Purpose: The objective of this study is to evaluate the impact of ultrasound treatment on the shelf-life and sensory properties of lettuce leaves based on the evaluation of a number of safety and quality indices.
Methods: The shelf-life of lettuce leaves was analysed following the application of an ultrasonic system operating at 26kHz, 90μm, 200W in continuous mode for 5minutes. Total aerobic count, psychrotrophic bacteria, Salmonella, Enterobacteria, yeasts and moulds levels were evaluated by using appropriate selective media. Sensory aspects such as appearance, browning, texture and odours were assessed by a semi-trained panel. Multivariate analysis was applied (i.e.,principal component analysis followed by a partial least squares analysis) in order to better understand the relationships between all the experimental variable inputs (i.e.,different bacteria, sensory scores and processes/preservation conditions).
Results: Overall, it was observed that storage time had the major influence on the bacterial growth, except for Salmonella for which temperature had the main impact. The ultrasound technology can be efficient against pathogens (Salmonella spp.) specifically at lower temperatures. Regarding the sensory characteristics of lettuce leaves, ultrasound yields some negative impact on the overall quality of theproduct towards the end of its shelf-life.
Significance: This work proposes an alternative technology for the decontamination of lettuce leaves during the application of ultrasound processing. Ultrasound could guarantee the quality and safety for the consumers under specific processing and storage conditions. The potential of this technology is highlighted based on the obtained safety and sensory assessments.