Untargeted Lipidomics Reveal Quality Changes in High-Moisture Japonica Brown Rice at Different Storage Temperatures

Abstract

Low temperatures are an effective way of delaying grain rancidity and deterioration. However, little is known about the difference in quality changes in high-moisture japonica brown rice at different storage temperatures. In this study, the storage quality changes in japonica brown rice with a 15.50% moisture content stored at 15 °C, 20 °C, and 25 °C were investigated. In addition, an untargeted lipidomics analysis coupled with gas chromatography and mass spectrometry (GC-MS) was applied to analyze the volatile compounds and metabolite changes in the high-moisture japonica brown rice. The results showed that storage at 15 °C could well maintain the color and aroma stability of the brown rice and delay the increase in fatty acid value (FAV). The lipidomics results showed that storage at 15 °C delayed glycerolipid and sphingolipid metabolism and reduced glycerophospholipid catabolism in the brown rice. The low-temperature environment regulated these three metabolic pathways to maintain higher contents of triglycerides (TG), phosphatidylserine (PS), abd phosphatidylethanolamine (PE), and lower contents of diglycerides (DG), OAcyl-(gamma-hydroxy) FA (OAHFA), ceramides (Cer), and glycosylceramides (Hex1Cer) in the high-moisture japonica brown rice, which maintained the storage stability of the brown rice. Our results proposed the cryoprotection mechanism of postharvest brown rice from the perspective of volatile compounds and metabolite changes, providing a foothold for the further exploration of low-temperature storage as a safe and efficient cryoprotectant in the grain storage field.

Oxidative Stability and Pasting Properties of High-Moisture Japonica Brown Rice following Different Storage Temperatures and Its Cooked Brown Rice Flavor

“…Subsequently, the SPME fiber containing flavor volatiles was rapidly injected into the GC inlet and resolved using an autosampler at a temperature of 250 • C for a duration of 5 min. In addition, the GC-MS run conditions were set up as previously reported [9].…”

“…In our previous study, hydrocarbons in brown rice with high moisture content in the japonica variety were identified after three months of storage. Specifically, dodecane and tridecane were found to produce an unpleasant petrol odor [9]. Additionally, some studies detected nonadecane in aromatic and non-aromatic varieties [40].…”

“…The storage moisture content of cooked rice grains was 15.70%, which was found to have the best texture [8]. Similarly, brown rice with 15.5% moisture content had better color and lower fatty acid values when stored at 15 • C [9]. However, there is less information on the oxidative stability and the pasting properties of high-moisture brown rice with 15.5%.…”