Applications of ultrasound in analysis, processing and quality control of food: A review

Inactivation of microbes using ultrasound: a review.

The consumers' demand for fresh fruits and vegetables has increased in recent years. These foods may be consumed raw or minimally processed, and therefore can be a vehicle of several pathogens. The microorganisms most frequently linked to produce-related outbreaks include bacteria ( Salmonella spp., Listeria monocytogenes , Escherichia coli , and Shigella spp.), viruses and parasites. There are many traditional technologies to reduce/eliminate the microorganisms present in food products. However, further research on this topic is still required, since none of the methods reported can control all the parameters necessary to achieve produce with an extending shelf-life, without compromising its quality. In this paper, an analysis of the alternative and traditional methodologies is made, pointing out the significant advantage and limitations of each technique. Industrial relevance The significant increase in the incidence of foodborne outbreaks caused by contaminated minimally processed produce in recent years has become of extreme importance. The extensive knowledge of gentle (non-thermal) processes to enhance safety, preservation and shelf-life of these products is crucial for the food industry. This manuscript presents non-thermal processes that have shown efficient microbial reductions on fresh produce and highlights some of their challenges and limitations.

Fresh fruits and vegetables—An overview on applied methodologies to improve its quality and safety

In the last decade power ultrasound has emerged as an alternative processing option to conventional thermal approaches for pasteurisation and sterilisation of food products. While sonication alone may not be adequate for inactivation of various spoilage and harmful enzymes present in food, ultrasound in combination with mild heat treatment and/or pressure has shown potential for both enzyme and pathogen inactivation. Numerous studies have investigated ultrasound for inactivating enzymes such as pectinmethylesterase, polyphenoloxidases and peroxidases responsible for deterioration of fruit & vegetable juice and various enzymes pertinent to milk quality. The efficacy of ultrasound for the inactivation of enzymes in food is outlined in this review along with a description of the inactivation mechanism to elucidate the effect of ultrasound on important enzymes in fruit juices and dairy products.

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Effect of ultrasonic processing on food enzymes of industrial importance

The use of many rapid detection technologies could be expanded if the bacteria were separated, concentrated, and purified from the sample matrix before detection. Specific advantages of bacterial concentration might include facilitating the detection of multiple bacterial strains; removal of matrix-associated assay inhibitors; and provision of adequate sample size reduction to allow for the use of representative food sample sizes and/or small media volumes. Furthermore, bacterial concentration could aid in improving sampling techniques needed to detect low levels of pathogens or sporadic contamination, which may perhaps reduce or even eliminate the need for cultural enrichment prior to detection. Although bacterial concentration methods such as centrifugation, filtration, and immunomagnetic separation have been reported for food systems, none of these is ideal and in many cases a technique optimized for one food system or microorganism is not readily adaptable to others. Indeed, the separation and subsequent concentration of bacterial cells from a food sample during sample preparation continues to be a stumbling block in the advancement of molecular methods for the detection of foodborne pathogens. The purpose of this review is to provide a detailed understanding of the science, possibilities, and limitations of separating and concentrating bacterial cells from the food matrix in an effort to further improve our ability to harness molecular methods for the rapid detection of foodborne pathogens.

Bacterial Separation and Concentration from Complex Sample Matrices: A Review

Summary The effectiveness of power ultrasound for the microbial decontamination of minimally processed fruits and vegetables was studied. Reductions in Salmonella typhimurium attached to iceberg lettuce obtained by cleaning with water, chlorinated water, ultrasound with water and ultrasound with chlorinated water were 0.7, 1.7, 1.5 and 2.7 logs, respectively, for small-scale (2 L) trials. The cleaning action of cavitation appears to remove cells attached to the surface of fresh produce, rendering the pathogens more susceptible to the sanitizer. For large-scale (40 L) trials, the addition of chlorine to water in the tank gave a systematic difference in Escherichia coli decontamination efficiency. However, the frequency of ultrasound treatment (25, 32–40, 62–70 kHz) had no significant effect on decontamination efficiency (P > 0.69). With the potentially high capital expenditure together with the expensive process of optimization and water treatment, it is unlikely that the fresh produce industry would be willing to take up this technology. Furthermore, the additional one log reduction achieved by applying ultrasound to a chlorinated water wash does not completely eliminate the risk of pathogens on fresh produce.

R. L. Smith

Papers

Ultrasound decontamination of minimally processed fruits and vegetables