## 4 Discussion  
HPP is a potential technique for producing high-quality food items with an extended shelf life. However, the applicability of the technique should be tested with various food products. There have been issues with high-oil products that can form a protective barrier against spoilage and pathogenic bacteria during thermal [44,45] and non-thermal processes [46], reducing the efficiency of these procedures in eradicating microorganisms. Furthermore, the high oil concentration might speed up the oxidation of lipids and reduce product quality. This study sought to evaluate the microbiological and chemical aspects of pesto sauce, a high-oil food. The microbiological study demonstrated that theHPP efficiently reduced the levels of _L. monocytogenes_ and \(S\). Typhimurium, with no significant influence of oil content on bacterial survival. However, the findings indicated that the presence of oil may alter the efficacy of thermal processing, potentially allowing _L. monocytogenes_ bacteria to survive. According to studies, high oil content can reduce the efficacy of thermal processing by lowering water activity (aw). This decrease in aw can lead to _L. monocytogenes_ bacteria more resistant to thermal and non-thermal processes [45]. A study by [PERSON] et al. (2014) reported that peanut butter formulations could reduce the impact ofHPP on _Salmonella_ bacteria [47]. The researchers adjusted the aw by adding oil and water, and the results showed that increasing the amount of oil (and therefore lowering aw) dramatically reduced the impact ofHPP on Salmonella bacteria. [PERSON] et al. (2006) found that the aw of cheese significantly affected the pressure resistance of _L. monocytogenes_ and proposed that fat improved microorganism resistance toHPP destruction in a similar way as thermal inactivation [19]. Cream presents a challenge in removing bacteria, due to its high fat content and reduced aw. Previous study has demonstrated that the microbial load of cream with 35% fat can be significantly reduced withHPP. For example, _Listeria innocua_ can be inactivated usingHPP at 450 MPa and 25 \({}^{\circ}\)C for 10-30 min. It has been suggested thatHPP could help extend the refrigerated shelf life of dairy creams [48]. These findings confirm theHPP process as a safe way of producing high-oil-content foods. [PERSON] et al. (2018) found that _Listeria_ inactivation increased with higher applied pressure, showing statistical differences based on the strains used (_L. innocua_, _L. monocytogenes_ CECT 4031 and _L. monocytogenes_ Scott _A_), inoculum levels (4-6 Log CFU/g), and sublethal injury. All three examined strains had the maximum lethality values at 600 MPa; however, _L. Figure 3: Effect ofHPP and thermal processing on lipid oxidation in pesto sauce. (**a**) Peroxide value results in day 1 (solid fill) and 60 (pattern fill) of storage time, (**b**) p-anisidine value results after 60 days storage time. Data represent the mean \(\pm\) standard deviation of three independent replicates; different superscript letters in each column indicate significant differences (\(p<0.05\), Same letters mean no significant differences). NP-34: 34% oil-content non-processed sample,HPP-34: 34% oil-content HPP sample, TP-34: 34% oil-content thermal-processed sample, NP-54: 54% oil-content non-processed sample,HPP-54: 54% oil-content HPP sample, TP-54: 54% oil-content thermal-processed sample. _inocua_ and _L. monocytogenes_ CECT 4031 also had high lethality at 500 MPa. Following treatment, the counts of _L. innocu_ and _L. monocytogenes_ CECT _4031_ in fresh cheese gradually increased during cold storage [49]. Another study determined that 6000 bar is the highest effective pressure for inactivating _L. monocytogenes_[10]. Furthermore, in our investigation, all samples containing bacteria showed a significant decrease in _Listeria_ and _Salmonella_ bacteria during storage.