Physical and Chemical Characterisation of Conventional and Nano/Emulsions: Influence of Vegetable Oils from Different Origins

Abstract

The processes of oil production play an important role in defining the final physical and chemical properties of vegetable oils, which have an influence on the formation and characteristics of emulsions. The objective of this work was to investigate the correlations between oils’ physical and chemical properties with the stability of conventional emulsions (d > 200 nm) and nanoemulsions (d < 200 nm). Five vegetable oils obtained from different production processes and with high proportion of unsaturated fatty acids were studied. Extra virgin olive oil (EVOO), cold-pressed rapeseed oil (CPRO), refined olive oil (OO), refined rapeseed oil (RO) and refined sunflower oil (SO) were used in this study. The results showed that the physicochemical stability of emulsion was affected by fatty acid composition, the presence of antioxidants, free fatty acids and droplet size. There was a significant positive correlation (p < 0.05) between the fraction of unsaturated fatty acids and emulsion oxidative stability, where SO, OO and EVOO showed a significantly higher lipid oxidative stability compared to RO and CPRO emulsions. Nanoemulsions with a smaller droplet size showed better physical stability than conventional emulsions. However, there was not a significant correlation between the oxidative stability of emulsions, droplet size and antioxidant capacity of oils.

Red Raspberry Seed Oil Low Energy Nanoemulsions: Influence of Surfactants, Antioxidants, and Temperature on Oxidative Stability

“…On the other hand, PG NEs were semi-transparent, due to very fine droplet sizes (Z-ave < 65 nm), also with notable differences between blank NE (F0 PG: 62.32 nm) and RO-loaded NEs (38.63–46.56 nm). Droplet size distribution was very narrow (PDI < 0.15) in both types of NE systems (i.e., 0.116–0.125 for P80 NEs, and 0.051–0.110 for PG NEs, respectively), indicating good preliminary stability [ 26 , 43 ].…”

“…One of the main reasons for increased instability of oil in emulsion system compared to bulk oil is a large contact area between the oil and the water phase containing prooxidants. Moreover, previous studies showed that structural and physicochemical properties of surfactants, as well as their interactions with antioxidants in formulations, significantly influence oxidative stability of emulsified oils [ 23 , 25 , 26 , 45 , 48 ].…”

“…Therefore, for the purpose of the current study, similar formulations were prepared with polysorbate 80 (P80 NEs) or polyglycerol ester-based surfactants (PG NEs), with or without additional antioxidants (BHT—0.02 wt%, EDTA—0.2 wt%, ORE—0.02 wt% or OAK—1 wt%), while the nanoemulsion oil phase composition was kept constant. The antioxidants concentrations were chosen to be suitable for topical application, based on the common practice in cosmetic or pharmaceutical formulations, producer specifications, and the available literature [ 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. After all NE components were added, a short homogenization of samples followed (for 2 min, at 1300 rpm) to obtain oil-in-water NEs containing 10 wt% surfactant, 10 wt% oil phase, and 80 wt% water phase, where wt% represents percentage weight by weight.…”

“…The NE composition is presented in Table 1 . The samples were kept in 10 mL glass bottles, capped tightly, and stored in the dark place for 30 days at different temperatures (5, 25, and 40 ± 2 °C, i.e., refrigeration, standard room temperature, and slightly elevated temperature, for example during summer, respectively), as a standard procedure to assess influence of the usual storage conditions for topical products and food [ 26 , 32 ].…”

“…The literature data regarding the lipid oxidation in classical emulsions are conflicting, since it was reported that lipid oxidation can be increased compared to bulk oil [ 20 ], but the opposite behavior was also described [ 21 ]. Due to the smaller size of nanodroplets compared to classical emulsions, the larger available oil–water interfacial surface area sometimes leads to even more pronounced oxidative instability [ 22 , 23 ], but the same controversy on the subject is evident in the reported results regarding NEs [ 24 , 25 , 26 ]. To avoid such problems, additional fine-tuning of the system composition may be required, based on elucidation of the role that surfactants and additional antioxidants play in the antioxidant stability of NE formulations [ 27 , 28 ].…”