Inactivation of Listeria innocua in dairy fluids by pulsed electric fields: influence of electric parameters and food composition

International audienc

Foreword

International audienc

Foreword

International audienc

High pressure–low temperature processing of food proteins

International audienc

Combined high pressure–sub-zero temperature processing of smoked salmon mince: phase transition phenomena and inactivation of Listeria innocua

International audienceSmoked salmon mince inoculated with Listeria innocua was subjected to various combined high pressure- low or sub-zero temperature treatments. Temperature in the sample and in the pressure-transmitting medium (PTM) were monitored against pressure in order to detail undercooling, ice nucleation and phase transition under pressure. Freezing at 0.1 MPa with subsequent storage at −28 °C or −40 °C for 5 days did not induce any microbial inactivation. Inactivation of L. innocua by pressurisation at 207 MPa for 60 min without ice crystal formation was higher (1.1 log cycle) at sub-zero temperatures (down to −21 °C) than at 4 °C (0.7 log cycle). Pressure-shift freezing from 207 MPa and −22 °C, followed by further freezing to −25 °C at 0.1 MPa, induced 1.4 or 1.9 log cycle reduction of L. innocua, depending on whether pressure was released rapidly (∼3 s) or slowly (18 min), respectively. Freezing samples at −28 °C and 0.1 MPa for 24 h followed by pressurisation at 207 MPa and −29 °C for 23 min, then fast pressure release resulted in a 2.5 log cycle reduction for L. innocua. When sample freezing was followed by pressure-assisted thawing at 207 MPa and in PTM at 10 °C for 23 min, a reduction of 1.2 log cycle was obtained. None of the combined high pressure–sub-zero temperature treatments was found to induce sub-lethal injury of L. innocua dispersed in smoked salmon mince

Microbial inactivation by pressure-shift freezing: effects on smoked salmon mince inoculated with Pseudomonas fluorescens, Micrococcus luteus and Listeria innocua

International audienceSmoked salmon mince inoculated simultaneously with Listeria innocua, Micrococcus luteus and Pseudomonas fluorescens was subjected to different pressure–temperature conditions. Control freeze–thaw at 0.1MPa with storage at −15°C or −40°C for 0–5 days did not induce microbial inactivation. Control pressurisation at 207MPa for 23min at 20°C (initial sample temperature) with fast (3s) pressure release had no significant effect on Gram+bacteria while P. fluorescens underwent a 2.8 log cycle reduction. Pressurisation at 207MPa for 23min at −3°C (without ice crystal formation) enhanced microbial reduction to 3.8 log cycles for P. fluorescens and to about 0.5 log cycle for Gram+bacteria. “Pressure-shift nucleation” (PSN) from 207MPa and −21°C (i.e. cooling at 207MPa for 23min followed by pressure release in 3s) caused 1.2, 1.4 and 4.3 log cycle reductions of L. innocua, M. luteus and P. fluorescens, respectively. A reduction of 1.7 log cycle was observed for L. innocua and M. luteus (4.6 log cycle for P. fluorescens) when salmon mince was subjected to pressure-shift freezing (PSF) (i.e. PSN from 207MPa and −21°C as above followed by further freezing to −25°C at 0.1MPa). PSF with pressure release in 18min enhanced reduction to 2 and 2.5 log cycles for L. innocua and M. luteus, respectively

Processing of phosphocasein dispersions by dynamic high pressure: Effects on the dispersion physico-chemical characteristics and the binding of α-tocopherol acetate to casein micelles

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Effects of high pressure homogenisation of raw bovine milk on alkaline phosphatase and microbial inactivation. A comparison with continuous short-time thermal treatments

International audienceRaw whole milk of high microbial quality (58 degrees C), but markedly decreased above 200 MPa when Tin=24 degrees C (T2>60 degrees C). In contrast to inactivation induced by continuous short-time thermal treatments, ALP inactivation induced by HP homogenisation was clearly due to mechanical forces (shear, cavitation and/or impact) in the HP valve and not to the short (<1 s) residence time at temperature T2 in the same valve. Inactivation of the three exogenous microorganisms led to similar conclusions. Homogenisation at 250 MPa or 300 MPa (Tin=24 degrees C) induced a 2-3 log cycle reduction of the total endogenous milk flora and a 1.5-1.8 log cycle reduction of inoculated List. innocua. Higher reduction ratios (2-4 log cycles) were obtained for the two other microorganisms. The highest levels of ALP inactivation corresponded to the highest extents of microbial reduction. Running the milk twice or three times through the homogeniser (recycling), keeping temperature T1 approximately 29 degrees C and pressure=200 MPa, increased homogenisation efficiency

Effect of dynamic high pressure on whey protein aggregation: A comparison with the effect of continuous short-time thermal treatments

International audienc