Publication
Milk preservation by ultrasound technology: Thermosonication and thermal inactivation of Staphylococcus aureus
| Summary: | Milk, while being a very nutritive liquid, is also extremely perishable. In addition, if not properly preserved, milk can endanger consumer’s health due to the potential growth of pathogenic microorganisms that might be present. Heat is the most common method used by the dairy industry for microbial inactivation and milk pasteurization. However, thermal treatments have negative effects on milk nutrients and structure, which are important for human nutrition and to produce other dairy products. Therefore, non-thermal technologies are being developed and studied for the inactivation of microorganisms. Ultrasound utilizes soundwaves that are above the hearing range for humans. When acoustic waves pass through a liquid, food cavitation occurs, with lethal effects on microorganisms. Ultrasound can be combined with heat (thermosonication, TS) for more efficient microbial inactivation. The main objective of this study was to evaluate the efficacy of thermosonication treatments for Staphylococcus aureus pathogen inactivation in whole milk. Thermal inactivation alone was also assessed. The thermal and TS inactivation kinetics were modeled, and thermal resistance parameters were determined. TS treatments using 10 W/mL and isothermal temperatures (58 ºC, 63 ºC, and 66 ºC) were carried out. Exclusively thermal inactivation was investigated for 58 ºC, 63 ºC, 66 ºC, and 72 ºC. Thermosonication demonstrated a significant advantage over conventional thermal inactivation for all tested temperatures. Ultrasound at 58 ºC was much more efficient for S. aureus inactivation, reducing the D-value from 27.93 ± 1.73 to 1.99 ± 0.07 minutes. Reductions in the D-values of much lower magnitude were observed at higher temperatures: at 63 ºC, the D-value decreased from 2.12 ± 0.15 to 1.20 ± 0.07 minutes, and at 66 ºC, it dropped from 1.02 ± 0.06 to 0.14 ± 0.02 minutes. Ultrasound is a promising technology to speed up microbial inactivation and reduce temperatures or times required for milk pasteurization. |
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| Main Authors: | Vaz, Vasco Prata Proença |
| Subject: | milk safety pasteurization heat assisted ultrasound mathematical modeling thermal resistance segurança do leite pasteurização ultrassons assistidos com calor modelação matemática resistência térmica |
| Year: | 2024 |
| Country: | Portugal |
| Document type: | master thesis |
| Access type: | embargoed access |
| Associated institution: | Universidade de Lisboa |
| Language: | English |
| Origin: | Repositório da Universidade de Lisboa |
| Summary: | Milk, while being a very nutritive liquid, is also extremely perishable. In addition, if not properly preserved, milk can endanger consumer’s health due to the potential growth of pathogenic microorganisms that might be present. Heat is the most common method used by the dairy industry for microbial inactivation and milk pasteurization. However, thermal treatments have negative effects on milk nutrients and structure, which are important for human nutrition and to produce other dairy products. Therefore, non-thermal technologies are being developed and studied for the inactivation of microorganisms. Ultrasound utilizes soundwaves that are above the hearing range for humans. When acoustic waves pass through a liquid, food cavitation occurs, with lethal effects on microorganisms. Ultrasound can be combined with heat (thermosonication, TS) for more efficient microbial inactivation. The main objective of this study was to evaluate the efficacy of thermosonication treatments for Staphylococcus aureus pathogen inactivation in whole milk. Thermal inactivation alone was also assessed. The thermal and TS inactivation kinetics were modeled, and thermal resistance parameters were determined. TS treatments using 10 W/mL and isothermal temperatures (58 ºC, 63 ºC, and 66 ºC) were carried out. Exclusively thermal inactivation was investigated for 58 ºC, 63 ºC, 66 ºC, and 72 ºC. Thermosonication demonstrated a significant advantage over conventional thermal inactivation for all tested temperatures. Ultrasound at 58 ºC was much more efficient for S. aureus inactivation, reducing the D-value from 27.93 ± 1.73 to 1.99 ± 0.07 minutes. Reductions in the D-values of much lower magnitude were observed at higher temperatures: at 63 ºC, the D-value decreased from 2.12 ± 0.15 to 1.20 ± 0.07 minutes, and at 66 ºC, it dropped from 1.02 ± 0.06 to 0.14 ± 0.02 minutes. Ultrasound is a promising technology to speed up microbial inactivation and reduce temperatures or times required for milk pasteurization. |
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