Investigating ways to improve food safety: ultrasonic salad cleaning

Abstract

Salads are prone to microbial contamination and have been reported as one of the common vehicles for foodborne pathogens that can cause foodborne diseases. Following the ban on chemical disinfectants to wash ready-to-eat (RTE) salads, the current multiple wash method, relies on its efficiency in the removal of pathogens instead of killing them. Therefore, enhancing its efficiency would be a significant achievement that would improve the microbiological safety and shelf life of RTE salads. In this thesis, the two main types of ultrasonic cleaning methods were compared, i.e. ultrasonic cleaning bath that cleans with inertial cavitation and ultrasonically activated stream (UAS) devices that clean with bubbles hosting surface wave activities. The cleaning performances of these ultrasonic cleaning devices and their potential in extending the shelf life of salads were evaluated by comparing microbial load remaining on treated salad leaves on day 0 and day 6. The effects of ultrasonic cleaning on leaf quality were examined to ensure that their cleaning mechanisms would not damage the leaf surface and leaf quality. Cleaning using ultrasonic bath achieved around 0.5 log reduction on day 0, and it did not improve shelf life because the cleaning action damaged the leaf surface. Such damage led to rapid proliferation of bacteria over shelf life, making the cleaning mechanism of ultrasonic bath unfit to be scaled up for industrial implementation. On the other hand, cleaning with UAS achieved around 1.2 and 1.5 log reduction on day 0 and the leaf samples cleaned with UAS also had significantly lower microbial load as compared to
samples cleaned without ultrasound on day 6 post cleaning. The cleaning mechanism employed in UAS devices did not cause surface damage that could affect the leaf quality and shelf life. These findings highlighted the potential of UAS systems to be scaled up for industrial implementation in improving the microbiological quality and shelf life of salad.

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Identifiers

ORCID for Timothy Leighton: orcid.org/0000-0002-1649-8750

ORCID for Charles Keevil: orcid.org/0000-0003-1917-7706

ORCID for Craig Dolder: orcid.org/0000-0002-0817-326X

ORCID for Thomas Secker: orcid.org/0000-0001-7168-8592

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