Ultrasound technology for controlling the food safety and quality of fresh produce

Abstract

Fresh produce contain bioactive compounds with diverse beneficial health effects. Due to the consumers’ awareness about these health benefits, consumption of fresh produce has increased. However, this has been accompanied by an increase in food-borne illnesses since fresh produce, apart from having a relatively short shelf-life; it also favours the growth of pathogenic food-borne microorganisms. Thus, the demand for novel technologies that enhance food safety of fresh produce has increased with time. Furthermore, consumers also demand the use of methods that avoid the use of chemicals and have a lower impact on the nutritional content and quality of food. The objective of this research was to assess the effect of ultrasound as an alternative decontamination technology on selective chemical (peroxidase, POD and pectin methylesterase, PME enzymes) and nutritional (polyphenols and vitamin C) properties of Romaine lettuce and yellow bell pepper. For this purpose a number of different experimental protocols were assessed and further improved to achieve reproducible and accurate measurements of these chemical and nutritional indices following the application of ultrasound. This was implemented so as to decide on the optimal ultrasound treatment parameters whereby the quality of the fresh produce was not affected if it had to be used as an alternative decontamination technology. PME and POD were present at a low concentration in yellow bell peppers. In lettuce, the most effective treatment to reduce PME activity was US 5 min continuous while in the case of POD, none of the applied ultrasound treatments significantly reduced POD activity. All ultrasound treatments reduced the total polyphenol content in lettuce, therefore, it can be concluded that the investigated ultrasound processes are not suitable to treat lettuce in terms of their effect on total polyphenol concentration. In bell peppers, the ultrasound process which caused the least reduction was ultrasound applied for 5 min continuous. Vitamin C in lettuce appeared to be present in insignificant levels. In bell peppers, the ultrasound process which caused the least degradation of vitamin C was ultrasound applied for 5 min continuous. When considering all the four analysed food quality indices, in the case of bell peppers, ultrasound applied for 5 min continuous was the best process since it caused the least reduction in both polyphenol content and vitamin C. However, in the case of lettuce, further research is required related to the application of ultrasound treatment since, only in the case of PME, conclusive results were obtained in favour of ultrasound application. It can be concluded that ultrasound is a decontamination technology that has the potential to be implemented in the fresh produce industry and needs to be further investigated with respect to different food products and a number of critical quality indices.