Variation of 2-Acetyl-1-Pyrroline Concentration in Aromatic Rice Grains Collected in the Same Region in Japan and Factors Affecting Its Concentration

Aroma strength of aromatic rice varies with the genetic and environmental conditions. We determined the concentration of 2-acetyl-1-pyrroline (2AP), a key compound of the aroma of aromatic rice, in 62 samples of rice grains (brown rice) from‘Hieri’ produced by 17˜24 farmers in 3 years in the Kubokawa area of Kochi Prefecture, Japan. Many ofthem showed similar values and the standard deviations were 27˜31%. However, a few samples showed extremely high (200%) or low (60%) 2AP concentrations compared to the individual year averages (100%). The influence of harvest time and temperature during ripening on the 2AP concentration in the brown rice was also examined using two cultivars. During grain development in an early-heading cultivar ‘Miyakaori’ , the 2AP concentration in the brown rice reached a peakat 4 or 5 weeks after heading (WAH) and then decreased rapidly to 20% of the maximum at 7 or 8 WAH. In a late-heading cultivar ‘Hieri’, the 2AP concentration peaked at 4 WAH then gradually decreased to 40% of the maximum at 8 WAH.The 2AP concentration was higher in brown rice ripened at a low temperature (day : 25°C/night : 20°C) than that ripened at a high temperature (day: 35°C/night: 30°C) in both a short-grain cultivar ‘Hieri’ and a long-grain cultivar ‘Sari Queen’