Borriello, Angela (2022) Novel approaches in healthy cream development: oleogels and a natural sweetener. [Tesi di dottorato]

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Physical and sensory performance of creams are strictly related to the presence of a large amount of saturated fat and sugar, whose consumption should be reduced since increases the incidence of cardiovascular diseases, obesity, diabetes and other health implications. With regards to hardstock fat reduction, oleogelation is a promising and healthy method to transform liquid oil into a ‘gel-like’ structure with viscoelastic properties called oleogels. On the other hand, an innovative approach to replace sugar could consist in the application of natural sweeteners plant-based with a low glycemic index, such as lucuma (Pouteria obovata) containing beneficial bioactive compounds. To date, very few studies exist regarding using wax oleogels in nut creams and there are no studies that have investigated the effect of using oleogels, as well as Lucuma, on refining in a ball mill. Based on this background, the study aimed to investigate novel approaches for healthy spreadable creams production in line with consumer needs. Firstly, a market online survey was carried out to define the concept of healthy cream to develop, taking into account the opinion of consumers with different healthy choice attitudes. Results showed that a healthy spread is in line with the current trend market. To develop a new healthy cream, the percentage of cocoa and dried fruit could be increased, the amount of sugar and fat could be reduced using alternative natural sweeteners and, the use of vegetable oils with beneficial properties could be considered as well. The second and third project sections focused on the development and characterization of novel oleogels prepared with uncommon vegetable oils naturally rich in vitamins and with an interesting nutritional profile, such as pumpkin seed oil. The effect of the oil type on the gelling capacity of oleogels was reported in the literature but not completely elucidated. Therefore, the crystallization and gelation kinetics of two oleogelators, beeswax and carnauba wax, in six different oils (pumpkin, hemp, almond, rice, sesame and grape seed), were studied and modelled by a modified Avrami model. Subsequently, the characterization of pumpkin seed oil was optimized by analyzing the effect of the beeswax and carnauba wax concentration (4%, 5%, 6% and 8%) on the formation mechanisms and physical properties of oleogels. To obtain information on the microstructure of oleogels, the fractal dimension model was used by exploiting their rheological properties. All developed oleogels were characterized in terms of physical properties. The oil type did not affect the crystal growth mechanism (Avrami index ranged from 1.00 to 1.43) since both, beeswax and carnauba wax, showed a 1D-2D mixed crystallization in all the oils analysed. On the other hand, the fatty acid composition of oils affected the self-assembling of oleogelators during the gelation, which occurs significantly later than the onset of nucleation. Hempseed, rice and pumpkin seed oils, the richest in saturated fatty acids among the oils analysed, formed a more interconnected structure when gelled with carnauba wax, following a 3-D network formation mechanism. The strength and yield stress of carnauba wax oleogels increased with increasing saturated fatty acid amount, while in beeswax-based oleogels a more interconnected structure was associated with the length of the saturated fatty acid chain. Considering the oleogels based on pumpkin seed oil, wax concentration affected both, thermal parameters and gelation kinetics. At the end of the cooling stage, all the oleogels has not completely formed and needed a setting 5 stage at 25°C to totally gel. The higher the concentration of oleogelator, the greater the floc number and their interactions, leading to the formation of a stronger crystalline network, hence a harder oleogel, with higher solid fat content, more resistant to melting. Carnauba wax proved to be a more efficient oleogelator in pumpkin seed oil than beeswax since a lower concentration is required to obtain an oleogel with excellent physical properties. Based on fractal dimension theory, all the oleogels followed a stronglink regime and the fractal dimension of the network (D) was comparable to fats widely used in food production, such as cocoa butter and palm oil. It was therefore highlighted how very small differences in the chemical composition of the oil can affect the formation mechanisms of oleogels, providing the criteria for choosing the most suitable oil and oleogelator to design oleogels with the desired physical properties. Finally, the impact of both, a novel oleogel and uncommon sweetener on the structure of healthy creams was studied. Three different creams were prepared in a stirred ball-mill: a reference cream R with cocoa butter and sugar; a cream A with a pumpkin seed oil and carnauba wax oleogel and sugar; a cream B with both oleogel and Lucuma powder. The effect of replacements on the structure of creams at different refining times was investigated analysing their granulometric and rheological behaviour and physical properties including apparent viscosity, oil binding capacity, water activity, colour and Turbiscan stability. Similar creams were obtained by changing only the fat phase, in terms of particle size distributions and rheological properties. Lucuma seemed to slow down the refining while the oleogel accelerated the refining process, which could also be stopped at 120 minutes since a particle size of 30 µm, do not perceive by papillae, was obtained. All the samples exhibited pseudo-plastic behaviour, showing a good oil binding capacity, and they were microbiologically and physically stable since showed water activity and Turbiscan stability index values close to 0.5 and 1, respectively. The oleogel based on pumpkin seed oil and carnauba wax could be totally replaced the cocoa butter, and Lucuma could partially decrease the sugar intake. Starting from the consumer's needs, it was possible to functionalize polyunsaturated and monounsaturated oils, designing novel structures, the oleogel, successfully applied in a complex food matrix such as cream, improving the nutritional profile, not only reducing the saturated fatty acids, but also by introducing a natural sweetener, providing viable alternatives for reformulating foods with healthier nutritional profiles.

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