Formation and cytotoxicity of fatty acid chlorohydrins during sodium hypochlorite bleaching of tree nuts.

Fatty acid chlorohydrins are an emerging class of contaminants formed when hypochlorous acid reacts with unsaturated fatty acids during food processing. While their formation has been reported under high sodium hypochlorite (NaOCl; ≤200 mg/L as Cl2) disinfection of vegetables, much higher levels-≤ 60,000 mg/L of Cl2 or 6% NaOCl-are used to brighten shells. Monochlorohydrins of palmitoleic, oleic, and linoleic acids, along with dichlorohydrins of linoleic acid, were measured in walnuts, pistachios, and hazelnuts after NaOCl bleaching. Formation increased with oxidant dose and kernel accessibility, with the shells acting as partial mass-transfer barriers. Pistachios exhibited the highest total chlorohydrins (34.4 µg/g), followed by hazelnuts (6.0 µg/g) and walnuts (2.8 µg/g) at 1% NaOCl. Surface area greatly affected chlorohydrin production: pulverized and bleached walnut kernels generated 25-fold more chlorohydrins than in-shell kernels, with significant loss of fatty acids. Testing three commercial walnut brands revealed chlorohydrin levels comparable to those from 3% NaOCl treatments (∼6.0 µg/g), demonstrating the presence in consumer products. Chinese hamster ovary (CHO) cell cytotoxicity assays showed the following LC50 order: palmitoleic monochlorohydrins (271 µM) > linoleic monochlorohydrins (340 µM) > linoleic dichlorohydrins (499 µM) >> 3-mono-chloro-1,2-propanediol (3-MCPD; 4780 µM), a European Union-regulated food processing contaminant (tolerable daily intake of 2 µg/kg body weight).Screening-level cytotoxicity equivalents indicated that chlorohydrin concentrations correspond to intake masses of 3.6-4.0 g relative to 3-MCPD limits and 6.6-7.3 g relative to drinking water contaminant benchmarks, both below a 30 g serving.