Inactivation of Escherichia coli K12 in phosphate buffer saline and orange juice by high hydrostatic pressure processing combined with freezing

Abstract

Synergistic action of high hydrostatic pressure (HHP) and freezing on inactivation of Escherichia coli K12 in phosphate buffered saline (PBS) was investigated by employing response surface methodology. Samples containing E. coli K12 were stored at 4, −24 and −80 °C overnight before they were pressurized. A maximum of 1.83 log reduction of CFU•ml -1 was obtained following a 9-min treatment at 400 MPa and 4±1 °C in samples stored at 4 °C whereas, 5.63 and 6.83 log reductions were obtained in samples frozen at −24 and −80 °C, respectively. Major disruption of E. coli cells observed by scanning electron microscopy and increased amounts of DNA and RNA measured in pressure treated frozen PBS samples indicated that the main mechanism of inactivation in frozen samples was due to cell rapture. The validity of enhanced microbial inactivation by freezing before HHP for a real food system was tested by using orange juice. Pressurization (250 MPa, 15 min) of frozen (−80 °C) orange juice resulted in 4.88, 4.15 and 4.61 log CFU•ml -1 reductions in number of E. coli for the samples having pH 3.2, 4.5 and 5.8, respectively. In the absence of freezing, the same treatment caused only up to 0.42 log reduction in samples having pH 4.5 and 5.8.

Synergetic Inactivation Mechanism of Protocatechuic Acid and High Hydrostatic Pressure against Escherichia coli O157:H7

“…According to Montiel et al [50], the combination of HHP (450 MPa for 5 min) and reuterin (16 mmol/L), lactoperoxidase system (2.8 U/g) or lactoferrin (1 g/L) treatments of cold-smoked salmon results in a 1.8-3.5 log CFU/mL reduction. In addition, Bulut and Karatzas [51] found that the combination of HHP (441 MPa for 5 min) and freezing, at 4 • C and −24 • C, leads to 1.01 and 5.19 log CFU/mL, respectively, which were lower than in our research. Thus, it could be inferred that this new method has a superior bactericidal effect.…”

Non-thermal Technologies for Food Processing

“…HHP treatment has been proven to be efficient in the inactivation of microbes in a wide range of food products, including processed fruits, meat and meat products, and dairy products, which serve as an excellent medium for microbial growth. The recently published study by Bulut and Karatzas ( 166 ) investigated the effectiveness of HHP against E. coli in liquid food. Orange juice was stored at −80°C, and then HHP treatment was applied to the juice with pressure of 250 MPa for 900 s. The HHP treatment reduced the microbial load by 4.88, 4.15, and 4.61 log CFU/ml for orange juice with pH 3.2, 4.5, and 5.8, respectively.…”

Frozen-Phase High-Pressure Destruction Kinetics of Escherichia coli as Influenced by Application Mode, Substrate, and Enrichment Medium

“…Recently, a good synergistic effect on the sterilization of pressure and subzero temperatures was achieved in a special container reported in our previous studies [ 9 , 10 ]. Freezing prior to HP processing achieved better inactivation effect compared with unfrozen samples [ 11 , 12 ]. A 5.63 log reduction was obtained in samples frozen at −24 °C, while only a 1.83 log reduction was obtained in unfrozen samples at 4 °C following a 9 min treatment at 400 MPa [ 11 ].…”

“…Freezing prior to HP processing achieved better inactivation effect compared with unfrozen samples [ 11 , 12 ]. A 5.63 log reduction was obtained in samples frozen at −24 °C, while only a 1.83 log reduction was obtained in unfrozen samples at 4 °C following a 9 min treatment at 400 MPa [ 11 ]. Further studies are necessary to better understand the influenced factors of the inactivation effect of HP treatment, including frozen phase, pressure levels, application modes, substrates, and recovery medium.…”