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.