Biochemistry and molecular aspects of 2-acetyl-1-pyrroline biosynthesis in rice (Oryza sativa L.): A review

Rice is used as a staple food in many countries due to its pleasant aroma and texture. Rice aroma is recognized as the single most important quality trait influencing consumer’s acceptance. In rice quality, 2-acetyl-1-pyrroline (2-AP) is one of the most highly unstable and key aroma characteristic compounds among more than 500 identified compounds that have contributed and attributed for popcorn- or pandan-like valuable aroma. 2-AP has the lowest odor threshold value compared to other identified rice aroma compounds. Therefore, this compound has received a lot of attention among scientists and researchers. This review highlights on Molecular biology and biotechnological progress of 2-AP in rice. Chemistry, formation, and synthesis, as well as factors influencing 2-AP content in rice, have also been reviewed.

Volatile Organic Compound Based Markers for the Aroma Trait of Rice Grain

A study was conducted to determine the volatile organic compounds (VOCs) associated with rice grain aroma in 37 commonly grown lines within Uganda, as well as elites. The aim of the study was to identify potential volatile biochemical markers, if any, for the rice grain aroma trait. Certified rice seeds were obtained from the Uganda National Crops Resources Research Institute germplasm collection. The seeds were sown into experimental plots, under field conditions and the mature paddy harvested. Polished rice grains were heated to 80 oC and the liberated VOCs subjected to untargeted metabolite analysis using gas chromatography-time-of-flight mass spectrometry. In total, nine functional groups were present; hydrocarbons, alcohols, ketones, aldehydes, N-containing compounds, S-containing compounds, esters, oxygen heterocycles and carboxylic acids. More specifically, 148 VOCs were identified across the 37 rice lines, of which 48 (32.4%) including 2-acetyl-1-pyrroline (2-AP) appeared to elucidate the difference between non-aromatic and aromatic rice. Furthermore, 41 (27.7%) VOCs were found to be significantly correlated with 2-AP abundance, the principle rice aroma compound. Amongst the 41 VOCs, only ten compounds were found to contribute highly towards variation in 2-AP abundance, indicative of their possible modulation roles in regard to rice aroma. Within the ten influential volatiles, three aroma active compounds; toluene, 1-hexanol, 2-ethyl and heptane, 2,2,4,6,6-pentamethyl- were established as the most reliable biochemical surrogates to the rice aroma trait. Thus, the aforementioned compounds may be used in rice breeding programme for enhancing development of the grain aroma trait.