Chlorotyrosines versus Volatile Byproducts from Chlorine Disinfection during Washing of Spinach and Lettuce

Abstract

Following the Food Safety Modernization Act of 2011 in the U.S., guidelines for disinfection washes in food packaging facilities are under consideration to control pathogen risks. However, disinfectant exposures may need optimization because the high concentrations of chlorine disinfectant promote the formation of high levels of disinfection byproducts (DBPs). When chlorine doses up through the 200 mg/L as Cl range relevant to the current practice were applied to spinach and lettuce, significant DBP formation was observed, even within 5 min at 7 °C. Concentrations of volatile chlorinated DBPs in washwater were far higher than typically observed in disinfected drinking water (e.g., 350 μg/L 1,1-dichloropropanone). However, these DBPs partitioned to the aqueous phase and so represent a greater concern for the disposal or reuse of washwater than for consumer exposure via food. The volatile DBPs represent the low-yield, final products of chlorination reactions with multiple biomolecular precursors. The initial, high-yield transformation products of such reactions may represent a greater concern for consumer exposure because they remain bound within the biopolymers in food and would be liberated during digestion. Using protein-bound tyrosine as an example precursor, the concentrations of the initial 3-chlorotyrosine and 3,5-dichlorotyrosine transformation products from this one precursor in the leaf phase were comparable to, and, in the case of some lettuces, exceeded, the aggregate aqueous concentration of volatile DBPs formed from multiple precursors. Chlorotyrosine formation increased when spinach was shredded due to the greater accessibility of chlorine to proteins in the leaf interiors. The cytotoxicity of chlorotyrosines to Chinese hamster ovary cells was higher than any of the trihalomethanes regulated in drinking water.

Structural Organizations of Qβ and MS2 Phages Affect Capsid Protein Modifications by Oxidants Hypochlorous Acid and Peroxynitrite

“…For other amino acids, the oxidation ranking order varies between studies and conditions, but Y residues are often cited as being significantly affected (Pattison and Davies, 2001;Hawkins et al, 2003;Bergt et al, 2004;Na and Olson, 2007). The chlorinated Y residue is therefore used as a marker of protein oxidation by HClO (Komaki et al, 2018). Moreover, HClO was shown to cause the formation of covalent bonds between amino acids and nucleotides in vitro .…”

Cytotoxicity of Halogenated Tyrosyl Compounds, an Emerging Class of Disinfection Byproducts

“…The 48 h IC 50 values for the chlorinated species, 3-Cl-Tyr and 3,5-di-Cl-Tyr, are approximately four to six times higher than those determined by Komaki and colleagues in CHO cells after 72 h exposure. 16 The observed difference is likely related to the different testing methods used (RTCA vs dye-based microplate assay) as well as the total exposure time and CHO clone type utilized. In the RTCA method, seeded cells grow for 24 h before treatment, a common practice for quality control of cellular growth in the assay, while the microplate assay applies DBP treatment at the time of cell seeding.…”

“…18,19 3-Chloro-tyrosine (3-Cl-Tyr) and 3,5-dichloro-tyrosine (3,5-di-Cl-Tyr) were also shown to be more cytotoxic than regulated THMs in Chinese hamster ovary (CHO) cells. 16 These compounds are also of toxicological interest, because the presence of free iodide or bromide during treatment can induce the formation of iodinated and brominated tyrosyl DBPs. 14,15 In general, the toxicity trend among analogous DBPs is iodo-> bromo-≥ chloro-DBPs.…”

“…With its two reactive sites, the amino acid tyrosine (Tyr) has been shown to be reactive to chlorination and can form highly stable reaction products, which was also observed with tyrosyl dipeptides . Halogenated tyrosyl compounds have been identified as DBPs in treated tap water − and in lettuce and spinach washed with treated water . Formation of these compounds is influenced not only by the identity of the peptides present, but also by the presence of free halogen ions, including iodide and bromide. , In the presence of iodide, 3-iodo-tyrosylalanine (3-I-Tyr-Ala) and 3,5-di-iodo-tyrosylalanine (3,5-di-I-Tyr-Ala) were identified as the predominant byproducts from chloramination of the tyrosyl dipeptide tyrosylalanine (Tyr-Ala), formed via electrophilic substitution .…”

Battling microbes: disinfecting water during fresh-cut lettuce processing

“…Another concern is the formation of other DBPs like 3-chlorotyrosine, which forms when hypochlorous acid reacts with tyrosine residues in proteins (Bao Loan, Jacxsens, Kurshed and De Meulenaer, 2016. ) Research suggests that depending on the exposure from consuming foods like fresh-cut lettuce or spinach, 3-chlorotyrosine could be a health concern, and additional toxicological data is required to assess this risk (Bao Loan et al, 2016;Komaki, Simpson, Choe, Plewa and Mitch, 2018).…”