The absorption of 2-acetyl-1-pyrroline during cooking of rice (Oryza sativa L.) with Pandan (Pandanus amaryllifolius Roxb.) leaves

摘要

Rice (Oryza sativa L.) is a staple food for about half of the population in the world. Aroma is one of the mostimportant rice sensory quality characteristics. The chemical compound that contributes mostly to the aromaprofile of aromatic rice (e.g. basmati rice) is 2-acetyl-1-pyrroline (2-AP). This highly volatile compound hasbeen found to occur naturally in Pandan leaves. As such 2-AP has been used as a good indicator fordifferentiating fragrant from non-aromatic rice. Adding fresh Pandan leaves to enhance the flavour profile ofnon-aromatic rice is as an old practice in South-East Asia. However, there has been little work done on how2-AP is extracted from Pandan leaves and the phenomena taking place during cooking. Thus, the aim of thisstudy was to investigate the mechanism of absorption of 2-AP from non-aromatic rice mixed with Pandanleaves during cooking. Non-aromatic rice was cooked with fresh Pandan leaves in a rice cooker andaluminium cylinder during optimal and excess water cooking conditions respectively. Moisture content ofraw and cooked rice was determined by drying and the amounts of 2-AP were determined by gaschromatography-flame ionization detector (GC-FID). All the samples were collected and temperature ofcooking was measured at 5, 10, 15 and 20 min of cooking time. Analysis revealed that 2-AP is present incooked non-aromatic rice, indicating that mass transfer occurs between Pandan leaves and rice. The releaseof 2-AP from Pandan leaves increased with increasing time and temperature of cooking. The amount of 2-APin rice grain was found to decrease at 10 min (optimal water) and 5 min (excess water) of cooking. Asignificantly increased amount of 2-AP rice has been observed after cooking at 15 min, which decreasedagain at 20 min of cooking time. This unexpected result indicated that the phenomena occurring duringcooking are quite complex. A possible explanation of this phenomena could be linked to starch gelatinizationand the effect it has on absorption of 2-AP from the rice grains. These results resulted in a more fundamentalunderstanding on the mechanism occurring during cooking. Of specific interest were the phenomenaoccurring during cooking of rice and the absorption of 2-AP. With an understanding of these phenomena,various methods will be reviewed to identify the potential hydrocolloid matrices to control the release of 2-AP during cooking and eating process.