Ready-To-eat vegetables : microbial quality and active packaging solutions

Ready-To-eat (RTE) vegetables belong to the convenience foods category: They offer features like freshness, commodity of use and good retention of nutritional qualities. Nevertheless, as the raw material is characterized by a high enzymatic content and water activity, it represents an excellent substrate for microorganisms. For these reason, microbial growth is a key factor in RTE product deterioration. Total bacterial count (TBC) was taken as the most relevant index to define hygiene and quality. Lactic acid bacteria, yeasts and moulds were present only occasionally. TBC was found lower when the product is packed under modified atmosphere. Gram-negative aerobic rods are dominant in air-packaged products, whilst the presence of Enterobacteriaceae becomes important in salads packaged under Modified Atmosphere. Pseudomonas fluorescens was the most frequently found species among the aerobic isolates, whilst for the Enterobacteriaceae strains no dominant species was found. These isolated strains were tested for their sensitivity against two natural antimicrobial compounds, carvacrol (essential oil, active in vapour form), and ethyl-lauroyl-Arginate (LAE, water soluble). Sensitivity was compared with that evidenced for strains belonging to official collections. Near 60 % of the tested Gram negative bacteria were found sensitive to LAE at a concentration of 20 mg/L, and near 90 % at 50 mg/L. Instead, carvacrol antimicrobial activity seemed more strain specific and not evidenced against lactic acid bacteria (LAB). A higher antimicrobial effect was found when the two antimicrobials were used in association. This combined approach, effective both in vapour and liquid phase, can represent an innovative solution to increase shelf life of RTE products.