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SCU researchers discover 'GI' gene


Brigid Veale
13 April 2005
Researchers at Southern Cross University have discovered the gene that controls the temperature at which rice cooks.

Professor Robert Henry and research scientist Dan Waters say the discovery has wide-ranging implications, from developing rice that can cook more quickly to manipulating the glycemic index (GI) of starch-based foods.

The research was undertaken at the Centre for Plant Conservation Genetics at Southern Cross University's Lismore campus in northern New South Wales.

Rice starch is the major food source for many millions of people around the world, and the temperature at which it cooks - its gelatinisation temperature - is considered an important factor in rice eating quality.

"The inspiration for this research was that we knew it was a priority for the rice industry as the gelatinisation temperature affects the cooking quality of the rice," Professor Henry said.

The researchers looked across a wide variety of rices and their gene sequences and found the key difference in the gene that determines what temperature the starch is cooked.

The Japanese-style medium grain rices, which have a low gelatinisation temperature, cook quickly and have a different texture to rices that have a high gelatinisation temperature.

As well as affecting the texture of cooked rice, the gelatinisation temperature is an important predictor of glycemic index (GI). Foods with a high glycemic index are absorbed and converted to glucose rapidly, leading to high spikes in blood sugar levels, while foods with a low glycemic index are absorbed more slowly.

This is particularly significant for people with diabetes, people who are glucose intolerant or who are prone to obesity. Diets composed of high GI foods can also be associated with an elevated risk of developing type 2 diabetes and cardiovascular disease.

The researchers found that the rices with a low gelatinisation temperature tend to have a higher GI index, while the slower-cooking rices had a low GI.

Dan Waters said the discovery of the gene that controls the gelatinisation temperature would allow more accurate selection of rices for particular properties, either in
terms of the cooked texture of the rice or its GI.

While the research was conducted specifically with rice, it has implications for all starch-based food including barley and wheat.

"This research has implications for any food or beverage that is starch-based, from bread to beer, there is the potential to apply this knowledge," Professor Henry said.

The next step is to commercialise the discovery.