Distilled spirits, particularly those made from sorghum, are important in Chinese culture. After harvest, grains are often stored in barns where growers use insecticides to keep pests at bay. Because of the potential for contamination with pesticides, Han et al. examined pesticide residues present in the production process of sorghum distilled spirits.
To do this, the team prepared spiked samples using stock solutions of dichlorvos (purity ≥98.0%), fenitrothion (purity ≥95.0%), pirimiphos-methyl (purity ≥96.2%), malathion (purity ≥95.0%), and deltamethrin (purity ≥99.0%). Through analyzing the calibration curves in five replicates at 5, 10, 50, 100, 500 ug/L resulting from the spiked samples, the researchers provided high accuracy and precision of their method. They calculated the mean recoveries for selected pesticides in all matrices ranged from 85% to 113% with RSDs (n = 5) lower than 12%, which was within acceptable limits for a pesticide analysis.
Next, the team simulated each stage of the distillation process by spraying 300mL of these stock solutions onto 3kg of sorghum. They stored the spiked sorghum in a fume hood for 24h to achieve a residue of 10 mg/kg.
The distillation process for this spiked sorghum began by soaking the coarse crushed sorghum with boiled water for 22 h and then steaming the soaked sorghum in a small steaming bucket for 1 h. At this point, the distillation process continued with the following stages:
Primary fermentation: they cooled the steamed sorghum with cold water, and mixed with Daqu (9–10%). Next, they fermented the mixture at 26–30 C for 28 days in an airtight glass jar (10 L).
Primary distillation: they mixed the primary fermented sorghum with rice hull (15–20%) homogeneously, then distilled in a steaming bucket to produce primary distilled spirits.
Secondary fermentation: they again cooled the the primary distilled sorghum and mixed with Daqu. Following this, they fermented the mixture at 26–30 C for 21 days in an airtight glass jar (10 L).
Secondary distillation: they mixed the secondary fermented sorghum with rice hull, and distilled the mixture in a steaming bucket to produce secondary distilled spirits.
Production of commercially distilled spirits: the team blended the primary and secondary distilled spirits together.
Before and after each stage in the distillation process, the team collected samples and analyzed them using a TSQ Quantum XLS GC triple quadrupole mass spectrometer with a Trace GC Ultra gas chromatograph and a TriPlus AI 13 Autosampler (all from Thermo Scientific).
Researchers found that each pesticide behaved a little differently. They found that soaking the crushing sorghum could reduce dichlorvos residue with 87% decrease, however it only reduced the others: fenitrothion, pirimiphos-methyl, malathion and deltamethrin by 36%, 28%, 32% and 29%, respectively.
The steaming process reduced pesticide residues and completely eliminated the residue of dichlorvos while reducing fenitrothion, pirimiphos-methyl, malathion and deltamethrin by 74%, 53%, 83% and 42%, respectively. The researcher explained this reduction was likely due to evaporation or thermal degradation.
During fermentation, the authors report that the residue of fenitrothion, pirimiphos-methyl, malathion and deltamethrin were reduced by 55%, 61%, 61% and 46% during primary fermentation, and further decreased by 43%, 43%, 63% and 40% in secondary fermentation in favor of biological degradation.
Distillation had the greatest reduction of pesticides compared with the others. At this stage, deltamethrin was reduced to undetectable levels, while a small quantity of fenitrothion, pirimiphos-methyl and malathion remained, 1.26%, 2.99% and 0.38% respectively.
Because of the potential for pesticide residues to persist in sorghum based foods, it is necessary to continually monitor pesticide levels to prevent adverse health effects.
For further discussion on pesticide analysis, visit our food and beverage learning center.
Han, Y. (2016) “Residue levels of five grain-storage-use insecticides during the production process of sorghum distilled spirits.” Food Chemistry. 2016 Sep 1;206:(pp. 12-17). doi: 10.1016/j.foodchem.2016.03.035. Epub 2016 Mar 11.