Sara Spilimbergo

Microbial inactivation by high-pressure

Abstract 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 CO 2 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 CO 2 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 Bacillus subtilis spores by supercritical CO2 treatment

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.

High-Power Ultrasound Assisted High-Pressure Carbon Dioxide Pasteurization of Fresh-Cut Coconut: a Microbial and Physicochemical Study

A combined treatment based on high-pressure carbon dioxide and high-power ultrasound (HPCDxa0+xa0HPU) technologies was investigated for the pasteurization of fresh-cut coconut. Inactivation kinetics of both the natural microbiota and Salmonella enterica typhimurium spiked on the product, were determined at 12xa0MPa and 10xa0W, delivered every 2xa0min of treatment, as a function of temperature (from 24 to 50xa0°C) and treatment time (from 5 up to 30xa0min). Additionally, to study the effect of HPCDxa0+xa0HPU on the quality of the product, physicochemical attributes (total acidity, pH, color, texture, dry matter, fat content, enzymatic activity, antioxidant capacity, phenols, flavonoids, and phenolic acids) were measured after the combined treatment and during a refrigerated shelf life of 4xa0weeks. The results revealed that HPCDxa0+xa0HPU increased microbial inactivation rates compared with HPCD alone: 8 log reductions of S. typhimurium were achieved with HPCDxa0+xa0HPU at 12xa0MPa, 40xa0°C, 20xa0min, while just a 4 log reduction was achieved with HPCD alone. Similar results were obtained for the natural microbiota; milder conditions of temperature and pressure were sufficient to assure inactivation to undetectable levels even of mesophilic microorganisms, the most resistant ones. Total acidity and pH did not change after the combined treatment and during the entire storage of 4xa0weeks while slight differences were observed for the other physicochemical parameters. Overall, the results showed the feasibility and the potential of HPCDxa0+xa0HPU as an innovative non-thermal technology for the pasteurization of fresh-cut fruits.AbstractA combined treatment based on high-pressure carbon dioxide and high-power ultrasound (HPCD + HPU) technologies was investigated for the pasteurization of fresh-cut coconut. Inactivation kinetics of both the natural microbiota and Salmonella enterica typhimurium spiked on the product were determined at 12 MPa and 10 W, delivered every 2 min of treatment, as a function of temperature (from 24 to 50 °C) and treatment time (from 5 up to 30 min). Additionally, to study the effect of HPCD + HPU on the quality of the product, physicochemical attributes (total acidity, pH, color, texture, dry matter, fat content, enzymatic activity, antioxidant capacity, phenols, flavonoids, and phenolic acids) were measured after the combined treatment and during a refrigerated shelf life of 4 weeks. The results revealed that HPCD + HPU increased microbial inactivation rates compared with HPCD alone: 8 log reductions of S. typhimurium were achieved with HPCD + HPU at 12 MPa, 40 °C, 20 min, while just a 4 log reduction was achieved with HPCD alone. Similar results were obtained for the natural microbiota; milder conditions of temperature and pressure were sufficient to assure inactivation to undetectable levels even of mesophilic microorganisms, the most resistant ones. Total acidity and pH did not change after the combined treatment and during the entire storage of 4 weeks, while slight differences were observed for the other physicochemical parameters. Overall, the results showed the feasibility and the potential of HPCD + HPU as an innovative non-thermal technology for the pasteurization of fresh-cut fruits.

In Situ Raman Analysis of CO2—Assisted Drying of Fruit-Slices

This work explores the feasibility of applying in situ Raman spectroscopy for the online monitoring of the supercritical carbon dioxide (SC-CO2) drying of fruits. Specifically, we investigate two types of fruits: mango and persimmon. The drying experiments were carried out inside an optical accessible vessel at 10 MPa and 313 K. The Raman spectra reveal: (i) the reduction of the water from the fruit slice and (ii) the change of the fruit matrix structure during the drying process. Two different Raman excitation wavelengths were compared: 532 nm and 785 nm. With respect to the quality of the obtained spectra, the 532 nm excitation wavelength was superior due to a higher signal-to-noise ratio and due to a resonant excitation scheme of the carotenoid molecules. It was found that the absorption of CO2 into the fruit matrix enhances the extraction of water, which was expressed by the obtained drying kinetic curve.

Enzymatic, physicochemical, nutritional and phytochemical profile changes of apple (Golden Delicious L.) juice under supercritical carbon dioxide and long-term cold storage

The impact of supercritical carbon dioxide (SCCD) (10-60u202fMPa/45u202f°C/30u202fmin) and subsequent 10u202fweeks storage at 4u202f°C on polyphenol oxidase (PPO), peroxidase (POD) activities, phenolic profile, vitamin C, sugars, physicochemical properties of cloudy apple juices was investigated. No significant changes in sugars and total polyphenols were observed, whereas significant degradation (≈28%) of vitamin C and individual polyphenols (≈18%) was noted after SCCD treatment. After 4u202fweeks storage only 34% of vitamin C was retained and no vitamin C was detected after this time. Ten weeks of storage caused hydrolysis of sucrose in 15%, whereas degradation of individual polyphenols ranged from 43 to 50% depending on the pressure applied. The highest pressure was applied the highest retention of polyphenols was observed. The lightness of juice significantly increased by 15% after SCCD and decreased during storage. Moreover, the synergistic effect of both enzymes with chlorogenic acid and catechol was found.

Microbial inactivation efficiency of supercritical CO2 drying process

ABSTRACT Conventional drying of spices, as hot air treatment, often needs an additional downstream inactivation step to decrease the microbial load of the dried product and improve its microbial safety and microbial quality. In this regard, the present work explored the possibility to dry and decontaminate food in a single step using supercritical carbon dioxide (scCO2) as a drying agent. A case study was focused on the drying of herbs and the antimicrobial effects were evaluated on the naturally present microbiota. For this purpose, experiments were carried out on coriander leaves using a high pressure vessel at 10u2009MPa, at two different temperatures (40 and 50°C) with drying time of 0 and 150u2009min to establish the influence of each parameter on the microbial inactivation. Yeasts and molds appeared to be the least resistant to scCO2 as they could never be detected after the treatment (<2 log CFU/g). Mesophilic bacteria were also significantly reduced, up to 4 log CFU/g, but remained above the limit of quantification. The quality of the dried product was comparable with the quality of air-dried samples in terms of phenolic constituents. Overall, the results indicated that scCO2 drying was a promising green drying technique combining both drying and microbial inactivation in a single step with a relevant impact on safety and costs.