Article pubs.acs.org/JAFC
Stability of Sodium Chlorate Residues in Frozen Tomato and Cantaloupe Homogenates David J. Smith*,† and Grant R. Herges† †
USDA ARS, Red River Valley Agricultural Research Center, Biosciences Research Laboratory, 1605 Albrecht Blvd., Fargo, North Dakota 58102-2765, United States ABSTRACT: The objective of this study was to determine the stability of sodium chlorate in frozen (−24 °C) tomato or cantaloupe homogenates for up to 17 weeks (119 days). Chlorate stability was assessed by ultraperformance liquid chromatography−mass spectrometry (UPLC-MS/MS) at two fortification levels (80 or 600 ng/g for tomato and 200 or 3000 ng/g for cantaloupe, n = 3 each) for each fruit after storage for 0, 1, 7, 14, 28, 56, or 119 d. Within matrix type, chlorate recovery was determined by fortifying duplicate blank homogenate samples on the day of analysis with the same concentrations used for the stability samples. Chlorate limits of quantitation for cantaloupe and tomato matrices were 30 and 60 ng/g, respectively. Sodium chlorate residues were stable (P > 0.05) in frozen tomato and cantaloupe homogenates during storage for 119 days at −24 °C. KEYWORDS: cantaloupe, chlorate, residue, stability, storage, tomato
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INTRODUCTION
in homogenates of seafood treated with aqueous chlorine dioxide. Whereas the aforementioned studies pursued the quantification of select chlorine dioxide degradation products, until recently no studies described the overall distribution and chemical fate of chlorine dioxide gas during food sanitation efforts. To this end, the disposition and chemical fate of radiolabeled chlorine dioxide gas (36ClO2) in tomato,16 cantaloupe,16,17 and ready-to-eat meat18 models of chlorine dioxide gas sanitation have been described. Collectively, these studies have consistently demonstrated that the major residue (typically 90% or greater) formed in, or on, chlorine dioxide treated foods is chloride ion (Cl−). Quantitatively, oxidative products such as chlorate and perchlorate (ClO4−) are of much less importance ( 0.05) during frozen storage within cantaloupe puree at −24 °C. Data supporting the notion that chlorate residues are stable in frozen vegetable matrices are perhaps not surprising given the effect of cold temperatures on attenuating chemical and biologic processes. However, numerous studies indicate that chlorate is susceptible to bacterial reduction and is generally not stable in biotic media at temperatures and organic matter compositions commensurate with bacterial growth. Numerous chlorate respiring bacteria exist in nature30,31 and are dispersed through a variety of diverse ecosystems.32 For example, in batch incubations containing a soil-urine-feces mixture, Oliver et al.23 demonstrated a marked effect of temperature on chlorate halflife, with the longest half-lives (2.9 to 28 days) occurring at 5 °C and the shortest at 30 °C (0.1 to 1.3 days). Similarly, the slowest rates of chlorate degradation in activated sludge were measured at 10 °C by Jiang et al.33 In soil, the microbial degradation of chlorate was greatly influenced by soil moisture and the presence of readily fermentable carbon source.34 In the absence of moisture and a carbon source, even at temperatures that would otherwise support microbiological growth, chlorate
regression parameters
a
stability data set
recovery corrected
80 ng/g 80 ng/ga 80 ng/g 600 ng/g 600 ng/g
no no yes no yes
slope 0.22 0.11 0.10 0.27 0.48
± ± ± ± ±
0.04 0.08 0.06 0.21 0.25
y-intercept
Rsquared
P
± ± ± ± ±
0.6352 0.1151 0.1436 0.0929 0.1921
0.05; Table 2); that is, there was no evidence for decomposition of 80 ng/g sodium chlorate residues frozen in tomato puree for 119 days. To verify the influence of the high recovery value on day 119, regression analysis was repeated on the uncorrected data with day 119 data removed from the analysis; through day 56, there was no evidence (P > 0.05) of sodium chlorate degradation. For the 600 ng/g sodium chlorate stability samples (Table 2; Figure 2), there was no (P > 0.05; Table 2) relationship between days D
DOI: 10.1021/acs.jafc.7b02520 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry
Table 3. Least Square Regression Analyses of Uncorrected and Recovery-Corrected Stability Data of Sodium Chlorate in Cantaloupe Homogenate Frozen at −24 °C for 119 Days stability
recovery
data set
corrected
200 ng/g 200 ng/g 3000 ng/g 3000 ng/g
no yes no yes
regression parameters y-intercept
slope −0.08 0.08 0.84 0.20
± ± ± ±
0.08 0.11 1.1 0.8
171 188 2294 2918
AUTHOR INFORMATION
Corresponding Author
*Tel: 701-239-1238. Fax: 701-239-1430. E-mail: david.j.smith@ ars.usda.gov. ORCID
David J. Smith: 0000-0001-8883-4744 Notes
Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. The authors declare no competing financial interest.
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4.7 6.0 58 43
R-squared
P
0.0621 0.0285 0.0374 0.0041
0.38 0.47 0.43 0.97
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residues have accumulated to appreciable levels (32000 to 530000 μg/kg) in some soils of the Atacama Desert of Chile and in Death Valley, CA.35 Our data are consistent with the notion that biotic influences on chlorate can be minimized under appropriate storage conditions. For analytical chemists measuring the chlorate content of foods, our data suggest that frozen storage of fruit samples for up to 120 days will not compromise sample integrity.
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