Effects of hypochlorite as a disinfectant for hydroponic systems on accumulations of chlorate and phytochemical compounds in tomatoes
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Recently, official food surveillance discovered high residues of chlorate (ClO3 −) and perchlorate (ClO4 −) in different plant-based foods, which was the start of a big discussion in the EU Commission. There is currently no knowledge about possible ClO3 − uptake quantities in vegetable, when hypochlorite (ClO−) is used as a disinfectant in plant production facilities. Therefore, the present study is focused on the identification of interactions between ClO− applications and ClO3 − accumulations in fruit, as well as findings in terms of suitable concentrations of ClO− to ensure food safety. Primary and secondary metabolites were analyzed as well. As such, on-site produced potassium hypochlorite (1 % KClO) solution was supplemented using proportional injection control once a week for 90 min, as a disinfectant, into a recirculating tomato production system (NFT) until a free chlorine concentration of 1 mg L−1 (D I) and 2 mg L−1 (D II) was reached, respectively. The chlorate (ClO3 −) content in fruit increased from 0.01 mg (Control) to 0.22 mg (D I) and 0.25 mg ClO3 − kg−1 FW (D II). A critical assessment of these values is given in the discussion section. Contrary to the expectations, a co-occurrence of ClO3 − and ClO4 − in fruit was not found. Compared to the control, the fruit contents of lycopene were increased by 21.3 % (D I) and 33.5 % (D II) and those of ß-carotene by 9.2 % (D I) and 23.9 % (D II), when calculated on a fresh weight basis. These results changed slightly when these substances were calculated on a dry weight basis. Furthermore, ClO3 − induced stress in fruit. In this context, a significant correlation (r) and a significantly increased slope (m) compared to zero were found between ClO3 − and lycopene (r = 0.74; m = 0.10), as well as ß-carotene (r = 0.70; m = 0.01). The content of soluble solids and that of titratable acids remained unaffected.
KeywordsHypochlorite Chlorate Carotenoids Disinfectant Recirculating systems Food safety
This study was funded by the Federal Ministry of Food and Agriculture. We would personally like to thank all gardeners from the Division Biosystems Engineering for plant care during the experiments. The corresponding author wishes to thank Melanie and Eddie for providing the time to write this paper.
Compliance with Ethical Standards
Conflict of interest
All authors declares that this article has no conflict of interests.
Compliance with Ethics Requirements
This article does not contain any studies with animal or human subjects.
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