Consumers increasingly demand convenience foods of the highest quality in terms of natural flavor and taste, and which are free from additives and preservatives. This demand has triggered the need for the development of a number of nonthermal approaches to food processing, of which high-pressure technology has proven to be very valuable. A number of recent publications have demonstrated novel and diverse uses of this technology. Its novel features, which include destruction of microorganisms at room temperature or lower, have made the technology commercially attractive. Enzymes and even spore forming bacteria can be inactivated by the application of pressure-thermal combinations, This review aims to identify the opportunities and challenges associated with this technology. In addition to discussing the effects of high pressure on food components, this review covers the combined effects of high pressure processing with: gamma irradiation, alternating current, ultrasound, and carbon dioxide or anti-microbial treatment. Further, the applications of this technology in various sectors— fruits and vegetables, dairy, and meat processing—have been dealt with extensively. The integration of high-pressure with other matured processing operations such as blanching, dehydration, osmotic dehydration, rehydration, frying, freezing / thawing and solid-liquid extraction has been shown to open up new processing options. The key challenges identified include: heat transfer problems and resulting non-uniformity in processing, obtaining reliable and reproducible data for process validation, lack of detailed knowledge about the interaction between high pressure, and a number of food constituents, packaging and statutory issues.

/pdf/opportunities-and-challenges-in-high-pressure-processing-of-3p4mjmljox.pdf

Opportunities and Challenges in High Pressure Processing of Foods

Current applications and new opportunities for the use of pulsed electric fields in food science and industry

Preservation of liquid foods by high intensity pulsed electric fields (PEF) is an interesting alternative to traditional techniques like thermal pasteurization. Based on the underlying mechanism of action, in this paper the crucial process parameters electrical field strength, total pulse energy input and treatment temperature were investigated experimentally. Inactivation studies were performed with three bacteria ( E. coli, Bacillus megaterium, Listeria innocua ) and one yeast ( Saccharomyces cerevisiae ). Stainless steel and carbon electrodes have been tested to investigate their applicability as electrode material. Simulating the influence of cell size and orientation as well as the presence of agglomerations or insulating particles indicated that the applied field strength has to be increased above the critical one to achieve product safety. It was found that temperatures higher than 40 °C can strongly increase the lethality of the PEF process. In this way also small cells like Listeria are easily affected by pulsed fields even at a field strength as low as 16 kV cm −1 . In addition, heating of the product prior to PEF has the advantage that most of the required process energy can be recovered using heat exchangers. Exemplary, such a process is analyzed by an enthalpy balance.

High intensity pulsed electric fields applied for food preservation

As an emerging cellulosic nanomaterial, microfibrillated cellulose (MFC) and nanofibrillated cellulose (NFC) have shown enormous potential in the forest products industry. The forest products industry and academia are working together to realise the possibilities of commercializing MFC and NFC. However, there are still needs to improve the processing, characterisation and material properties of nanocellulose in order to realise its full potential. The annual number of research publications and patents on nanocellulose with respect to manufacturing, properties and applications is now up in the thousands, so it is of the utmost importance to review articles that endeavour to research on this explosive topic of cellulose nanomaterials. This review examines the past and current situation of wood-based MFC and NFC in relation to its processing and applications relating to papermaking.

Processing of wood-based microfibrillated cellulose and nanofibrillated cellulose, and applications relating to papermaking: a review

The present review concerns homogenisation processing, and more particularly high-pressure homogenisation. Recent developments in high-pressure technology and the design of new homogenisation valves able to withstand pressures up to 350–400 MPa have indeed opened new opportunities to homogenisation processing in the dairy, pharmaceutical and cosmetic industries. Homogenisers equipped with high-pressure valves or interaction chambers of different designs, and consequently different flow characteristics (laminar or turbulent flow, cavitation, impingement on solid walls, fluid jet collision) are available. The present review will more particularly concern piston-gap type high-pressure homogenisers equipped with specially designed HP-valves able to reach 300–400 MPa for ultra-high-pressure homogenisation (UHPH). An overview of some recent UHPH studies will be summarised in the following sections including UHPH-induced microbial inactivation, characteristics of submicron emulsions and UHPH-induced protein structural changes and functionality.

Technological aspects and potential applications of (ultra) high-pressure homogenisation

High-pressure homogenisation of raw bovine milk. Effects on fat globule size distribution and microbial inactivation

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

Raw whole milk of high microbial quality (≤ 4 x 10 4 cfu/ml) was processed using a ∼ 15 l/h homogeniser with a high pressure (HP) valve immediately followed by cooling heat exchangers. The effects of homogenisation between 100 and 300 MPa (HP valve) with an initial milk temperature T in = 4 °C or 24 °C was investigated on the inactivation of: (i) endogenous alkaline phosphatase (ALP); (ii) endogenous milk flora and (iii) two Gram positive (Listeria innocua and Micrococcus luteus) and one Gram negative (Pseudomonas fluorescens) strains inoculated into milk. Temperatures T 1 and T 2 measured before and immediately after the HP valve, and fat globule size distributions were also determined. ALP activity slightly decreased after homogenisation above 250 MPa when T in = 4 °C (corresponding T 2 > 58 °C), but markedly decreased above 200 MPa when T in = 24 °C (T 2 > 60 °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 T 2 in the same valve. Inactivation of the three exogenous microorganisms led to similar conclusions. Homogenisation at 250 MPa or 300 MPa (T in = 24 °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 T 1 ≈29°C and pressure = 200 MPa, increased homogenisation efficiency.

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

The inactivation of 3 strains of Listeria innocua (S1, S2, S3) by pulsed electric fields (PEF) in a batch treatment chamber (exponential decay pulses) was studied as a function of treatment time In 16 mM Na phosphate buffer, pH 70, the resistance order of the strains to PEF (46 kV/cm, 11 Hz: S2>S1>S3) differed from that of heat resistance (60 °C: S1>S2>S3) Inactivation of L innocua S2 (in the 16 mM phosphate buffer) increased with field strength (from 17 to 45 kV/cm) or treatment time Increasing pulse repeat frequency from 11 to 100 Hz at 29 kV/cm markedly increased L innocua S2 inactivation in whole milk (pH 66) (from 067 to 18 log cycles for 250 μs of cumulated treatment time), but less so in skim milk (pH 66) No influence of pulse repeat frequency on L innocua S2 inactivation was observed in the 16 mM phosphate buffer (at 45–46 kV/cm), in 40 mM Na phosphate buffer (pH 66 at 29 kV/cm) or in liquid dairy cream (pH 67, at 30 or 37–38 kV/cm) Upon PEF processing in the 16 mM phosphate buffer at 36 or 45 kV/cm (100 Hz), the number of total survivors and of non-stressed survivors (able to grow on a selective medium) markedly decreased when the energy input to samples increased, most survivors becoming stressed L innocua S2 suspended in skim milk and subjected to PEF were observed by atomic force microscopy 3D images revealed collapsed and/or segmented bacteria

Laetitia Picart

Papers

High-pressure homogenisation of raw bovine milk. Effects on fat globule size distribution and microbial inactivation

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

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

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

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