Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 Page 53 Page 54 Page 55 Page 56 Page 57 Page 58 Page 59 Page 60 Page 61 Page 62 Page 63 Page 64 Page 65 Page 66 Page 67 Page 68 Page 69 Page 70 Page 71 Page 72 Page 73 Page 74 Page 75 Page 7667 IREC Farmers' Newsletter No. 195 ­ – Rice R&D 2016 2-acetyl-1-pyrroline or 2AP, was checked when screening for aroma in rice breeding programs. This was because 2AP is characterised by a sweet, baked-bread scent and can be detected by the human nose at very low concentration (0.06 parts per billion in air). However, consumers can easily differentiate the aroma quality of different 2AP-producing rice types and varieties (e.g. jasmine and basmati), which means that other volatile organic compounds also contribute to aroma. The ability to comprehensively detect, identify and understand the right combinations of volatile organic compounds contributing to rice aroma — dubbed ‘flavour metabolomics’— is thus essential in analysis of aroma. Flavour metabolomics was performed at The University of Queensland using a process called two dimensional gas chromatography (GCxGC). This process does not require lengthy chemical extractions; it simply requires heating of a sample of ground rice in a sealed container and detecting the volatile organic compounds emitted. The process enables comprehensive detection of all compounds instead of just 2AP. It is a relatively simple method of collecting volatile organic compounds, and more closely resembles the release of volatiles when consumers cook rice. Biomarker discovery Sensory evaluation remains an important aspect in the rice fragrance project because ultimately, the consumers’ perception of the product is of utmost priority. Sensory evaluation was used in combination with metabolomics to determine which of the volatile organic compounds could be used as indicators of favourable or unfavourable scent or tagged as ‘biomarkers’. So when screening commercial rice samples, researchers need only look for these biomarkers to predict the flavour of that rice variety. A group of sensory panellists was trained to distinguish and precisely score the intensity of 13 descriptors of rice aroma and taste (Table 1). Once trained, the panellists were subjected to a series of blind tests of rice varieties with different aroma quality. The panellists reported significant variation in aroma perception for each of the rices, ranging from sweet floral to eggy sulphurous. It was confirmed that 2AP- producing rice varieties have differences in flavour and these variations are attributed to unique combinations of several volatile organic compounds. The volatile organic compounds detected may either be unpleasant compounds, such as indole, thiols, sulphides and furans, which mask the sweet, pandan scent of 2AP, or pleasant smelling compounds, such as acetophenone, limonene and decanal, which combine with 2AP increasing palatability and consumer acceptance of rice. Furthermore, using the intensity scores from the sensory panel and the quantitative data from metabolite profiling (the GCxGC analysis), the project team was able to draw out phenotype–metabolite associations and pick out the compounds that contribute to a specific type of scent (Table 2). There is now a range of volatile organic compounds that can be useful as biomarkers for excellent rice flavour quality. These volatile organic compounds are recommended to be considered in rice breeding programs. What’s next? In modern plant breeding, small segments of DNA (or molecular markers) that are linked to a desired plant trait, such as disease resistance or a specific type of grain quality, are being increasingly used for precise and efficient selection of lines in breeding programs. Therefore, the quickest way of incorporating the discovered biomarkers in breeding programs is by developing molecular markers that are linked to their production. The rice fragrance group has developed a diverse collection of rice, comprising aromatic rice varieties from twelve countries and advanced breeding lines from Australia. These lines will be used for mapping genes or genetic regions that are associated with the production of desired volatile organic compounds in rice. RIRDC Project PRJ-008568 Developing superior aromatic rice germplasm for Australia Acknowledgements This research was funded by RIRDC, NSW Department of Primary Industries and The University of Queensland. Further information Dara Daygon T: 0413 464 158 E: [email protected] Table 2.Volatile organic compounds associated with specific types of scent that can potentially be used as biomarkers for aroma. VOC Odour threshold Scent (ppm* in air or water) 2AP 0.06 sweet, pandan 2 acetyl pyrrole 170,000 baked bread Acetophenone 65 floral Acetoin 800 butter, cream Limonene 10 citrus 1-hexanol 2500 fruity 1-butanol 360 fruity 2,3 butanedione 0.05 creamy butter Decanal 0.1 sweet floral Indole 140 faecal 1, 5, hexdien-3-ol 10 sewer 2-ethyl furan 2300 beany 2-methyl butanal 1000 musty, nutty 3-methyl butanal 1100 musty, nutty 1-pent-3-one, 2 methyl na sour 2 butanone 50000 sour 2 methyl 2 undecanethiol na sulphurous Dimethyl trisulphide 0.005 sulphurous *ppm - parts per million Table 1. Descriptors assessed by the sensory panel members, who were trained to distinguish and precisely score the intensity of rice aroma and taste. Sensory descriptor Very pleasant Good Bad Pandan Grainy Sewer Floral Corn Sour Sweet aromatic Grassy Hay-like Popcorn Dairy Metallic Sweet taste