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 by the use of supercritical carbon dioxide (scCO 2) 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 10 MPa, at two different temperatures (40 and 50 °C) with drying time of 0 and 150 min 2 to establish the influence of each parameter on the microbial inactivation. Yeasts and molds appeared to be the least resistant to scCO 2 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 scCO 2 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.

Viability of Molds and Bacteria in Tempeh Processed with Supercritical Carbon Dioxides during Storage

“…Other finding showed that yeasts and molds were undetected in herbs dried with supercritical CO 2 at 10 MPa for 150 min “Zambon [15]” which was in agreement with our results. The type and chemical contents of products processed with the supercritical CO 2 could be the reason for differences in findings.…”

Supercritical CO2 drying of food matrices

“…The plant includes a CO2 tank, kept at room temperature, a chiller reservoir (M418-BC MPM Instruments, Milan, Italy), a HPLC pump (307 Gilson, Milan, Italy), and a thermostatic water bath (ME-Julabo, Seelbach, Germany) to keep the vessel at the desired temperature. Further details of the reactor and drying procedure are reported elsewhere [11,13]. Experiments were carried out between 40/60°C and 100/140 bar up to 16 hours of drying for red peppers, while 40°C and 100 bar were chosen for the other food products.…”

“…Samples were weighted before (Wstart) and after (Wend) the treatment and the weight loss in terms of percentage ∆W was calculated as (Wstart-Wend)/Wstart. Chemical characterization was performed for flavonoids as previously described [11]. For all the HPLC analysis an Agilent 1260 system equipped with Diode array (126 series) and Ion trap Mass spectrometer (Varian/Agilent MS500) were used.…”

“…Mesophilic bacteria, mesophilic bacterial spores and yeasts and molds were counted before and after the treatments by means of the standard plate count technique, as previously described [11]. Breefly, mesophilic bacteria and spores were cultured using total plate count agar (Microbial Diagnostici, Catania, Italy) at 30°C within pour plate, while yeasts and molds were cultured with DRBC agar (Bitec S.r.l., Grosseto, Italy) supplemented with chloramphenicol at 22°C within spread plate.…”

“…Recently the use of carbon dioxide at supercritical conditions (Sc-CO2) has been investigated as alternative drying food process, specifically for carrots [8], basil [9], mango and persimmon [10] and coriander [11], demonstrating to be a promising process for the retention of the original structure and the preservation of the most valuable compounds. Within Sc-CO2 drying the vapour-liquid interface can be avoided meaning that the water is removed as a liquid dissolved in the supercritical fluid.…”