Science of Rice Aroma and Environmental Factors Influencing Basmati Aroma and Other Grain Quality Traits

Aromatic rice varieties such as Basmati, Jasmine, and Della are known for their distinctive fragrance, a key attribute of grain quality. The aroma, often described as ‘popcorn-like’ or ‘pandan-like’, is evaluated through sensory analysis and instrumental methods. It is primarily governed by a single recessive allele, as identified by Bradbury et al., which encodes betaine aldehyde dehydrogenase 2 (BADH2) on chromosome 8. In Basmati rice, Amaravathi et al. reported three quantitative trait loci (QTLs) on chromosomes 3, 4, and 8, indicating a more complex genetic basis. The primary aroma-contributing volatile compound, 2-acetyl-1-pyrroline (2-AP), was first identified by Buttery et al. Aromatic rice varieties contain 0.04–0.09 ppm of 2-AP, approximately ten times higher than in non-aromatic types. In addition to 2-AP, several other odour-active compounds contribute to the unique flavour and variation in aroma strength among different fragrant rice types. Measurement of 2-AP content at different crop growth stages in aromatic Basmati rice showed that it increased from the seedling to booting stages, decreased during flowering and milky grain stages, again showed a steep increase during the dough grain stage, and reached its maximum at the mature grain stage. It shows that 2-AP from leaves and the stem sheath gets transported to grains and gets accumulated in mature grains. The area specificity of aroma in Basmati and other aromatic rices like Jasmine shows that though the aroma may be genetically controlled, environmental factors like climate, soil characteristics, cultural practices, post-harvest storage, milling, and cooking conditions also influence the intensity of aroma and flavour. A minimum temperature of less than 24°C and a shorter day length duration during flowering and maturity have been found necessary for good aroma development in Basmati.