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 7669 IREC Farmers' Newsletter No. 195 ­ – Rice R&D 2016 water is very important in determining grain quality. Rice is an unusual cereal in that glutelins are the dominant grain protein, while prolamins dominate grain proteins of most other cereals including wheat. In order to understand rice grain protein, a method of grain protein analysis had to be developed. When proteins are analysed, they are extracted, separated, and then measured. Proteins can be separated on the basis of size, charge or solubility differences. The researchers chose to use a system that separates proteins on the basis of solubility because rice eating quality is related to how the rice cooks in and interacts with water. Many different extraction and separation protocols were trialled on long and medium grain samples before settling on the most efficient method. As the method was being developed, clear differences between the long and medium grains were observed, with the basmati types having the most distinctive profile. Quality differences Once developed, the rice grain protein analysis method, which only needs 0.25 grams of rice flour, was applied to more than 300 long and medium-grain advanced breeding lines from the 2013 and 2014 harvests and a small sample set of sushi rice. The results were evaluated to find correlations with data derived from the Quality Evaluation Program. The levels of the protein prolamin and the prolamin/glutelin ratio explained variation in medium grain quality, particularly hardness. The prolamins are the ‘oiliest’ of the proteins and are very important in wheat, sticking together to give dough much of its elasticity and allowing bread to rise. It is possible that the prolamins in medium grain rice also link together in some way and this affects grain quality. The prolamins did not affect long grain quality to the same extent as they affected medium grain quality. Although the prolamin content of long grain rice was higher than medium grain, it was much less variable and this may explain some of the differences in grain quality between long and medium grain rice. The breeding history of long grain and medium grain rice are different and it is also possible there are differences in long grain starch structure, compared with medium grain, that are not fully understood, and these differences in starch structure may be more important in long grain quality than medium grain quality. Protein in broken and unbroken grains Milling improves the shelf life and visual appearance of rice by removing the husk and oil-rich outer layers of the rice grain. A significant proportion of the grain breaks during milling and this makes milling yield an important grain quality parameter. Many factors affect the propensity of grain to break, including grain wetting and drying, the amount of chalk and the level of grain maturity. Work by other research groups over the years suggests protein may play a role in rice grain breakage. It is known for example that broken grains have lower protein content, and that increasing grain protein content by adding nitrogen fertiliser improves milling yield of some varieties. In this project, when the protein composition of broken and unbroken long and medium rice grains from the same breeding lines was analysed, the results showed characteristic differences in protein composition between broken and unbroken grain for each grain type, long and medium grain. On average the medium grain prolamins were reduced by 21%, glutelins by 39% and globulins by 0.4% in the broken grains compared with unbroken grains. The corresponding long grain fractions were reduced by 27%, 69% and 16% respectively. Surprisingly, although globulins differed least between broken and unbroken grain, statistical analysis found globulins differentiated between unbroken and broken medium grains while a combination of prolamins and globulins discriminated between unbroken and broken long grains. Hard wheats break easily when milled and largely due to the lack of a particular protein. Although it is too early to say definitively, protein composition in combination with other factors may influence rice grain breakage. It is possible, for example, that globulins as the most water soluble of the rice grain storage proteins may play a protective role in rice grain breakage through their capacity to hold water. Understanding protein to develop new varieties This project has found protein composition, particularly the prolamin/ glutelin ratio, plays an important role in medium grain rice quality which will allow more accurate selection of high quality medium grain rice lines. Differences in protein composition may also play a role in grain breakage. Better understanding the component traits of grain breakage will help breed better milling rice. RIRDC Project PRJ-008768 Defining the link between rice grain protein profiles and rice grain quality Further information Daniel Waters T: 02 6620 3443 E: [email protected] W: www.scu.edu.au/scps/ Basmati alcohol extract Long grain alcohol extract Medium grain alcohol extract Sushi alcohol extract l Protein bodies can be pulled apart and separated using specialised equipment. When separated by solubility differences, the proteins of basmati, long and medium grains have distinctive signatures.