Rapid spatial distribution analysis of lipids in wheat grain using DESI/PI mass spectrometry imaging

Wheat is an important cereal grain. Understanding lipid composition and distribution in wheat grain is valuable for plant, food and nutritional research. Conventional methods can analyze lipid composition and content in wheat grain, while the spatial native distribution of lipids is inevitably lost. In this paper, an effective mass spectrometry imaging (MSI) analysis protocol combining desorption electrospray ionization/post-photoionization (DESI/PI) with high-resolution mass spectrometer was established. To overcome the hardness of wheat grains and fragility of wheat grain sections, a rapid hand plane sectioning (HPS) method was developed. By employing accurate mass spectrometry peak identification, the HPS samples detection results achieved ∼23 % similarity with cryosectioning sample (same compounds). DESI/PI has good sensitivity for both non-polar and polar lipids. A small mass spectrum database for wheat grain was established which may provide strong data support for wheat grain component analysis. The rapid MSI analysis protocol was further used to explore the spatial distribution changes of lipids in wheat grain with different storage years, indicating that DESI/PI was a potential means of studying wheat grain aging. This study provides a convenient sectioning method, a comprehensive identification checklist, and spatial distribution information of lipids in wheat grains, which holds potential significance for guiding improvements in wheat grain processing & storage, slowing down the aging, and ensuring grain quality.