La nostra ricerca è comprovata dalle numerose pubblicazioni su riviste scientifiche di riferimento in campo alimentare, biologico e di processo. A seguire una selezione dei lavori più citati (secondo l’Indice H) fra quelli pubblicati.
High pressure carbon dioxide inactivation of microorganisms in foods: The past, the present and the future
International Journal of Food Microbiology
— 2007 10
Thermal pasteurization is a well known and old technique for reducing the microbial count of foods. Traditional thermal processing, however, can destroy heat-sensitive nutrients and food product qualities such as flavor, color and texture. For more than 2 decades now, the use of high-pressure carbon dioxide (HPCD) has been proposed as an alternative cold pasteurization technique for foods. This method presents some fundamental advantages related to the mild conditions employed, particularly because it allows processing at much lower temperature than the ones used in thermal pasteurization. In spite of intensified research efforts the last couple of years, the HPCD preservation technique has not yet been implemented on a large scale by the food industry until now. This review presents a survey of published knowledge concerning the HPCD technique for microbial inactivation, and addresses issues of the technology such as the mechanism of carbon dioxide bactericidal action, the potential for inactivating vegetative cells and bacterial spores, and the regulatory hurdles which need to be overcome. In addition, the review also reflects on the opportunities and especially the current drawbacks of the HPCD technique for the food industry.
Non-thermal bacterial inactivation with dense CO2
Biotechnology and Bioengineering
— 2003 9
The use of CO2 under pressure (dense CO2) is one of the most promising techniques to achieve cold pasteurization and/or sterilization of liquid and solid materials, and is likely to replace or partially substitute currently and widely applied thermal processes. Although the ability of CO2 to inactivate microorganisms has been known since the 1950’s, only within the last 15 years it has received special attention, and the scientific and economic interest towards practical applications is presently growing more and more. Here we collect and discuss the relevant current knowledge about the potentials of dense CO2 as a non-thermal technology in the field of microbial inactivation. We summarize the state of the art, including definitions, description of the equipment, relevant applications, in both simple suspensions and complex media, for the treatment of a wide range of microorganisms in both liquid and solid substrates. Finally, we also summarize and discuss the different hypotheses about the mechanisms of inactivation.
Microbial inactivation by high-pressure
The Journal of Supercritical Fluids
— 2002 8
High-pressure treatments are receiving a great deal of attention for the inactivation of micro-organisms in foodstuff processing, pressure instead of temperature is used as stabilizing factor. In this context, high hydrostatic pressure treatment is the most studied alternative process, many works reported successful results in inactivating a wide range of micro-organisms under different operative conditions such as temperature, cycles of pressure, exposure time. Furthermore, a number of processes using high pressure treatment (HPT) has already been put into the market. Nevertheless this new technology presents the main limitation to be very expensive and difficult to control and manage because of the extremely high pressure employed, so that the widespread industrial diffusion in industry field appears cumbersome. The treatment with supercritical CO2 could become a relevant alternative to HPT in the field of microbial inactivation of food as well as an innovative technique for the sterilization of thermally and hydrolytically sensitive polymeric materials in biomedical applications, such as polymeric particles for drug delivery or polymeric implants. It has been demonstrated that the effect of microbial inactivation assuring healthy food preservation is already consistent at pressures moderated (lower than 200 bar) when compared with those employed by traditional hydrostatic-pressure HPT methods (2000–7000 bar). In this work the anti-microbial potential of compressed CO2 was investigated against gram-negative bacteria, gram-positive bacteria and spores; as model species, Pseudomonas aeruginosa, Bacillus subtilis and spores of B. subtilis were used. The experiments were performed in a semi-continous apparatus at different but mild operative conditions. Excellent results were obtained for micro-organisms, under appropriate conditions the survival ratio of bacteria could be reduced to about seven orders of magnitude. Inactivation of spores under the same conditions, found to be conflicting in open literature, was not satisfactory. Spore inactivation was possible by coupling combination of higher temperature and longer contact time conditions. The application of pressure cycles was also found to be beneficial.
Inactivation of bacteria and spores by pulse electric field and high pressure CO2 at low temperature
Biotechnology and Bioengineering
— 2003 7
he common methods for inactivation of bacteria involve heating or exposure to toxic chemicals. These methods are not suitable for heat-sensitive materials, food, and pharmaceutical products. Recently, a complete inactivation of many microorganisms was achieved with high-pressure carbon dioxide at ambient temperature and in the absence of organic solvent and irradiation. The inactivation of spores with CO2 required long residence time and high temperatures, such as 60°C. In this study the synergistic effect of pulsed electric field (PEF) in combination with high-pressure CO2 for inactivation was investigated. The bacteria Escherichia coli, Staphylococcus aureus, and Bacillus cereus were suspended in glycerol solution and treated in the first step with PEF (up to 25 KV/cm) and then with high-pressure CO2 not higher than 40°C and 200 bar. The inactivation efficiency was determined by counting the colony formation units of control and sample. Samples of the cells subjected to PEF treatment alone and in combination with CO2 treatment were examined by scanning electron microscopy to determine the effect of the processes on the cell wall. Experimental results indicate that the viability decreased with increasing electrical field strength and number of pulses. A further batch treatment with supercritical CO2 lead to complete inactivation of bacterial species and decreased the count of the spores by at least three orders of magnitude, the inactivation being enhanced by an increase of contact time between CO2 and the sample. A synergistic effect between the pulsed electric field and the high-pressure CO2 was evident in all the species treated. The new low temperature process is an alternative for pasteurization of thermally labile compounds such as protein and plasma and minimizes denaturation of important nutrient compounds in the liquid media.
High pressure carbon dioxide pasteurization of solid foods: Current knowledge and future outlooks
Trends in Food Science & Technology
— 2011 6
High pressure carbon dioxide (HPCD) technology applied to foods has gained a particular scientific interest considering the number of publications and patents published in the last decades. Although the antimicrobial effect of HPCD has been demonstrated mainly for liquid foodstuffs, very few research papers investigated the possibility to exploit the treatment on solid foods. In this concern, the main objective of the present review is to give a general survey of the published knowledge concerning the HPCD applied to solid foods. Remarks and future outlooks will be highlighted with the aim to suggest a research line to follow for future studies.
Effects of supercritical CO2 and N2O pasteurisation on the quality of fresh apple juice
— 2009 5
Supercritical pasteurisation is receiving increasing attention as an alternative technology for foodstuff pasteurisation, but often the possible effects on the perceptible quality are not sufficiently considered. To address this latter issue, besides standard microbial analysis, we here investigate the impact of CO2/N2O supercritical pasteurisation (100 bar, 36 °C and 10 min treatment time) on the quality traits of fresh apple juice, linked to consumer perception. Discriminative sensory analysis (triangle test) and basic chemical characterization (total solids, sugars, organic acids, polyphenols) could not clearly demonstrate any induced modification of the treated juice, while head space analysis of volatile compounds (both by GC–MS and PTR–MS) indicated a general depletion of the volatile compounds that must be considered in the development of a stabilization method based on supercritical gases.
Carbon Dioxide Induced Silk Protein Gelation for Biomedical Applications
— 2012 4
We present a novel method to fabricate silk fibroin hydrogels using high pressure carbon dioxide (CO2) as a volatile acid without the need for chemical cross-linking agents or surfactants. The simple and efficient recovery of CO2 post processing results in a remarkably clean production method offering tremendous benefit toward materials processing for biomedical applications. Further, with this novel technique we reveal that silk protein gelation can be considerably expedited under high pressure CO2 with the formation of extensive β-sheet structures and stable hydrogels at processing times less than 2 h. We report a significant influence of the high pressure CO2 processing environment on silk hydrogel physical properties such as porosity, sample homogeneity, swelling behavior and compressive properties. Microstructural analysis revealed improved porosity and homogeneous composition among high pressure CO2 specimens in comparison to the less porous and heterogeneous structures of the citric acid control gels. The swelling ratios of silk hydrogels prepared under high pressure CO2 were significantly reduced compared to the citric acid control gels, which we attribute to enhanced physical cross-linking. Mechanical properties were found to increase significantly for the silk hydrogels prepared under high pressure CO2, with a 2- and 3-fold increase in the compressive modulus of the 2 and 4 wt % silk hydrogels over the control gels, respectively. We adopted a semiempirical theoretical model to elucidate the mechanism of silk protein gelation demonstrated here. Mechanistically, the rate of silk protein gelation is believed to be a function of the kinetics of solution acidification from absorbed CO2 and potentially accelerated by high pressure effects. The attractive features of the method described here include the acceleration of stable silk hydrogel formation, free of residual mineral acids or chemical cross-linkers, reducing processing complexity, and avoiding adverse biological responses, while providing direct manipulation of hydrogel physical properties for tailoring toward specific biomedical applications.
Inactivation of Bacillus subtilis spores by supercritical CO2 treatment
Innovative Food Science & Emerging Technologies
— 2003 3
Bacillus subtilis spores were suspended in saline solution (107 cfu/ml) and treated by both conventional heating and CO2 batch treatment at an operating pressure in the range of 70–150 bar under identical temperature conditions. Temperatures tested were in the range of 36–75 °C. Survival curves indicated significantly higher lethality when spores were treated with supercritical CO2 (SC-CO2) rather than with heating alone. These results appear particularly evident at 60 °C, a temperature at which conventional heating gave no spore-inactivation after a treating time as long as 24 h, whereas a 6 h SC-CO2 treatment led to complete sterilization. At 75 °C spores were partially killed with conventional heating but a treatment of 2 with SC-CO2 hours assured total inactivation. It is concluded that spore-inactivation during SC-CO2 treatment was only in part due to thermal effect (at the higher temperature of 75 °C) and there was a significant additional effect caused by CO2 penetration inside the latent bacteria forms.
Determination of extracellular and intracellular pH of Bacillus subtilis suspension under CO2 treatment
Biotechnology and Bioengineering
— 2005 2
In this study, we consider the effect of carbon dioxide (CO2) on the intracellular and extracellular pH of a saline solution of a test-microorganisms Bacillus subtilis. The cytoplasmatic pH was determined by means of a flow cytometry with the fluorescent probe 5(and 6-)-carboxyfluorescein ester (cFSE). The physiological suspension of cells with the addition of the probe was first exposed to high pressure CO2 for 5 min at different temperatures. The flow cytometry analysis indicated an intracellular depletion inside the cell caused by the action of CO2, down to 3, the depletion being dependent on inactivation ratio. In addition, the extracellular pH was determined theoretically by means of the statistical associated fluid theory equation of state (SAFT EOS): it was demonstrated that CO2 under pressure dissolves into liquid phase and acidifies the medium down to 3 at 80 bar and 303.15K. The results show a strong influence between extracellular and intracellular pH, and lead to the conclusion that a strong reduction of the pH homeostasis of the cell can be claimed as one of the most probable cause of inactivation of CO2 pasteurization.
Exploitation of κ-carrageenan aerogels as template for edible oleogel preparation
— 2017 1
In the current research, oleogels were prepared by using κ-carrageenan aerogels as template. In particular, hydrogels containing increasing concentration (0.4, 1.0, and 2.0% w/w) of κ-carrageenan were firstly converted into alcoholgel and subsequently dried by using supercritical CO2 to obtain aerogels. The latter were porous and structurally stable materials with high mechanical strength. The polymer content affected the aerogel structure: increasing the initial k-carrageenan concentration a coarser structure with larger polymer aggregates was obtained. However, the aerogel obtained at intermediate polymer concentration resulted the firmest one, probably due to the formation of a less aerated and more isotropic structure. Aerogels demonstrated a reduced capacity of water vapor sorption, remaining glassy and porous at room temperature at relative humidity lower than 60%. Aerogels showed a good capacity of oil absorption. The maximum oil loading capacity (about 80%) was obtained for aerogel containing the highest κ-carrageenan content. Thus, it can be concluded that aerogels based on the structuring of water soluble polymers have potential as material for oil absorption and delivery.