Proteomics of Seed Nutrition-Associated Proteins in Germinated Brown Rice in Four Thai Rice Cultivars Analyzed by GeLC-MS/MS

Brown rice (BR) and germinated brown rice (GBR) of Oryza sativa L. are popularly consumed by Asians because of their important healthy diet components. They are known to contain bioactive compounds and nutrients, such as phenolics, vitamins, fatty acids, and sugars, which help to maintain good health and reduce the incidences of various chronic diseases. The objective of this study was to investigate the effects of germination on changes of nutrition-associated proteins in 4 rice cultivars. After germination for 24 h, the changes of seed nutrition-associated proteins were examined by shotgun proteomics. The total proteins from non-germinated seeds and 24 h germinated seeds of 4 rice cultivars were extracted and analyzed by in-gel digestion coupled with tandem mass spectrometry (GeLC-MS/MS). A total phenolic content was analyzed from the crude methanol extract of those grains after germination for 0, 24, and 48 h using Folin-Ciocalteu assay. The analysis showed that seed nutritional-associated proteins, especially phenolic-associated proteins, increased after germination according to the accumulation of the total phenolic content. The expressions of 6 phenolic-associated proteins, including phenylalanine ammonia-lyase, serine carboxypeptidase-like protein, isoflavone-7-O-methyltransferase, isoflavonoid glucosyltransferase, glycosyltransferase family 61 protein and UDP-glucose flavonoid 3-O-glucosyltransferase were increased by 2.20 - 15.90 folds after germination. This study provides evidence that rice germination for 24 h has essentially influenced the increased nutritional values of BR and the phenolic biosynthetic pathway.