Behavior of Yersinia enterocolitica strains inoculated in model cheese treated with high hydrostatic pressure

Effect of High Hydrostatic Pressure in the Storage of Spanish-Style Table Olive Fermented with Olive Leaf Extract and Saccharomyces cerevisiae

Olives treated according to the Spanish-style are firstly treated with caustic soda and then fermented in brine to reduce phenols. Next, olives are packed and subjected to pasteurization. The effect of different high hydrostatic pressure treatments (400 MPa, 4 and 6 min) was evaluated in Spanish-style table olives fermented with olive leaf extract (OLE) and S. cerevisiae compared with thermal pasteurization (P) at 80 °C for 15 min. HHP and P led to a significant reduction in yeast and aerobic mesophiles after the conservation treatment and during storage (300 days). The physical-chemical properties changed slightly during storage, except for olive hardness; olives treated with HHP presented a higher hardness than pasteurized ones. The CIELAB parameter L* decreased until day 300 in most of the treatments, as well as phenols. The HHP treatment led to significantly higher contents of phenolics (even during storage) than olives submitted to P. Some sensory attributes (colour, aspect, hardness, and overall evaluation) decreased during storage. P treatment caused a decrease in appearance, aroma, hardness, and overall evaluation compared to olives treated with HHP. Thus, the application of HHP in table olives to increase the shelf-life can be considered a valid alternative to P.

Monitoring of acrylamide and phenolic compounds in table olive after high hydrostatic pressure and cooking treatments

Acrylamide and phenolic compounds on both fresh and cooked olives were monitored by HPLC/MS-MS and reversed-phase-HPLC methods along different procedures: elaboration process, high hydrostatic pressure (HHP), cooking treatment and bioavailability evaluation. Acrylamide was not detected during the elaboration process and after HHP treatment. Hydroxytyrosol, tyrosol, oleuropein and verbascoside were the most important phenols after HHP treatment. The frying and baking processes on olives enhanced the formation of acrylamide and a significant reduction in the phenolic compounds. The frying process produced lower acrylamide concentration and less reduction of phenolic compounds than the baking process, while in the gastrointestinal digestion these compounds were slightly reduced if compared to the initial stage. As a conclusion, the best way to ingest high quantities of phenols and reduce acrylamide consumption is by ingesting the olives when they are fresh. In case the olives need to be cooked, specific time and temperature conditions shall be applied.

High hydrostatic pressure technology in dairy processing: a review

Consumers demand high quality foods, which are fresh, tasty and nutritious; this has created considerable interest in the development of new food processing techniques. Presently, non-thermal techniques, including high hydrostatic pressure (HHP), are regarded with special interest by the food industry. Pressure ranges between 100 and 1200 MPa have been considered as effective to inactivate microorganisms including food-borne pathogens. HHP also improves rennet or acid coagulation of milk without any detrimental effect on flavour, body and texture and nutrients. Extended shelf-life and a "fresh-like" product presentation emphasize the need to take full account of food safety risks, alongside possible health benefits to consumers. These characteristics offer the dairy industry numerous practical applications to produce microbially safe and minimally processed dairy products with improved characteristics. Thus HHP is a powerful tool to develop novel dairy products of better nutritional and sensory quality, novel texture and increased shelf-life.

Response of Two Salmonella enterica Strains Inoculated in Model Cheese Treated with High Hydrostatic Pressure

The aim of this work was to determine the response to high hydrostatic pressure and the ability for survival, recovery, and growth of 2 strains of Salmonella enterica (Salmonella enteritidis and Salmonella typhimurium) inoculated in a washed-curd model cheese produced with and without starter culture. Inoculated samples were treated at 300 and 400 MPa for 10 min at room temperature and analyzed after treatment and after 1, 7, and 15 d of storage at 12 degrees C to study the behavior of the Salmonella population. Cheese samples produced with starter culture and treated at 300 and 400 MPa showed maximum lethality; no significant differences in the baroresistant behavior of both strains were detected. Nevertheless, when starter culture was not present, the maximum lethality was only observed in cheese samples treated at 400 MPa, in the case of S. enteritidis. Ability to repair and grow was not observed in model cheese produced with starter culture and cell counts of treated samples decreased after 15 d of storage at 12 degrees C. In cheese produced without starter culture, Salmonella cells showed the ability to repair and grow during the storage period, reaching counts over 3 log(10) (cfu/mL) in both applied treatments and serotypes. These results suggest that high hydrostatic pressure treatments are effective to reduce Salmonella population in this type of cheese, but the presence of the starter culture affects the ability of this microorganism to repair and grow during the storage period.

Fate of Escherichia coli strains inoculated in model cheese elaborated with or without starter and treated by high hydrostatic pressure

The aim of this research was to study high hydrostatic pressure inactivation of two strains of Escherichia coli (E. coli O59:H21 [CECT 405] and E. coli O157:H7 [CECT 5947]) inoculated in washed-curd model cheese elaborated with and without starter and the ability of these strains for survival, recovery, and growth. Samples were treated at 300, 400, and 500 MPa for 10 min at 20 degrees C and analyzed after the treatment and after 1, 7, and 15 days of storage at 8 degrees C to study the behavior of Escherichia populations. Cheeses elaborated with starter showed the maximum lethality at 400 and 500 MPa, and no significant differences in the baroresistant behavior of either strains were detected, except for E. coli O157:H7 at 400 MPa in cell counts obtained with thin agar layer method medium, where the decrease value was significantly lower. In cheese elaborated without starter, the highest decrease value was observed at 500 MPa, except for E. coli O59:H21 in cell counts obtained with selective culture medium, where the highest decrease value was also found at 400 MPa. The ability to repair and grow was not observed in model cheese elaborated with starter, as cell counts of treated samples decreased after 15 days of storage at 8 degrees C. By contrast, in cheese elaborated without starter, all pressurized samples showed the trend to repair and grow during the storage period in both strains. These results suggest that the presence of starter and low pH values are the main factors that control the ability of Escherichia strains inoculated in this type of cheese and treated by high hydrostatic pressure to recover and grow.

Inactivation of Mycobacterium avium subsp. paratuberculosis in cow's milk by means of high hydrostatic pressure at mild temperatures

Two strains of Mycobacterium avium subsp. paratuberculosis (3644/02 and ATCC 19698) were inoculated (approximately 6 log CFU/ml) into sterilized milk to evaluate inactivation by high hydrostatic pressure. Reductions of M. avium subsp. paratuberculosis increased with pressure level. Significant differences were also found between M. avium subsp. paratuberculosis strains and between the media used. Average reductions of 4 log CFU/ml after treatment with 500 MPa are comparable to those caused by thermal treatments.

Inactivation by ultrahigh-pressure homogenization of Escherichia coli strains inoculated into orange juice

The aim of this work was to evaluate the efficacy of ultrahigh-pressure homogenization (UHPH) for inactivation and/or sublethal injury of two strains of Escherichia coli (O58:H21 ATCC 10536 and O157:H7 CCUG 44857) inoculated into orange juice (pH 3.6). The effects of orange juice inlet temperature (6 and 20 degrees C) on the lethality values and the capacity of these strains for survival, repair, and growth during refrigerated storage after UHPH treatment also was evaluated. Samples of orange juice that had been treated with ultrahigh temperatures were inoculated with E. coli in the stationary phase of growth until a final concentration of approximately 7.0 log CFU/ml was reached. These samples were then treated for one cycle with a double-valve UHPH machine, with 300 MPa at the primary homogenizing valve and 30 MPa at the secondary valve. Counts of viable and injured bacterial cells were obtained for samples taken 2 h after UHPH treatment and after 3, 6, 9, 12, 15, 18, 21, 27, and 33 days of storage at 4 degrees C. The inlet temperature and the strain type both influenced significantly (P < 0.05) the lethality effect on E. coli, which was higher when the inlet temperature was 20 degrees C. No sublethal injuries were detected after any treatment. The changes in viable counts over time for both strains in pressurized and control samples were similar. The viable counts remained high from day 0 to day 18 and then tended to decrease. After 27 days of storage at 4 degrees C, E. coli O157: H7 was more resistant in orange juice samples pressurized at inlet temperatures of 6 and 20 degrees C, with viable counts of 3.41 and 3.20 log CFU/ml, respectively.

Inactivation of Listeria innocua in milk and orange juice by ultrahigh-pressure homogenization

The aim of this work was to evaluate the bactericidal efficacy of ultrahigh-pressure homogenization (UHPH) against Listeria innocua ATCC 33090 inoculated into milk and orange juice. We also intended to study the effect of inlet temperature on the lethality and production of sublethal injuries in this microorganism and its ability to survive, repair, and grow in refrigerated storage after UHPH treatment. Samples of ultrahigh-temperature whole milk and ultrahigh-temperature orange juice inoculated at a concentration of approximately 7.0 log (CFU per milliliter) were immediately pressurized at 300 MPa on the primary homogenizing valve and at 30 MPa on the secondary valve, with inlet temperatures of 6.0 +/- 1.0 degrees C and 20 +/- 1.0 degrees C. L. innocua viable counts and injured cells were measured 2 h after UHPH treatment and after 3, 6, and 9 days of storage at 4 degrees C for milk and after 3, 6, 9, 12, 15, 18, and 21 days of storage at 4 degrees C for orange juice. Both the inlet temperature and the food matrix influenced significantly (P < 0.05) the inactivation of L. innocua, which was higher in whole milk at the 20 degrees C inlet temperature. The UHPH treatment caused few or no sublethal injuries in L. innocua. During storage at 4 degrees C after treatments, counts increased by approximately 2 logarithmic units from day 0 to 9 in whole milk, whereas in orange juice counts diminished by approximately 2.5 logarithmic units from day 0 to 18.