Supercritical carbon dioxide combined with high power ultrasound: An effective method for the pasteurization of coconut water

• Ultrasound (HPU) enhanced supercritical carbon dioxide (SC-CO2) inactivation of Salmonella enterica and natural microbial flora in coconut water.
• SC-CO2 + HPU inactivation kinetics were highly dependent on the type of microorganisms tested and the temperature conditions.
• 4 weeks shelf life was assured for SC-CO2 + HPU treated coconut water without any regrowth phenomena.

Industrially, thermal treatments are extensively used to inactivate microorganisms in foods. However, the demand for new pasteurization methods with reduced impact on the nutritional content and overall food quality is increasing. In this context, this study investigated and compared the effect of supercritical carbon dioxide (SC-CO2) alone or in combination with high power ultrasound (HPU) on both the natural microbial flora (mesophilic, lactic acid bacteria and yeast and molds) of coconut water and the pathogenic Gram-negative bacteria Salmonella enterica inoculated in the product. Inactivation kinetics were obtained at 12 MPa, by means of batch apparatuses, at different times (from 1 up to 60 min) and temperature conditions (from 25 up to 45 °C). The synergistic effect of SC-CO2 + HPU was evident and a higher microbial reduction was achieved compared to SC-CO2 alone: at 12 MPa and 40 °C about 5 log reductions were achieved for natural microbial flora in about 15 min while about 30 min were needed for SC-CO2 treatment. The storage study highlighted that SC-CO2 treated coconut water resulted microbiologically unstable and showed heavy regrowth phenomena during the storage, while, a full shelf life of 4 weeks was assured for SC-CO2 + HPU treated samples.

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