Gluten contamination in manufactured gluten-free foods in Turkey: a five-year follow-up study

This study presents a five-year follow-up assessment of gluten contamination in domestically manufactured gluten-free foods (mGFFs) in Turkey, building upon the first nationwide survey conducted between 2016 and 2018. A total of 253 samples from 67 companies collected between 2023 and 2025 were analysed using an ELISA method with a 5 mg kg^-1 limit of quantification. Results were evaluated across nine product categories, eight main ingredient groups, and four company-level contamination profiles. During this period, the market expanded by 27% in product count and tripled in manufacturer number, reflecting rapid diversification. Gluten contamination was assessed at both 5 and 20 mg kg^-1 thresholds. Findings revealed a substantial increase in contamination, with 34.0% of products exceeding 5 mg kg^-1 and 18.6% surpassing 20 mg kg^-1, compared with 28.5 and 17.5% observed during 2016-2018. Buckwheat remained a major contributor, while chickpeas, oats, and maize emerged as additional ingredients with higher risk. When normalised to total market share, cereal mixtures and buckwheat accounted for over 20% of contaminated items, with maize, oats, and chickpeas contributing an additional 10%. At the company level, contamination control was very variable, with only a minority of manufacturers consistently maintaining <5 mg kg^-1, while others showed recurrent low- or high-level contamination across product lines.