Evaluation of High Protein Rice Lines.

Future market driven by nutrigenomics may require significant improvement of nutritional values for each food product.   Current preventive life styles provide an indication of potential future consumers.  Emerging rice-based products, such as rice milk, high-protein rice flour and rice whole grain cereals, are examples of potential products for markets that emphasize the nutritional quality of rice.  As a rich source of natural dietary energy, rice is also a good source of thiamine, riboflavin, and niacin.  Un-milled (brown) rice contains a significant amount of dietary fiber.  Rice bran is a natural source of dietary fiber, vitamins, minerals, specific oils (γ-oryzanol), and some disease-fighting phytochemicals.  Our research objective was to improve protein content of rice.

Over 2,000 new lines have been developed from Louisiana cultivars and germplasm lines.  Crude protein contents as high as 14.51% were found among new entries derived from the cultivar Cocodrie.  The highest protein content found among new entries derived from the cultivar Cypress was 14.2%.  Typical protein contents in varieties Cocodrie and Cypress are between 7 to 8.5%.  Base on its amino acid profiles, the highest amino acid increase in a Cocodrie-derived line HP-1570 was in arginine (48.22%).   The lowest increase (17.41%) was in the methionine content.  An average increase of 33.21% was observed in the lysine content.  Lysine is synthesized through a branch of the Asp family pathway that also leads to the synthesis of two additional essential amino acids, methionine and threonine.  HP-1570 showed an increase of 17.41 and 34.50% for methionine and threonine, respectively.  The lysine biosynthetic branch is strongly regulated by a feedback inhibition loop in which lysine inhibits the activity of dihydrodipicolinate synthase (DHDPS), the first enzyme specifically committed to lysine biosynthesis.