Effects Of High Hydrostatic Pressure (HHP) On Walnut Pastes: Characterization and Stability Evaluation

The study aimed to characterize and check the stability of different wal-nut pastes obtained from roasted or unroasted kernels. The samples were processed through a High Hydrostatic Pressure treatment (HHP), a mild technology used on food products to reduce microbial contamination while maintaining sensorial characteristics and nutritional quality. Samples were characterized (moisture, proteins, fats, fibers content) to highlight any difference due to the roasting procedure and to monitor how the structure of the product might be influenced during the storage period. HPP processing was performed at 600 MPa at 16 °C for 6 min. HPP treated and untreated samples were analysed to verify how this mild technology could affect the paste’s rheology, color, oxidative stability, and microbiological safety. At this aim, the pastes were maintained at 40 °C for 60 days to simulate a storage period of about 18 months at 21 °C (Ea of 90 kJ/mol); and periodically checked through some comprehensive physical and chemical tests (water ac-tivity, pH, total acidity, lipid oxidation, lipoxygenase activity, antioxidant activity, color), rheological measurements (flow and oscillatory tests), and microbiological analyses (total microbial count, yeasts and moulds, total coliforms, and Enterobacteriaceae). Data showed that HPP treatment can affect the microbiological safety of the product and its rheological characteristics. The treatment also contributed in improving the extractability of some nutrients (such as soluble fiber). Yeasts and moulds resulted the most sensitive to HHP. This mild technology showed a significant effect on pastes’ rheo-logical behaviour creating changes or rearrangements in the inner structure. HHP treatment can be applied on nuts derivates giving higher stability and guaranteeing their microbiological safety. Deepened studies should be done to verify how HPP could affect foods rich in lipids on their long term stability deepening its action on the product’s structure.