Ultrasonic decontamination in smoked salmon experimentally contaminated with Listeria monocytogenes: Preliminary results

Low-frequency focused thermosonication for Salmonella typhimurium inactivation: an in vitro study

Customer requests are addressed to safe products that best express their characteristics of "naturalness" and "freshness" for their entire shelf life; therefore, scientific research has been exploring the use of "non-thermal technologies". Thermosonication using low-frequency focused ultrasound determines bacterial inactivation through the phenomenon of "cavitation", guaranteeing high-quality standards of safety, nutrition, and freshness of the products. The present work aims to evaluate the effectiveness of the inactivation of Salmonella typhimurium in culture broth by low-frequency focused thermosonication with two different operational parameters: sublethal temperature (40°C, 50°C) and treatment time (5, 10, and 15 minutes). Treatment determined a bacterial load reduction compared to the negative control (untreated inoculum), which was statistically significant at the t-test (p<0.05). Average decreases of 1.5 log and 3.5 CFU/mL were observed, respectively, after treatment and after 24 hours of storage at +4°C. Treatment at 50°C for 15 minutes was the most effective (average value: 3.06 log CFU/mL; minimum value: 2.13 log CFU/mL; maximum value: 4.59 log CFU/mL). However, strains have shown markable variability: one of them even showed an increase in the microbial load 24 hours after treatment at 40°C for 5 minutes (-0.20 log CFU/mL); however, the same treatment showed a reduction of bacterial charge in all the other strains (average value: 1.05 log CFU/mL; minimum value: -0.20 log CFU/mL; maximum value: 2.28 log CFU/mL). This study poses numerous perspectives on the use of low-frequency focused thermosonication treatment in the food industry as a sustainable and safe alternative to classic thermal treatments.

Microbial decontamination assisted by ultrasound-based processing technologies in food and model systems: A review

Ultrasound (US) technology is recognized as one of the emerging technologies that arise from the current trends for improving nutritional and organoleptic properties while providing food safety. However, when applying the US alone, higher power and longer treatment times than conventional thermal treatments are needed to achieve a comparable level of microbial inactivation. This results in risks, damaging food products' composition, structure, or sensory properties, and can lead to higher processing costs. Therefore, the US has often been investigated in combination with other approaches, like heating at mild temperatures and/or treatments at elevated pressure, use of antimicrobial substances, or other emerging technologies (e.g., high-pressure processing, pulsed electric fields, nonthermal plasma, or microwaves). A combination of US with different approaches has been reported to be less energy and time consuming. This manuscript aims to provide a broad review of the microbial inactivation efficacy of US technology in different food matrices and model systems. In particular, emphasis is given to the US in combination with the two most industrially viable physical processes, that is, heating at mild temperatures and/or treatments at elevated pressure, resulting in techniques known as thermosonication, manosonication, and manothermosonication. The available literature is reviewed, and critically discussed, and potential research gaps are identified. Additionally, discussions on the US's inactivation mechanisms and lethal effects are included. Finally, mathematical modeling approaches of microbial inactivation kinetics due to US-based processing technologies are also outlined. Overall, this review focuses only on the uses of the US and its combinations with other processes relevant to microbial food decontamination.