A case study on Norwegian commercial harvesting and production of Saccharina latissima (part 2): Strategies for food safety sampling of farmed seaweed

In Europe, seaweed cultivation for food and feed is shifting from small to large-scale production. Various food safety hazards, ranging from iodine to metals, allergens, and pathogens, may occur in seaweed, and with upscaling seaweed production, an increased need to ensure food safety is required. However, little guidance is available for food business operators (FBOs) on how to set up sampling schemes efficiently and reliably for food safety control. Therefore, this study aimed to explore sampling strategies for food safety hazards during commercial-scale seaweed harvesting. We used a commercial harvest of the brown seaweed Saccharina latissima (commonly known as sugar kelp), grown in Norway and harvested in May 2022, as a case study. We analyzed iodine, metals (including inorganic arsenic), the allergen tropomyosin, and four pathogens during harvesting and seaweed processing. We found that different hazards required different approaches for reliable sampling. For most hazards, there was no need to pre-process (i.e., cut and mix) seaweed samples before sending small subsamples to the laboratory. We found that for farm-cultivated S. latissima, determining a reliable estimate within a large seaweed batch required fewer samples for contaminants with low within-batch variation (e.g., observed for iodine) than for contaminants with a more scattered distribution or larger variability (e.g., observed for tropomyosin and copper). When an FBO aims to determine the effect of processing on hazards, taking one sample from three different seaweed batches is sufficient for hazards that show little variation and a large processing effect (iodine in our study). However, taking individual samples from five different batches is preferred for contaminants that show a moderate processing effect (inorganic arsenic and cadmium in our study). Finally, for contaminants that strongly vary within batches (copper and tropomyosin in this study), replicate sampling of three batches is considered the optimal strategy. This study provides a basis for seaweed stakeholders, including FBOs, to optimize further the risk-based sampling strategy of cultivated S. latissima.