Extra virgin olive oil, olive milling by-products and “virgin grape seed oil”: chemical characterization, biological activity and sensorial studies for their nutraceutical valorization

This thesis was focused on the nutraceutical valorization of extra virgin olive oil, “virgin” grape seed oil and olive milling by-products. This objective was pursued by a multidisciplinary approach involving chemical characterization and studies of biological activity and sensorial characteristic of the products. In particular, the following specific objectives have been pursued: 1. to study the impact of several factors on olive oil quality and to develop suitable analytical methods to check this quality 2. to characterize composition and biological activities of phenolic fractions from “virgin” grape-seed oils 3. to develop suitable strategies for using by-products from virgin olive oil production for human consumption. Regarding the first objective, a new methodological approach for evaluate the percentage of phenolic compounds transferred from olive fruits to olive oil during milling was developed and applied. Our results showed that up to 0.40% of phenols are transferred by the two-phase system and up to 0.19% with the three-phase system. These data are up to 25 times lower than those previously reported in the literature. At the same time, we studied the effect of olive paste moisture on content and profile of phenolic compounds in extractable oil at lab scale, by diluting freeze-dried olive pastes at a moisture range of 0-60%. Results showed that the % of extracted phenols reaches a maximum at a certain moisture content, that is lower than 40%, so that processing procedures able to control the olive fruit moisture may led to technological innovations. In a further part of the thesis, we described, for the first time, the presence of new lignans, isobaric to the well known pinoresinol and 1-acetoxypinoresinol, in olive oil. Studying partially and fully-refined oils, it emerged that these isobaric lignans are formed during the bleaching step of the refining process, so that we were able to propose the detection of these molecules as markers of undeclared refining procedures in commercial virgin and extra virgin olive oils. Again, in order to check the quality of virgin olive oil, we developed and validated a new analytical method for the quantification of volatile organic compounds of virgin olive oil, with the aim to support the panel test in olive oil classification. This method, based on HS-SPME-GC-MS, uses up to 11 internal standard for area normalization and allows quantifying 70 VOCs in wide ranges of calibration. 4 In the second part, we investigated the phenolic composition of 17 monocultivar commercial cold-pressed grape seed oils, by HPLC-DAD-MS-TOF. Total phenolic content ranged between 1-15 mg/kg, and pinoresinol, ethyl caffeate and ethyl gallate were detected for the first time in this type of oil. Our studies also highlighted a good correlation between total phenolic content and inhibitory power of PTP-1B, an enzyme overexpressed in type-two diabetes, with pinoresinol, p-coumaric acid and quercetin that making the great contribution. Thid work contributed to clarify this matter because contradictory results were reported in the literature. Finally, in the third part, we proposed different possible use of olive milling by-products, mainly for human nutrition. A first study was aimed to evaluate the quality and the stability of retentates obtained from olive mill wastewaters treated with a membrane filtration system. Results showed a reproducibility of the process over years, a high stability of hydroxytyrosol in the liquid retentates at 18-24°C over 24 months of storage and that retentates of reverse osmosis have the highest phenolic content. These retentates could be good sources of natural antioxidants and potassium and are suitable to formulate new food ingredient or food products. At the same time, we characterized pâté, a new type of olive pomace, potentially suitable for human consumption. In the first part of the work, we determined the phenolic profile of pâté in fresh, dried and stored samples, and evaluated the antiaging effect in a cell senescence model. Results showed antiaging effects in vitro, comparable to those of pure hydroxytyrosol and that 1 g of paté provides a daily intake of total phenols comparable to that derived from 200 g of a typical virgin olive oil, demonstrating the potential value of this natural ingredient for human nutrition. However, before an ingredient could be successfully marketed, foods including this ingredient in their recipes must be perceived as pleasant by the consumer. For this reason, in the last part of my thesis, we tested the consumer acceptance of pasta, bread and granola bar fortified with suitable % of pâté, characterizing their sensory profile and evaluating the acceptance of naïve consumers. This part, performed at the University of California, Davis, allowed us highlighting that consumers accepted these products, confirming pâté as potential nutraceutical ingredient for improving the daily intake of phenolic compounds from Olea europaea L., also giving additional economic value to the olive oil production chain