Plasma-activated water can maintain quality of fresh Spirulina (Limnospira platensis, formerly Arthrospira platensis)

Abstract Spirulina ( Limnospira platensis, formerly Arthrospira platensis ) is a protein-rich cyanobacterium that has been used as a source of dietary supplements for over 50 years. However, microbial contamination during outdoor cultivation poses a major challenge, leading to nutrient degradation and reliance on drying for preservation. This study evaluated plasma-activated water (PAW) as a non-thermal alternative for microbial decontamination. Two PAW treatments, immersion and spraying, were assessed for their effects on the physicochemical and microbiological properties of Spirulina biomass. PAW immersion preserved biomass integrity for up to 21 days, with only a 6.5% weight loss compared to 20% in the control. It maintained total bacterial counts at 2 log CFU mL -1 and Escherichia coli levels below 10 CFU mL -1 , while preserving cellular integrity for 28 days, whereas the control group showed an increase in both E. coli and bacterial counts to 7 log CFU mL -1 . However, PAW immersion resulted in high nitrate/nitrite levels (~140 mg L -1 /~30 mg L -1 ), exceeding allowable limits for safe consumption. To mitigate this, PAW spraying was tested at biomass:PAW ratios of 1:5, 1:10, and 1:15, which successfully reduced bacterial loads by up to 90% without accumulation of nitrate/nitrite. The 1:10 ratio maintained bacterial counts at 1 log CFU mL -1 for 7 days, while controls increased to 4 log CFU mL -1 . These results demonstrate that PAW spraying is an effective non-thermal postharvest decontamination strategy for improving the microbiological safety of fresh Spirulina biomass.