Effect of Non-Thermal Atmospheric Cold Plasma on Surface Microbial Inactivation and Quality Properties of Fresh Herbs and Spices

Culinary herbs and spices are highly valued for their contribution to aroma, color, and overall flavor in traditional foods. Microbial inactivation in fresh herbs and spices is challenging due to their complex surface structures and dense natural microflora, which limit the effectiveness of conventional methods. Atmospheric cold plasma (ACP) is an innovative non-thermal technology with potential applications in the fresh spice industry. This study investigates the efficacy of ACP, generated using a practical, simple, and original system that allows uniform treatment without complex equipment, on microbial inactivation and quality attributes of fresh spices. Treatments of 1 and 3 min were applied, and their effects on natural microflora, Escherichia coli, and Pseudomonas syringae spp. were evaluated on the first day and after 7 days of storage. Results showed that 3 min treatments achieved higher reductions in natural microflora (2.91 log CFU g⁻¹), E. coli (2.76 log CFU g⁻¹), and P. syringae spp. (2.24 log CFU g⁻¹) compared to 1 min treatments (1.87, 1.93, and 1.65 log CFU g⁻¹, respectively). Different herbs exhibited varying responses to ACP, reflecting differences in leaf structure and chemical composition, which highlights the need for tailored treatment strategies. ACP treatment did not significantly affect water activity, color, or moisture content (except for rosemary, bay leaf, and thyme), nor total anthocyanin content (TAA), total phenolic content (TPC), total antioxidant capacity (TAC), or total flavonoid content (TFC). However, total chlorophyll content (TCC) and pH increased significantly in most samples (except rosemary and dill). Scanning electron microscopy (SEM) revealed that the tissue integrity of rosemary and mint was affected by ACP, although more than 50% of carvone in mint was preserved, and its concentration increased. The observed microbial reductions and 3–8-day shelf-life extension suggest meaningful improvements in safety and storage stability for industrial applications. Overall, ACP demonstrates promise as a safe, efficient, and scalable alternative to conventional decontamination methods, with broad potential for enhancing the quality and shelf life of fresh spices.