More Protein in Rice: Improving the Nutritional Profile

Linda Benedict, Utomo, Herry S., Linscombe, Steven D., Wenefrida, Ida  |  12/4/2013 9:37:43 PM

Ida Wenefrida, Herry S. Utomo and Steve D. Linscombe

Grain protein content is an important component that determines a nutritional value of rice. Improving protein content in rice will help enhance its nutritional profile. Recent trends indicate that developing healthy lifestyles is an increasingly important goal for many. To help achieve this goal, nutrient profiling systems were developed to assist individuals in identifying and selecting foods based on their criteria and preferences to establish individualized healthy lifestyles. Rice with higher protein content will have a better status in the nutrient-profiling systems.

Rice provides a source of carbohydrates. It is also a natural source of dietary fiber, vitamins, minerals, specific oils and other disease-fighting phyto-compounds. Continuing advancements in nutrigenomics and nutrigenetics will help improve public knowledge of the importance of specific aspects of food nutrition for optimum fitness and health. Improving the nutritional values of rice becomes increasingly important. Through a better understanding of the molecular basis for human health and genetic predisposition to certain diseases through human genomes, establishing personalized nutritional requirements are becoming more attainable. High-protein grains can provide the base for developing novel foods and fibers or nutrient-dense food products that can be tailored as functional foods to meet the needs for individuals with specific genetic traits.

Improving protein content of rice also could have worldwide practical applications in addition to helping establish healthy lifestyles. Rice feeds nearly a half of the world’s population, and rice consumption per capita has remained stable since the 1960s. Current total world rice production is 476.8 million metric tons – mostly for human consumption. The United States produces around 9.4 million metric tons of rice, about a half of which is exported, providing around 12 percent of the world rice trade. Rice alone provides nearly 34 million metric tons of protein, which is about half of total protein provided by legumes. In many parts of Asia, rice is the main source of diets, and in these regions, widespread malnutrition occurs.

Between 2010 and 2012, nearly 870 million people in the world were chronically malnourished. This represents 12.5 percent of the global population. Every year, about 19 million children suffer from severe acute malnutrition, and at least 3.5 million of them die from malnutrition-related causes. High-protein rice could help remediate malnutrition problems worldwide.

Grain amino acid content
Protein is made of amino acids. Similar to other cereals, rice has imbalanced amino acid profiles, lacking a few essential amino acids. Lysine, threonine and methionine are among the most critical and are limiting factors in rice grain for human nutrition (Table 1). A significant amount of research has been put into efforts to improve these essential amino acids. Each amino acid is synthesized through specific biochemical pathways. Lysine, for example, is synthesized through a branch of the aspartate (Asp)-family pathway that also gives arise to the synthesis of two additional essential amino acids – methionine and threonine. This synthetic pathway has been researched extensively and has provided a road map in developing models for improving the lysine grain content. The excess of free lysine, however, can be harmful to plant growth and seed development. Because lysine is an easily soluble amino acid, the free lysine can be lost during food preparation. Genetic engineering has been used to improve seed lysine content.

Methods for improving protein content
Improving protein content can be outlined in four different approaches:

  • Manipulating seed protein bodies. 
  • Modulating certain biosynthetic pathways to overproduce essential and limiting amino acids. 
  • Increasing nitrogen relocation to the grain through the introduction of transgenes. 
  • Exploiting new genetic variance.

 The discovery of opaque2 and other opaque mutant genotypes in maize (corn) is an example of manipulating seed protein bodies to cause higher protein content. It has accelerated the development and commercialization of “quality protein maize” varieties. These varieties have been planted in 23 developing countries and grown on more than 10 million acres. Various technologies have been employed to improve protein content, including conventional and mutational breeding, genetic engineering, marker-assisted selection and genomic analysis.

Development of high-protein rice
The grain-quality enhancement program at the Rice Research Station is working on improving protein content in rice. Promising protein-rice lines are being tested in advanced trials. Protein contents of five select protein lines are shown in Table 2 together with their yield and milling qualities. In addition to the advanced lines, new protein lines are being developed from Louisiana varieties and germplasm lines. For example, 79 lines have been developed from the variety Cocodrie with a range of crude protein content between 10.5 percent and 14.5 percent (Figure 1) and 183 lines from the variety Cypress having protein content ranging from 10.5 percent to 14.2 percent (Figure 1). Future releases of high-protein rice as commercial varieties will open the door for producing high-quantity rice products for various purposes.

High-protein rice can be used to facilitate production of rice-based food products that are more nutritious. Rice milk, high-protein rice flour and whole-grain rice cereals are examples of potential markets that emphasize the nutritional quality of rice. High-protein rice can be used as an effective tool to reduce acute world malnutrition. A bag of rice, for example, will be well received because the utensils and the know-how to cook the food are already in place in many parts of the world. Because rice is the staple food of diverse populations from various cultures and religious backgrounds, it can be used to reach to almost any target population. Rice is acceptable in any religious belief or vegetarian population. Besides rice-based products with higher protein content, high-protein rice can directly be used to produce ready-to-be-delivered bulk rice to support humanitarian programs.

Ida Wenefrida is an assistant professor-research, Herry S. Utomo is an associate professor, and Steve D. Linscombe is professor and director, Rice Research Station, Crowley, La.

(This article was published in the fall 2013 issue of Louisiana Agriculture magazine.)

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