Novel antimicrobial agents as alternative to chlorine with potential applications in the fruit and vegetable processing industry

There has been an increasing demand for fresh fruit and vegetables in recent years. Along the processing line in fresh-cut vegetable production, disinfection is one of the most important processing steps affecting the quality and safety, and the shelf-life of the end produce. Although a range of antimicrobial compounds commonly termed biocides or disinfectants are available, chlorine has long been used to disinfect washing waters of fresh cut vegetables. However, since chlorine reactions with organic matter lead to the production of by-products, alternative disinfectants to chlorine must be evaluated. A synthetic washing water formula has been developed to determine the antimicrobial efficiency of different families of potential disinfectants: quaternary ammonium compounds (QACs) as benzalkonium chloride (BZK), and didecyldimethylammonium chloride (DDAC); isothiazolinones (mixture of methylchloroisothiazolinone and methylisothiazolinone, CMIT:MIT 3:1 and 1:1); and essential oils (carvacrol, CAR). The twin configuration and higher length of the chains of alkyl groups of DDAC compared to BZK have led to a higher antimicrobial efficiency. In both cases, Gram-positive bacteria seemed to be much more sensitive to the QAC attack than Gram-negative. The opposite happened for CMIT:MIT. The chloro-substituted isothiazolinone (CMIT) has been proven to be much more effective than its unsubstituted form (MIT). In addition, in contrast to chlorine, its antimicrobial activity together with that of DDAC was not decreased when increasing the organic matter content of the water. Synergetic antimicrobial effects have been confirmed when combining BZK and CAR. MBC values were determined in SWW, during 90 s of contact time and Salmonella concentration of 10(3) CFU/mL, corresponding to: 100 (BZK), 30 (DDAC), 50 (CMIT:MIT 3:1), 100 (CMIT:MIT 1:1), 300 (CAR), 75 (BZK)-200 (CAR), and 9 (free chlorine) mg/L. MBC values for inactivating similar concentration of E. faecalis corresponded to: 50 (BZK), and 10 (DDAC) mg/L. Increasing contact times up to 5 min did not lead to higher antimicrobial efficiencies. CMIT:MIT 3:1 together with DDAC, and combinations of BZK-CAR seem to be a plausible alternative to chlorine.