Effect of cold plasma treatment on microbial load, color and cuticle in baby kale (Brassica oleracea)

Urvi Bharat Shah

doi:10.17918/etd-7404

Kale leaves are consumed worldwide because of their promoting health and nutritional benefits. However, in the past two decades, there has been an increase in foodborne diseases outbreaks caused by microorganisms associated with leafy vegetables. Leafy vegetables are majorly consumed raw or are minimally processed, increasing the risk of pathogenic entry. The food industry faces challenges in improving food safety while maintaining quality of the food. Chemicals in water wash and heat treatments (70oC to 121oC) are the most common industrial methods of killing microorganisms which have negative effect on the aesthetic quality (color) and nutritional properties of the product respectively. Cold plasma treatment of fresh produce, an emerging food preservation process, is a fast and environmental- friendly process that disinfects the product at a low temperature (30-40oC). It uses an ionized gas comprised of charged ions and free electrons for treatment of the product. Cold plasma kills microorganisms by altering their metabolic pathways. This suggests that this technology may also modify chemical and physical surface properties of food product. Till date, very little research has been focused on the effect of cold plasma on the quality and shelf life of fresh produce. The purpose of this study was to evaluate the efficacy of cold plasma technology in disinfecting baby kale leaves and to study its effect on color and cuticle composition. Cuticle is the extracellular wax present on the surface of leaves and forms a protective barrier between product surface and environment. Baby kale leaf samples were treated with cold plasma system for different treatment times and color and microbial load was evaluated at each treatment time. Untreated leaves and leaves treated with tap water mist were used as control. Cuticle analysis was conducted for samples treated with plasma mist at 240s. This research demonstrated the ability of the cold plasma system in complete inactivation of E. coli O157:H7 when baby kale leaves were treated with plasma for 300s. The number of viable microorganisms (E. coli) in baby kale leaves reduced from 3.3x102 ± 330 CFU/mL to 0.0 ± 0.0 CFU/mL when the plasma treatment time was increased from 60s to 300s respectively. While no significant changes in color values were observed when baby kale leaves were treated with plasma for 300s, leaf damage and extreme browning was observed in leaves treated with plasma for 600s. Tap water was used as a control for plasma treatment. At each treatment time, lower microbial load was observed for plasma treated leaves compared to tap water treated leaves. Further, tap water treated leaves at 300s and untreated leaves showed extremely high browning index of 109.0 ± 8.0 and 80.1 ± 6.2 respectively, after 12 days of storage in refrigerator compared to plasma treated leaves. On the other hand, plasma treatment enhanced color stability of the leaves during storage and their browning index value did not exceed 62.7 ± 7.1. Plasma treatment of 240s resulted in cuticular changes but further studies are required to examine the extent of change. These results show potential of cold plasma technology as an efficient disinfection technology which not only kills microorganisms, but may enhance shelf life of fresh leafy greens.

Effect of cold plasma treatment on microbial load, color and cuticle in baby kale (Brassica oleracea)

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Effect of cold plasma treatment on microbial load, color and cuticle in baby kale (Brassica oleracea)

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