High Hydrostatic Pressure treatment of fresh pork sausages: effects on microbiological shelf-life and safety

Fresh sausages are unfermented meat products obtained by mixing lean and fatty pork meat with NaCl, pepper, spices. The mixture is stuffed into natural/synthetic casing, packed under modified atmosphere or vacuum and stored at refrigerated temperatures for maximum 12-15 days. Due to the intrinsic product characteristics (pH close to 6, high water activity), shelf-life and safety are guaranteed by storage at 0-4°C, often difficult to maintain. High Hydrostatic Pressure (HHP) has been proposed as an adjunctive hurdle to control microbial proliferation, since alone cannot be considered a sterilization method. In this study the effect of a 5-minute HHP treatment at 600 MPa on microbiological features was assessed. In particular, the evolution of main microbial groups (total mesophilic count TMC, lactic acid bacteria LAB, staphylococci) was monitored in relation to different storage conditions including thermal abuses before HHP treatment or during storage. In addition, challenge tests with Salmonella Enteritidis, Staphylococcus aureus and Listeria innocua were performed. The results showed an increase in shelf-life up 90 days in HHP treated samples (compared to 15-20 days for conventional products). Concerning thermal abuses, an overnight storage at 15°C before HHP affected TMC of untreated samples, while in HHP treated sausages was negligible. The storage at 8°C after HHP strongly influenced TMC and LAB counts, with values higher than 7 log CFU/g after 60 days, while in not-thermally abused sausages (4°C) they remained below 4 log CFU/g. According to the challenge tests carried out, HHP treatment was effective against S. Enteritidis, while L. innocua, whose cells counts were always below the detection limit during storage, was qualitatively detected after 90 days. Staph. aureus was most resistant, with a 3-log reduction due to HHP, followed by stable values during storage. Further analyses are in progress to evaluate the effects of HHP on colour and texture parameters.