The consumption of fresh cut fruits and vegetables continues to increase, but the use of chemical preservatives not always are able to guarantee the safety of fresh cut fruits and vegetables during their shelf-life that is of 4-10 days at refrigerated temperatures. For this reason, scientists are stimulated to develop alternative methods for increasing the safety and the shelf-life of fresh cut produce.
Recently, the use of protective cultures, particularly lactic acid bacteria (LAB), microorganisms from indigenous microflora and their antimicrobial products, has been proposed for fresh cut produce. In this perspective, Italian scientists from University of Bologna have published a review to summarize the state-of-the-art application of biocontrol agents in minimally processed fruits and vegetables and their action mechanisms against spoilage and/or pathogenic microorganisms.
The same research team led by Siroli Lorenzo characterized several LAB strains isolated from commercial minimally processed fruits and vegetables for their ability to grow at low temperatures and low pH values and to antagonize the pathogenic species frequently associated with these food products. Scientists selected Lactobacillus plantarum V7B3 and Lactobacillus casei V4B4 to be used as biocontrol agents alone or in combination with thyme essential oil (EO) in lamb's lettuce.
The results obtained indicated that applying the Lb. plantarum V7B3 strain to lettuce during the washing phase at a level of 6 log CFU/ml instead of chlorine increased product shelf-life and safety. In fact, Lb. plantarum V7B3 showed an interesting potential for controlling Listeria monocytogenes and Escherichia coli when deliberately inoculated in washing solution at levels ranging between 3 and 4 log CFU/ml.
Scientists experienced also the use of Lactococcus lactis CBM21 and/or thyme EO added in the tap water used for lamb's lettuce washing at the industrial level, confirming their potential as an alternative to chlorine. The products obtained with the innovative washing solutions showed the same safety and shelf-life of the control but with improved sensorial properties. Moreover, the products added with the biocontrol agent maintained a good appearance for up to 12 days.
From review result encouraging effects of biocontrol agents on the safety and shelf-life of fresh cut fruits and vegetables. The results also highlight the importance of the isolation and selection of appropriate biocontrol agents from the products themselves. In fact, the superior performance of the strains used was not only against deliberately inoculated pathogens but also against spoilage microorganisms that are naturally present in fruits and vegetables.
These abilities have been attributed to the capability of the strains to colonize the product and survive under the stringent conditions of refrigerated storage. In addition, the ability of biocontrol agents to not adversely affect the quality of the product is important.
Scientists conclude that some of the proposed biocontrol agents, especially in combination with other preservative methods, may represent a good strategy to increase the safety and shelf-life of minimally processed fruits and vegetables. However, the introduction of biocontrol agents can be further optimized by focusing on the level and mode of inoculation and by limiting the negative effects observed on the colour parameters.
