Ultrasound and heat treatment effects on Staphylococcus aureus cell viability in orange juice

• Published in: Ultrasonics sonochemistry Vol. 78; p. 105743
• Main Authors: Tahi, Akila Amir, Sousa, Sérgio, Madani, Khodir, Silva, Cristina L.M., Miller, Fátima A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.10.2021; Elsevier
• Subjects: Cell damage; Citrus sinensis; Colony Count, Microbial; Heat treatment; Hot Temperature; Kinetic inactivation modelling; Special Section: Ultrasound Food Processing; Staphylococcus aureus; Thermosonication; Ultrasonics; Ultrasound; Thermosonication; Heat treatment; Cell damage; Ultrasound; Kinetic inactivation modelling; Staphylococcus aureus
• ISSN: 1350-4177; 1873-2828
• DOI: 10.1016/j.ultsonch.2021.105743

[Display omitted] •Thermosonication (TS) was more effective than sonication and heat treatment alone.•Ultrasounds reduced the bacterial counts by 4 log cycles at the end of treatments.•TS leads to 5-log reductions at 50 and 60 °C after 1 and 25 min, respectively.•Weibull model was adequate to describe the majority of the inactivation behaviour.•Morphological changes were observed in S. aureus TS-treated cells by SEM images. Ultrasounds are being considered an excellent alternative technology in juice preservation. Yet, when combined with heat treatment, the process seems to be further intensified. This work aimed to evaluate and compare the impact of ultrasounds and heat treatments, when applied alone or in combination, on Staphylococcus aureus survival in orange juice. Inoculated commercial pasteurized orange juice was treated at different times at 20, 30, 40, 50 and 60 °C. SEM analyses were applied to identify morphological changes in S. aureus cells appearance. The microbial inactivation data were fitted using two mathematical models, depending on the behaviour observed. Sonication at 20, 30, and 40 °C induced 4.02 ± 0.52, 3.80 ± 0.49 and 4.30 ± 0.74 log cycles reduction of S. aureus after treatments of 90, 60 and 60 min, respectively. The heat treatments at the same temperatures had no impact on S. aureus survival. When 50 and 60 °C were applied, more than 5-log reductions were attained for both thermosonication and heat treatments alone. A synergistic effect was observed between sonication and high temperatures. At 50 °C, the thermosonication reduced the treatment time from 60 to 35 min and the microbial load from 5.14 ± 0.08 to 10.76 ± 0.28 log cycles reduction, compared to heat treatment alone. Results from SEM images showed that cells undergo membrane damage during sonication exposure. This was observed by collapsed cells, cell disruption, and holes in the cell’s membrane. Thermosonication proved to be a viable alternative to thermal pasteurization of orange juice since milder treatments can be safely applied, improving the final product quality.