The relatively simple cooking method could help families and food manufacturers increase resistant starch (RS) in staple food products – meaning that less of the rice is digested and fewer calories are absorbed.
Led by Sudhair A. James from the College of Chemical Sciences in Colombo, Sri Lanka, the team behind the discovery noted that in addition to consuming more fats and sugars, many people may choose to fill up on starchy carbohydrates like rice, which has about 240 calories per cup.
As a result the team experimented with 38 kinds of rice to develop a new way of cooking rice that increased resistant starch content.
"Because obesity is a growing health problem, especially in many developing countries, we wanted to find food-based solutions," said James. "We discovered that increasing rice resistant starch (RS) concentrations was a novel way to approach the problem."
By using a specific heating and cooking regimen, the scientists increased the levels of RS by ‘at least’ ten-fold – meaning that there are less digestible calories in the rice. Indeed, the team concluded that "if the best rice variety is processed, it might reduce the calories by about 50-60%."
Results from the investigation will be presented at the 249th National Meeting & Exposition of the American Chemical Society (ACS).
Reduced resistant starch
The team experimented with 38 kinds of rice from Sri Lanka, developing a new way of cooking rice that increased the RS content. The initial RS concentrations ranged from 0.30 to 4.65%, with traditional rice varieties found to contain significantly higher RS concentrations than old and improved varieties.
In this method, they added a teaspoon of coconut oil to boiling water before adding a half a cup of rice.
They simmered this for 40 minutes, although it could be boiled for 20-25 minutes instead, the researchers noted. The team then refrigerated the rice for 12 hours.
This novel method procedure increased the RS by 10 times for traditional, non-fortified rice, said the team.
“The increase in RS content could be attributed to the increase in RS3 and RS5 types, suggesting potential to increase these types of RS in rice,” wrote the authors.
Novel cooking method
James explained that the simple cooking method can make a big difference because oil enters the starch granules during cooking, changing its architecture so that it becomes resistant to the action of digestive enzymes.
This means that fewer calories ultimately get absorbed into the body, he commented.
"The cooling is essential because amylose, the soluble part of the starch, leaves the granules during gelatinization," James said. "Cooling for 12 hours will lead to formation of hydrogen bonds between the amylose molecules outside the rice grains which also turns it into a resistant starch."
Reheating the rice for consumption after this cooking method does not affect the RS levels, he confirmed.
James suggested that the next step will be to complete studies with human subjects to learn which varieties of rice might be best suited to the calorie-reduction process. The team also will assess whether other oils besides coconut have the effect.
Source: to be presented at the American Chemical Society
“Rice (Oryza sativa L.) resistant starch and novel processing methods to increase resistant starch concentration”
Authors: Sudhair A. James, et al