cationic species. Stability at low pH was attributed mostly to steric repulsions as the pectin emulsions had very low charge (< -13 mV). On the contrary, at high pH electrostatic repulsions presented a substantial contribution (< -60 mV) to the overall stability. In terms of stability towards cations, the order was (more stable) Ca2+ > Al3+ > Cr3+ > Mg2+ > Zn2+ > Fe3+ (less stable) in terms of their behaviour at pH 2.0, respectively. On the other hand, at pH 6.0 ions behave slightly different, (more stable) Ca2+ > Mg2+ >Al3+> Cr3+ > > Zn2+ > Fe3+ (less stable). More stable emulsions were formed with sugar beet pectin, which showed change in the presence of cations, followed by high- and then low-methyl esterified and okra samples. At pH 2.0 all pectins showed their best emulsification performance whereas shifting pH to 6.0 severely disrupts emulsification capacity and longer-term stability. Smaller droplets were created with hexadecane under all conditions studied followed by MCT and orange oil in agreement with their aqueous solubilities. Okra pectin had larger droplet size distributions when compared with LM (low-methyl), SBP (sugar beet pectin) and HM high-methyl) pectin. The present results improve our comprehension of the stabilisation of emulsions using pectin under a wide range of industrially relevant conditions allowing tailoring of applications for the food, pharmaceutical and biomedical industries.
|Date of Award||28 Mar 2023|
|Supervisor||Gordon Morris (Main Supervisor) & Alan Smith (Co-Supervisor)|