Direct non-thermal plasma treatment for the sanitation of fresh corn salad leaves: Evaluation of physical and physiological effects and antimicrobial efficacy

• Published in: Postharvest biology and technology Vol. 84; pp. 81 - 87
• Main Authors: Baier, M., Foerster, J., Schnabel, U., Knorr, D., Ehlbeck, J., Herppich, W.B., Schlüter, O.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.10.2013; Elsevier
• Subjects: Biological and medical sciences; Chlorophyll fluorescence imaging; Escherichia coli; Food industries; Fresh produce; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; General aspects; Hygiene and safety; Noninvasive methods; Physical sanitation treatment; Postharvest quality; Physical sanitation treatment; Chlorophyll fluorescence imaging; Fresh produce; Noninvasive methods; Postharvest quality; Monocotyledones; Production quality; Postharvest; Antimicrobial agent; Sanitary control; Gramineae; Angiospermae; Pigments; Biological effect; Salad; Chlorophyll; Evaluation; Fluorescence detector; Zea mays; Plant leaf; Non thermal plasma; Physical properties; Biological activity; Fresh product; Non invasive method; Spermatophyta; Hygiene
• ISSN: 0925-5214; 1873-2356
• DOI: 10.1016/j.postharvbio.2013.03.022

•Non-thermal plasma shows high antimicrobial efficacy.•Treatments at 20W for 1min successfully inactivated Escherichia coli by 4 log-cycles.•At higher plasma power settings, heat was the main detrimental factor.•Critical process parameters must be determined to maintain product quality. Current problems with outbreaks of serious infections caused by human pathogens on fresh-cut greens highlight the need for new, optimized postharvest sanitation treatments to effectively meet recent food safety standards. In contrast to various chemical treatments, non-thermal plasma (NTP) has a high potential as a gentle target sanitation technique. However, possible interactions between NTP and the physiology of treated fresh products have not been investigated in detail. Here, chlorophyll fluorescence image analysis (CFIA) was used to study the potential impacts of non-thermal plasma on the photosynthetic activity of highly perishable corn salad leaves as a model produce. For this purpose, an atmospheric pressure plasma jet, driven at radio frequency, and transforming argon with flow rates of 20Lmin−1 into non-thermal plasma at 10, 20, 30, and 40W generator power was applied for various times to the surface of corn salad leaves. Thermographic measurements indicated maximum temperatures of 39.0°C, 44.4°C, 60.1°C, and 66.0°C, respectively, on treated leaf surfaces. CFIA revealed that treatment at moderate generator power of 20W for up to 1min was the maximum setting for quality retention. Furthermore, the microbial inactivation efficiency of the plasma jet system at these operating parameters was successfully tested on Escherichia coli bacteria, inoculated on corn salad surface at 107cfucm−2 and 104cfucm−2. At 20W, bacteria with lower initial load could be inactivated by 3.6 (±0.6) log-cycles within 15s of treatment duration; whereas at the higher initial load of 107cfucm−2, bacteria were reduced by 2.1 (±0.2) log-cycles after 30s.