Oil Structuring for Improving Healthy and Sustainable Diets: The Case Study of Extra Virgin Olive Oil Oleogelation

The aim of this PhD research project is to develop novel and sustainable strategies to structure liquid oils into pseudoplastic materials, called oleogels, to be used as saturated fat substitutes or as functional components able to modulate lipolysis during human digestion as well as deliver bioactive lipophilic molecules. In this context, the use of extra virgin olive oil (EVOO) as a target oil to be gelled would be particularly interesting due to its well- recognized health-promoting capacity. In this case study, EVOO-based oleogels were developed by using different gelation strategies. The oleogels, after structural characterization, were in vitro digested to study the impact of oil structure on the free fatty acids (FFA) release and polyphenols’ bioaccessibility. 1. Introduction In accordance with the PhD thesis project previously described (Ciuffarin, 2021), this poster reports the main results of the following activities: (A1) Study of strategies for oil structuring (e.g., methods and selection of gelators). (A3) Evaluation of the effect of oleogelation on the gastrointestinal behavior of oleogels by determining the bioaccessibility of selected bioactive molecules (e.g., polyphenols) as well as the lipolysis degree by using in vitro digestion methodologies. 2. Materials and Methods Oleogels were obtained by adding 10 % (w/w) of saturated monoglycerides (MG), rice bran waxes (RW), sunflower waxes (SW), and β-sitosterol/γ-oryzanol mixture (PS) in EVOO heated at temperatures higher than the melting temperatures of the different gelators. Additionally, a whey protein-based oleogel (WP) was prepared by mixing EVOO with a WP aerogel prepared following the methodology of Plazzotta et al. (2020). The final oil content in WP-based oleogels was 80% (w/w). Oleogels were characterized for their structure using a texture analyzer (35 mm-diameter cylindrical probe for 5 mm of distance at a crosshead speed of 1.5 mm/s, TA. XT Plus, Stable Micro Systems Ltd, Godalming, UK) and an accelerated release test by centrifuging samples (10000g for 15 min, Mikro 120, Hettich Zentrifugen, Andreas Hettich GmbH and Co, Tuttlingen, Germany). Unstructured EVOO and oleogels were then subjected to in vitro digestion according to the protocol proposed by Brodkorb et al. (2019). The FFAs released during digestion were assessed by titration (pH-stat). The bioaccessibility of tyrosol (T) and hydroxytyrosol (HT) was evaluated as the percentage ratio between the concentration of these components included in the micellar phase after intestinal in vitro digestion and their concentration in the undigested sample. The polyphenols were determined by HPLC. 3. Results and Discussion 3.1 Oleogel physical properties Table 1 shows the oil retention capacity and firmness of the considered oleogels. All the samples presented a very high oil retention capacity upon centrifugation (<99%) despite the different firmness. The MG-based oleogel was the weakest gel, followed by WP, RW, SW, and PS. These mechanical properties can be associated with the different natures of the networks structuring EVOO. In agreement with the literature, MG, RW, and SW formed a crystalline network (da Pieve et al., 2010; Doan et al., 2015), PS generated a fibrillar structure (Scharfe et al., 2019) and protein aerogels absorbed oil in the protein porous structure (Plazzotta et al., 2021). 3.2 In-vitro digestion: FFA release and bioaccessibility Figure 1 shows the FFA release as a function of the digestion time of structured into oleogels and unstructured EVOO. The typical curve of lipid hydrolysis was obtained. The unstructured oil presented FFA release % of about 68%, followed by PS, SW, RW, and MG with 59.1, 50.8, 50.7, and 42.8% respectively. A different behavior was acquired for WP- based oleogels showing the complete digestion of the oil. These results clearly show that the extent of lipid lipolysis was significantly affected by oil structure. In the case of liposoluble gelators (i.e., MG, RW, SW, PS), it can be inferred that the lipase activity was hindered by the presence of a structuring network behaving like a physical barrier to the access of the enzyme to the substrate sites. On the contrary, WP probably completely dissolved in the gastrointestinal environment thus favouring the emulsification of the oil and thus the lipase activity. In summary, the results demonstrated that the digestibility of the oil can be steered by selecting the proper oleogelator. In the next part of the study, the bioaccessibility of the major EVOO polyphenols (i.e., tyrosol and hydroxytyrosol) was assessed. Despite the higher content of hydroxytyrosol (HT) in EVOO than tyrosol (T) (HT: 248 mg/kg, T: 96 mg/kg), the bioaccessibility of T was significantly higher than that of HT. This result can be explained by considering the different susceptibility to oxidation of the two molecules during digestion (Alberdi-Cedeño et al., 2020). Moreover, differences were recorded among oleogels. Unstructured oil and WP presented the higher T bioaccessibility values, followed by SW, MG and RW, and PS. Since it is impossible to observe a direct effect of gel strength on polyphenol bioaccessibility, it can be speculated a possible interaction between the polyphenols and oleogel network structures. In fact, as well-known, polyphenols are surface-active molecules with the potentiality to interact with other food components. In conclusion, the results reported in the present study confirm that oleogelation could be a profitable strategy to modulate lipid digestion while delivering bioactive molecules. 4. References Alberdi-Cedeño, J., Ibargoitia, M. L., & Guillén, M. D. (2020). Study of the in vitro digestion of olive oil enriched or not with antioxidant phenolic compounds. Relationships between bioaccessibility of main components of different oils and their composition. Antioxidants, 9(6). Brodkorb, A., Egger, L., Alminger, M., Alvito, P., Assunção, R., Ballance, S., Bohn, T., Bourlieu-Lacanal, C., Boutrou, R., Carrière, F., Clemente, A., Corredig, M., Dupont, D., Dufour, C., Edwards, C., Golding, M., Karakaya, S., Kirkhus, B., le Feunteun, S., ... Recio, I. (2019). INFOGEST static in vitro simulation of gastrointestinal food digestion. Nat. Protoc., 14(4), 991–1014. da Pieve, S., Calligaris, S., Co, E., Nicoli, M. C., & Marangoni, A. G. (2010). Shear Nanostructuring of monoglyceride organogels. Food Biophys., 5(3), 211–217. Doan, C. D., van de Walle, D., Dewettinck, K., & Patel, A. R. (2015). Evaluating the oil-gelling properties of natural waxes in rice bran oil: Rheological, thermal, and microstructural study. JAOCS,92(6). Plazzotta, S., Calligaris, S., & Manzocco, L. (2020). Structural characterization of oleogels from whey protein aerogel particles. Int. Food Res. J., 132, 109099. Plazzotta, S., Jung, I., Schroeter, B., Subrahmanyam, R. P., Smirnova, I., Calligaris, S., Gurikov, P., & Manzocco, L. (2021). Conversion of whey protein aerogel particles into oleogels: Effect of oil type on structural features. Polym. J., 13(23). Scharfe, M., Ahmane, Y., Seilert, J., Keim, J., & Flöter, E. (2019). On the Effect of Minor Oil Components on β- Sitosterol/γ-oryzanol Oleogels. Eur. J. Lipid Sci. Technol., 121(8).