Valorisation of Myrtle Liqueur Processing and Olive Pomace By-products as Ingredients for Functional Dairy Foods

This research has deepened the potential for valorisation of by-products of the Sardinian agri-food industry, in particular olive pomace (OP) and exhausted myrtle berries (MSB), for the formulation of functional yogurts based on whole sheep's milk. The activity was developed with a view to sustainability and the circular economy, with the aim of creating an innovative product capable of combining nutritional benefits, the best chemical-physical, rheological and sensorial properties. The experimental work was divided into three phases. In the initial phase of the study, the incorporation of freeze-dried olive pomace (1% w/w) was assessed at two distinct points during the manufacturing process: prior to heat treatment and subsequent to fermentation. The insertion of the pomace prior to pasteurization yielded optimal results, characterised by a substantial augmentation in water retention capacity, a decline in syneresis, an escalation in total phenolic content, and an enhancement in antioxidant activity. Furthermore, no deleterious effects were observed on sensory characteristics. The rheological and textural analyses indicated comparable or superior performance in comparison to the control, while the SEM images substantiated the effective incorporation of the pomace into the yogurt matrix, thereby enhancing the stability of the gel. This phase thus demonstrated the validity of olive pomace as a functional and sustainable ingredient for dairy products. The second phase of the project was dedicated to the valorisation of exhausted myrtle berries (Myrtus communis L.), a by-product of the production of the liqueur known as "Myrtle of Sardinia". The incorporation of MSB powder (1% w/w) prior to pasteurization or subsequent to fermentation has been demonstrated to enhance the total phenolic content and antioxidant activity, whilst concomitantly reducing syneresis and promoting optimal microbiological stability. However, a lower water retention capacity and reduced gel consistency and adhesiveness were observed, suggesting the need for further technological optimisations. Once more, the pre-pasteurization addition was shown to be the most appropriate, particularly with regard to food safety. In the third stage, a technological improvement was introduced via milk homogenization, which was applied to both control and MSB-enriched samples. The efficacy of this treatment was demonstrated by its ability to enhance the distribution of plant particles and the cohesion of protein networks, thereby augmenting the capacity to retain serum. However, the presence of myrtle fibres and polyphenols led to a partial attenuation of the structuring effect of homogenization, likely due to interactions with milk proteins. In order to optimise the product, the addition of inulin (3%) and lactase (0.3 g/kg) was finally evaluated. Inulin has been demonstrated to enhance texture, thereby enabling the assertion of a high fibre content. Conversely, lactase has been shown to mitigate the bitter and astringent qualities of phenolic compounds, rendering yogurt more palatable and suitable for individuals with lactose intolerance. These modifications resulted in enhanced gel structure, reduced syneresis, and increased creaminess, without adverse effects on acidification or color properties. Sensory analysis, facilitated by Penalty Analysis, corroborated an enhancement in the perception of creaminess and colour, accompanied by favourable overall acceptability. The results obtained demonstrate that the valorisation of local by-products, such as olive pomace and exhausted myrtle berries, represents an effective strategy for the development of sustainable functional yogurts with high added value. This highlights the feasibility of an innovative technological approach oriented towards industrial transferability and construction of a more circular and competitive Sardinian dairy supply chain.