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Name of project:

Quantitative Tools for Sustainable Food and Energy in the food chain (QSAFE) (Project No: 2014-1-MT01-KA200-000327)


30/09/2015 – 28/11/2015

Name of student:

Myrsini Kakagianni

Name of supervisor:

Konstantinos Koutsoumanis

Name of host supervisor:

Vasilis Valdramidis


Effect of ultrasound on kinetic behavior of Alicyclobacillus acidoterrestris spores


Consumer demand for healthy, safe and minimally processed foods with high-quality attributes has increased in the last decades. Increased consumption of fruit juices has direct influence on economy in positive way but in negative way also when food borne disease outbreaks and spoilage problems occur. Change in the appearance, smell or taste of a food that makes it unacceptable to the consumer is called food spoilage. In recent years, Alicyclobacillus acidoterrestris has emerged as a new thermoacidophilic, endospore-forming spoilage bacterium for commercialized fruit juices that can survive pasteurization and spoil heat treated fruit juices by the production of taint chemicals (guaiacol and halophenolic). The most common method to inactivate microbial spores and enzymes for increasing the shelf life of fruit juices is by thermal processing; however, loss of original taste and flavor compounds occur in fruit juices. Therefore, non-thermal technologies, such as ultrasound, are receiving good attention as an alternative because of their potential for quality and safety improvement of food.

In this study, the objective was to investigate the effect of the ultrasound on the kinetic behaviour of Alicyclobacillus acidoterrestris spores at the population and individual level. Regarding the population level, A. acidoterrestris growth was studied in K broth (2.5g/l yeast extract; 5.0g/l peptone; 1.0g/l glucose; 1.0g/l tween 80) adjusted to pH=4.5 with filtered 25% (w/v) citric acid at 35°C and 45°C. K broth samples were either only treated with an ultrasound probe system (26 kHz, 90 μm, 200 W, 14 mm Ø) or then heat treated (at 80°C for 10min). Different processing time durations (5, 10 and 15min) were applied with continuous mode. As a control, the only heat treated (at 80°C for 10min) samples were used. As expected, with the increasing processing time the microbial lag phase, in both cases, was greater at 35°C than that at 45°C. Moreover, aiming at evaluating the lag time derived from single spores after the application of ultrasound (10min) and thermal treatment (at 80°C for 10min), using the microplate absorbance reader TECAN Xfluor 4, the distributions obtained at 40°C were wider and more dispersed, compared with the lag time distributions resulted from only heat treated samples.

Concluding, the effectiveness of the ultrasound process was dependent on the processing time duration and the incubation growth temperature. Furthermore, the heat combined with ultrasound treatment could work synergistically on delaying the germination and outgrowth of the tested bacterial spores.

This study has been co-funded by the Erasmus+ programme of the European Union (Project No. 2014-1-MT01-KA200-000327).

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Last Updated: 9 December 2015

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