Cereulide is a heat-stable cyclic depsipeptide toxin produced by Bacillus cereus and is responsible for foodborne emetic syndrome. Recent reports of Bacillus cereus contamination and cereulide occurrence in infant formula have raised increasing food safety concerns. Due to the immature immune and metabolic systems of infants, exposure to cereulide through contaminated formula may lead to potential health risks. However, direct application of existing cereulide analytical methods to infant formula remains challenging because of the unique processing technologies, encapsulated nutrients, and variable matrix composition of this product category, which may hinder toxin release and cause significant matrix interference. In practical analysis, inter-laboratory comparisons revealed that existing methods exhibited relatively large deviations and insufficient sensitivity, making them not specifically optimized for infant formula matrices. The present study was motivated by the need for a matrix-specific, sensitive, and reliable analytical method for cereulide determination in infant formula. In this study, a method based on solid-phase extraction coupled with ultra-performance liquid chromatography–tandem mass spectrometry (SPE–UPLC–MS/MS) was developed and validated. To improve the applicability of cereulide analysis to infant formula, this method incorporates a hydration-assisted extraction step tailored to infant formula, which increased the detected cereulide response by approximately fourfold, together with optimized SPE clean-up and improved chromatographic conditions to reduce matrix effects and enhance quantitative reproducibility. The method showed good linearity (0.1–10 μg·L⁻¹, R² > 0.999), low values for limit of detection (LOD) (0.03 μg·kg⁻¹) and limit of quantification (LOQ) (0.1 μg·kg⁻¹), and acceptable recoveries (94.4–110.3%) with RSDs below 3.7%. The developed method was successfully applied to commercial infant formula samples, and cereulide-positive samples were identified. This method provides a reliable analytical tool for the monitoring of cereulide in infant formula and contributes to improved food safety surveillance and exposure risk assessment.

Few information of the function of stearoyl-coenzyme A (CoA) desaturase (SCD) in apicomplaxan parasite has been obtained. In this study, we retrieved a putative fatty acyl-CoA desaturase (TGGT1_238950) by a protein alignment with Plasmodium falciparum SCD in ToxoDB. A typical Δ9-desaturase domain was revealed in this protein. The putative desaturase was tagged with HA endogenously in Toxoplasma gondii, and the endoplasmic reticulum localization of the putative desaturase was revealed, which was consistent with the fatty acid desaturases in other organisms. Therefore, the TGGT1_238950 was designated T. gondii SCD. Based on CRISPR/Cas9 gene editing technology, SCD conditional knockout mutants in the T. gondii TATi strain were obtained. The growth in vitro and pathogenicity in mice of the mutants suggested that SCD might be dispensable for tachyzoite growth and proliferation. The SCD-overexpressing line was constructed to further explore SCD function. The portion of palmitoleic acid and oleic acid were increased in SCD-overexpressing parasites, compared with the RH parental strain, indicating that T. gondii indeed is competent for unsaturated fatty acid synthesis. The SCD-overexpressing tachyzoites propagated slower than the parental strain, with a decreased invasion capability and weaker pathogenicity in mice. The TgIF2α phosphorylation and the expression changes of several genes demonstrated that ER stress was triggered in the SCD-overexpressing parasites, which were more apt toward autophagy and apoptosis. The function of unsaturated fatty acid synthesis of TgSCD was consistent with our hypothesis. On the other hand, SCD might also be involved in tachyzoite autophagy and apoptosis.

Arachidonic acid (ARA) is an essential long-chain polyunsaturated fatty acid for infant growth and development, commonly added to infant formula and supplementary foods as ARA oil or ARA powder. Since December 2025, infant formula products have been recalled in several countries due to cereulide contamination in ARA ingredients. Cereulide, a heat-resistant emetic toxin produced by Bacillus cereus, presents a serious threat to infant health. However, specific analytical methods for cereulide detection in ARA raw materials remain scarce, hindering effective quality control and source prevention of food safety hazards. This study developed and validated a rapid ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) method for the quantitative determination of cereulide in ARA oil and powder. Sample pretreatment was optimized according to matrix characteristics: for microencapsulated ARA powder, water dissolution was performed to release cereulide before acetonitrile extraction, whereas direct extraction was applied to ARA oil. Subsequent HLB-P pass-through solid-phase extraction effectively eliminated matrix interference in both matrices. The method exhibited excellent linearity (R² > 0.999) from 0.1 to 20 μg·L⁻¹, with an LOD of 0.03 μg·kg⁻¹ and an LOQ of 0.1 μg·kg⁻¹, respectively. Spike recoveries reached 90.7–107.0% for ARA oil (RSDs ≤ 6.5%) and 88.5–107.9% for ARA powder (RSDs ≤ 7.0%). This rapid and reliable method provides a critical analytical tool to monitor cereulide in ARA raw materials and mitigate infant safety hazards at the source.