Impact of phosphine and of sulfuryl fluoride fumigation on walnut quality

 Food products are often fumigated to protect them from pest damage and to meet phytosanitary requirements. While fumigants undergo a risk assessment prior to approval for use, additional studies are necessary to evaluate their effects on food quality. We investigated the effect of the fumigants phosphine (PH₃) and sulfuryl fluoride (SO₂F₂) on three markers of walnut quality: peroxide value (PV), p-anisidine value (pAV) and fatty acid profile. Walnuts were treated with PH₃, SO₂F₂, or left untreated. They were allowed to desorb any excess gas at 20°C for 2 weeks and then stored at 60°C for 4 weeks to simulate the walnuts' shelf life in an accelerated way. Samples were tested at four time points for PV, pAV, and fatty acid profile. Storage at 60°C caused increases in PV (2-way ANOVA, F³ = 700, P = 3E-57) and in pAV (2-way ANOVA, F³ = 54, P = 4E-18), with walnuts reaching PVs exceeding the industry standards for sale. No significant difference in PV was observed between PH₃-treated and untreated walnuts or between SO₂F₂-treated and untreated walnuts at any time point (Tukey's HSD test for multiple comparisons, α = 0.05). pAV was not affected by fumigation at all (2-way ANOVA, F³ = 0.02, P = 1.0). Storage did not significantly change the levels of any of the five main fatty acids in the walnuts (2-way ANOVA, α = 0.05). Phosphine fumigation resulted in a 2% increase in linolenic acid content during the 2 weeks at 20°C, but this small effect disappeared afterwards (Tukey's HSD test, α = 0.05). In summary, no major effects of PH₃ or SO₂F₂ on walnuts' commercial value or nutritional profile were found as assessed with PV, pAV and fatty acid profile.